WO2023122143A1 - Methods and compositions for pfas defluorination detection - Google Patents

Abstract

Aspects of the disclosure relate to methods of detecting defluorination of a per- or polyfluoroalkyl substance (PFAS).

Description

METHODS AND COMPOSITIONS FOR PFAS DEFLUORINATION DETECTION CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No.63/292,250, filed December 21, 2021, entitled “METHODS AND COMPOSITIONS FOR PFAS DEFLUORINATION DETECTION,” the entire disclosure of which is hereby incorporated by reference in its entirety. FIELD OF THE INVENTION The present disclosure relates to methods and kits for detecting fluoride using esterases, e.g., to detect PFAS defluorination. BACKGROUND Per- and polyfluoroalkyl substances (PFASs) are a large group of compounds with uses ranging from providing stain and grease repelling properties in consumer products to components in fire-fighting foams. Widespread consumer use combined with continued production of PFASs have resulted in PFASs becoming ubiquitous pollutants in the environment, including in drinking water, rivers, groundwater, wastewater, household dust, and soils. PFASs have bioaccumulation potential and have been shown to negatively affect human health upon absorption into the body in a variety of ways, including altering kidney function, altering thyroid function, suppressing the immune system, and producing deleterious effects on reproduction and development. SUMMARY The disclosure relates to the development of methods and compositions for detection of PFAS removal or degradation. These methods and compositions can be used to rapidly and accurately assess the progress of PFAS removal/degradation efforts. Accordingly, in one aspect, the disclosure is directed to a method of detecting fluoride in a sample comprising contacting the sample with: an esterase capable of converting an ester to a detectable product; and an ester comprising the detectable product, and detecting the presence of the detectable product, thereby detecting fluoride in the sample. In some embodiments, contacting a sample with an esterase and an ester produces a reaction mixture. In another aspect, the disclosure is directed to a method of detecting defluorination of a PFAS, comprising contacting a sample containing or suspected of containing a PFAS with: an esterase capable of converting an ester to a detectable product; and an ester comprising a detectable product, and detecting the presence of the detectable product. In some embodiments, detecting the presence of the detectable product comprises determining the level of the detectable product. In some embodiments, determining the level of the detectable product comprises quantifying the level of the detectable product. In some embodiments, detecting fluoride or defluorination comprises determining the level of fluoride or determining the level of defluorination. In some embodiments, determining the level of fluoride or determining the level of defluorination comprises quantifying the level of fluoride or quantifying the level of defluorination. In some embodiments, the level of detectable product is inversely correlated with the level of fluoride. In some embodiments, the level of detectable product is inversely correlated with the level of defluorination of a PFAS. In some embodiments, converting an ester to a detectable product comprises cleaving an ester to release a detectable product. In some embodiments, the esterase is inhibited by fluoride. In one aspect, the disclosure is directed to a method of determining the level of fluoride in a sample, comprising: contacting the sample with: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride; and an ester comprising the detectable product, thereby producing a reaction mixture, and determining the level of the detectable product in the reaction mixture, wherein the level of the detectable product is inversely correlated with the level of fluoride. In some embodiments, defluorination of a PFAS produces fluoride. In one aspect, the disclosure is directed to a method of determining the level of defluorination of a PFAS, comprising: contacting a sample containing or suspected of containing a defluorinated PFAS with: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride; and an ester comprising a detectable product, thereby producing a reaction mixture, and determining the level of the detectable product in the reaction mixture, wherein the level of the detectable product is inversely correlated with the level of defluorination of the PFAS. In one aspect, the disclosure is directed to a method of screening for a composition capable of defluorination of a PFAS, comprising: contacting a sample containing or suspected of containing a composition capable of defluorination of a PFAS with: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride; and an ester comprising a detectable product, thereby producing a reaction mixture, and determining the level of the detectable product in the reaction mixture, wherein the level of the detectable product is inversely correlated with the presence, level, or potency of a composition capable of defluorination of a PFAS. In some embodiments, the composition is a polypeptide, a small molecule, or a large molecule. In some embodiments, the polypeptide is an enzyme. In some embodiments, a method described herein further comprises, responsive to determining the level of the detectable product in the reaction mixture is below a predetermined value, determining that the sample contains a composition capable of defluorination of a PFAS. In some embodiments, a method described herein further comprises, responsive to determining the level of the detectable product in the reaction mixture is above a predetermined value, determining that the sample does not contain a composition capable of defluorination of a PFAS. In some embodiments, a method described herein further comprises, responsive to determining the level of the detectable product in the reaction mixture is within a predetermined value range, performing an additional evaluation of the sample to determine if it contains a composition capable of defluorination of a PFAS. In some embodiments, the additional evaluation comprises: repeating the contacting and determining steps, an ionic chromatography (IC) step, and/or a liquid chromatography-mass spectrometry (LCMS) step. In some embodiments, the level of the detectable product is quantified over time. In some embodiments, determining the level of fluoride in the sample comprises evaluating inhibition of the esterase by fluoride in the sample. In some embodiments, the detectable product is detected by measuring a colorimetric, fluorescent, or luminescent signal. In some embodiments, the detectable product is detected by measuring a fluorescent signal. In some embodiments, a method described herein further comprises an ionic chromatography (IC) step and/or a liquid chromatography-mass spectrometry (LCMS) step. In some embodiments, the ionic chromatography (IC) step and/or liquid chromatography-mass spectrometry (LCMS) step is conducted after the contacting and determining steps. In some embodiments, the esterase comprises a pig liver esterase (PLE). In some embodiments, the sample comprises a per- or polyfluoroalkyl substance (PFAS). In some embodiments, the PFAS is Perfluorooctane Sulfonate (PFOS), Perfluorooctanoic Acid (PFOA), or Perfluorohexane Sulfonate (PFHxS). In some embodiments, the sample does not comprise a per- or polyfluoroalkyl substance (PFAS). In some embodiments, the sample comprises fluoride ions. In some embodiments, the sample does not comprise fluoride ions. In some embodiments, the sample is a soil sample, a groundwater sample, or an artificial water source sample. In some embodiments, the sample has been treated with a PFAS-degrading agent. In some embodiments, a method described herein further comprises diluting the sample prior to the contacting step. In some embodiments, the PFAS-degrading agent comprises an enzyme or is heat. In some embodiments, the enzyme comprises a ligninolytic enzyme or a reductive dehalogenase (RDase). In some embodiments, the PFAS- degrading agent comprises a microbe comprising a ligninolytic enzyme or reductive dehalogenase (RDase). In some embodiments, a method further comprises, responsive to determining the level of fluoride or determining the level of PFAS degradation, treating the soil, groundwater, or artificial water source with a PFAS-degrading agent. In some embodiments, the ester comprises 4-methylumbelliferone butyrate (4-MUB). In some embodiments, the detectable product comprises 4-methylumbelliferone (4-MU). In some embodiments, contacting further comprises contacting the sample with a buffer. In some embodiments, contacting the sample with a buffer occurs in combination with contacting the sample with the ester enzyme, the ester, or both. In some embodiments, the buffer has a pH of about 4, about 5, about 6, about 7, or about 8. In some embodiments, the buffer comprises citrate, DMSO, and/or phosphate. In some embodiments, the ester concentration in the reaction mixture is 0.01-0.5 mM, 0.025-0.5 mM, 0.05-0.5 mM, 0.075-0.5 mM, 0.1-0.5 mM, 0.15-0.5 mM, 0.2-0.5 mM, 0.25- 0.5 mM, 0.3-0.5 mM, 0.35-0.5 mM, 0.4-0.5 mM, 0.45-0.5 mM, 0.01-0.3 mM, 0.025-0.3 mM, 0.05-0.3 mM, 0.075-0.3 mM, 0.1-0.3 mM, 0.15-0.3 mM, 0.2-0.3 mM, 0.25-0.3 mM, 0.01-0.2 mM, 0.025-0.2 mM, 0.05-0.2 mM, 0.075-0.2 mM, 0.1-0.2 mM, 0.15-0.2 mM, 0.01-0.1 mM, 0.025-0.1 mM, 0.05-0.1 mM, or 0.075-0.1 mM. In some embodiments, the esterase concentration in the reaction mixture is 1-10 µg/ml, 2-10 µg/ml, 3-10 µg/ml, 4-10 µg/ml, 5- 10 µg/ml, 6-10 µg/ml, 7-10 µg/ml, 8-10 µg/ml, 9-10 µg/ml, 1-9 µg/ml, 2-9 µg/ml, 3-9 µg/ml, 4-9 µg/ml, 5-9 µg/ml, 6-9 µg/ml, 7-9 µg/ml, 8-9 µg/ml, 1-8 µg/ml, 2-8 µg/ml, 3-8 µg/ml, 4-8 µg/ml, 5-8 µg/ml, 6-8 µg/ml, 7-8 µg/ml, 1-7 µg/ml, 2-7 µg/ml, 3-7 µg/ml, 4-7 µg/ml, 5-7 µg/ml, 6-7 µg/ml, 1-6 µg/ml, 2-6 µg/ml, 3-6 µg/ml, 4-6 µg/ml, 5-6 µg/ml, 1-5 µg/ml, 2-5 µg/ml, 3-5 µg/ml, 4-5 µg/ml, 1-4 µg/ml, 2-4 µg/ml, 3-4 µg/ml, 1-3 µg/ml, 2-3 µg/ml, or 1-2 µg/ml. In some embodiments, the buffer concentration in the reaction mixture is about 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, or 500 mM. In some embodiments, the method does not comprise heating the sample. In some embodiments, the method comprises: contacting multiple samples with the esterase and ester to produce multiple reaction mixtures, and determining the level of the detectable product in the multiple reaction mixtures, thereby determining the level of fluoride, the level of defluorination of a PFAS, or screening for a composition capable of defluorination of a PFAS in the multiple samples. In some embodiments, the method analyzes at least 10, 20, 50, 96, 100, 150, 200, 250, 300, 350, 384, 400, 450, or 500 samples in less than 120, 110, 100, 90, 80, 70, 60, 50, 40, or 30 minutes. In some embodiments, the method is capable of detecting the presence of the detectable product in greater than or equal to 10, 20, 50, 96, 100, 150, 200, 250, 300, 350, 384, 400, 450, or 500 samples and requires less than 120, 110, 100, 90, 80, 70, 60, 50, 40, or 30 minutes to detect fluoride or PFAS degradation in the samples. In one aspect, the disclosure is directed to a kit for detecting fluoride, comprising: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride, and an ester comprising a detectable product. In one aspect, the disclosure is directed to a kit for detecting defluorination of a per- or polyfluoroalkyl substance (PFAS), comprising: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride, and an ester comprising a detectable product. In some embodiments, the kit comprises a buffer. In some embodiments, the kit comprises instructions. In some embodiments, the instructions describe how to contact a sample with the esterase, the ester, and/or the buffer. In some embodiments, the sample is a soil sample, a groundwater sample, or an artificial water source. In some embodiments, the instructions comprise the steps of a method described herein. Each of the limitations of the invention can encompass various embodiments of the invention. It is, therefore, anticipated that each of the limitations of the invention involving any one element or combinations of elements can be included in each aspect of the invention. This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used in this disclosure is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations of thereof in this disclosure, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. As used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the content clearly dictates otherwise. BRIEF DESCRIPTION OF THE DRAWINGS The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present disclosure, which may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented in this disclosure. The accompanying drawings are not intended to be drawn to scale. The drawings are illustrative only and are not required for enablement of the disclosure. