WO2000000048A1

WO2000000048A1 - Tobacco smoke filter

Info

Publication number: WO2000000048A1
Application number: PCT/GB1999/002039
Authority: WO
Inventors: Mohammad Azam Mansoor
Original assignee: Rf-Procom As; Cockbain, Julian
Priority date: 1998-06-29
Filing date: 1999-06-29
Publication date: 2000-01-06
Also published as: NO306492B1; NO983015D0; NO983015A; AU4524299A

Abstract

The invention provides a tobacco smoke filter comprising at least two metal binding agents, e.g. chelating agents.

Description

Tobacco Smoke Filter

This invention relates to a tobacco smoke filter, e.g. a filter for cigarettes, cigars or pipes, and to tobacco products containing such filters, e.g. cigarettes or cigars.

More particularly, the present invention relates to a cigarette filter in the form of a longitudinal section of a complete cigarette, in the form of a filter tip to be used in connection with cigarettes, and in the form of separate filter sections to be inserted into cigarette holders. Generally, the purpose of cigarette filters of this kind is to filter away and retain substantial amounts of undesirable components of tobacco smoke (e.g. heavy metals, free radicals, and possibly nicotine, tar etc.), so that the smoker receives those and other harmful substances to a substantially reduced extent .

There is reason to estimate that almost one fourth of the world's adult population use tobacco, e.g. are smokers of cigarettes. The production of cigarettes world-wide reached a number of more than 5.4 thousand billion in 1992.

Smoking is a risk factor for cardiovascular diseases . Tobacco smoking increases the risk of developing cancer and pulmonary diseases. In the United States it has been estimated that every day almost 1000 persons die because of diseases associated with tobacco smoking. Despite enormous efforts from organisations throughout the world to make people quit smoking cigarettes, people go on smoking.

Therefore, it is very important to provide cigarettes and other smokable tobacco products with filters which are capable of reducing the toxic, atherogenic and carcinogenic effects of tobacco smoke.

Cigarettes produced with low nicotine content tobaccos do exist, as so do cigarette filters with tobacco smoke channels extending longitudinally through the filter/filter cigarette. However, neither cigarettes with reduced nicotine content, nor ordinary cigarette filters, in which the nicotine and tar etc. deposit on the internal partitions defining the longitudinal channels in the filters, have proved particularly effective. The efficiency of porous cigarette filters in retaining harmful substances of the tobacco smoke does indeed increase with the filtering material's tightness to tobacco smoke, but with a fairly efficient degree of tightness, the tobacco smoke can no longer be sucked by moderate suction force through the filter, and so the product is unsatisfactory to the smoker .

It is not yet known, to a reasonable degree of certainty, how low the concentration of nicotine in tobacco smoke has to be in order not to damage health. Moreover, in tobacco smoke there are also heavy metals, free radicals, acids, bases, and other organic and inorganic constituents.

Increased concentrations in the blood of heavy- metals, free radicals, nicotine or other harmful components of tobacco smoke may contribute to the onset or progress of cardiovascular diseases, cancer and pulmonary diseases.

More particularly, tobacco smoke contains almost 4000 constituents. Some of the classes of constituents in cigarette smoke, are: heavy metals (e.g. cadmium, nickel, aluminium, iron, copper, chromium etc.); various types of free radicals; various types of alcohol, aldehydes, amides, amines, carbohydrates, carboxylic acids, esters, ethers, hydrocarbons, ketones, N- heterocyclics, nitriles, phenols; various gases (e.g. carbon monoxide, carbon dioxide, nitrogen oxides, hydrogen cyanide, etc.); nicotine; cathecol; benzpyrene etc. Heavy metals like cadmium, chrome, nickel and ²¹⁰Po may be carcinogenic.

