Reviews

UDC 613.34:628.162(047)

A. A. Korolev, V. T. Mazaev

Transformation of Chemical Substances in Water Bodies and During Water Treatment as a Public Health Problem

Department of Environmental Hygiene, I. M. Sechenov First Moscow Medical Institute

The transformation¹ of chemical substances in water bodies and during water treatment is closely connected with the self-purification of water bodies and the setting of water pollution standards. In our country, this issue was first raised by S. N. Cherkinsky. To predict the condition of water bodies accurately and plan studies for the establishment of health-based standards for harmful substances in water bodies, it is necessary to understand both the direction and chemistry of changes in substances in the aquatic environment and the rate and dynamics of these changes, which are particularly important in the formation of trace contaminants in drinking water. Brebio and coauthors, Leclerc, Malaney and Davis, and a number of other authors consider that trace contaminants—trace quantities of chemical substances that have passed through water treatment facilities or formed as a result of changes in chemical compounds during treatment—can impair the organoleptic properties of water and also adversely affect humans when ingested in drinking water over a long period. It should not be forgotten that the barrier function of water treatment facilities against chemical contamination of water is very limited (S. N. Cherkinsky and coauthors).

From a public health standpoint, the most important task is to identify and study classes, groups, or individual substances whose transformation in the aquatic environment may intensify their adverse effects on the human body or on living conditions. The symposium at the 162nd meeting of the American Chemical Society (1973) and, in particular, Leclerc consider the study of changes and transformations of toxic substances during the self-purification of water bodies and the preparation of drinking water to be an important area of research in the protection of water bodies.

The first synthesis of information on the adverse effects of the transformation of chemical compounds in water was made by S. N. Cherkinsky and G. N. Krasovsky in 1967, based on an analysis of the material accumulated by that time on the establishment of health-based standards for harmful substances in water bodies. At present, information on the adverse consequences of the accumulation and transformation of chemical compounds in the aquatic environment and during treatment is available for DDT, a number of heavy metals, chlorinated biphenyls, phenols, and organochlorine and organophosphorus pesticides. This reflects both the considerable contamination of water by these substances owing to their widespread use and certain distinctive characteristics of these substances as chemical and toxic agents.

Does this mean that other classes of chemical compounds cannot exhibit adverse effects as a result of their transformation in the aquatic environment? Obviously not. Therefore, if no clearly pronounced adverse effects have been recorded during the transformation of various substances entering water bodies in industrial wastewater,

…aspects of this process, this by no means implies that effects of this kind are absent. However, appropriate studies are needed to determine how often, under what conditions, and for which chemical compounds adverse effects of transformation may occur. Such studies are provided for in the methodological framework for hygienic standard-setting (S. N. Cherkinsky), but to date they have not received due attention (stability studies).

A number of dyes are known to produce more intense coloration of water when the pH changes, although their molecules undergo no significant structural changes. E. M. Trofimovich observed intensified coloration of aqueous solutions of p- and o-aminophenols, accompanied by gradual clouding of the solutions and subsequent precipitation. Intensified coloration of water on standing was also observed in the presence of other aniline derivatives (o-, m-, and p-phenylenediamine, diphenylamine, etc.).

When water contains aromatic nitro derivatives (dinitrotoluene, dinitrobenzene, p-nitrophenol, trinitrophenol, etc.), a shift in pH toward the alkaline range intensifies the coloration owing to conversion of the colorless benzenoid form of these compounds into the colored aci-form. Solutions of certain mono-, di-, and trihydric phenols, as well as naphthols, acquire or develop a more intense color on exposure to light or when the pH of the water shifts toward the alkaline range (B. N. Stepanenko).

Studies by N. D. Rubinsky, A. A. Rudenko, and E. V. Chekhovskaya established that certain nitriles (lactonitrile, malononitrile, and acetonitrile) can hydrolyze at alkaline pH values in water, forming the highly toxic cyanide ion. V. I. Timokhina, studying the degradation products of four ethoxyacrylate polymers in water at pH 7.4, found that highly toxic formaldehyde and formic acid are formed at considerable concentrations. According to Nager and Leibman, decaborane decomposes in water into several intermediate products, some of which, the authors report, are more toxic than decaborane itself.

Faust and Gomaa, studying the hydrolysis of a number of carbamate and organophosphorus pesticides in water, showed that the hydrolysis products of these compounds are substituted phenols that impart an unpleasant odor and taste to the water. In the authors’ opinion, some oxidation and hydrolysis products may be more toxic than the parent substances (paraoxon, acetoxon, p-nitrophenol, 1-naphthol). When diisocyanates enter bodies of water in industrial effluents, they undergo hydrolysis and polymerization to form diamines and polyurea, which are highly stable and can therefore persist in water for a long time (E. D. Sopach and L. P. Boltromenyuk).

In view of the substantial pollution of surface water sources, the barrier role of water treatment facilities with respect to chemicals present in water undergoing treatment has attracted particular research attention in recent years (S. N. Cherkinsky et al.; E. V. Shtannikov, S. Sadovsky; K. P. Ershova and L. S. Kanunnikova; and others). Studies have established that water treatment facilities have a limited barrier function against many chemical agents present in water and that a number of chemicals can pass through these facilities virtually unhindered. At the same time, analysis of the literature indicates that adverse changes in water quality are most often observed during chlorination and less often during ozonation and the use of other oxidants, especially when large doses of chlorine are used to render wastewater harmless and disinfect it. Chlorine is known to exert an oxidizing effect on chemicals present in water. Other types of reaction between chlorine molecules and substances, such as addition, are not excluded, however. Therefore,

Changes in the Chemical and Toxicological-Hygienic Properties of Substances during Wastewater Chlorination

Note. A dash indicates that information is unavailable.