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: FIGs.1A-1E show graphs and tables of calibration curves evaluating the effects of pH, enzyme and substrate concentrations on fluoride inhibition of esterase activity. FIG.1A shows a graph of fluorescence as a function of fluoride concentration for different combinations of concentrations of exemplary esterase PLE and exemplary ester 4-MUB at pH 7. FIG.1B shows a table of the IC50 values obtained for different combinations of enzyme and substrate concentrations at pH 7. FIG.1C shows the fluorescence curves as a function of fluoride concentration for a PLE concentration of 0.006 mg/mL and a 4-MUB concentration of 0.06 mM at pH 4. FIG.1D shows the fluorescence curves as a function of fluoride concentration for a PLE concentration of 0.006 mg/mL and a 4-MUB concentration of 0.06 mM at pH 7. FIG.1E shows the IC50 values obtained for a PLE concentration of 0.006 mg/mL and a 4-MUB concentration of 0.06 mM at pH 4 and pH 7. FIGs.2A-2D show graphs of fluorescence over fluoride concentration, both as measured and fitted calibration curves, for reactions containing PLE, 4-MUB, and a matrix. FIG.2A shows the measured and fitted curves for water which serves as a control sample. FIG.2B shows the measured and fitted curves for a first groundwater sample (groundwater 1) from a first site. FIG.2C shows the measured and fitted curves for a second groundwater sample (groundwater 2) from a second site. FIG.2D shows a table listing the calculated fluoride IC50 value for each of the three samples. FIGs.3A-3D show high throughput fluoride quantification in groundwater samples containing added fluoride using the fluoride esterase inhibition assay using exemplary esterase PLE and exemplary ester 4-MUB. FIG.3A shows the fluorescence levels of groundwater samples from two environmental sources (groundwater 1 and groundwater 2); samples 4, 9, 17, 29, 40, and 45 (indicated by arrows) were supplemented with known amounts of fluoride and show lower levels of fluorescence compared to other samples. FIG. 3B shows fluorescence levels for samples 4, 9 and 17 (groundwater 1) at different dilution levels. FIG.3C shows fluorescence levels for samples 29, 40, and 45 (groundwater 2) at different dilution levels. FIG.3D shows a table comparing fluoride quantification using the fluoride esterase inhibition assay (using the arrow-indicated dilutions of samples 4, 9, 17, 40, and 45 from FIGs.3B and 3C) and ionic chromatography (IC). FIGs.4A-4G show graphs measuring the effects of heat treatment on detected fluorescence levels, esterase activity, and fluoride inhibition of esterase activity. FIG.4A shows the standard curve of initial fluorescence generated by varying concentrations of exemplary detectable product 4-MU. FIG.4B shows fluorescence generated by varying concentrations of 4-MU after a set incubation time and quenching of the reaction with SDS, with or without heat. FIG.4C shows the initial read of fluorescence over time as a function of fluoride levels in a reaction mixture comprising exemplary esterase PLE and exemplary ester 4-MUB at pH 4 prior to quenching and/or heat treatment. FIG.4D shows the fluorescence over time as a function of fluoride levels in the reaction mixture quenched with SDS without heat treatment. FIG.4E shows the fluorescence over time as a function of fluoride levels in the reaction mixture with SDS quenching and heat treatment. FIG.4F shows the fitted curve for the measurement of fluoride IC50 without heat treatment FIG.4G shows the fitted curves for the measurement of fluoride IC50 with heat treatment. DETAILED DESCRIPTION OF THE INVENTION The present disclosure provides, in some aspects, methods for detecting fluoride in a sample, methods for detecting degradation of a PFAS, and kits and compositions related thereto. The disclosure is based, at least in part, on the discoveries that: inhibition of esterases by fluoride can be used to quickly and accurately detect fluoride in a sample; esters comprising detectable products (e.g., 4-methylumbelliferone butyrate (4-MUB)) can be used as substrates to rapidly quantify the progress of consumption of ester by esterases in a high- throughput manner; and an assay that sensitively detects fluoride in a rapid, high-throughput manner can be used to detect the progress of defluorination of PFASs in environmental samples. Methods and compositions provided in this disclosure can be used to rapidly and accurately assess the progress of PFAS removal/degradation efforts. PFASs As used in this disclosure, a “PFAS” refers to a fluorinated substance that contains 1 or more C atoms on which all the H substituents (i.e., H substituents present in the nonfluorinated analog of the substance) have been replaced by F atoms, in such a manner that they contain the perfluoroalkyl moiety, –C_nF_2n– and/or C_nF_2n+1–. See, e.g., OECD Report (2018), ENV/JM/MONO(2018)7, Series on Risk Management, No.39, OECD Publishing, Paris; and Buck et al. Integr Environ Assess Manag.2011 Oct; 7(4): 513–541. In some embodiments, PFASs are synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain; or are fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it). PFASs represent a large group of Synthetic Organic Compounds (SOCs). PFASs are able to act as a surfactant by interacting between two immiscible fluid phases, as described in and incorporated by reference from Shasavari et al. Front. Bioeng. Biotechnol., 07 January 2021 | https://doi.org/10.3389/fbioe.2020.602040. PFASs exhibit amphiphilic properties due to their polarity and due to the presence of carbon-fluorine bonds. Some PFASs are produced industrially for their surfactant/amphiphilic properties, while others are byproducts of the production of other fluoro-carbon chemical manufacturing. PFASs generally are heat resistant, chemically stable, and resistant to biological degradation. PFASs can be broadly divided into perfluoroalkyl substances and polyfluoroalkyl substances. Perfluoroalkyl substances can comprise short or long carbon chains with a polar functional group at one end where fluorine is attached to every carbon bonding site along the chain except for the polar functional group (also known as full fluorination). Polyfluoroalkyl substances, in contrast, are not fully fluorinated, comprising at least one lapse in fluorine attachment (e.g., a hydrogen or oxygen bonded to a carbon of the chain). Exemplary PFASs include, but are not limited to: Perfluorooctane Sulfonate (PFOS), CAS number 1763-23-1; Perfluorooctanoic Acid (PFOA), CAS number 335-67-1; and Perfluorohexane Sulfonate (PFHxS), CAS number 355-46-4. Further exemplary PFASs include, but are not limited to: N-Ethyl-N-(2-hydroxyethyl)perfluorooctanesulfonamide, N- Methyl-N-(2-hydroxyethyl)perfluorooctanesulfonamide, 8:2 Fluorotelomer alcohol, 10:2 Fluorotelomer alcohol, Perfluorobutanesulfonic acid, Perfluorodecanoic acid, Perfluorododecanoic acid, Perfluorohexanoic acid, Perfluorononanoic acid, Perfluorooctanesulfonic acid, Perfluorooctanoic acid, Lithium perfluorooctanesulfonate, N- Ethylperfluorooctanesulfonamide, Perfluoroheptanoic acid, Potassium perfluorooctanesulfonate, Potassium perfluorobutanesulfonate, Ammonium perfluorooctanoate, Potassium perfluorohexanesulfonate, 10:2 Fluorotelomer acrylate, 6:2 Fluorotelomer acrylate, Perfluorooctanesulfonamide, Perfluorodecanesulfonic acid, Perfluorohexanesulfonic acid, 6:2 Fluorotelomer sulfonamide betaine, Trifluoroacetic acid, Potassium N-ethyl-N-((heptadecafluorooctyl)sulphonyl)glycinate, 6:2 Fluorotelomer alcohol, Perfluoro(4-methyl-3,6-dioxaoct-7-ene)sulfonyl fluoride, Perfluoroundecanoic acid, 6:2 Fluorotelomer methacrylate, Perfluoro-3-(1H-perfluoroethoxy)propane, Sodium perfluorohexanoate, 7:1 Fluorotelomer alcohol, Perfluorobutanoic acid, Perfluoroheptanesulfonic acid, Perfluorotetradecanoic acid, Perfluoropropanoic acid, 8:2 Fluorotelomer methacrylate, 4:2 Fluorotelomer alcohol, 10:2 Fluorotelomer methacrylate, Perfluoropentanoic acid, Perfluoropentanesulfonic acid, 2-(N- Ethylperfluorooctanesulfonamido)acetic acid, Potassium perfluoropentanesulfonate, Perfluorooctane sulfonamido amine, Perfluorostearic acid, Ammonium perfluorononanesulfonate, 6:2 Fluorotelomer sulfonic acid, 8:2 Fluorotelomer acrylate, Ammonium perfluorooctanesulfonate, N-Methylperfluorooctanesulfonamide, Perfluorohexane sulfonamido amine, Potassium perfluoroheptanesulfonate, Perfluoroheptane sulfonamido amine, Perfluorohexadecanoic acid, Ammonium perfluorodecanesulfonate, Ammonium perfluoroheptanesulfonate, Ammonium perfluorohexane-1-sulphonate, Ammonium perfluoropentanesulfonate, Ammonium perfluorobutanesulfonate, Perfluorononanesulfonic acid, Perfluorobutane sulfonamido amine, Perfluoropentane sulfonamido amine, Lithium perfluoroheptanesulfonate, Ammonium perfluoro-2-methyl-3- oxahexanoate, Perfluorooctanesulfonate, Trifluoroacetate, 6:1 Fluorotelomer alcohol, Perfluoro-3-methoxypropanoic acid, 8:2 Fluorotelomer sulfonic acid, 8:2 Fluorotelomer phosphate diester, Perfluoro-4-(perfluoroethyl)cyclohexylsulfonic acid, Perfluoro-(2,5,8- trimethyl-3,6,9-trioxadodecanoic)acid, 8:1 Fluorotelomer alcohol, 9:1 Fluorotelomer alcohol, 11:1 Fluorotelomer alcohol, Perfluoro-3,6,9-trioxatridecanoic acid, 10:1 Fluorotelomer alcohol, Perfluoro-3,6,9-trioxadecanoic acid, Perfluoro-3,6-dioxadecanoic acid, Perfluoro- 3,6-dioxaheptanoic acid, 5:1 Fluorotelomer alcohol, 3-Perfluoroheptylpropanoic acid, Difluoro(perfluoromethoxy)acetic acid, 2-Perfluorooctyl ethanoic acid, 2-Perfluorohexyl ethanoic acid, Perfluoro(4-methoxybutanoic) acid, 7:2 sFluorotelomer alcohol, Perfluoro-2- (perfluoromethoxy)propanoic acid, 6:2 Fluorotelomer phosphate monoester, 6:2 Fluorotelomer phosphate diester, 2-(N-Methylperfluorooctanesulfonamido)acetic acid, Sodium