Tobacco smoke may be divided into two phases, namely the gas phase and the tar phase. Both the gas phase and the tar phase of the smoke contain free radicals. Smoke in the gas phase contains both carbon- centred and oxygen-centred free radicals resulting from NO/N0₂-reactions of isoprene and other related compounds (examples of these free radicals being NO-, NO-₂, R_\ ROO-, ROONO-, and ROONO-₂ (wherein R is an organic group)) . Tar contains semiquinones which produce, in the presence of an aqueous tar solution, superoxide (0-₂) and hydrogen peroxide (H₂0₂) . In the presence of iron or copper, tar in an aqueous solution may produce hydroxyl radicals (HO) .

One single inhalation of cigarette smoke may contain 10¹⁵ free radicals. Free radicals are highly reactive species which are capable of harming genetic material (e.g. deoxyribonucleic acid - DNA) , proteins, lipoids, vitamins and other essential components of the body.

In smokers, increased concentrations of lipoid peroxides (products resulting from lipoid damage by free radical) have been measured. Such lipoid peroxides have also been identified and measured in patients who have cardiovascular diseases.

Smokers have also been found to have depressed concentrations of vitamin C, vitamin E, β-carotene, folate, vitamin B6 and vitamin B12 in their blood. The low concentrations of vitamins in the blood of smokers may well be due to increased concentrations of free radicals. Vitamin C and vitamin E work as antioxidants, and low concentrations of those vitamins may be associated with the increased risk of cardiovascular disease and cancer. Increased intake of these vitamins is associated with protection against these diseases. Folate, vitamin B12 and vitamin B6 are important coenzymes in homocysteine metabolism, and decreasing concentrations of any of folate, vitamin B12 and vitamin B6 in blood may increase the concentration of homocysteine in plasma. Increased concentration of plasma homocysteine is an independent risk factor for early vascular diseases. In smokers, elevated concentrations of homocysteine in plasma have been measured.

Free radicals may also cause mutations in DNA. Mutations in DNA may result in some types of cancer and other diseases.

Free radicals may also change or reduce the activity of thiol group containing enzymes.

The nicotine content of cigarette smoke may vary from 0.8 to 2.0 mg per cigarette. Nicotine may be present in the smoke in the protonated or the non- protonated form depending on the pH-value of the smoke. The non-protonated form is the most toxic one. Almost 25% of the nicotine of tobacco may be present in the smoke of the main flow, and up to 95% may be absorbed by the body. Increased concentration of nicotine may increase the blood pressure and the rate of the heart beat .

Nicotine may also stimulate the secretion of epinephrine, norepinephrine and other hormones. Hormones of various kinds may activate adenyl cyclase of adipose tissues, which causes lipolysis of stored triglycerides and release of fatty acids in plasma. Free fatty acids combine with plasma proteins and are transported to different parts of the body, especially to the liver. The increased inflow of free fatty acids stimulates the synthesis of liver very low density lipoproteins (VLDL) and triglycerides. The increased concentrations of triglycerides and liver lipoproteins is associated with decreased concentrations of high density lipoproteins HDL. The increased concentrations of triglycerides and liver lipoproteins VLDL and liver low density lipoproteins (LDL) , and decreased concentrations of high density lipoproteins is associated with increased risk of cardiovascular disease .

Liver VLDLP may lose some of their components and be transformed into medium density lipoproteins (intermediate low-density lipoprotein; IDL) . Removal of triglycerides from medium density lipoproteins transforms these lipoproteins into low density lipoproteins. Free radicals may destroy antioxidants in low density lipoprotein and chemically modify the protein. The modified form of low density lipoprotein may be toxic and chemotactic. The modified form of low density lipoprotein may be absorbed by macrophages . Later these macrophages are transformed into foam cells. The formation of foam cells in the artery wall may be an indication that a vascular disease is developing.

Accordingly there have been several proposals for chemical modification of tobacco smoke filters, in particular cigarette filters. However, to a large extent, such proposals have been aimed at reducing nicotine content (see for example 091/14381) , to reduce aldehydes or smoke acids (see for example EP-A-374861, O96/00019, GB-A-1313259, GB-A-2174284 and GB-A- 2230687) , to remove organic carcinogens (see for example GB-A-2083998 and WO96/10929) or to remove undesired gases (see for example GB-A-2065091 and EP-A-351252) .

