CN113009079A - Analysis method for releasing PAHs to water phase by using DOM of crabs in rice-crab farming farmland - Google Patents

Analysis method for releasing PAHs to water phase by using DOM of crabs in rice-crab farming farmland Download PDF

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CN113009079A
CN113009079A CN202110196498.3A CN202110196498A CN113009079A CN 113009079 A CN113009079 A CN 113009079A CN 202110196498 A CN202110196498 A CN 202110196498A CN 113009079 A CN113009079 A CN 113009079A
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crab
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phenanthrene
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孙楠
刘靳
蔡振兴
于士杰
杨安培
朱广雷
刘爽
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Northeast Agricultural University
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Abstract

An analysis method for releasing PAHs to a water phase by using crab DOM in a rice-crab co-farming farmland, which relates to an analysis method for releasing PAHs to a water phase by using crab DOM. The invention aims to solve the problem that the release of PAHs to a water phase is influenced when the concentration of the crab DOM is 9mg/L and 45 mg/L. The method comprises the following steps: firstly, collecting the DOM of the crabs; secondly, constructing a test of influence of the crab DOM on phenanthrene; thirdly, analyzing the adsorption distribution condition; fourthly, analyzing the composition of the crab DOM; and fifthly, testing and analyzing the ultraviolet characteristics. The advantages are that: the combination of high performance liquid chromatography, fluorescence spectroscopy and ultraviolet-visible spectroscopy reveals that when the concentration of the crab DOM is 9mg/L, the crab DOM shows the characteristics of an L-shaped adsorption isothermal curve; when the concentration of the crab DOM is 45mg/L, the crab DOM shows the characteristic of an F-shaped adsorption isothermal curve, and is used for researching a mechanism of releasing PAHs in the bottom sediment of the rice-crab co-farming farmland into a water phase.

Description

Analysis method for releasing PAHs to water phase by using DOM of crabs in rice-crab farming farmland
Technical Field
The invention relates to an analysis method for releasing PAHs to a water phase by using a crab DOM.
Background
The rice and crab co-farming agriculture is a typical high-efficiency ecological agricultural production mode, organically combines crab culture and rice planting together, and gives play to unique economic advantage benefits together. Like the development of most ecological agriculture in China, the development method only focuses on enhancing scientific experiments and systematic research of a rice and crab co-cropping ecological agriculture system at present, establishes a safe, high-quality and efficient production theory and technical system, and neglects potential risks possibly brought by rice and crab co-cropping. The risk is caused by complex environmental behaviors of the bottom sediment pollutants of the paddy field in the aquaculture process, particularly the release, migration and biological enrichment of the bottom sediment pollutants caused by the disturbance of crabs and other benthonic animals.
Due to various reasons such as pollution irrigation, atmospheric sedimentation, fertilizer use, surface water input and the like, Polycyclic Aromatic Hydrocarbons (PAHs) become common pollutants in farmlands in China. The PAHs content in farmland soil in China is reported to be 9.90 ng/g-5911 ng/g, and the total level is high. PAHs, as Hydrophobic organic pollutants (HOCs), are one of the most interesting organic pollutants due to their difficult degradation, durability, bioaccumulation and strong "triple effect" (carcinogenesis, teratogeny and mutagenesis). However, in a rice and crab co-farming farmland system, the release rule of PAHs in bottom sediment under biological disturbance is how, the influence mechanism is not known at present, the research is helpful for deeply understanding the biological availability and ecological effect of pollutants, comprehensively understanding the environmental significance of biological disturbance, guaranteeing green agriculture and food safety, providing reference and theoretical basis for secondary release prevention and control of polluted bottom sediment, and urgent need to be found.
In a rice-crab co-farming farmland system, due to the existence of crabs, the rule of releasing PAHs in the sediment to a water body is more complicated. The earlier stage research of the subject group finds that the dissolved organic matter DOM enables PAHs on the sediment particles to be desorbed and released to the water body. Because the DOM that the zoobenthos produced is difficult to distinguish with the DOM of sediment oneself, which kind of DOM plays the leading role to the release of sediment PAHs, is used in the technical problem who waits to solve now.
Disclosure of Invention
The invention aims to solve the problem that how PAHs are released to a water phase cannot be analyzed in detail by the conventional method when the concentration of the DOM of the crabs is 9mg/L and 45mg/L, and provides an analysis method for the DOM of the crabs in a rice-crab co-farming farmland to release the PAHs to the water phase.