perfluorooctanesulfonate, Perfluoro-4-isopropoxybutanoic acid, Perfluorooctanesulfonamido amine oxide, Perfluoro-3,5,7,9-butaoxadecanoic acid, Perfluoro- 3,5,7,9,11-pentaoxadodecanoic acid, 2H-Perfluoro-2-decenoic acid, Difluoro(perfluoropropoxy)acetic acid, Perfluorooctanesulfonamido ammonium, 8- Fluorosulfonylperfluoro(2,5-dimethyl-3,6-dioxaoctanoyl) fluoride, Perfluorotridecanoic acid, Perfluoroethanesulfonic acid, Perfluoropropanesulfonic acid, Perfluorononanesulfonate, Perfluorohexanesulfonate, Perfluorodecanesulfonate, Perfluorobutanesulfonate, 6:2/8:2 Fluorotelomer phosphate diester, 8:2 Fluorotelomer sulfonate, 6:2 Fluorotelomer sulfonate, Ammonium 4,8-dioxa-3H-perfluorononanoate, 8:2 Fluorotelomer phosphate monoester, 2H,2H,3H,3H-Perfluorooctanoic acid, Sodium perfluorooctanoate, Potassium perfluorooctanoate, Ammonium perfluorodecanoate, Sodium perfluorodecanoate, Silver perfluorooctanoate, Sodium perfluorobutanoate, Sodium perfluoropentanoate, Ammonium 2- (N-ethylperfluorooctanesulfonamido)acetate, Ammonium perfluoro-9-(methyl)decanoate, Silver perfluorobutanoate, Sodium 2-(N-ethylperfluorooctanesulfonamido)acetate, Ammonium perfluorononanoate, Ammonium perfluoroheptanoate, Perfluoro-2-methyl-3- oxahexanoic acid, Sodium perfluoroheptanoate, Ammonium perfluorohexanoate, 8:2 Fluorotelomer sulfonamide betaine, 10:2 Fluorotelomer sulfonamide betaine, Lithium perfluorohexanesulfonate, Ammonium perfluoropentanoate, Potassium 9- chlorohexadecafluoro-3-oxanonane-1-sulfonate, 4,8-Dioxa-3H-perfluorononanoic acid, Perfluorosulfonic acid, PTFE copolymer, 4:2 Fluorotelomer thioether amido betaine, Perfluorooctanesulfonamido betaine, 4:2 Fluorotelomer sulfonic acid, 4:2 Fluorotelomer sulfonate, 2-Perfluorodecyl ethanoic acid, 2H-Perfluoro-2-octenoic acid, Perfluoro-4- (perfluoroethyl)cyclohexylsulfonate, Perfluorooctanesulfonamido ethanol, 6:2 Fluorotelomer thioether amido sulfonic acid, 6:2 Fluorotelomer thioether amido sulfonate, 8:2 Fluorotelomer thioether amido sulfonic acid, 8:2 Fluorotelomer thioether amido sulfonate, 5:3 Fluorotelomer betaine, Perfluoro-3,5,7-trioxaoctanoic acid, Perfluoro-3,5-dioxahexanoic acid, Perfluoro-2-{[perfluoro-3-(perfluoroethoxy)-2-propanyl]oxy}ethanesulfonic acid, Perfluoro-3,6-dioxa-4-methyl-7-octene-1-sulfonic acid, Perfluoro-2-(perfluoropropoxy)-2- (perfluoromethyl)propanoic acid, Perfluoro-2-[(perfluoropentyl)oxy]propanoic acid, Perfluoro-2-(perfluorobutoxy)-2-(perfluoromethyl)propanoic acid, Perfluoro-3- ethoxypropanoic acid, Perfluoro(2,5,8,10-tetramethyl-3,6,9-trioxaundecanoic) acid, Perfluoro-2,5-dimethyl-3,6-dioxanonanoic acid, Sodium perfluorodecanesulfonate, Perfluoro(2,5,8,11,14-pentamethyl-3,6,9,12,15-pentaoxaoctadecanoic) acid, Potassium 11- chloroeicosafluoro-3-oxaundecane-1-sulfonate, Sodium 4,8-dioxa-3H-perfluorononanoate, Perfluoroundecanoate, Sodium perfluorohexanesulfonate, Perfluoropropanoate, Perfluoropentanesulfonate, Perfluorobutanoate, Perfluorodecanoate, Perfluorododecanoate, Perfluoroheptanoate, Perfluorohexanoate, Perfluorononanoate, Perfluorooctanoate ion(1-), Perfluoropentanoate, Perfluorotetradecanoate, Perfluorotridecanoate, 2-(N- Methylperfluorooctanesulfonamido)acetate, 2-(N-Ethyl-perfluorooctanesulfonamido)acetate, Perfluoroheptanesulfonate, 5:1:2 Fluorotelomer betaine, 7:1:2 Fluorotelomer betaine, 7:3 Fluorotelomer betaine, 9:1:2 Fluorotelomer betaine, 9:3 Fluorotelomer betaine, 8:2 Fluorotelomer sulfonamido N,N-dimethyl amine ion, 6:2 Fluorotelomer sulfonamido N,N- dimethyl amine, 12:2 Fluorotelomer sulfonamido betaine, 4:2 Fluorotelomer thioether amido sulfonate, 4:2 Fluorotelomer thioether amido sulfonic acid, 6:2 Fluorotelomer thioether hydroxyammonium, Perfluorobutane sulfonamide amino carboxylates, Perfluoroheptane sulfonamide amino carboxylates, Perfluorohexane sulfonamide amino carboxylates, Perfluorooctane sulfonamide amino carboxylates, Perfluoropentane sulfonamide amino carboxylates, Perfluorooctaneamido amine oxide, and Perfluorooctaneamido ammonium. See, e.g., United States Environmental Protection Agency. (n.d.) PFAS|EPA: Cross-Agency Research List (https://comptox.epa.gov/dashboard/chemical_lists/EPAPFASRL), which is incorporated by reference in its entirety. The stability of PFASs, their potential for bioaccumulation, and their association with a number of deleterious health effects in living organisms has produced significant environmental problems. Accordingly, there is a need for the removal or degradation of PFASs from environments such as soil, farms, and drinking water. Defluorination of PFASs renders the PFAS more vulnerable to degradation by other means and decreases potential for bioaccumulation. The disclosure is directed, in part, to methods and kits for detecting and quantifying this important process. Methods The methods of the disclosure may be used to detect (e.g., quantify) fluoride (e.g., fluoride released from a PFAS comprising the fluoride, or released fluoride) in a sample. In some embodiments, detecting fluoride can be used to detect (e.g., quantify) defluorination of a PFAS. In some embodiments, a method of detecting a fluoride is indirect and comprises a method of detecting a detectable product released from an ester by an esterase, wherein the esterase is inhibited by fluoride; and wherein the level of fluoride is calculable from its inverse correlation to the level of the detectable product. In some embodiments, a method of the disclosure comprises contacting a sample with an esterase and an ester. Contacting may comprise any type of addition and/or mixing known to those of skill in the art. Contacting may comprise, e.g., pipetting, shaking, stirring, or decanting, and may be accomplished manually (e.g., by a human operator or user), via automation (e.g., using a robotic pipetter), or any combination thereof. In some embodiments, the sample is added to the esterase (e.g., and optionally the ester). In some embodiments, the esterase is added to the sample (e.g., and optionally the ester). In some embodiments, the ester is added to the sample (e.g., and optionally the esterase). In some embodiments, the esterase, ester, and sample are contacted with one another simultaneously. In some embodiments, a container (e.g., plate) containing one or more wells is prepared with the esterase and the ester (and optionally any other agent, e.g., buffer, needed for the assay) in the one or more wells, and a sample or plurality of different samples is added to the one or more wells. After contacting a sample with an esterase and ester, the mixture of the sample, esterase, and ester, and optionally other components, may be referred to in this disclosure as a reaction mixture. In some embodiments, a method of the disclosure comprises diluting a sample, e.g., prior to contacting the sample with an esterase and an ester. In some embodiments, the methods described in the disclosure are characterized by a detection range, comprising the range of fluoride concentrations which the method is capable of accurately detecting and/or quantifying. In some embodiments, diluting the sample achieves a fluoride concentration in said range of fluoride concentrations, e.g., increasing detectability of fluoride and/or inhibition of the esterase by fluoride. Alternately or additionally, a sample may comprise interfering inorganic compounds or biologic matrices which interfere with esterase activity, with fluoride inhibition of esterase activity, and/or with detection (e.g., by absorbing or emitting in a wavelength that interferes with detecting the detectable product). In such embodiments, dilution may decrease the level of the interfering inorganic compounds or biologic matrices to an extent that the compounds or matrices no longer interfere with esterase activity, with fluoride inhibition of esterase activity, and/or with detection. Without wishing to be bound by theory, one advantage of the methods and kits described in the disclosure is their insensitivity (e.g., relative to existing methods of detecting fluoride or PFAS defluorination) to interfering inorganic compounds or biologic matrices that may be present in samples or environmental sources from which samples are obtained. In some embodiments, a method of the disclosure comprises detecting the presence of a detectable product (e.g., a detectable product released from an ester comprising the detectable product). As used in the methods of the disclosure, “detecting the presence of a detectable product,” “determining the level of a detectable product,” or other similar expressions encompass detecting the presence or absence of the detectable product. Detecting may comprise any appropriate technique known to those of skill in the art. In some embodiments, detecting comprises using a technique compatible with rapid, accurate, and/or high-throughput sample analysis. In some embodiments, detecting comprises using spectroscopy, e.g., absorbance or fluorescence spectroscopy, e.g., a plate reader capable of measuring absorbance and/or fluorescence (e.g., of multiple samples rapidly and/or simultaneously). In some embodiments, detecting comprises detecting a colorimetric, fluorescent, or luminescent detectable product. In some embodiments, a method of the disclosure comprises quantifying the level of the detectable product. In some embodiments, quantification occurs over time, e.g., measuring the level of detectable product (e.g., the production of detectable product) over the course of the assay. In some embodiments, a method of the disclosure comprises quantifying the level of fluoride in a sample. Without wishing to be bound by theory, the disclosure is based in part on the idea that fluoride inhibits esterase activity in a manner that reduces the rate of consumption of an ester and the rate of production of a detectable product, thereby enabling calculation of the level of fluoride in a sample. Accordingly, quantifying the level of fluoride in a sample may comprise evaluating inhibition of the esterase by fluoride in the sample. In some embodiments, a method of the disclosure comprises determining whether a PFAS was defluorinated. The PFAS may have been defluorinated in the environmental source of the sample, e.g., in the groundwater, wastewater, drinking water, soil, or other environmental location where a PFAS might accumulate and where the sample was taken from. The fluoride produced by PFAS defluorination in said environmental source may have made its way to the sample (e.g., by flow of groundwater) or may have been produced in the sample itself (e.g., defluorination occurring in soil that is later gathered as a sample). In some embodiments, the detection of fluoride in the sample (as determined indirectly using an esterase inhibited by fluoride) may indicate the presence of a PFAS-degrading agent. In some embodiments, a method of the disclosure comprises quantifying the level of defluorination of PFAS. As described above, the disclosure is based in part on the discovery that PFAS defluorination can be detected by detecting and/or quantifying the level of fluoride in a sample, itself calculable by evaluating the inhibition of an esterase by fluoride. Accordingly, quantifying the level of defluorination of PFAS may comprise evaluating inhibition of an esterase by fluoride in a sample. In some embodiments, determining whether a PFAS was defluorinated or determining the level of defluorination of PFAS is based upon detecting