The present invention is based on the concept that tobacco smoke may be rendered less harmful, in particular by reducing its ability to cause free radical damage. While, as mentioned above, the smoke contains free radicals, these are very short-lived chemical species and perhaps the greater danger of free radical associated damage arises from the presence in the smoke of heavy metals which can promote free radical generation in the body. Metals of particular concern are cadmium, nickel, aluminium, arsenic, selenium, mercury, zinc, iron, copper, cobalt, titanium and chromium. Such metals, in conjunction with biological thiols such as cysteine, glutathione and ascorbic acid, may promote free radical generation in vivo, and in particular the generation of highly active free radicals such as the hydroxyl radical OH- . OH- radicals are capable of damaging important biological molecules in the cells, especially near to the site of OH- generation. Since OH- generation may often be as a result of hydrogen peroxide reaction with metal ions associated with nucleic acids such as DNA, OH- generation may be accompanied by DNA mutation.

Several heavy metals have been identified in cigarette smoke, for example aluminium, arsenic, cadmium, copper, iron, lead, mercury, nickel, selenium, zinc etc. Tobacco plants have great affinity with and absorb heavy metals such as cadmium and nickel from the soil. Meat, fish and fruit may contain 1-50 μg/kg of cadmium. A cigarette contains 1-2 μg of cadmium and almost 10-15% of the cadmium of a cigarette may be inhaled, so that smoking one packet of cigarettes a day may at least double the load of cadmium absorbed on a daily basis. Smokers have increased concentrations of cadmium in plasma compared to non-smokers, and there is a very close connection between blood-cadmium levels and the number of cigarettes smoked per day. The effect of cadmium on the development of hypertension is controversial, but cadmium does reduce the availability of selenium and has an antagonistic effect on zinc, a contributing factor for the enzyme, superoxide dismutase. Increased concentrations of the transition metal copper in plasma is associated with coronary disease. The transition metals copper, iron etc. may also take part in the Fenton-reaction to produce free radicals .

The present invention is directed at reducing the content of such undesired metals and pseudometals in tobacco smoke by including in a smoke filter at least one chemical compound capable of binding such metals in chelate complexes .

Different metal binding agents, e.g. metal complex forming agents such as chelating agents, have different properties for binding different metal ions and viewed from one aspect the invention provides a tobacco smoke filter comprising at least two different metal binding agents (preferably chelating agents) , preferably at least three different metal binding agents (preferably chelating agents) and more preferably at least four, e.g. 4 to 10, different metal binding agents (preferably chelating agents) .

The chelating agents used in the filters of the invention preferably are ones which form relatively stable metal chelate complexes. Chelate complex stability may be measured relatively simply as log₁₀ K where K = [ML] / [M] [L] where [ML] , [M] and [L] are concentrations in mol/L of metal chelate, metal and chelating agent, e.g. in aqueous solution at 0.1 ionic strength at 25°C (see "Critical Stability Constants" by Martell and Smith, Plenum, New York, 1916 ff) . The filters of the invention preferably contain chelating agents which have log₁₀ K values for ions of at least one of Fe, Cu, Pb, Hg, Ni, Cd and Zn of at least 10, more preferably at least 12, especially at least 14. Especially preferably at least one such chelating agent has log₁₀ K values for Pb⁺ and Cd²⁺ of at least 15. Also preferably, at least one such chelating agent has a log₁₀ K value for Fe²⁺ or Fe³⁺ of at least 13, more preferably at least 14.

Viewed from an alternative aspect, the invention provides a tobacco smoke filter containing at least one chelating agent selected from chelating agents having log₁₀ K values for chelates with Pb²⁺ ions of at least 15 and log₁₀ K values for chelates with Fe²⁺ or Fe³⁺ ions of at least 13.