An analysis method for releasing PAHs to a water phase by using a crab DOM in a rice and crab co-farming farmland is characterized by comprising the following steps:
firstly, collecting crab DOM: preparing a bottom-mud-free culture solution according to the growth requirement of the crabs, and adopting a bottom-mud-free feeding technology to feed the crabs at a density of 35 crabs/cm2Putting crabs into a sediment-free culture solution, wherein the depth of the sediment-free culture solution is 4.5-5.5 cm, culturing for 30 days, the oxygen concentration in the sediment-free culture solution is 5-7 mg/L in the culture process, centrifuging and separating to retain supernatant, performing suction filtration to obtain a solution after suction filtration, namely a crab DOM solution, measuring the concentration of crab DOM in the crab DOM solution by using a total organic carbon analyzer, and hermetically storing the crab DOM solution at the temperature of 4 ℃;
secondly, constructing a crab DOM to phenanthrene influence test: firstly, simulating the adsorption process of practical field crab DOM on PAHs in sediment to construct an indoor microcosm system, wherein the volume of the indoor microcosm system is 50mL, the mass of the sediment to be tested in the indoor microcosm system is 0.2g, 6 indoor microcosm systems with different phenanthrene concentration gradients are arranged according to different phenanthrene concentrations, the phenanthrene concentrations in the indoor microcosm systems are sequentially 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L, 10mg/L and 25mg/L, and a control group and an experimental group are arranged in each indoor microcosm system with the phenanthrene concentration according to different crab DOM concentrationsI and II, wherein the indoor microcosm system of the control group is not added with the crab DOM, the concentration of the crab DOM in the indoor microcosm system of the experimental group I is 9mg/L, the concentration of the crab DOM in the indoor microcosm system of the experimental group II is 45mg/L, and CaCl is added into each indoor microcosm system2As supporting electrolyte, CaCl in indoor micro-cosmos system2The concentration of the NaN is 0.005mol/L, the pH of the solution in the indoor micro-cosmos system is adjusted to be 7, and NaN with the mass fraction of 0.05 percent is added into the indoor micro-cosmos system3Placing the indoor microcosm system in a constant temperature oscillator, and oscillating at the temperature of 20 ℃ in a dark place at the rotating speed of 250rpm for 6 hours; secondly, performing solid-liquid separation on the indoor microcosm system by adopting a centrifugal machine to obtain supernatant A, filtering the supernatant A into a beaker by using a 0.45 mu m fiber filter membrane, adding a standard phenanthrene D-12, wherein the mass of the standard phenanthrene D-12 is 0.1mg, and adding NaCl and CH2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, the shaking extraction is firstly carried out for 10min, then the standing layering is carried out, and then the separation and collection are carried out, so as to obtain an extract I and a supernatant B; ③ adding NaCl and CH into the supernatant B2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, firstly oscillation extraction is carried out for 10min, then standing and layering are carried out, separation and collection are carried out to obtain an extract II, and the extract I and the extract II are combined to obtain an extract; fourthly, anhydrous Na is firstly adopted for the extract liquor2SO4Dehydrating, rotary steaming to constant weight, accurately metering volume to 1mL with methanol, filtering with 0.22 μm filter membrane, and testing with high performance liquid chromatography to obtain the concentration C of adsorbed substance when it is balancede；
Thirdly, analyzing the adsorption distribution condition: quantifying the adsorption distribution condition of the crab DOM on the phenanthrene at a sediment-water interface by utilizing a Freundlich adsorption isothermal model and a Langmuir adsorption isothermal model:
the equilibrium equation for the Freundlich adsorption isothermal model is as follows:
Freundlich：Qe＝K*Ce 1/nformula I;
q in formula IeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; n and K are adsorption model constants;
the Langmuir adsorption isothermal model equilibrium equation is as follows:
Langmuir：Qe＝b*qm*Ce/(1+b*Ce) Formula II;
q in formula IIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; q. q.smThe maximum adsorption capacity of the adsorption material is mg/g; b is an adsorption model constant;
② utilizing the water distribution coefficient K of soildValue analysis the degree of binding of phenanthrene on the sediment:
soil-water distribution coefficient KdThe values are calculated as follows:
Kd＝Qe/Ceformula III;
q in formula IIIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L;
③ C is the initial concentration of phenanthrene in the indoor micro-cosmos system and the concentration of adsorbed substance when balancingeDrawing an adsorption isothermal curve, and fitting the adsorption isothermal curve through Origin 8.6 to determine that the adsorption isothermal curve conforms to a Langmuir model or a Freundlich model;
fourthly, analyzing the composition of the crab DOM: analyzing the composition of the crab DOM solution obtained in the step one by adopting a three-dimensional synchronous fluorescence spectrum scanner, and setting instrument parameter indexes: the xenon arc light of an excitation light source is 150W, the power supply multiplication voltage is 400V, the slit width of excitation and emission is 10nm, the instrument operation response time is 0.002s, the scanning speed is set to be 2400nm/min, the excitation wavelength is 200 nm-500 nm, the emission wavelength is 246 nm-550 nm, and Milli-Q ultrapure water is used as a blank substrate for automatically correcting the three-dimensional synchronous fluorescence spectrum scanner; diluting the crab DOM solution obtained in the first step by 10 times by using Milli-Q ultrapure water to obtain diluted crab DOM solution, transferring 2.5mL of the diluted crab DOM solution by using a liquid transfer gun, injecting the diluted crab DOM solution into a 1cm quartz fluorescence cuvette, measuring three-dimensional and synchronous fluorescence spectra by using a three-dimensional synchronous fluorescence spectrum scanner automatically corrected in the third step, dividing a three-dimensional fluorescence spectrum chart of the crab DOM into 5 regions, sequentially forming an aromatic protein substance I fluorescence region, an aromatic protein substance II fluorescence region, a fulvic acid substance fluorescence region, a soluble microbial metabolite fluorescence region and a humic acid substance fluorescence region, and collecting the substance components of the crab DOM through the peak searching function of MATLAB 7.0;
and fifthly, testing and analyzing ultraviolet characteristics: firstly, repeating the processes of the second step and the third step to obtain extract liquor; secondly, using Milli-Q ultrapure water as a blank for correction, adopting an ultraviolet-visible spectrophotometer, transferring 2.5mL of extract liquor by using a liquid transfer gun, injecting the extract liquor into a quartz cuvette with a 1cm optical path, setting the wavelength of instrument parameters to be 200 nm-850 nm, and testing the absorbance:
SUV254the calculation method of (2) is as follows:
SUV254＝a254TOC formula IV;
TOC in the formula IV is the concentration of the DOM of the crabs in the indoor micro-cosmos system, and the unit is mg/L; a is254The absorption coefficient of the measured substance at a wavelength of 254 nm;
slope ratio S of absorption spectrumRThe calculation method of (2) is as follows:
a(λ))＝a(λ0)exp[-S(λ-λ0)]formula V;
SR＝S(275～295)/S(350～400)formula VI;
λ in formula V and formula VI0Is the reference wavelength in nm, and S is the absorption spectrum slope in nm-1。
The invention has the advantages that:
firstly, the invention can know that when the concentration of the crab DOM in the indoor micro-universe system is 9 mg/mlAt L, the adsorption quantity Q of phenanthrenee0.02 mg/g-5.14 mg/g, and the maximum saturated adsorption capacity of the solution at equilibrium is 5.14mg/g, which is approximately the same level as that of a system without DOM, i.e. the adsorption capacity Q of phenanthrene in a control groupe0.02 mg/g-6.94 mg/g, and the maximum saturated adsorption capacity of the solution at equilibrium is 6.94 mg/g. The Duncan significance test is adopted to obtain that the adsorption quantity of the two has certain correlation, and R is20.78. When the concentration of the crab DOM in the indoor microcosm system is 45mg/L, the adsorption quantity Q of the phenanthrene iseThe maximum saturated adsorption capacity of the solution is 28.71mg/g when the solution is balanced, and the SPSS 21.0 is adopted to carry out variance analysis on test data, so that compared with an adsorption system without DOM, the adsorption system shows a certain difference, and the coefficient of variation of the adsorption system reaches CV 51.92%; and fitting the adsorption isothermal curve through Origin 8.6 to determine that the adsorption isothermal curve conforms to a Langmuir model when the concentration of the crab DOM in the indoor micro-universe system is 9mg/L, and conforms to a Freundlich model when the concentration of the crab DOM in the indoor micro-universe system is 45 mg/L; when the concentration of the crab DOM in the indoor microcosm system is 9mg/L, the adsorption isotherm curve of phenanthrene is a Langmuir model, and the adsorption index b is less than 1, which indicates that the adsorption sites on the sediment gradually tend to be saturated along with the increase of the concentration of the phenanthrene in the solution, and the crab DOM and the phenanthrene compete for the adsorption sites on the sediment together, so that the adsorption capacity of the sediment on the phenanthrene is gradually reduced, and the extra phenanthrene molecules in the system are difficult to absorb; and when the concentration of the crab DOM in the indoor microcosm system is 45mg/L, the adsorption isotherm of phenanthrene is a Freundlich model, and at the moment, 1/n is more than 1, which shows that the DOM molecules which are subjected to co-adsorption can change the physicochemical property of the sediment and can generate new adsorption sites on the sediment, so that the adsorption quantity of phenanthrene is further increased.