and/or quantifying the level of fluoride in a sample (e.g., by evaluating inhibition of an esterase). Methods provided in this disclosure are capable of accurately and rapidly detecting fluoride and/or defluorination of a PFAS in multiple samples in a high-throughput manner. For example, by utilizing a detectable product that may be detected quickly and accurately, e.g., by fluorescence or absorbance spectroscopy, high-throughput methodologies such as use of multi-well plates and plate readers can be applied to analyze a large number of samples in a relatively short time period. In some embodiments, a method described in this disclosure may be used to screen a large number of samples in which fluoride is detected or PFAS defluorination is detected. In some embodiments, a method described in this disclosure further comprises using an additional technique to detect fluoride in a sample or to detect defluorination of a PFAS in a sample. For example, a method described in this disclosure may be used to screen an initial batch of samples for fluoride and/or PFAS defluorination, and a subset of the initial batch of samples (e.g., those putatively showing the presence or a threshold level of fluoride and/or PFAS defluorination) may be analyzed by an additional technique. In some embodiments, an additional technique comprises liquid chromatography mass spectroscopy (LCMS). In some embodiments, an additional technique comprises ionic chromatography (IC). Without wishing to be bound by theory, while either LCMS or IC may be used to detect defluorination of a PFAS, both LCMS and IC are limited to running individual samples at a time. High-throughput sample processing is advantageous when a large number of samples, e.g., from a large scale PFAS degradation/removal project, must rapidly be screened. Accordingly, in some embodiments, a method described in this disclosure comprises contacting multiple samples with an esterase and ester and detecting the presence of a detectable product in the multiple samples, thereby detecting and/or quantifying fluoride or the defluorination of a PFAS in the multiple samples. In some embodiments, a method described in this disclosure is capable of analyzing at least 10, 20, 50, 96, 100, 150, 200, 250, 300, 350, 384, 400, 450, or 500 samples in less than a unit time. In some embodiments, the unit time is about 120, 119, 118, 117, 116, 115, 114, 113, 112, 111, 110, 109, 108, 107, 106, 105, 104, 103, 102, 101, 100, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, or 30 minutes. In some embodiments, a method described in this disclosure is capable of analyzing more samples in a unit time than IC or LCMS. In some embodiments, contacting comprises contacting one, two, or all of the sample, the esterase, and the ester with a buffer. In some embodiments, the buffer comprises one, two, or all of citrate, DMSO, or phosphate. The buffer may comprise any compound (e.g., known to those of skill in the art) capable of establishing or maintaining conditions suitable for esterase activity, e.g., pH and ionic strength. In some embodiments, the concentration of buffer in the sample (i.e., after contacting) is about 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, or 500 mM. As used in the disclosure, the terms “about” and “approximately” when used in connection with a number or numerical range can mean ±1%, ±5%, ±10%, ±15%, or ±20% from said number or the numerical limits of the numerical range, unless specifically indicated otherwise. In some embodiments, the buffer has a pH of about 4, about 5, about 6, about 7, or about 8. Without wishing to be bound by theory, the disclosure is based, at least in part, on the discovery that the pH of the reaction mixture comprising the sample, esterase, and ester can affect the detection range and detectability of a detectable product. In some embodiments, the pH affects the lower limit of detection (LLOD) and/or the half-maximal inhibitory concentration (IC50). In some embodiments, an acidic pH increases the sensitivity of a method described in this disclosure; an acidic pH may decrease the LLOD and/or the IC50, such that a lower amount of fluoride can be detected. In some embodiments, the acidic pH is about 4, about 5, or about 6. In some embodiments, the pH affects the quantifiable detection range of a method described in this disclosure. As used in this disclosure with reference to methods of detecting fluoride or PFAS defluorination, the quantifiable detection range refers to the range of concentrations of fluoride or levels of PFAS defluorination that can be accurately quantified by the method. In some embodiments, a neutral or slightly alkaline pH improves (e.g., broadens) the quantifiable detection range of a method described in the disclosure. Without wishing to be bound by theory, a neutral or slightly alkaline pH may increase the fluorescence of fluorescent detectable products, e.g., 4- MU, which can broaden the quantifiable detectable range of fluoride in a method described in the disclosure. In some embodiments, a method described in the disclosure does not comprise a heating step (e.g., does not comprise heating the sample). Without wishing to be bound by theory, the disclosure is based, at least in part, on the discovery that heating a sample did not have a significant effect (e.g., an improving effect) on LLOD, IC50, or quantifiable detection range of fluoride detection via esterase inhibition. In other embodiments, a method described in the disclosure comprises heating a sample (e.g., as part of a quenching step). Methods and kits of the disclosure can be used to determine whether PFAS defluorination has occurred in a sample or an environmental source of a sample, and the level of PFAS defluorination that occurred. In some embodiments, a method described in this disclosure further comprises, responsive to determining whether PFAS defluorination occurred or the level of PFAS defluorination that occurred, treating an environmental source with a PFAS-degrading agent. For example, a method or kit described in this disclosure may determine that PFAS defluorination has not occurred in a sample or the environmental source of a sample, and accordingly that treating the environmental source with a PFAS-degrading agent is necessary to remove or degrade PFAS in the environmental source. As a further example, a method or kit described in this disclosure may determine that PFAS defluorination has occurred but to an insufficient level, and accordingly that treating the environmental source with a PFAS-degrading agent (e.g., a further PFAS-degrading agent in addition to a previously applied agent) is necessary to remove or degrade PFAS in the environmental source. As a further example, a method or kit described in this disclosure may be used to screen a large number of samples from a plurality of different environmental sources, and may determine that a subset of the samples (and, correspondingly, the environmental sources from which the samples were gathered) do not show PFAS defluorination or show an insufficient level of PFAS defluorination, and accordingly that treating the environmental sources associated with that subset of samples with a PFAS-degrading agent is necessary to remove or degrade PFAS in the environmental source. A variety of PFAS-degrading agents are known to those of skill in the art and may be used in the methods and kits of the disclosure. As used in this disclosure, a PFAS-degrading agent refers to any inorganic compound, biological molecule, or treatment that degrades PFAS or alters PFAS in a way that increases the rate or ease at which it is removed or degraded from an organism or environmental source. In some embodiments, a PFAS- degrading agent comprises heat treatment (e.g., of a sample or material from an environmental course). In some embodiments, a PFAS-degrading agent is a PFAS- defluorinating agent, which as used in this disclosure refers to any inorganic compound, biological molecule, or treatment that removes or catalyzes the removal of one or more fluorine atoms or fluoride ions from a PFAS. In some embodiments, a PFAS-defluorinating agent is a ligninolytic enzyme. In some embodiments, a PFAS-defluorinating agent is a reductive dehalogenase (RDase). In some embodiments, a PFAS-degrading agent (e.g., PFAS-defluorinating agent) comprises a microbe comprising a biological molecule that degrades PFAS or alters PFAS in a way that increases the rate or ease at which it is removed or degraded from an organism or environmental source. In some embodiments, the microbe comprises a ligninolytic enzyme or RDase. In some embodiments, a method described in this disclosure comprises contacting a reaction mixture with a quenching treatment. A quenching treatment can comprise any chemical, electromagnetic, or physical treatment that inactivates the esterase. In some embodiments, the quenching treatment has little or no effect on the detectable product (e.g., the quenching treatment does not degrade the detectable product or interfere with the detectability of the detectable product). Without wishing to be bound by theory, a quenching treatment can preserve a temporal snapshot of the level of detectable product in a reaction mixture for a given incubation time of sample with esterase and ester; such control over the progression of esterase activity can have many diagnostic or experimental advantages that will be clear to one of skill in the art. In some embodiments, a quenching treatment comprises a detergent (e.g., SDS). In some embodiments, a quenching treatment comprises heat (e.g., heating the sample, e.g., above the denaturation temperature of the esterase). Samples for use in the methods and with the kits described in the disclosure may come from any environmental source. In some embodiments, a sample is obtained from groundwater, an artificial water source (e.g., wastewater or drinking water (e.g., a well or a municipal water system)), or from soil. Samples obtained from groundwater may be referred to in this disclosure as groundwater samples, samples obtained from soil may be referred to in this disclosure as soil samples, and so forth. In some embodiments, the sample is an aqueous sample obtained from an environmental source. In some embodiments, the sample is solid sample, e.g., a soil sample wherein the majority of the mass of which does not consist of water. In some embodiments, a soil sample comprises soil from 1, 2, 3, or all, of organic horizon, the surface horizon, the subsoil horizon, or the substratum horizon. In some embodiments, a method described in the disclosure comprises providing a sample. In some embodiments, providing comprises obtaining the sample from an environmental source or from another party. In some embodiments, providing comprises performing one or more processing steps to ready the sample for use in a downstream step (e.g., a detection step) of a method described in the disclosure. In some embodiments, a processing step is selected from: filtering the sample (e.g., to remove insoluble or biological matter), treating the sample with a chemical agent (e.g., an antibiotic, a salt, or chelating agent), treating the sample with a biological agent (e.g., an enzyme, e.g., that lyses cells or breaks down biologic matrices that could interfere with the method), rehydrating the sample (e.g., rehydrating a dry soil sample), mixing the