Especially preferably, the filters of the invention contain a plurality of chelating agents including agents having log₁₀ K values for chelates with Ni, Cd, Fe, Pb and Cu ions of at least 10, more preferably at least 14, still more preferably at least 16 (nb. each chelating agent need not meet these requirements for all of the listed ions) .

Metal chelating agents are well known from the diagnostic imaging and radiochemistry fields. Suitable classes include polyaminopolycarboxylic acids (e.g. DTPA, EDTA, DOTA, D03A, etc.) which may be linear, branched or cyclic, cyclic polyazaalkanes, cyclic ethers, N₂S₂ and N₃S chelators, terpyridines, etc. Examples may be found in the patent literature of the Nycomed Amersham group (e.g. Amersham, Nycomed Salutar, Nycomed Imaging, etc.), Schering AG, Mallinckrodt , Sterling Winthrop, Bracco, Squibb, Guerbet, etc. Such chelating agents may be capable of binding a single metal ion (i.e. to form a monochelate) or alternatively they may be capable of binding multiple ions (i.e. to form polychelates) . Such polychelants may for example be based on a linear or dendrimeric polymer structure (see the patent publications of Dow, Schering and Nycomed Amersham) .

The chelating agents used according to the invention may be in the form of derivatives, e.g. salts, complexes, esters or amides of known chelating agents, e.g. sodium calcium pentetate or DTPA-bismethylamide . However where the agent contains a metal this should not be a transition or heavy metal but should generally be a group 1 or 2 metal .

Examples of particular chelating agents include: ammonium N-nitrosophenyl-hydroxylamine; ammonium purpurate; α-benzoinoxime; N,N-bis (hydroxyethyl) glycine; 2 , 3-butane-dione dioxime; Chelex resin; desferrioxamine (and derivatives thereof) (which bind Fe and Al) ; trans 1 , 2-diaminocyclohexane-tetraacetic acid (CDTA) ; DTPA; 4 , 5-dihydroxybenzene-l , 3 -disulphonic acid; 2,3- dimercaptopropan-1-ol (which binds Pb, As and Hg) ; 2,3- dimercapto-1-propanesulphonic acid (DMPS) (which binds Pb, As, Hg and Cd) ; 2 , 3 -dimercaptosuccinic acid (DMSA) (which binds Pb, As and Hg) ; dimethylcysteine (penicillamine) ; 2 , 9-dimethyl-4 , 7-diphenyl-l , 10- phenanthroline; diphenyl-thiocarbazone; 2 , 2 ' -dipyridyl ; 3 , 6-disulpho-l, 8-dihydroxy-naphthalene; diethylcarbamodithioic acid, sodium salt (Dithiocarb) ; diethyl dithiocarbamic acid (DETC) ; dithiooxamide; ethylenediamine; EDTA; ethylene-dioxy diethylenedinitrilotetraacetic acid (EGTA) ; O-hydroxy- benzaldehyde,- N- (2 ' -hydroxyethyl) iminodiacetic acid (HIMDA) ; HIDA; DPDP; TMT; DOTA; nitrilotriacetic acid (NTA) ,- triethylenetetramine (tren) (which binds Cu) ; tetraazacyclo-dodecane (cyclen) ; 8-hydroxyquinoline; 8- hydroxy-quinoline-5-sulphonic acid; 1- (l-hydroxy-2- naphthalazo) -2-hydroxy-5-nitro-naphthalene-4-sulphonic acid; 4-methyl-l, 2-dimercaptobenzene; 5-nitro-l , 10- phenanthroline; 1, 10-phenanthrolilne; potassium ethyl xanthate; picolinic acid; salicylic acid; 2-thenoyl-2- furoylmethane ,- thiocarbamide (thiourea) ; dimethylhydroxypyridone (which binds Fe) ; alanine; α- aminobutyric acid; arginine; asparagine; aspartic acid; cysteine; glutamic acid; glycine; glycylglycine; histamine; histidine; imidazole; leucine; lysine; methionine; norleucine; ornithine; phenylalanine; proline; serine; tryptophan; tyrosine; valine; N-(2- acetamido) -2-aminoethane-sulphonic acid (ACES); N-(2- acetamido) -iminodiacetic acid (ADA) ; 2- (N-morpholino) - ethanesulphonic acid (MES) ; N-tris (hydroxy- methyl) methyl-glycine (Tricine) ; tris (hydroxy- methyl) methyl-amine (Tris) ; citric acid; adenine; aureomycin; flavine adenine dinucleotide (FAD) ; flavine adenine mononucleotide (FMN) ; guanosine; glucose 1- phosphate; glucose 6 -phosphate; hypoxanthine ; inosine; phosphoarginine,- phosphocreatine; phosphoenol-pyruvic acid; 2-phosphoglyceric acid; pteroglutamic acid (folic acid) ; pyridoxime; riboflavin; terramycin; and xanthosine; and salts thereof with organic amines, ammonium, alkali metals and alkaline earth metals.