Secondly, calculating the soil-water distribution coefficient KdThe results of the values show: when the concentration of the crab DOM in the indoor microcosm system is 9mg/L, KdThe value is between 0.03L/g and 1.20L/g; when the concentration of the crab DOM in the indoor microcosm system is 45mg/L, KdThe value is between 0.48L/g and 36.97L/g; especially when the concentration of phenanthrene is gradually increasedLarger and smaller, the former being in comparison with the latter KdThe value is enlarged by about 20-30 times, which fully reflects the existence of high-concentration crab DOM in the system, so that the binding capacity of the sediment to phenanthrene is further enhanced, and the mobility of the sediment in an aqueous medium is limited.
Thirdly, displaying analysis results of crab DOM components: a large number of complex absorption peaks exist in the crab DOM at the wavelengths of 220 nm-240 nm, 240 nm-270 nm and 270 nm-320 nm, which shows that different functional groups and conjugated structures, such as benzene rings, phenylhydroxy groups, phenylcarboxylic acid groups and the like, exist in the crab DOM. Meanwhile, because a large number of functional groups with similar absorption peaks exist in the crab DOM, the functional groups are overlapped with each other, and a certain wide and blunt platform and a band are also generated.
IV, according to SUV254And SRThe results of (a) show that SUV increases with phenanthrene concentration in the indoor Microcosmos System254Gradually increasing the value of (c); when the concentration of the crab DOM in the indoor microcosm system is 9mg/L, and the concentration of the phenanthrene in the indoor microcosm system is 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L and 10mg/L, SRThe value gradually increases, and when the concentration of phenanthrene in the indoor micro-cosmos system is 25mg/L, SRThe value decreases; and when the concentration of the crab DOM in the indoor microcosm system is 45mg/L, and the concentration of the phenanthrene in the indoor microcosm system is 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L and 10mg/L, SRThe value is gradually reduced, and when the concentration of phenanthrene in the indoor micro-cosmos system is 25mg/L, SRThe value increases; this confirms that when the concentration of the crab DOM in the indoor micro-universe system is 9mg/L, the macromolecular crab DOM is easily adsorbed in the sediment medium; when the concentration of phenanthrene in the indoor micro-cosmos system is 25mg/L, the situation is completely opposite to the situation, and the small molecular crab DOM is more adsorbed in the sediment medium.
In conclusion, when the concentration of the crab DOM in the indoor micro-universe system is 9mg/L, hydrophilic groups on the crab DOM macromolecules are preferentially combined with hydrogen bonds and coordination bonds in the sediment to occupy adsorption sites on the sediment and form competitive adsorption with phenanthrene, and the hydrophilic groups are combined with hydrophobic groups on crab DOM micromolecules along with the increase of the concentration of the phenanthrene in the indoor micro-universe system, so that a wide aromatic conjugation effect is generated, the solubilization effect is exerted on the phenanthrene, the adsorption of the phenanthrene on the sediment is inhibited, the mobility of the phenanthrene in an aqueous medium is increased, and the characteristic of an L-shaped adsorption isothermal curve is presented; when the concentration of the crab DOM in the indoor microcosm system is 45mg/L, on one hand, the increased concentration of the crab DOM enables the binding capacity of small molecules of the crab DOM to phenanthrene to be stronger, so that when the small molecules of the crab DOM are adsorbed on the sediment together, new active sites can be generated on the sediment, and the adsorption quantity of the sediment to the phenanthrene is further increased; on the other hand, the increased concentration of the crab DOM enables phenanthrene and crab DOM macromolecules to be subjected to co-adsorption and accumulated adsorption coagulation, so that the adsorption quantity of the crab DOM to the phenanthrene is increased along with the increase of the concentration of the phenanthrene in an indoor microcosm system, the two effects are superposed, and the characteristic of an F-shaped adsorption isothermal curve is presented.