sample, or resuspending a sample (e.g., a colloidal sample). The disclosure also provides methods for screening for a composition capable of defluorination of a PFAS. For example, a method of screening may comprise contacting a sample (as described in the disclosure) containing or suspected of containing a composition capable of defluorination of a PFAS with an esterase and an ester (e.g., each as described in the disclosure) to form a reaction mixture. An exemplary method of screening may comprise detecting (e.g., determining the level of) the detectable product in the reaction mixture (as described in the disclosure). In some embodiments, a sample containing or suspected of containing a composition capable of defluorination of a PFAS is incubated with a PFAS prior to a contacting step described in the disclosure (e.g., to allow the composition time to produce fluoride by defluorination of the PFAS prior to contact with the esterase). Accordingly, in some embodiments, a method of screening for a composition capable of defluorination of a PFAS comprises contacting a sample containing or suspected of containing a composition capable of defluorination of a PFAS with a PFAS, followed at a later point by contacting the sample with an esterase and an ester. In some embodiments, contacting a sample containing or suspected of containing a composition capable of defluorination of a PFAS with a PFAS comprises incubating the sample with the PFAS (e.g., for at least about 1, 2, 3, 4, 5, 10, 15, 20, 30, 45, or 60 minutes, or at least about 2, 3, 4, 5, 6, 8, 10, 12, 18, or 24 hours, or at least about 2, 3, 4, 5, 6, or 7 days). In other embodiments, a method of screening for a composition capable of defluorination of a PFAS comprises contacting a sample containing or suspected of containing a composition capable of defluorination of a PFAS with an esterase, an ester, and a PFAS in close temporal proximity to one another, e.g., simultaneously adding the esterase, ester, and PFAS to the sample, or adding the sample to the esterase, ester, and PFAS. Methods provided in this disclosure are capable of accurately and rapidly screening for compositions capable of defluorination of a PFAS in multiple samples in a high- throughput manner. In some embodiments, the presence of a composition capable of defluorination of a PFAS is inversely correlated with the presence or level of detectable product. In some embodiments, the level of a composition capable of defluorination of a PFAS is inversely correlated with the presence or level of detectable product. Compositions that may be screened for capability for defluorination of a PFAS include, but are not limited to: polypeptides (e.g., enzymes), small molecules (e.g., molecules less than 900 daltons, e.g., non-polypeptide and/or non-polynucleotide compounds), and large molecules (e.g., molecules 900 daltons or larger, e.g., a polypeptide- or polynucleotide-containing compound). In some embodiments, the potency of a composition capable of defluorination of a PFAS is inversely correlated with the presence or level of detectable product. As used in the disclosure, potency of a composition capable of defluorination of a PFAS refers to the strength of the capacity of the composition to defluorinated a PFAS. In some embodiments, potency refers to or comprises rate (e.g., kcat) of defluorination of a PFAS (e.g., an enzyme having a higher rate of catalysis of the defluorination of a PFAS has a higher potency than a reference agent). In some embodiments, potency refers to or comprises avidity or binding strength (e.g., KD) of a composition for PFAS or its defluorinated product. In some embodiments, potency refers to or comprises catalytic efficiency (e.g., of an enzyme), e.g., k_cat/K_m. In some embodiments, a method of screening for a composition capable of defluorination of a PFAS comprises, responsive to detecting (e.g., determining the level of) the detectable product in the reaction mixture, determining that the sample contains a composition capable of defluorination of a PFAS, does not contain a composition capable of defluorination of a PFAS, or is indeterminate (e.g., meriting additional evaluation). In some embodiments, a method of screening comprises comparing the level of detectable product, or a level of defluorination calculated therefrom, to a predetermined value to determine whether the sample contains or does not contain a composition capable of defluorination of a PFAS, or if the sample’s status is indeterminate. The predetermined value may be a threshold value determined by calculating a standard curve, e.g., assessing fluoride inhibition of an esterase, e.g., as in the Examples of the disclosure. A predetermined range of values may be used to determine that a sample is indeterminate. For example, an exemplary method of screening may comprise determining that a sample contains a composition capable of defluorination of a PFAS if it has a level of detectable product less than or equal to X, does not contain a composition capable of defluorination of a PFAS if it has a level of detectable product greater than or equal to Y, and is indeterminate if it has a level of detectable product greater than X and less than Y. Indeterminate samples may be further evaluated to determine whether they contain a composition capable of defluorination of a PFAS by repeating analysis of the sample by a method described in the disclosure, or employing another technique, such as ionic chromatography or LC/MS. Kits The disclosure provides kits for detecting fluoride and/or detecting defluorination of a PFAS. In some embodiments, a kit comprises an esterase (e.g., described in the disclosure) capable of converting an ester to a detectable product, and an ester (e.g., described in the disclosure) comprising the detectable product. The kits provided may comprise the esterase and ester, and a container (e.g., a vial, ampule, bottle, tube, and/or plate, or other suitable container), e.g., comprising the esterase and ester. In some embodiments, the container is configured for receiving one or more samples and containing (e.g., for the incubation of) the reaction mixture. In some embodiments, kits may optionally further include a second container comprising a buffer, e.g., for dilution or suspension of an esterase, ester, or sample. In some embodiments, a kit comprises the esterase and/or the ester and the buffer pre- combined, e.g., a container comprising the esterase and the buffer or the ester and the buffer. In some embodiments, a kit comprises a sample gathering device, e.g., a container for scooping, shoveling, or aspirating a sample (e.g., a groundwater, wastewater, drinking water, or soil sample) from an environmental source. In some embodiments, the sample gathering device comprises or is controlled by a robot, and/or the sample gathering device is controlled robotically and/or remotely. In some embodiments, a kit comprises a processing step tool that facilitates a sample processing step, e.g., described in this disclosure, to be performed prior to contacting a sample with an esterase or ester. A kit may also include one or more additional agents described in this application, e.g., a PFAS-degrading agent, as a separate composition. In some embodiments, a kit comprises one or more control compositions, e.g., a control composition comprising fluoride, e.g., for use in calibrating the assay the kit provides. Exemplary buffers for use in a kit or method described in this disclosure include citrate buffer solutions, acetate buffer solutions, phosphate buffer solutions, ammonium chloride, calcium carbonate, calcium chloride, calcium citrate, calcium glubionate, calcium gluceptate, calcium gluconate, D-gluconic acid, calcium glycerophosphate, calcium lactate, propanoic acid, calcium levulinate, pentanoic acid, dibasic calcium phosphate, phosphoric acid, tribasic calcium phosphate, calcium hydroxide phosphate, potassium acetate, potassium chloride, potassium gluconate, potassium mixtures, dibasic potassium phosphate, monobasic potassium phosphate, potassium phosphate mixtures, sodium acetate, sodium bicarbonate, sodium chloride, sodium citrate, sodium lactate, dibasic sodium phosphate, monobasic sodium phosphate, sodium phosphate mixtures, tromethamine, magnesium hydroxide, aluminum hydroxide, alginic acid, pyrogen-free water, isotonic saline, Ringer’s solution, ethyl alcohol, and mixtures thereof. In certain embodiments, a kit described in this application further includes instructions for using the kit. A kit may also include information as required by a regulatory agency, such as the U.S. Environmental Protection Agency (EPA), a U.S. state environmental agency, or a non-U.S. governmental agency or a non-profit environmental agency. In certain embodiments, the information included in the kits provides instructions to perform a method described in the disclosure. Esterases The disclosure provides methods and kits utilizing esterases. As used in this disclosure, an esterase refers to an enzyme that is capable of catalyzing the breakdown (e.g., hydrolysis) of an ester. In some embodiments, an esterase is capable of converting an ester into a carboxylic acid and an alcohol. In some embodiments, an esterase catalyzes a reaction that produces a detectable product. The disclosure is based, at least in part, on the detection of fluoride and/or the defluorination of a PFAS using the inhibiting effect of fluoride on the activity of some esterases. Accordingly, an esterase for use in the methods of the disclosure is an esterase that is inhibited by fluoride. In some embodiments, inhibition of an esterase by fluoride is used to determine the presence or level of fluoride in a sample. In some embodiments, determining the presence or level of fluoride in a sample by measuring the inhibition of esterase activity allows for detecting or quantifying a fluoride-producing process, e.g., defluorination of a PFAS. Any esterase capable of producing a detectable product and that is inhibited by fluoride can be used with the methods and kits of the disclosure. Numerous such esterases are known to those of skill in the art. An exemplary esterase is pig liver esterase (PLE). See, e.g., Junge and Heymann Eur. J. Biochem.95, 519-525 (1979). PLE is available commercially, e.g., from Sigma-Aldrich. Further examples of esterases for use in the methods and kits of the disclosure include, but are not limited to, esterases of the following types: neuropathy target esterase (NTE), acetylcholinesterase, butyrylcholinesterase, cinnamoyl esterase, alpha- naphthyl acetate esterase (ANAE), alpha-naphthyl butyrate esterase, phenyl valerate esterase, arylacetamide deacetylase (AADAC), feruloyl esterase, paraoxonase, serine carboxyl esterase, serine esterase, carboxyl esterase, acetyl esterase, cholinesterase, naphthyl esterase, acetyl esterase, butyryl esterase, acetyl butyryl esterase, alpha-amino-acid esterase, amino acid esterase, cellular esterase, monocyte esterase, brain esterase, gut esterase, liver esterase, microsomal esterase, and nonspecific esterase, and also those found in: J Yourno, W Mastropaolo; Blood 1981; 58 (5): 939–946. doi: https://doi.org/10.1182/blood.V58.5.939.939; Fukami T, Yokoi T. Drug Metab Pharmacokinet.2012;27(5):466-77. doi: 10.2133/dmpk.dmpk-12-rv-042; and Montella IR, Schama R, Valle D. Mem Inst Oswaldo Cruz.2012 Jun;107(4):437-49. doi: 