The chelating agents used in the filters of the invention are preferably water-soluble.

Particularly preferably, the chelating agents used according to the invention include polyaminopolycarboxylic acids, thiols, thiol-carboxylic acids, thiol-sulphonic acids, thiocarbamates, and thioic acids. Thus for example DMPS forms complexes with lead; DMSA also forms complexes with lead, dithiocarbamate (DTC) and dithiocarb (DDC) form complexes with metals such as nickel and cadmium, sodium N- (4-methoxybenzyl) - D-glucamine dithiocarbamate (MeOBGDTC) forms complexes with cadmium, desferrioxamine forms complexes with iron, EDTA and DTPA form complexes with many heavy metals, and penicillamine forms complexes with copper.

One example of a combination of chelating agents that can be used is DMPS, DTC (or DDC) , MeOBGDTC, penicillamine, and desferrioxamine, and, optionally, EDTA.

Although chelating agents are the most preferred metal binding agents for use according to the invention, other materials with metal binding properties may be used in place of or in addition to the chelating agents. Examples include cation exchange resins and buffers, e.g. HEPES buffer.

The filters according to the invention may be incorporated in ready-made cigarettes or cigars or the like. Alternatively they may be separate filters to be incorporated in hand-rolled cigarettes or placed in filter holders in pipe stems or bowls. Likewise such filters may be positioned within cigarette or cigar holders. While the filters of the invention are primarily intended for use in decontaminating tobacco smoke, they can of course be used in conjunction with non-tobacco vegetative smoking material, e.g. in herbal cigarettes .

The filters of the invention preferably comprise a smoke filter, e.g. a cellulosic substrate such as cellulose acetate, for example as in conventional cigarette filters. The chelating agents may be impregnated into such cellulosic substrates, e.g. by treating the cellulosic substrate with a solution (for example an aqueous, acidic or alkanolic solution) of the chelating agents. Alternatively the chelating agents may be located on a porous particulate support (e.g. silica, activated charcoal, calcium carbonate, etc.) which can be dispersed within the body of the filter. In a further alternative embodiment, the chelating agents are disposed in one (or more) axially extending portion of the filter, separated by gas permeable means, e.g. porous discs, from adjacent axially extending portions of the filter. Typically the chelating agents will be present at less than 2% wt relative to the overall filter weight, e.g. 0.005 to 0.5% wt .

Beside the chelating agents, the filter of the invention preferably comprises at least one other chemical decontaminant , e.g. selected from acids, bases, reducing agents, antioxidants, synergistic antioxidants, antioxonants, free radical scavengers, nicotine absorbers, carbon monoxide scavengers, nitric oxide scavengers, aldehyde absorbers, nitrosamine absorbers, etc. Especially preferably, the filters contain a reducing agent (i.e. an electron or hydrogen donor), for example 5-methyl -tetrahydrofolate or a reducing agent containing citrus extract or cruciferous vegetable extract. (5-Methyl -tetrahydrofolate is found in citrus extracts) .

The use in this fashion of reducing agents is especially preferred as they may function to reduce still further the free radical content of the smoke emerging from the filter.