Detailed Description
The first embodiment is as follows: the embodiment is an analysis method for releasing PAHs to a water phase by using the DOM of crabs in a rice-crab farming farmland, which is specifically completed according to the following steps:
firstly, collecting crab DOM: preparing a bottom-mud-free culture solution according to the growth requirement of the crabs, and adopting a bottom-mud-free feeding technology to feed the crabs at a density of 35 crabs/cm2Putting crabs into a sediment-free culture solution, wherein the depth of the sediment-free culture solution is 4.5-5.5 cm, culturing for 30 days, the oxygen concentration in the sediment-free culture solution is 5-7 mg/L in the culture process, centrifuging and separating to retain supernatant, performing suction filtration to obtain a solution after suction filtration, namely a crab DOM solution, measuring the concentration of crab DOM in the crab DOM solution by using a total organic carbon analyzer, and hermetically storing the crab DOM solution at the temperature of 4 ℃;
secondly, constructing a crab DOM to phenanthrene influence test: firstly, simulating the adsorption process of practical field crab DOM on PAHs in sediment to construct an indoor microcosm system, wherein the volume of the indoor microcosm system is 50mL, the mass of the sediment to be tested in the indoor microcosm system is 0.2g, 6 indoor microcosm systems with different phenanthrene concentration gradients are arranged according to phenanthrene concentration differences, the concentration of the phenanthrene in the indoor microcosm system is 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L, 10mg/L and 25mg/L in sequence, and each indoor microcosm system is provided with the phenanthrene concentration gradients of 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/LThe indoor microcosm system with the phenanthrene concentration is provided with three different reaction types of a control group, an experimental group I and an experimental group II according to the different concentrations of the crab DOM, wherein the crab DOM is not added in the indoor microcosm system of the control group, the concentration of the crab DOM in the indoor microcosm system of the experimental group I is 9mg/L, the concentration of the crab DOM in the indoor microcosm system of the experimental group II is 45mg/L, and CaCl is added into each indoor microcosm system2As supporting electrolyte, CaCl in indoor micro-cosmos system2The concentration of the NaN is 0.005mol/L, the pH of the solution in the indoor micro-cosmos system is adjusted to be 7, and NaN with the mass fraction of 0.05 percent is added into the indoor micro-cosmos system3Placing the indoor microcosm system in a constant temperature oscillator, and oscillating at the temperature of 20 ℃ in a dark place at the rotating speed of 250rpm for 6 hours; secondly, performing solid-liquid separation on the indoor microcosm system by adopting a centrifugal machine to obtain supernatant A, filtering the supernatant A into a beaker by using a 0.45 mu m fiber filter membrane, adding a standard phenanthrene D-12, wherein the mass of the standard phenanthrene D-12 is 0.1mg, and adding NaCl and CH2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, the shaking extraction is firstly carried out for 10min, then the standing layering is carried out, and then the separation and collection are carried out, so as to obtain an extract I and a supernatant B; ③ adding NaCl and CH into the supernatant B2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, firstly oscillation extraction is carried out for 10min, then standing and layering are carried out, separation and collection are carried out to obtain an extract II, and the extract I and the extract II are combined to obtain an extract; fourthly, anhydrous Na is firstly adopted for the extract liquor2SO4Dehydrating, rotary steaming to constant weight, accurately metering volume to 1mL with methanol, filtering with 0.22 μm filter membrane, and testing with high performance liquid chromatography to obtain the concentration C of adsorbed substance when it is balancede；
Thirdly, analyzing the adsorption distribution condition: quantifying the adsorption distribution condition of the crab DOM on the phenanthrene at a sediment-water interface by utilizing a Freundlich adsorption isothermal model and a Langmuir adsorption isothermal model:
the equilibrium equation for the Freundlich adsorption isothermal model is as follows:
Freundlich：Qe＝K*Ce 1/nformula I;
q in formula IeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; n and K are adsorption model constants;
the Langmuir adsorption isothermal model equilibrium equation is as follows:
Langmuir：Qe＝b*qm*Ce/(1+b*Ce) Formula II;
q in formula IIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; q. q.smThe maximum adsorption capacity of the adsorption material is mg/g; b is an adsorption model constant;
② utilizing the water distribution coefficient K of soildValue analysis the degree of binding of phenanthrene on the sediment:
soil-water distribution coefficient KdThe values are calculated as follows:
Kd＝Qe/Ceformula III;
q in formula IIIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L;
③ C is the initial concentration of phenanthrene in the indoor micro-cosmos system and the concentration of adsorbed substance when balancingeDrawing an adsorption isothermal curve, and fitting the adsorption isothermal curve through Origin 8.6 to determine that the adsorption isothermal curve conforms to a Langmuir model or a Freundlich model;
fourthly, analyzing the composition of the crab DOM: analyzing the composition of the crab DOM solution obtained in the step one by adopting a three-dimensional synchronous fluorescence spectrum scanner, and setting instrument parameter indexes: the xenon arc light of an excitation light source is 150W, the power supply multiplication voltage is 400V, the slit width of excitation and emission is 10nm, the instrument operation response time is 0.002s, the scanning speed is set to be 2400nm/min, the excitation wavelength is 200 nm-500 nm, the emission wavelength is 246 nm-550 nm, and Milli-Q ultrapure water is used as a blank substrate for automatically correcting the three-dimensional synchronous fluorescence spectrum scanner; diluting the crab DOM solution obtained in the first step by 10 times by using Milli-Q ultrapure water to obtain diluted crab DOM solution, transferring 2.5mL of the diluted crab DOM solution by using a liquid transfer gun, injecting the diluted crab DOM solution into a 1cm quartz fluorescence cuvette, measuring three-dimensional and synchronous fluorescence spectra by using a three-dimensional synchronous fluorescence spectrum scanner automatically corrected in the third step, dividing a three-dimensional fluorescence spectrum chart of the crab DOM into 5 regions, sequentially forming an aromatic protein substance I fluorescence region, an aromatic protein substance II fluorescence region, a fulvic acid substance fluorescence region, a soluble microbial metabolite fluorescence region and a humic acid substance fluorescence region, and collecting the substance components of the crab DOM through the peak searching function of MATLAB 7.0;
and fifthly, testing and analyzing ultraviolet characteristics: firstly, repeating the processes of the second step and the third step to obtain extract liquor; secondly, using Milli-Q ultrapure water as a blank for correction, adopting an ultraviolet-visible spectrophotometer, transferring 2.5mL of extract liquor by using a liquid transfer gun, injecting the extract liquor into a quartz cuvette with a 1cm optical path, setting the wavelength of instrument parameters to be 200 nm-850 nm, and testing the absorbance:
SUV254the calculation method of (2) is as follows:
SUV254＝a254TOC formula IV;
TOC in the formula IV is the concentration of the DOM of the crabs in the indoor micro-cosmos system, and the unit is mg/L; a is254The absorption coefficient of the measured substance at a wavelength of 254 nm;
slope ratio S of absorption spectrumRThe calculation method of (2) is as follows:
a(λ))＝a(λ0)exp[-S(λ-λ0)]formula V;
SR＝S(275～295)/S(350～400)formula VI;
λ in formula V and formula VI0Is the reference wavelength in nm, and S is the absorption spectrum slope in nm-1。
The second embodiment is as follows: the first embodiment and the second embodiment are as follows: in the fourth step, Ex/Em in the fluorescent region of the aromatic protein substance I is (200-250) nm/(260-320) nm; the Ex/Em in the fluorescent region of the aromatic protein substance II is (200-250) nm/(320-380) nm; the Ex/Em in the fluorescence region of the fulvic acid substances is (200-250) nm/(380-550) nm; the Ex/Em in the fluorescence region of the soluble microbial metabolite is (250-450) nm/(260-380) nm; the Ex/Em in the fluorescent region of the humic acid substances is (250-450) nm/(380-550) nm. The rest is the same as the first embodiment.