10.1590/s0074- 02762012000400001, each of which is incorporated by reference. In some embodiments, an esterase is present in the reaction mixture at a concentration that is configured, in the context of the enzyme’s activity, the ester concentration and detectability, and the anticipated properties of the sample (e.g., the level of fluoride in the sample), to produce a detectable product that can be detected by the methods described in this disclosure. In some embodiments, the esterase concentration in the reaction mixture is about 1-10 µg/ml, 2-10 µg/ml, 3-10 µg/ml, 4-10 µg/ml, 5-10 µg/ml, 6-10 µg/ml, 7-10 µg/ml, 8-10 µg/ml, 9-10 µg/ml, 1-9 µg/ml, 2-9 µg/ml, 3-9 µg/ml, 4-9 µg/ml, 5-9 µg/ml, 6-9 µg/ml, 7-9 µg/ml, 8-9 µg/ml, 1-8 µg/ml, 2-8 µg/ml, 3-8 µg/ml, 4-8 µg/ml, 5-8 µg/ml, 6-8 µg/ml, 7-8 µg/ml, 1-7 µg/ml, 2-7 µg/ml, 3-7 µg/ml, 4-7 µg/ml, 5-7 µg/ml, 6-7 µg/ml, 1-6 µg/ml, 2-6 µg/ml, 3-6 µg/ml, 4-6 µg/ml, 5-6 µg/ml, 1-5 µg/ml, 2-5 µg/ml, 3-5 µg/ml, 4-5 µg/ml, 1-4 µg/ml, 2-4 µg/ml, 3-4 µg/ml, 1-3 µg/ml, 2-3 µg/ml, or 1-2 µg/ml. In some embodiments, contacting a sample with an esterase in a method described in the disclosure comprises contacting the sample with an esterase stock solution that comprises a higher concentration of esterase. In some embodiments, a kit described in the disclosure comprises an esterase in the form of such a stock solution. In some embodiments, a kit described in the disclosure directs, or a method described in the disclosure comprises, providing a stock solution of an esterase by rehydrating a lyophilized esterase. A person of skill in the art would be able to determine the various corresponding stock solution concentrations of esterases that would produce the reaction mixture concentrations described in the disclosure. Methods of Producing Esterases In some embodiments, esterases for use in the methods and kits of the disclosure are obtained from a third party (e.g., commercially). In some embodiments, an esterase is produced from an organism (e.g., an organ, tissue, cell of an organism, or single-celled organism (e.g., a eukaryotic or prokaryotic microbe)) that endogenously expresses the esterase. In some embodiments, an esterase is produced from a host cell that recombinantly expressed the esterase (i.e., such that the esterase is a recombinant polypeptide). In some embodiments, a step of contacting a sample with an esterase comprises the step of contacting a sample with an organism that produces an esterase. In some embodiments, the esterase is a recombinant polypeptide (i.e., a polypeptide produced from a recombinant polynucleotide). The terms “heterologous”, “exogenous”, and “recombinant” with respect to a polynucleotide, such as a polynucleotide comprising a gene encoding an esterase, are used interchangeably in this disclosure and refer to: a polynucleotide that has been artificially supplied to a biological system; a polynucleotide that has been modified within a biological system, or a polynucleotide whose expression or regulation has been manipulated within a biological system. A heterologous polynucleotide that is introduced into or expressed in a host cell may be a polynucleotide that comes from a different organism or species than the host cell, or may be a synthetic polynucleotide, or may be a polynucleotide that is also endogenously expressed in the same organism or species as the host cell. For example, a polynucleotide that is endogenously expressed in a host cell may be considered heterologous when it is situated non-naturally in the host cell; expressed recombinantly in the host cell, either stably or transiently; modified within the host cell; selectively edited within the host cell; expressed in a copy number that differs from the naturally occurring copy number within the host cell; or expressed in a non-natural way within the host cell, such as by manipulating regulatory regions that control expression of the polynucleotide. In some embodiments, a heterologous polynucleotide is a polynucleotide that is endogenously expressed in a host cell but whose expression is driven by a promoter that does not naturally regulate expression of the polynucleotide. In other embodiments, a heterologous polynucleotide is a polynucleotide that is endogenously expressed in a host cell and whose expression is driven by a promoter that does naturally regulate expression of the polynucleotide, but the promoter or another regulatory region is modified. In some embodiments, the promoter is recombinantly activated or repressed. For example, gene- editing based techniques may be used to regulate expression of a polynucleotide, including an endogenous polynucleotide, from a promoter, including an endogenous promoter. See, e.g., Chavez et al., Nat Methods.2016 Jul; 13(7): 563–567. A heterologous polynucleotide may comprise a wild-type sequence or a mutant sequence as compared with a reference polynucleotide sequence. A recombinant esterase can be produced from a host cell. Suitable host cells include, but are not limited to: yeast cells, bacterial cells, algal cells, plant cells, fungal cells, insect cells, and animal cells, including mammalian cells. In one embodiment, suitable host cells include E. coli (e.g., Shuffle™ competent E. coli available from New England BioLabs in Ipswich, Mass). The term “cell,” as used in this application, may refer to a single cell or a population of cells, such as a population of cells belonging to the same cell line or strain. Use of the singular term “cell” should not be construed to refer explicitly to a single cell rather than a population of cells. The host cell may comprise genetic modifications relative to a wild-type counterpart. A vector encoding any one or more of recombinant polypeptides (e.g., the esterase) described in this application may be introduced into a suitable host cell using any method known in the art. Host cells may be cultured under any conditions suitable as would be understood by one of ordinary skill in the art. For example, any media, temperature, and incubation conditions known in the art may be used. For host cells carrying an inducible vector, cells may be cultured with an appropriate inducible agent to promote expression. Any of the cells disclosed in this application can be cultured in media of any type (rich or minimal) and any composition prior to, during, and/or after contact and/or integration of a nucleic acid. The conditions of the culture or culturing process can be optimized through routine experimentation as would be understood by one of ordinary skill in the art. Culturing of the cells described in this application can be performed in culture vessels known and used in the art. In some embodiments, the esterase is lyophilized. In some embodiments, a method described in the disclosure comprises rehydrating the esterase, e.g., by contacting the esterase with a buffer. In some embodiments, a kit described in the disclosure provides the esterase in lyophilized form, e.g., along with instructions for rehydrating the esterase. Variants of esterases described in this disclosure are also encompassed by the present disclosure. For example, the disclosure encompasses variant esterases capable of converting an ester to a detectable product (e.g., a carboxylic acid and a detectable product) and that are inhibited by fluoride. A variant may share at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 71%, at least 72%, at least 73%, at least 74%, at least 75%, at least 76%, at least 77%, at least 78%, at least 79%, at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a reference sequence (e.g., a wild-type or commercially available esterase amino acid sequence), including all values in between. Unless otherwise noted, the term “sequence identity,” as known in the art, refers to a relationship between the sequences of two polypeptides or polynucleotides, as determined by sequence comparison (alignment). In some embodiments, sequence identity is determined across the entire length of a sequence (e.g., esterase sequence). In some embodiments, sequence identity is determined over a region (e.g., a stretch of amino acids or nucleic acids, e.g., the sequence spanning an active site) of a sequence (e.g., esterase sequence). As used in this disclosure, variant sequences may be homologous sequences. As used in this disclosure, homologous sequences are sequences (e.g., nucleic acid or amino acid sequences) that share a certain percent identity (e.g., at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 71%, at least 72%, at least 73%, at least 74%, at least 75%, at least 76%, at least 77%, at least 78%, at least 79%, at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% percent identity, including all values in between). Homologous sequences include but are not limited to paralogous or orthologous sequences. Paralogous sequences arise from duplication of a gene within a genome of a species, while orthologous sequences diverge after a speciation event. Functional variants of the recombinant esterase disclosed in this application are also encompassed by the present disclosure. For example, functional variants may bind one or more of the same substrates or produce one or more of the same products. Functional variants may be identified using any method known in the art. For example, the algorithm of Karlin and Altschul Proc. Natl. Acad. Sci. USA 87:2264-68, 1990 described above may be used to identify homologous proteins with known functions. Putative functional variants may also be identified by searching for polypeptides with functionally annotated domains. Databases including Pfam (Sonnhammer et al., Proteins. 1997 Jul;28(3):405-20) may be used to identify polypeptides with a particular domain. The activity (e.g., specific activity) of any of the recombinant polypeptides described in this disclosure (e.g., esterase) may be measured using routine methods. As a non-limiting example, a recombinant polypeptide’s activity may be determined by measuring its substrate specificity, product(s) produced, the concentration of product(s) produced, or any combination thereof. As used in this disclosure, “specific activity” of a recombinant polypeptide refers to the amount (e.g., concentration) of a particular product produced for a given amount (e.g., concentration) of the recombinant polypeptide per unit time. Variants can be prepared according to methods for altering polypeptide sequence known to one of ordinary skill in the art such as are found in references which compile such methods, e.g., Molecular Cloning: A Laboratory Manual, J. Sambrook, et al., eds., Fourth Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, 2012, or Current Protocols in Molecular Biology, F.M. Ausubel, et al., eds., John Wiley & Sons, Inc., New York, 2010. Non-limiting examples of functionally equivalent variants of polypeptides may include conservative amino acid substitutions in the amino acid sequences of proteins disclosed in this application. As used in this disclosure “conservative substitution” is used interchangeably with “conservative amino acid substitution” and refers to any one of the amino acid substitutions provided in Table 1. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 residues can be changed when preparing variant polypeptides. In some embodiments, amino acids are replaced by conservative amino acid substitutions. Table 1. Conservative Amino Acid Substitutions.