The reducing agents used in the filters of the invention may be in the form of derivatives, e.g. amides, esters, salts or complexes, of known reducing agents as long as such derivatives have a reductive effect. Other examples of reducing agents include alkyl gallates (e.g. methyl gallate) , butylated hydroxyanisole, butylated hydroxytoluene, nondihydroguaiaretic acid, tocopherols, ascorbic acid, araboascorbic acid, hydroxysuccinic acid, green tea, melanin, potassium and sodium salts of sulphurous acid, citric acid, lecithin, editronic acid, anthranilic acid, calcium lactate, sodiuim sulphite, thiodipropionic acid, sodium hypophosphite, diethylsafranin, guaiacol, hydroquinone , phenylenediamine, tetramethyl-p-phenylene- diamine, pyrogallol, and tartaric acid. Again such components may conveniently be impregnated into the filter substrate or into porous particulate supports, e.g. using aqueous, acidic or alkanolic solutions.

Typically the reducing agent content per filter may be in the micromole range, e.g. 0.1 to 10 micromoles.

The use of acidic and basic decontaminants, preferably disposed in different axially extending sections of the filter or in separate porous particulate supports, has the advantage of removing smoke acids and potentially carcinogenic polycyclic organic chemicals.

Examples of acids which may be included in the filters of the invention include citric acid, ascorbic acid, fumaric acid, gluconic acid, lactic acid, maleic acid, malonic acid, tartaric acid, succinic acid, gluconic acid, oxalic acid, propionic acid, etc. Citric and ascorbic acids are preferred and in particular may be used in combination with the chelating agents and reducing agents.

Thus the filter according to the invention may take the form of a cigarette filter/cigar filter/pipe filter in the form of (a) a longitudinal section of a complete filter cigarette/filter cigar, in the form of (b) a filter tip/insert to be used in the rolling of filter cigarettes or for (c) placing in a cigarette holder/cigar holder/pipe bit, wherein the filter contains active agents as metal chelators, reducing agents (electron donor or hydrogen donor) and/or acid or basic substances, in order to reduce the concentration of heavy metals, free radicals, and other toxic substances etc. in cigarette smoke/cigar smoke/pipe smoke. These effective substances may be added together to a homogenous cylindrical filter section of an ordinary cigarette filter material/cigar filter material/pipe filter material, such as cellulose acetate. Alternatively the effective substances may be added together to small filter elements of random shape of a substantially smaller size than the cigarette diameter/cigar diameter/pipe stem diameter, of regular cigarette filter material/cigar filter material/pipe filter material, such as cellulose acetate. In a still further embodiment the effective substances, may each be added to different small filter elements of random shape positioned randomly or in layers, and of substantially smaller sizes than the cigarette diameter/cigar diameter/ pipe stem diameter, of a regular cigarette material/cigar material, such as cellulose acetate. In a yet further embodiment, the effective substances may be added separately to the cylindrical filter element. In the filter according to the invention, the filter elements may if desired kept enclosed in the main filter section by intermediate pieces of a common cigarette filter material/cigar filter material/pipe filter material, such as cellulose acetate, e.g. by axially spaced smoked-transmitting elements.

In a preferred embodiment of the invention the chemical substances in the filter section or in filter elements contain: metal chelators (for example in the form of a mixture of DMPS (which forms complexes with lead) , DTC or DDC (which form complexes with nickel and cadmium), sodium, N (4-methoxybenzyl) -D-glucamine dithiocarbamate (MeOBGDTC) which forms complexes with cadmium, and penicillamine (a thiol that forms complexes with copper) , desferrioxamine (which forms complexes with iron) and a reducing agent (i.e. an electron donor or hydrogen donor) which serves to chemically react with free radicals and neutralise them. These may be dissolved in water or in an acid, for example, acetic or citric acid, at a low pH (for example a pH-value of 3- 4) . Alternatively they may be dissolved in an alkaline solution, for example sodium hydroxide, and they may be in solution in^' charcoal or other filtering material, preferably at a high pH, for example a pH-value of 8-10, which and serves to neutralise harmful acid constituents of the cigarette smoke/cigar smoke/pipe smoke.