The invention is not limited to the above embodiments, and one or a combination of several embodiments may also achieve the object of the invention.
The following tests are adopted to verify the effect of the invention:
example 1: an analysis method for releasing PAHs to a water phase by using crab DOM in a rice and crab co-farming farmland is specifically completed according to the following steps:
firstly, collecting crab DOM: preparing a bottom-mud-free culture solution according to the growth requirement of the crabs, and adopting a bottom-mud-free feeding technology to feed the crabs at a density of 35 crabs/cm2Putting crabs into a sediment-free culture solution, wherein the depth of the sediment-free culture solution is 5cm, culturing for 30 days, the oxygen concentration in the sediment-free culture solution is 6mg/L in the culturing process, performing centrifugal separation to retain supernatant, performing suction filtration to obtain a solution after suction filtration, namely a crab DOM solution, measuring the concentration of crab DOM in the crab DOM solution by using a total organic carbon analyzer (the concentration of the crab DOM in the crab DOM solution is 93.05mg/L), and hermetically storing the crab DOM solution at the temperature of 4 ℃;
secondly, constructing a crab DOM to phenanthrene influence test: firstly, simulating the adsorption process of practical field crab DOM on PAHs in sediment to construct an indoor microcosm system, wherein the volume of the indoor microcosm system is 50mL, the mass of the sediment to be tested in the indoor microcosm system is 0.2g, 6 indoor microcosm systems with different phenanthrene concentration gradients are arranged according to different phenanthrene concentrations, the phenanthrene concentrations in the indoor microcosm systems are sequentially 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L, 10mg/L and 25mg/L, and a control group, an experimental group I and an experimental group are arranged in each indoor microcosm system with the phenanthrene concentration according to different crab DOM concentrationsII, three different reaction types, wherein the control group of indoor microcosm system is not added with the crab DOM, the experimental group I of indoor microcosm system is 9mg/L in the concentration of the crab DOM, the experimental group II of indoor microcosm system is 45mg/L in the concentration of the crab DOM, and each indoor microcosm system is added with CaCl2As supporting electrolyte, CaCl in indoor micro-cosmos system2The concentration of the NaN is 0.005mol/L, the pH of the solution in the indoor micro-cosmos system is adjusted to be 7, and NaN with the mass fraction of 0.05 percent is added into the indoor micro-cosmos system3Placing the indoor microcosm system in a constant temperature oscillator, and oscillating at the temperature of 20 ℃ in a dark place at the rotating speed of 250rpm for 6 hours; secondly, performing solid-liquid separation on the indoor microcosm system by adopting a centrifugal machine to obtain supernatant A, filtering the supernatant A into a beaker by using a 0.45 mu m fiber filter membrane, adding a standard phenanthrene D-12, wherein the mass of the standard phenanthrene D-12 is 0.1mg, and adding NaCl and CH2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, the shaking extraction is firstly carried out for 10min, then the standing layering is carried out, and then the separation and collection are carried out, so as to obtain an extract I and a supernatant B; ③ adding NaCl and CH into the supernatant B2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, firstly oscillation extraction is carried out for 10min, then standing and layering are carried out, separation and collection are carried out to obtain an extract II, and the extract I and the extract II are combined to obtain an extract; fourthly, anhydrous Na is firstly adopted for the extract liquor2SO4Dehydrating, rotary steaming to constant weight, accurately metering volume to 1mL with methanol, filtering with 0.22 μm filter membrane, and testing with high performance liquid chromatography to obtain the concentration C of adsorbed substance when it is balancede；
Thirdly, analyzing the adsorption distribution condition: quantifying the adsorption distribution condition of the crab DOM on the phenanthrene at a sediment-water interface by utilizing a Freundlich adsorption isothermal model and a Langmuir adsorption isothermal model:
the equilibrium equation for the Freundlich adsorption isothermal model is as follows:
Freundlich：Qe＝K*Ce 1/npublicFormula I;
q in formula IeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; n and K are adsorption model constants;
the Langmuir adsorption isothermal model equilibrium equation is as follows:
Langmuir：Qe＝b*qm*Ce/(1+b*Ce) Formula II;
q in formula IIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; q. q.smThe maximum adsorption capacity of the adsorption material is mg/g; b is an adsorption model constant;
② utilizing the water distribution coefficient K of soildValue analysis the degree of binding of phenanthrene on the sediment:
soil-water distribution coefficient KdThe values are calculated as follows:
Kd＝Qe/Ceformula III;
q in formula IIIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L;
③ C is the initial concentration of phenanthrene in the indoor micro-cosmos system and the concentration of adsorbed substance when balancingeDrawing an adsorption isothermal curve, and fitting the adsorption isothermal curve through Origin 8.6 to determine that the adsorption isothermal curve conforms to a Langmuir model or a Freundlich model;
fourthly, analyzing the composition of the crab DOM: analyzing the composition of the crab DOM solution obtained in the step one by adopting a three-dimensional synchronous fluorescence spectrum scanner, and setting instrument parameter indexes: the xenon arc light of an excitation light source is 150W, the power supply multiplication voltage is 400V, the slit width of excitation and emission is 10nm, the instrument operation response time is 0.002s, the scanning speed is set to be 2400nm/min, the excitation wavelength is 200 nm-500 nm, the emission wavelength is 246 nm-550 nm, and Milli-Q ultrapure water is used as a blank substrate for automatically correcting the three-dimensional synchronous fluorescence spectrum scanner; diluting the crab DOM solution obtained in the first step by 10 times by using Milli-Q ultrapure water to obtain diluted crab DOM solution, transferring 2.5mL of the diluted crab DOM solution by using a liquid transfer gun, injecting the diluted crab DOM solution into a 1cm quartz fluorescence cuvette, measuring three-dimensional and synchronous fluorescence spectra by using a three-dimensional synchronous fluorescence spectrum scanner automatically corrected in the third step, dividing a three-dimensional fluorescence spectrum chart of the crab DOM into 5 regions, sequentially forming an aromatic protein substance I fluorescence region, an aromatic protein substance II fluorescence region, a fulvic acid substance fluorescence region, a soluble microbial metabolite fluorescence region and a humic acid substance fluorescence region, and collecting the substance components of the crab DOM through the peak searching function of MATLAB 7.0;