Amino acid substitutions in the amino acid sequence of a polypeptide to produce a recombinant polypeptide (e.g., esterase) variant having a desired property and/or activity can be made by alteration of the coding sequence of the polypeptide (e.g., esterase). Similarly, conservative amino acid substitutions in the amino acid sequence of a polypeptide to produce functionally equivalent variants of the polypeptide typically are made by alteration of the coding sequence of the recombinant polypeptide (e.g., esterase). Mutations (e.g., substitutions, additions, and/or deletions) can be made in a nucleotide sequence by a variety of methods known to one of ordinary skill in the art. For example, mutations can be made by PCR-directed mutation, site-directed mutagenesis according to the method of Kunkel (Kunkel, Proc. Nat. Acad. Sci. U.S.A.82: 488-492, 1985), by chemical synthesis of a gene encoding a polypeptide, by gene editing techniques, or by insertions, such as insertion of a tag (e.g., a HIS tag or a GFP tag). Esters The disclosure provides methods and kits utilizing esters. As used in this disclosure, an “ester” refers to an organic (i.e., carbon- and hydrogen-containing) compound comprising at least one carbon-oxygen-carbon moiety where one of said carbons is also part of a carbonyl moiety. An ester for use in the disclosure is capable of being a substrate of an esterase described in this disclosure. In some embodiments, an ester can be converted by an esterase (e.g., by hydrolysis) into a carboxylic acid and an alcohol. In some embodiments, an ester comprises a detectable product. In some embodiments, the detectable product is not detectable or less detectable while present in the ester than as a free molecule. In some embodiments, a detectable product is more fluorescent when present as a free molecule than when present in an ester. In some embodiments, a detectable product is fluorescent when present as a free molecule and is not fluorescent when present in an ester. In some embodiments, an esterase is capable of converting the ester into a detectable product, e.g., by freeing the detectable product from the ester or rendering a severable moiety of the ester detectable. For example, an ester may comprise a moiety that is fluorescent when not part of the ester, and the esterase may produce a fluorescent detectable product by hydrolyzing the ester and freeing the moiety, thereby producing a detectable product. In some embodiments, a detectable product has a color or is detectable by colorimetric techniques (e.g., absorbance spectroscopy). In some embodiments, a detectable product is fluorescent. In some embodiments, a detectable product is luminescent. Examples of fluorescent detectable products for use in the methods and kits of the disclosure include any fluorescent molecules known in the art, that, when present in an ester (e.g., an ester described in the disclosure) exhibit altered (e.g., decreased) fluorescence relative to their fluorescence when not present in the ester. In some embodiments, the detectable product is 4- MU. In some embodiments, the detectable product is p-nitrophenol. Any ester comprising a detectable product (e.g., a fluorescent detectable product) and capable of being a substrate of an esterase can be used with the methods and kits of the disclosure. Numerous esters comprising detectable products are known to those of skill in the art. An exemplary ester is 4-methylumbelliferone butyrate (4-MUB).4-MUB comprises the detectable product 4-methylumbelliferone (4-MU), which is fluorescent. Another exemplary group of esters are p-nitrophenol esters. p-nitrophenol is fluorescent and that fluorescence is altered when, e.g., the phenol hydroxyl group is restored by cleavage of the p-nitrophenol ester. Further examples of esters for use in the methods and kits of the disclosure include, but are not limited to, esters of the following types: 4-methylumbelliferyl caprylate (MU-C8), an alpha-naphthyl acetate ester, an alpha-naphthyl butyrate ester, a ferulic acid ester, a phenyl valerate ester, an amino acid ester, a carboxylic ester, an acetyl ester, an acetate ester, an acrylate ester, an adipate ester, an aminobenzoate ester, a benzoate ester, a buciclate ester, a butyrate ester, a butyryl ester, a caproate ester, a carbamate, a chloroformate, a choline ester, a chrysanthemate ester, a cinnamate ester, a citrate ester, a cyanoacrylate ester, a cypionate ester, a decanoate ester, an enanthate ester, a fatty acid ester, a fibrate, a formate ester, a fumarate ester, a furoate, a hydroxycinnamic acid ester, an isobutyrate ester, an isocaproate ester, an isonicotinate, an isovalerate ester, a ketoester, a lactate ester, a lactone, a laurate ester, a maleate ester, a malonate ester, a methacrylate ester, a naphthyl ester, a nicotinate, a nonanoate ester, an oxalate ester, a palmitate ester, a phthalate ester, a pivalate ester, a propionate ester, a pyrethroid, a salicylate ester, a stearate ester, a succinate ester, a tartrate ester, a terephthalate ester, an undecanoate ester, an undecylenate ester, and a valerate ester. In some embodiments, an ester is present in the reaction mixture at a concentration that is configured, in the context of the esterase (e.g., its concentration and activity) and the anticipated properties of the sample (e.g., the level of fluoride in the sample), to produce a detectable product that can be detected by the methods described in the disclosure. In some embodiments, the ester concentration in the reaction mixture is about 0.01-0.5 mM, 0.025-0.5 mM, 0.05-0.5 mM, 0.075-0.5 mM, 0.1-0.5 mM, 0.15-0.5 mM, 0.2-0.5 mM, 0.25-0.5 mM, 0.3-0.5 mM, 0.35-0.5 mM, 0.4-0.5 mM, 0.45-0.5 mM, 0.01-0.3 mM, 0.025-0.3 mM, 0.05-0.3 mM, 0.075-0.3 mM, 0.1-0.3 mM, 0.15-0.3 mM, 0.2-0.3 mM, 0.25-0.3 mM, 0.01-0.2 mM, 0.025-0.2 mM, 0.05-0.2 mM, 0.075-0.2 mM, 0.1-0.2 mM, 0.15-0.2 mM, 0.01-0.1 mM, 0.025- 0.1 mM, 0.05-0.1 mM, or 0.075-0.1 mM. In some embodiments, contacting a sample with an ester in a method described in this disclosure comprises contacting the sample with an ester stock solution that comprises a higher concentration of ester. In some embodiments, a kit described in this disclosure comprises an ester in the form of such a stock solution. A person of skill in the art is able to determine the various corresponding stock solution concentrations of ester that would produce the reaction mixture concentrations described in this disclosure. EXAMPLES In order that the invention described in the present application may be more fully understood, the following examples are set forth. The examples described in this application are offered to illustrate the systems and methods provided in this disclosure and are not to be construed in any way as limiting their scope. Example 1: Development of an Esterase Inhibition Assay for Fluoride Detection To more efficiently detect fluoride and, e.g., to detect and quantify fluoride-producing processes such as the defluorination of PFAS, an esterase inhibition assay was developed. An exemplary embodiment of this esterase inhibition assay uses pig liver esterase (PLE) and 4- methylumbelliferone butyrate (4-MUB). Assay reagents An esterase inhibition reaction mixture for fluoride detection was developed that comprised an esterase that is inhibited by fluoride, a substrate, a sample, and a buffer.4- methylumbelliferone butyrate (4-MUB, >98%, Sigma Aldrich) was used as the substrate and pig liver esterase (PLE; Sigma Aldrich) was used as the esterase.4-MUB is converted to the fluorescent product 4-MU by the pig liver esterase. The 4-MUB was stored as 15 or 25 mM stocks in DMSO at room temperature and the esterase was stored as 0.5 mg/mL stocks in 10 mM phosphate buffer (pH 7) with 20% glycerol at -80ºC. To obtain calibration curves, reactions included samples with known concentrations of sodium fluoride (Sigma Aldrich), which were prepared from 0.25 M sodium fluoride stocks in water stored at -20ºC. Samples tested included Millipore water and two groundwater samples obtained from different areas known to contain PFAS contamination.100 mM sodium phosphate buffer (Boston Bioproducts) was used in assay development experiments. For pH optimization experiments, 100 mM sodium phosphate buffer was adjusted to a pH of 4 using hydrochloric acid.100 mM pH 4 citrate buffer (Boston Bioproducts) was used for all other experiments. Exemplary Assay and Results Fluoride dilution series were prepared by diluting the 0.25 M sodium fluoride stock solution into Millipore water. Working stocks of 1 mM and 5 mM 4-MUB were prepared by diluting 25 mM 4-MUB stock solutions in DMSO. Working stocks of 0.05 mg/mL and 0.1 mg/mL PLE were prepared by diluting the 0.5 mg/mL PLE stock into water.34 µL of 100 mM pH 4 or pH 7 sodium phosphate buffers, and 3 µL of 1 mM or 5 mM 4-MUB were added to the appropriate wells of a 384-well black clear bottom plate.5 µL of the fluoride dilution series samples were added to the appropriate wells of the plate. Lastly, 3 µL of 0.05 mg/mL or 0.1 mg/mL PLE were added to the appropriate wells. Plates were quickly sealed, mixed using a thermomixer, and spun on a benchtop centrifuge. Fluorescence was measured in a Biotek® Neo2 plate reader every minute for 1 hour at an excitation wavelength of 365 nm, an emission wavelength of 410 nm, and a gain of 80. Unless otherwise noted, fluorescence values measured at 1 hour were used for the analyses. FIG.1A shows fluorescence after incubation of PLE at concentrations of 0.003 or 0.006 mg/mL with 4-MUB at concentrations of 0.06 or 0.3 mM at pH 7 over a fluoride dilution series of 0 to 10 mM. The fluoride IC50 is shown in the table in FIG.1B. A fluoride IC50 of 0.11 mM was calculated for a PLE concentration of 0.006 mg/mL and a 4-MUB concentration of 0.06 mM. Using this combination of enzyme and substrate concentrations, fluorescence was measured for a fluoride dilution series of 0 to 10 mM at pH 4 and pH 7 (FIGs.1C-1D). As shown in FIG.1E, the fluoride IC50 was 0.0001 at pH 4 and 0.1 at pH 7, indicating that the esterase inhibition assay showed a higher sensitivity to the presence of fluoride at pH 4. Fluorescence signal was higher at pH 7, suggesting that the esterase inhibition assay has greater dynamic detection range, and that the fluoride concentration is correspondingly more quantifiable, at pH 7. The results show that the esterase inhibition assay using the exemplary esterase PLE and the exemplary ester 4-MUB can detect inhibition of esterase by fluoride at a variety of concentrations of reagents and fluoride, and with an IC50 and dynamic detection range tunable by reaction mixture conditions (e.g., pH). Activity assays for detection of fluoride in groundwater A series of experiments was conducted to demonstrate high-throughput detection of fluoride in groundwater samples using the esterase inhibition assay described above. Samples obtained from non-laboratory environments such as groundwater can contain interfering inorganic compounds or biologic matrices that might interfere with esterase activity or with measurable inhibition of esterase activity by fluoride. To prepare samples spiked with known quantities of fluoride, their dilutions, and fluoride calibration curves, a 0.25 M sodium fluoride stock solution was diluted into the appropriate samples (Millipore water or groundwater). Working stocks of 4-MUB and PLE were prepared by diluting a 15 mM 4-MUB stock in DMSO to 0.625 mM and diluting a 0.5 mg/mL stock of PLE to 0.06 mg/mL, respectively.30 µL of 100 mM pH 4 citrate buffer and 5 µL of a 0.6254-MUB solution in DMSO were added to each well of a 384-well black clear bottom plate.5 µL of the sample was added to the appropriate wells of the same plate followed by 5 µL of 0.06 mg/mL PLE. The plates were quickly sealed, mixed using a thermomixer, and spun on a benchtop centrifuge. The fluorescence was measured in a Biotek® Synergy plate reader every 7 minutes for 1 hour at an excitation wavelength of 365 nm, an emission wavelength of 410 nm, and a gain of 80. The fluorescence values measured at 1 hour were used for all analysis. Data analysis and estimation of fluoride concentrations All inhibition calibration curves were fit to the functional form: y = D + (A-D) / (1 + (x/C)^B) where y is the endpoint fluorescence intensity, x is the fluoride concentration, and A, B, C, and D are fit parameters. The uncertainty in the fit parameters was estimated using a Monte Carlo simulation in which 1,000,000 fluorescence values were sampled at each concentration from distributions with the same average and standard deviation as the measured values and fit to obtain a distribution of fit parameters. Uncertainties reported are one standard deviation. The fluorescence measurements for Millipore water and two groundwater samples are shown in FIGs.2A-2C. The fitted curves using the fit parameters are also shown and align well with the experimental curves. The fluoride IC50 was determined for each sample (FIG.2D). To estimate the fluoride concentration in an unknown sample, the dilution which produced an endpoint fluorescence intensity closest to the IC50 was used to back-calculate fluoride concentration using the functional form and fit parameters discussed above. Uncertainties reported are one standard deviation. FIGs.3A-3D show the measurement of fluoride concentration in groundwater samples, with some groundwater samples containing known levels of added fluoride (indicated by arrows on the graphs). Samples 4, 9, and 17 were obtained from groundwater 1 (from a first environmental source) and were supplemented with 0.008, 0.005 and 2 mM fluoride, respectively. Samples 29, 40, and 45 were obtained from groundwater 2 (from a second environmental source different from groundwater 1) and were supplemented with 0.9, 0.1 and 0.02 mM fluoride, respectively. Endpoint fluorescence was significantly lower for these samples compared to other samples from groundwater 1 and groundwater 2 (FIG.3A), which were not supplemented with fluoride. This indicates inhibition of PLE activity in the presence of added fluoride. At low dilution levels (< 10,000 dilution factor), fluorescence levels between samples with different levels of added fluoride are significantly different (FIGs.3B-3C). Fluoride levels were measured for these samples at low dilution using the PLE-based assay described above or ionic chromatography (IC) (FIG.3D). The PLE-based assay was found to exhibit comparable accuracy to IC in determining the amount of added fluoride, but, significantly, the PLE-based assay is capable of operating in a high-throughput manner to analyze many more samples per unit time. These results show that an esterase inhibition assay, exemplified using PLE and 4- MUB, was developed that can detect fluoride in a scalable, high-throughput manner in groundwater samples with similar accuracy to slower, single sample detection methods such as IC. The potential presence of interfering inorganic compounds or biologic matrices did not interfere with the assay. Example 2: Fluoride Inhibition of Esterase Activity with Quench Solution and Heat Treatment Heating is an abiotic method of promoting defluorination of PFAS and temperature can have significant effects on enzymatic activity generally. Additionally, it may be possible to exercise temporal control over esterase activity by quenching the esterase, e.g., using a denaturing detergent. Experiments were performed to evaluate the effect of heat treatments and quenching on fluoride detection and inactivation of PLE. Reaction mixtures were prepared comprising 10 µL of a diluted fluoride solution, 34 µL of pH 4 citrate buffer, 3 µL of DMSO or 4-MUB, and 3 µL of 0.1 mg/mL PLE. Fluorescence levels were measured over time for a period of 35 minutes after either: (i) adding the reaction mixture to a quench solution of Tris pH 8.5 with 2% SDS, or (ii) heat treating the reaction mixture at 95ºC for 5 minutes prior to adding the quench solution. The kinetic read over 35 minutes after the quenching reactions was performed to ensure that the PLE activity had been effectively inactivated. Initial fluorescence levels were also measured over a period of 35 minutes under no-quench, no-heat conditions. Standard fluorescence curves were obtained for different concentrations (0-12 mM) of 4-MUB in the reaction mixture at pH 4, in the absence of PLE, to show the effect of quenching, with or without heat treatment. FIG.4A shows a standard fluorescence curve without quenching or heat treatment. FIG.4B shows the fluorescence curves after quenching with SDS, with or without heat treatment. Quenching with SDS increases the pH of the reaction mixture which boosts the 4-MU signal and leads to higher overall fluorescence values, allowing a better detection (e.g., quantification) of the fluorescent product. Observed fluorescence levels observed in FIG.4B were significantly higher than those observed without quenching in FIG.4A. There was good agreement in the fluorescence levels between the heated and non-heated curves (FIG.4B), indicating that heat treatment does not significantly affect fluorescence signal. The quench reaction was also used to inactivate esterase activity, allowing the observation, on the concentration curves, of a temporal snapshot of PLE inhibition. Additional heat treatment was used to further inactivate esterase activity. FIG.4C shows the initial concentration curve with the fluorescence level as a function of fluoride concentration in the reaction mixture with PLE, prior to the quenching reactions. The fluorescence levels immediately following the quenching reactions and over a period of 35 minutes are shown in FIG.4D (without heat treatment) and in FIG.4E (with heat treatment). FIGs.4D-4E show that the SDS quench- and heat-fluorescence levels were in overall agreement with SDS quench-only fluorescence levels immediately upon quenching, and that both sets of data showed detectable inhibition of esterase activity over the fluoride concentrations examined, with higher levels of detected fluorescence due to the shift in pH immediately after quenching (initial timepoints in FIGs.4D and 4E), as compared to the final timepoints of the initial read which were obtained immediately prior to quenching (FIG.4C). When the samples were heated, more variation was observed, over time, between the wells (FIG.4E). The results show that heat treatment and quenching increase overall fluorescence levels of esterase inhibition assay samples, and do not appear to convey significant changes in fluoride detection, e.g., in fluoride IC50 (FIGs.4F-4G). EQUIVALENTS Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described in the present application. Such equivalents are intended to be encompassed by the following claims. All references, including patent documents, are incorporated by reference in their entirety.