In an alternative preferred embodiment, a filter element of the filter-section of the filter of the invention contains an acid solution, preferably acetic acid in charcoal, of low pH, for example a pH-value of 3-4, that serves to neutralise harmful basic constituents of the cigarette smoke/cigar smoke/pipe smoke, the same or a further filter element contains an alkaline solution, for example sodium hydroxide solution in charcoal, or another filtering material, at a high pH, for example a pH-value of 8-10, that serves to neutralise harmful acid components of cigarette smoke/cigar smoke/ pipe smoke; another filter element contains metal chelators (for example in the form of DMPS, DTC or DDC, MeOBGDTC, penicillamine and desferrioxamine) , dissolved in water or in an acid, for example acetic acid, at a low pH, for example a pH-value of 3-4; a still further filter element contains a reducing agent (i.e. an electron donor or hydrogen donor) dissolved in water or in an acid, for example citric acid, at a low pH, for example a pH-value of 3-4, which neutralises the free radicals of cigarette smoke/cigar smoke/pipe smoke; and, if desired, a yet further filter element may contain substances which neutralise free radicals (e.g. a reducing agent (i.e. electron donor or hydrogen donor) dissolved in acetic acid, at a low pH, for example of 3-4) .

Therefore, in accordance with the present invention, a novel cigarette filter has been developed. The object of the filter is to reduce the concentration of heavy metals, free radicals and other harmful components in that part of the tobacco smoke which reaches the smoker, i.e. that part of the smoke that has passed the filter which is placed, in a manner known in itself, closest to the cigarette end portion not lit. Alternatively to constituting a regular component of a ready-made cigarette, cigarette filters according to the invention may be produced as separate filter pieces to be used in rolling cigarettes from hand rolling tobacco. Filter or cigarette holders represent further alternative applications of such a filter.

A cigarette filter according to the present invention contains metal chelators, thiols and other substances whose task it is to reduce concentrations of heavy metals, free radicals and other constituents of cigarette smoke, so that smokers smoking cigarettes with filters produced in accordance with the present invention, will get fewer of these harmful constituents of cigarette smoke into their blood than they would otherwise have got by smoking the same number of identical cigarettes per day without the filter according to the invention. Thus, cigarette filters according to the invention may minimise the harmful effects of smoking without the smoker having to quit smoking or reduce his tobacco consumption.

Viewed from a further aspect the invention provides a filter-tipped cigarette wherein the filter is a filter according to the invention.

Viewed from a further aspect the invention provides a cigarette holder incorporating a filter according to the invention. The documents referred to herein are hereby incorporated by reference.

Non-limiting examples of currently preferred embodiments of a cigarette filter according to the invention are illustrated schematically in the accompanying drawings, in which Figs. 1 to 5 show side views of a cigarette in which the filter, which is shown in axial section, constitutes an important component of the filter cigarette, and in which small filter sections are provided in the main filter. The filtering material or filter components which contain the various decontaminating chemical compounds may be cellulose or a different material .

Fig. 1 shows a filter cigarette in side view, in which the tobacco section and the filter section disposed in the axial extension thereof, may be positioned end surface to end surface, and, among other things, be joined together by means of a common cigarette paper or in a different manner known in itself;

Fig. 2 shows a corresponding filter cigarette, but here the filter section is defined, at each of its axial ends, by means of a smoke/gas/air-admitting transverse disc which may consist, for example, of a neutral filtering material;

Fig. 3 is an axial section through the filter section, in which the actual filtering materials are disposed between the two transverse discs;

Likewise, Fig. 4 is an axial section through the filter section, which is divided here by means of, for example, four intermediate transverse partitions into five consecutive compartments in the longitudinal direction of the filter section/filter cigarette; and

Fig. 5 shows an axial section through an integrated filter portion containing the filtering agents not separated from each other, and possibly directly encased in tobacco material . Referring to the figures, reference numeral 10 identifies a tobacco section of a filter cigarette, whereas reference numeral 12 identifies the filter section. The cigarette paper may also cover the filter section 12.