and fifthly, testing and analyzing ultraviolet characteristics: firstly, repeating the processes of the second step and the third step to obtain extract liquor; secondly, using Milli-Q ultrapure water as a blank for correction, adopting an ultraviolet-visible spectrophotometer, transferring 2.5mL of extract liquor by using a liquid transfer gun, injecting the extract liquor into a quartz cuvette with a 1cm optical path, setting the wavelength of instrument parameters to be 200 nm-850 nm, and testing the absorbance:
SUV254the calculation method of (2) is as follows:
SUV254＝a254TOC formula IV;
TOC in the formula IV is the concentration of the DOM of the crabs in the indoor micro-cosmos system, and the unit is mg/L; a is254The absorption coefficient of the measured substance at a wavelength of 254 nm;
slope ratio S of absorption spectrumRThe calculation method of (2) is as follows:
a(λ))＝a(λ0)exp[-S(λ-λ0)]formula V;
SR＝S(275～295)/S(350～400)formula VI;
λ in formula V and formula VI0Is the reference wavelength in nm, and S is the absorption spectrum slope in nm-1。
In the fourth step of this embodiment, the aromatic protein substance i in the fluorescent region Ex/Em ═ 200 to 250 nm/(260 to 320) nm; the Ex/Em in the fluorescent region of the aromatic protein substance II is (200-250) nm/(320-380) nm; the Ex/Em in the fluorescence region of the fulvic acid substances is (200-250) nm/(380-550) nm; the Ex/Em in the fluorescence region of the soluble microbial metabolite is (250-450) nm/(260-380) nm; the Ex/Em in the fluorescent region of the humic acid substances is (250-450) nm/(380-550) nm.
The total organic carbon analysis used in the first step of this example is Shimadzu Total organic carbon Analyzer TOC-L.
In the second step of this embodiment, the HPLC using the HPLC is a seemefei/Thermo U3000 HPLC/liquid chromatograph.
The three-dimensional synchronous fluorescence spectrum scanner adopted in the fourth step of this example is Hitachi fluorescence spectrophotometer F-7100.
In the fifth step of this embodiment, the ultraviolet-visible spectrophotometer adopted is an ultraviolet-visible spectrophotometer TN 5000.
The results of the collected material composition of the crab DOM through the peak finding function of MATLAB 7.0 in step four of this example are shown in table 1.
TABLE 1
Figure BDA0002946947470000111
The concentration of the crab DOM in the indoor micro-universe system of the experimental group I is 9mg/L, the concentration of the crab DOM in the indoor micro-universe system of the experimental group II is 45mg/L,
the adsorption amount of phenanthrene in the system after the experiment is finished, as measured by high performance liquid chromatography, is shown in table 2, and the data is counted by using Microsoft Excel 201. By contrast, under the condition that the concentration of the crab DOM is 9mg/L, the adsorption quantity Q of the crab DOM to phenanthrene ise0.02 mg/g-5.14 mg/g, and the maximum saturated adsorption capacity of the solution at equilibrium is 5.14mg/g, which is approximately the same level as that of a system without DOM, i.e. the adsorption capacity Q of phenanthrene in a control groupe0.02 mg/g-6.94 mg/g, and the maximum saturated adsorption capacity of the solution at equilibrium is 6.94 mg/g. The Duncan significance test is adopted to obtain that the adsorption quantity of the two has certain correlation, and R is20.78. On the contraryThe absorption quantity Q of the phenanthrene is equal to the concentration of 45mg/L of the crab DOMeThe maximum saturated adsorption capacity of the solution is 28.71mg/g when the solution is balanced, and the SPSS 21.0 is adopted to carry out variance analysis on test data, so that compared with an adsorption system without DOM phenanthrene, the adsorption system shows a certain difference, and the coefficient of variation of the adsorption system reaches CV 51.92%.
TABLE 2
Figure BDA0002946947470000112
Figure BDA0002946947470000121
In the fourth step of this embodiment, the initial concentration of phenanthrene in the indoor micro-cosmos system and the concentration C of the adsorbed substance during equilibriumeDrawing an adsorption isothermal curve, fitting the adsorption isothermal curve through Origin 8.6, and determining that the adsorption isothermal curve conforms to a Langmuir model when the concentration of the crab DOM in the indoor micro-cosmos system is 9mg/L, and conforms to a Freundlich model when the concentration of the crab DOM in the indoor micro-cosmos system is 45 mg/L; the fitting correlation parameters are shown in table 3. When the concentration of the crab DOM in the indoor microcosm system is 9mg/L, the adsorption isothermal curve of phenanthrene conforms to a Langmuir model, and the adsorption index b is less than 1, which indicates that with the increase of the concentration of phenanthrene in the solution, adsorption sites on the sediment gradually tend to be saturated, the DOM and the phenanthrene compete for the adsorption sites on the sediment together, so that the adsorption capacity of the sediment on the phenanthrene is gradually reduced, and additional phenanthrene molecules in the system are difficult to absorb; when the concentration of the crab DOM in the indoor microcosm system is 45mg/L, the adsorption isothermal curve of the phenanthrene conforms to the Freundlich model, and at the moment, 1/n is larger than 1, which indicates that the DOM molecules which are subjected to co-adsorption can change the physicochemical property of the sediment and generate new adsorption sites on the DOM molecules, so that the adsorption quantity of the phenanthrene is further increased. At the same time, the soil-water distribution coefficient KdThe results of the values show that K is the K for the crab DOM in the indoor Microcosmic System at a concentration of 45mg/LdThe value has a magnitude between 0.48 to 36.97L/g, and K of the microbial organic model is K when the concentration of the crab DOM in the indoor micro-cosmos system is 9mg/LdThe value is between 0.03L/g and 1.20L/g, especially when the concentration of phenanthrene is gradually increased, the K of the former is higher than that of the latterdThe value is enlarged by about 20-30 times, which fully reflects the existence of high-concentration DOM in the system, so that the binding capacity of the sediment to phenanthrene is further enhanced, and the mobility of the sediment in an aqueous medium is limited.