Claims

CLAIMS 1. A method of determining the level of fluoride in a sample, the method comprising: (1) contacting the sample with: (a) an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride; and (b) an ester comprising the detectable product, thereby producing a reaction mixture, and (2) determining the level of the detectable product in the reaction mixture, wherein the level of the detectable product is inversely correlated with the level of fluoride.

2. A method of determining the level of defluorination of a per- or polyfluoroalkyl substance (PFAS), the method comprising: (1) contacting a sample containing or suspected of containing a defluorinated PFAS with: (a) an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride; and (b) an ester comprising a detectable product, thereby producing a reaction mixture, and (2) determining the level of the detectable product in the reaction mixture, wherein the level of the detectable product is inversely correlated with the level of defluorination of the PFAS.

3. A method of screening for a composition capable of defluorination of a per- or polyfluoroalkyl substance (PFAS), the method comprising: (1) contacting a sample containing or suspected of containing a composition capable of defluorination of a PFAS with: (a) an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride; and (b) an ester comprising a detectable product, thereby producing a reaction mixture, and (2) determining the level of the detectable product in the reaction mixture, wherein the level of the detectable product is inversely correlated with the presence, level, or potency of a composition capable of defluorination of a PFAS.

4. The method of claim 3, wherein the composition is a polypeptide, a small molecule, or a large molecule.

5. The method of claim 4, wherein the polypeptide is an enzyme.

6. The method of any one of claims 3-5, further comprising: responsive to determining the level of the detectable product in the reaction mixture is below a predetermined value, determining that the sample contains a composition capable of defluorination of a PFAS.

7. The method of any one of claims 3-5, further comprising: responsive to determining the level of the detectable product in the reaction mixture is above a predetermined value, determining that the sample does not contain a composition capable of defluorination of a PFAS.

8. The method of any one of claims 3-5, further comprising: responsive to determining the level of the detectable product in the reaction mixture is within a predetermined value range, performing an additional evaluation of the sample to determine if it contains a composition capable of defluorination of a PFAS.

9. The method of claim 8, wherein the additional evaluation comprises: repeating steps (1) and (2), an ionic chromatography (IC) step, and/or a liquid chromatography-mass spectrometry (LCMS) step.

10. The method of any one of claims 1-9, wherein the level of the detectable product is quantified over time.

11. The method of any one of claims 1 or 10, wherein determining the level of fluoride in the sample comprises evaluating inhibition of the esterase by fluoride in the sample.

12. The method of any one of claims 1-11, wherein the detectable product is detected by measuring a colorimetric, fluorescent, or luminescent signal.

13. The method of any one of claims 1-12, wherein the detectable product is detected by measuring a fluorescent signal.

14. The method of any one of claims 1-13, wherein the method further comprises an ionic chromatography (IC) step and/or a liquid chromatography-mass spectrometry (LCMS) step.

15. The method of claim 14, wherein the ionic chromatography (IC) step and/or liquid chromatography-mass spectrometry (LCMS) step is conducted after the steps of claim 1 or claim 2.

16. The method of any one of claims 1-15, wherein the esterase comprises a pig liver esterase (PLE).

17. The method of any one of claims 1-16, wherein the sample comprises a per- or polyfluoroalkyl substance (PFAS).

18. The method of claim 17, wherein the PFAS is Perfluorooctane Sulfonate (PFOS), Perfluorooctanoic Acid (PFOA), or Perfluorohexane Sulfonate (PFHxS).

19. The method of any one of claims 1-16, wherein the sample does not comprise a per- or polyfluoroalkyl substance (PFAS).

20. The method of any one of claims 1-19, wherein the sample comprises fluoride ions.

21. The method of any one of claims 1-19, wherein the sample does not comprise fluoride ions.

22. The method of any one of claims 1-21, wherein the sample is a soil sample, a groundwater sample, or an artificial water source sample.

23. The method of any one of claims 1-22, wherein the sample has been treated with a PFAS-degrading agent.

24. The method of either one of claims 22 or 23, further comprising diluting the sample prior to the contacting step.

25. The method of either of claim 23 or 24, wherein the PFAS-degrading agent comprises an enzyme or heat.

26. The method of claim 25, wherein the enzyme comprises a ligninolytic enzyme or a reductive dehalogenase (RDase).

27. The method of claim 26, wherein the PFAS-degrading agent comprises a microbe comprising a ligninolytic enzyme or reductive dehalogenase (RDase).

28. The method of any one of claims 1-27, further comprising, responsive to determining the level of fluoride or determining the level of PFAS degradation, treating the soil, groundwater, or artificial water source with a PFAS-degrading agent.

29. The method of any one of claims 1-28, wherein the ester comprises 4- methylumbelliferone butyrate (4-MUB).

30. The method of any one of claims 1-29, wherein the detectable product comprises 4- methylumbelliferone (4-MU).

31. The method of any one of claims 1-30, wherein contacting further comprises contacting the sample with a buffer.

32. The method of claim 31, wherein contacting the sample with a buffer occurs in combination with contacting the sample with the ester enzyme, the ester, or both.

33. The method of either one of claims 31 or 32, wherein the buffer has a pH of about 4, about 5, about 6, about 7, or about 8.

34. The method of any one of claims 31-33, wherein the buffer comprises citrate, DMSO, and/or phosphate.

35. The method of any one of claims 1-34, wherein the ester concentration in the reaction mixture is 0.01-0.5 mM, 0.025-0.5 mM, 0.05-0.5 mM, 0.075-0.5 mM, 0.1-0.5 mM, 0.15-0.5 mM, 0.2-0.5 mM, 0.25-0.5 mM, 0.3-0.5 mM, 0.35-0.5 mM, 0.4-0.5 mM, 0.45-0.5 mM, 0.01- 0.3 mM, 0.025-0.3 mM, 0.05-0.3 mM, 0.075-0.3 mM, 0.1-0.3 mM, 0.15-0.3 mM, 0.2-0.3 mM, 0.25-0.3 mM, 0.01-0.2 mM, 0.025-0.2 mM, 0.05-0.2 mM, 0.075-0.2 mM, 0.1-0.2 mM, 0.15-0.2 mM, 0.01-0.1 mM, 0.025-0.1 mM, 0.05-0.1 mM, or 0.075-0.1 mM.

36. The method of any one of claims 1-35, wherein the esterase concentration in the reaction mixture is 1-10 µg/ml, 2-10 µg/ml, 3-10 µg/ml, 4-10 µg/ml, 5-10 µg/ml, 6-10 µg/ml, 7-10 µg/ml, 8-10 µg/ml, 9-10 µg/ml, 1-9 µg/ml, 2-9 µg/ml, 3-9 µg/ml, 4-9 µg/ml, 5-9 µg/ml, 6-9 µg/ml, 7-9 µg/ml, 8-9 µg/ml, 1-8 µg/ml, 2-8 µg/ml, 3-8 µg/ml, 4-8 µg/ml, 5-8 µg/ml, 6-8 µg/ml, 7-8 µg/ml, 1-7 µg/ml, 2-7 µg/ml, 3-7 µg/ml, 4-7 µg/ml, 5-7 µg/ml, 6-7 µg/ml, 1-6 µg/ml, 2-6 µg/ml, 3-6 µg/ml, 4-6 µg/ml, 5-6 µg/ml, 1-5 µg/ml, 2-5 µg/ml, 3-5 µg/ml, 4-5 µg/ml, 1-4 µg/ml, 2-4 µg/ml, 3-4 µg/ml, 1-3 µg/ml, 2-3 µg/ml, or 1-2 µg/ml.

37. The method of any one of claims 34-36, wherein the buffer concentration in the reaction mixture is about 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, or 500 mM.

38. The method of any one of claims 1-37, wherein the method does not comprise heating the sample.

39. The method of any one of claims 1-38, wherein the method comprises: contacting multiple samples with the esterase and ester to produce multiple reaction mixtures, and determining the level of the detectable product in the multiple reaction mixtures, thereby determining the level of fluoride, the level of defluorination of a PFAS, or screening for a composition capable of defluorination of a PFAS in the multiple samples. 40. The method of claim 39, wherein the method analyzes at least 10, 20, 50, 96, 100, 150, 200, 250, 300, 350, 384, 400, 450, or 500 samples in less than 120, 110, 100, 90, 80, 70, 60, 50,

40, or 30 minutes.

41. The method of any one of claims 1-40, wherein the method is capable of detecting the presence of the detectable product in greater than or equal to 10, 20, 50, 96, 100, 150, 200, 250, 300, 350, 384, 400, 450, or 500 samples and requires less than 120, 110, 100, 90, 80, 70, 60, 50, 40, or 30 minutes to detect fluoride or PFAS degradation in the samples.

42. A kit for detecting fluoride, comprising: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride, and an ester comprising a detectable product.

43. A kit for detecting defluorination of a per- or polyfluoroalkyl substance (PFAS), comprising: an esterase capable of cleaving an ester to release a detectable product, wherein the esterase is inhibited by fluoride, and an ester comprising a detectable product.

44. The kit of either one of claims 42 or 43, wherein the esterase is a pig liver esterase (PLE).

45. The kit of either one of claims 43 or 44, wherein the ester comprises 4- methylumbelliferone butyrate (4-MUB).

46. The kit of any one of claims 42-45, wherein the kit further comprises a buffer.

47. The kit of any one of claims 42-46, further comprising instructions describing how to contact a sample with the esterase, the ester, and/or the buffer.

48. The kit of claim 47, wherein the sample is a soil sample, a groundwater sample, or an artificial water source.

49. The kit of any prior claim, further comprising instructions comprising the steps of a method of any one of claims 1-41.