Referring to Fig. 2 the filter section 12 is defined between two transverse end discs 14 of an air- admitting (smoke-admitting) material, for example a neutral cigarette filtering material (cellulose or similar material) .

Referring to Fig. 3 the filter section 12 and the immediately adjacent portion of the cigarette tobacco section 10 are shown in a partial axial section. Schematically visualised tobacco is identified by 16. The filter section 12 contains a mixture of DMPS, DMSA, DTC, MeOBGDTC, EDTA desferrioxamin and penicillamin dissolved in water or in an acid solution, for example acetic acid with, for example, a pH-value of 3-4. The mixture of metal chelators will form complexes with toxic metals and neutralise them. DMPS forms complexes with lead. DMSA also forms complexes with lead. DTC

(dithiocarbamate) or dithiocarb (DDC) may be useful for forming complexes with metals such as nickel and cadmium. MeOBGDTC (sodium, N (4- methoxybenzyl) -D- glucamine dithiocarbamate) forms complexes with cadmium. EDTA forms complexes with various metals. Desferrioxamine forms complexes with iron. Penicillamine is a thiol that forms copper :thiol complexes. Other thiols may also be used.

Filter components may also contain a reducing agent

(electron donor or hydrogen donor), e.g. an extract from citrus fruits or cruciferous vegetables dissolved in water or in an acid, for example citric acid, preferably with a low pH, for example a pH-value of 3-4.

Metal chelators and other substances will minimise the toxic, atherogenic and carcinogenic effects of the cigarette smoke. In Fig. 4 is shown a filter section 12 which is divided by transverse partitions 18 into five longitudinally consecutive compartments 20. Each of these compartments 20 may contain a particular filtering material. However, one or more of the compartments 20 may contain two or more chemically compatible filtering materials .

In Fig. 5 is shown a filter section 12' which is entirely encased in the cigarette's tobacco material and in which the cigarette paper is common for the cigarette section and the filter section.

Filters of the kind described above could, of course, also be used in the smoking of cigars and in pipe smoking. For pipe smoking the filter may be inserted into the stem/bit of the pipe.

Claims

1. A tobacco smoke filter comprising at least two different metal binding agents.

2. A filter as claimed in claim 1 containing at least three different metal binding agents.

3. A filter as claimed in either of claims 1 and 2 containing as said metal binding agents at least two different chelating agents.

4. A filter as claimed in any one of claims 1 to 3 containing at least two chelating agents selected from polyaminopolycarboxylic acids, thiols, thiol carboxylic acids, thiol sulphonic acids, thiocarbamates, thioic acids, and derivatives thereof.

5. A filter as claimed in any one of claims 1 to 4 containing chelating agents having log₁₀ K values for ions of at least one of Fe, Cu, Pb, Hg, Ni , Cd and Zn of at least 10.

6. A filter as claimed in claim 5 containing at least one chelating agent having a log₁₀ K value for Pb²⁺ and Cd²⁺ of at least 15.

7. A filter as claimed in any one of claims 1 to 6 further containing a reducing agent .

8. A filter as claimed in any one of claims 1 to 7 further containing at least one acid or base.

9. A filter as claimed in any one of claims 1 to 8 comprising a plurality of axially spaced elements at least one of which comprises a said metal binding agent.

10. A filter as claimed in claim 9 wherein said axially spaced elements are separated by axially spaced smoke transmitting elements.

11. A tobacco smoke filter containing at least one chelating agent selected from chelating agents having log₁₀ K values for chelates with Pb²⁺ ions of at least 15 and log₁₀ K values for chelates with Fe²⁺ or Fe³⁺ ions of at least 13.

12. A filter-tipped cigarette incorporating a filter as claimed in any one of claims 1 to 11.

13. A cigarette holder incorporating a filter as claimed in any one of claims 1 to 11.