TABLE 3
Figure BDA0002946947470000131
In the fifth step of this example, ultraviolet-visible absorption spectrum is used to measure that the DOM absorbance value of the crabs after the reaction is finished and the adding concentration form a certain proportional relationship. In the test result, a large number of complex absorption peaks exist in the crab DOM at the wavelengths of 220-240 nm, 240-270 nm, 270-320 nm and the like, which shows that different functional groups and conjugated structures exist in the crab DOM, such as benzene rings, phenylhydroxy groups, phenylcarboxylic acid groups and the like. Meanwhile, because a large number of functional groups with similar absorption peaks exist in the crab DOM, the functional groups are overlapped with each other, and a certain wide and blunt platform and a band are also generated. According to SUV254And SRThe results show that, with the increase of the phenanthrene concentration of the reaction system, after the reaction is finished, the SUV254Gradually increases in value. Wherein when the concentration of the DOM of the crabs in the indoor micro-space system is 9mg/L, the SUV254From 13.37 to 62.87, and when the concentration of crab DOM in the indoor Microcosmic System is 45mg/L, the SUV254Increased from 24.69 to 49.02, SUV before and after reaction254The increase of the DOM represents the increase of the DOM aromaticity of the sediment and the DOM aromaticity, which shows that the adsorption affinity of the sediment to aromatic carbon in the DOM of the crabs is weaker than that of aliphatic carbon, and the DOM aromaticity is consistent with the result of the absorbance change trend of a characteristic peak measured by an ultraviolet spectrum. Meanwhile, when the concentration of the DOM of the crabs in the indoor micro-space system is 9mg/L and the concentration of the DOM is within the concentration range of 0.1 mg/L-10 mg/L of phenanthrene, the S of the DOM isRGradually increasing values, i.e. gradually decreasing DOM molecular weight (inversely proportional), gradually increasing small DO molecules in solutionM is the main component; and in the case of a phenanthrene concentration of 25mg/L, SRThe value decreases, i.e. the molecular weight of DOM increases, which confirms that macromolecular DOM is easily adsorbed in the sediment medium in the presence of low-concentration DOM of crabs; when the concentration of the crab DOM in the indoor micro-space system is 45mg/L, the small-molecule DOM is more adsorbed in the sediment medium in contrary to the above situation.
In conclusion, when the concentration of the crab DOM in the indoor micro-universe system is 9mg/L, hydrophilic groups on the crab DOM macromolecules are preferentially combined with hydrogen bonds and coordination bonds in the sediment to occupy adsorption sites on the sediment and form competitive adsorption with phenanthrene, and the hydrophilic groups are combined with hydrophobic groups on crab DOM micromolecules along with the increase of the concentration of the phenanthrene in the indoor micro-universe system, so that a wide aromatic conjugation effect is generated, the solubilization effect is exerted on the phenanthrene, the adsorption of the phenanthrene on the sediment is inhibited, the mobility of the phenanthrene in an aqueous medium is increased, and the characteristic of an L-shaped adsorption isothermal curve is presented; when the concentration of the crab DOM in the indoor microcosm system is 45mg/L, on one hand, the increased concentration of the crab DOM enables the binding capacity of small molecules of the crab DOM to phenanthrene to be stronger, so that when the small molecules of the crab DOM are adsorbed on the sediment together, new active sites can be generated on the sediment, and the adsorption quantity of the sediment to the phenanthrene is further increased; on the other hand, the increased concentration of the crab DOM enables phenanthrene and crab DOM macromolecules to be subjected to co-adsorption and accumulated adsorption coagulation, so that the adsorption quantity of the crab DOM to the phenanthrene is increased along with the increase of the concentration of the phenanthrene in an indoor microcosm system, the two effects are superposed, and the characteristic of an F-shaped adsorption isothermal curve is presented.

Claims (2)

1. An analysis method for releasing PAHs to a water phase by using a crab DOM in a rice and crab co-farming farmland is characterized by comprising the following steps:
firstly, collecting crab DOM: preparing a bottom-mud-free culture solution according to the growth requirement of the crabs, and adopting a bottom-mud-free feeding technology to feed the crabs at a density of 35 crabs/cm2Putting the crabs into a culture solution without the bottom mud, wherein the depth of the culture solution without the bottom mud is 4.5 cm-5.5 cm, culturing for 30 days, and culturing the crabs without the culture solution without the bottom mud in the process of culturingThe concentration of medium oxygen is 5 mg/L-7 mg/L, the supernatant is firstly centrifugally separated and retained, then the solution is subjected to suction filtration to obtain a solution after suction filtration, namely the crab DOM solution, the concentration of the crab DOM in the crab DOM solution is determined by adopting a total organic carbon analyzer, and the crab DOM solution is hermetically stored at the temperature of 4 ℃;
secondly, constructing a crab DOM to phenanthrene influence test: firstly, simulating the adsorption process of actual field crab DOM on PAHs in sediment to construct an indoor microcosm system, wherein the volume of the indoor microcosm system is 50mL, the mass of the sediment to be tested in the indoor microcosm system is 0.2g, 6 indoor microcosm systems with different phenanthrene concentration gradients are arranged according to different phenanthrene concentrations, the phenanthrene concentrations in the indoor microcosm systems are sequentially 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L, 10mg/L and 25mg/L, three different reaction types of a control group, an experimental group I and an experimental group II are arranged in each indoor microcosm system with phenanthrene concentration according to different crab DOM concentrations, wherein the crab DOM is not added in the indoor microcosm system of the control group, the concentration of the DOM in the indoor microcosm system of the experimental group I is 9mg/L, and the concentration of the DOM in the indoor microcosm system of the experimental group II is 45mg/L, CaCl is added into each indoor micro-universe system2As supporting electrolyte, CaCl in indoor micro-cosmos system2The concentration of the NaN is 0.005mol/L, the pH of the solution in the indoor micro-cosmos system is adjusted to be 7, and NaN with the mass fraction of 0.05 percent is added into the indoor micro-cosmos system3Placing the indoor microcosm system in a constant temperature oscillator, and oscillating at the temperature of 20 ℃ in a dark place at the rotating speed of 250rpm for 6 hours; secondly, performing solid-liquid separation on the indoor microcosm system by adopting a centrifugal machine to obtain supernatant A, filtering the supernatant A into a beaker by using a 0.45 mu m fiber filter membrane, adding a standard phenanthrene D-12, wherein the mass of the standard phenanthrene D-12 is 0.1mg, and adding NaCl and CH2Cl2NaCl mass 1g, CH2Cl2The volume of the extract is 5mL, the extract is poured into a separating funnel, the shaking extraction is firstly carried out for 10min, then the standing layering is carried out, and then the separation and collection are carried out, so as to obtain an extract I and a supernatant B; ③ adding NaCl and CH into the supernatant B2Cl2NaCl mass 1g, CH2Cl2Is 5mL, poured into a separating funnel, and is firstly shaken and extracted for 10min, thenStanding for layering, separating and collecting to obtain an extract II, and combining the extract I and the extract II to obtain an extract; fourthly, anhydrous Na is firstly adopted for the extract liquor2SO4Dehydrating, rotary steaming to constant weight, accurately metering volume to 1mL with methanol, filtering with 0.22 μm filter membrane, and testing with high performance liquid chromatography to obtain the concentration C of adsorbed substance when it is balancede；
Thirdly, analyzing the adsorption distribution condition: quantifying the adsorption distribution condition of the crab DOM on the phenanthrene at a sediment-water interface by utilizing a Freundlich adsorption isothermal model and a Langmuir adsorption isothermal model:
the equilibrium equation for the Freundlich adsorption isothermal model is as follows:
Freundlich：Qe＝K*Ce 1/nformula I;
q in formula IeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; n and K are adsorption model constants;
the Langmuir adsorption isothermal model equilibrium equation is as follows:
Langmuir：Qe＝b*qm*Ce/(1+b*Ce) Formula II;
q in formula IIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L; q. q.smThe maximum adsorption capacity of the adsorption material is mg/g; b is an adsorption model constant;
② utilizing the water distribution coefficient K of soildValue analysis the degree of binding of phenanthrene on the sediment:
soil-water distribution coefficient KdThe values are calculated as follows:
Kd＝Qe/Ceformula III;
q in formula IIIeRepresents the adsorption quantity of the adsorbed substance in the balance, and the unit is mg/L; ceRepresents the concentration of the adsorbed substance at the equilibrium, and the unit is mg/L;
③ C is the initial concentration of phenanthrene in the indoor micro-cosmos system and the concentration of adsorbed substance when balancingeDrawing an adsorption isothermal curve, and fitting the adsorption isothermal curve through Origin 8.6 to determine that the adsorption isothermal curve conforms to a Langmuir model or a Freundlich model;
fourthly, analyzing the composition of the crab DOM: analyzing the composition of the crab DOM solution obtained in the step one by adopting a three-dimensional synchronous fluorescence spectrum scanner, and setting instrument parameter indexes: the xenon arc light of an excitation light source is 150W, the power supply multiplication voltage is 400V, the slit width of excitation and emission is 10nm, the instrument operation response time is 0.002s, the scanning speed is set to be 2400nm/min, the excitation wavelength is 200 nm-500 nm, the emission wavelength is 246 nm-550 nm, and Milli-Q ultrapure water is used as a blank substrate for automatically correcting the three-dimensional synchronous fluorescence spectrum scanner; diluting the crab DOM solution obtained in the first step by 10 times by using Milli-Q ultrapure water to obtain diluted crab DOM solution, transferring 2.5mL of the diluted crab DOM solution by using a liquid transfer gun, injecting the diluted crab DOM solution into a 1cm quartz fluorescence cuvette, measuring three-dimensional and synchronous fluorescence spectra by using a three-dimensional synchronous fluorescence spectrum scanner automatically corrected in the third step, dividing a three-dimensional fluorescence spectrum chart of the crab DOM into 5 regions, sequentially forming an aromatic protein substance I fluorescence region, an aromatic protein substance II fluorescence region, a fulvic acid substance fluorescence region, a soluble microbial metabolite fluorescence region and a humic acid substance fluorescence region, and collecting the substance components of the crab DOM through the peak searching function of MATLAB 7.0;
and fifthly, testing and analyzing ultraviolet characteristics: firstly, repeating the processes of the second step and the third step to obtain extract liquor; secondly, using Milli-Q ultrapure water as a blank for correction, adopting an ultraviolet-visible spectrophotometer, transferring 2.5mL of extract liquor by using a liquid transfer gun, injecting the extract liquor into a quartz cuvette with a 1cm optical path, setting the wavelength of instrument parameters to be 200 nm-850 nm, and testing the absorbance:
SUV254the calculation method of (2) is as follows:
SUV254＝a254TOC formula IV;
TOC in formula IV is interior microcosmThe concentration of the crab DOM in the system is mg/L; a is254The absorption coefficient of the measured substance at a wavelength of 254 nm;
slope ratio S of absorption spectrumRThe calculation method of (2) is as follows:
a(λ))＝a(λ0)exp[-S(λ-λ0)]formula V;
SR＝S(275～295)/S(350～400)formula VI;
λ in formula V and formula VI0Is the reference wavelength in nm, and S is the absorption spectrum slope in nm-1。
2. The method for analyzing the release of PAHs from the crabs DOM in the rice-crab farming farmland according to claim 1, wherein in the fourth step, Ex/Em in the fluorescent region of the aromatic protein substance I is (200-250) nm/(260-320) nm; the Ex/Em in the fluorescent region of the aromatic protein substance II is (200-250) nm/(320-380) nm; the Ex/Em in the fluorescence region of the fulvic acid substances is (200-250) nm/(380-550) nm; the Ex/Em in the fluorescence region of the soluble microbial metabolite is (250-450) nm/(260-380) nm; the Ex/Em in the fluorescent region of the humic acid substances is (250-450) nm/(380-550) nm.
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