During chlorination of wastewater contaminated with certain natural and synthetic chemicals, not only may organoleptic properties deteriorate, but more toxic substances may also appear (see table).

It should be noted that ozonation also sometimes worsens the organoleptic properties of water and produces more toxic degradation products, although ozone is less prone to substitution and addition reactions (P. F. Kandzas and A. A. Mokina; A. A. Korolev et al.). Drinking-water and wastewater treatment methods such as ultraviolet and ultrasonic irradiation, the use of potassium permanganate, and ionizing radiation also produce degradation products, some of which have been shown to have greater toxicity and biological activity than the original substances present in the water or wastewater (L. A. Kulsky et al.; P. Kerny and Kaufman; R. D. O’Brien, Adamson and Weeks). The greatest likelihood of dangerous products forming arises when weak oxidants such as $\mathrm{KMnO_4}$ are used (V. I. Tsipriyan et al.), or when the treatment agents act for too short a time to oxidize the substances thoroughly to simple, safe products.

As is well known, many heavy metals are highly toxic to warm-blooded organisms and possess cytogenetic activity (I. V. Sanotsky et al.). The emergence in Japan of itai-itai disease (cadmium poisoning) and Minamata disease (methylmercury poisoning) sharply intensified interest in studying the distribution and behavior of heavy metals in bodies of water. In particular, it has been shown that, when introduced with industrial—

…with wastewater into bodies of water, mercury ions can be converted by microorganisms into methylmercury compounds that can accumulate in phytoplankton and zooplankton and enter food chains (Jensen and Jernelov; Iouyama). According to N. N. Melnikov, microorganisms can convert metallic mercury into mercury sulfide, one of the most dangerous and toxic compounds for warm-blooded animals. Biological methylation has also been demonstrated for selenium, tellurium, and arsenic. The resulting dimethyl selenide, dimethyl telluride, and trimethylarsine are considerably more dangerous compounds than the metals themselves (G. Dyson and P. May). Another interesting example of a change in toxicity resulting from transformation in the environment is the conversion of tetraalkyltin into the more toxic trialkyltin, followed by dealkylation to dialkyl compounds, which are considerably less toxic (Salguain).

Relatively recently, it was demonstrated that carcinogenic nitrosamines can be synthesized in the gastrointestinal tract from a number of organic amines and amides under the influence of nitrosating agents—nitrites and nitrates (Sander and Barkle). V. A. Aleksandrov demonstrated the synthesis of highly carcinogenic nitrosourea from dimethyl- and diethylurea and nitrites in animals. Studies of this kind give grounds for supposing that nitrosamines may also be synthesized in bodies of water by saprophytic microflora from nitrites and secondary amines, which are constantly present in water. Although there is as yet no direct evidence of nitrosamine synthesis in bodies of water, owing to the absence of a specific, highly sensitive method for detecting them in water, this possibility cannot be ruled out, particularly since a correlation has been observed between nitrite and nitrate levels in water and the number of gastric neoplasms in humans.¹

Chemical substances may undergo transformation during wastewater treatment to an even greater extent than during the self-purification of bodies of water or the treatment of drinking water. As Northington and coauthors noted, wastewater as a result sometimes acquires a distinctive odor and becomes enriched with new organic substances of unknown toxicity.

The most widely used method of wastewater treatment is biochemical treatment. Yet very few studies have examined the degree of toxicity and, consequently, the dilution required in the receiving body of water for biochemically treated wastewater. Such wastewater generally contains a complex mixture of incompletely oxidized chemicals and their transformation products, whose combined effects on the organism are virtually unknown. V. V. Kustov and L. A. Tiunov demonstrated the high biological activity and toxicity of a number of human metabolic products that are constantly present in domestic wastewater undergoing biochemical treatment together with industrial wastewater.

G. S. Nekhamkina found that biochemically treated wastewater from an oil refinery caused substantial disturbances in warm-blooded animals. Biochemically treated wastewater from the production of phthalic acid dinitriles lost its toxicity upon tenfold dilution (V. V. Gaidamaka), whereas wastewater from an organic synthesis plant lost its toxicity upon sixtyfold dilution (A. A. Styazhkina), even though specific pollutants were absent or present at concentrations close to the maximum permissible levels for water in bodies of water. Ottoboni and Greenberg showed that biochemically treated domestic wastewater caused massive tumors not characteristic of this strain at such an early age.

¹ Toxicity of nitrosamines. Brit. Med. J., 1973, no. 5898, 372–373.

Thus, the complex and mechanistically diverse processes by which a chemical substance is transformed in water can not only reduce its concentration but also alter its chemical nature. Ultimately, this may change the nature of its hygienic and toxicological effects: toxicity may be diminished or, conversely, enhanced; odors, tastes, and coloration may disappear or arise; and the substance itself and its transformation products may be destroyed or accumulate in the aquatic environment, even entering food chains. Processes of chemical transformation must therefore be considered dialectically, taking both their positive and negative aspects into account.

The published data on the transformation of chemicals in water and under the influence of various treatment factors are scattered and fragmentary. Nevertheless, the information presented here attests not only to researchers’ growing interest in this problem but also to the indisputable importance of such research for hygiene science and sanitary practice.

References

Aleksandrov V. A. In: Carcinogenic N-Nitroso Compounds: Action, Synthesis, Detection. Proceedings of the 1st Symposium. Tallinn, 1973, pp. 84–86. — Burmistrov I. F., Trofimov Yu. M., Shimansky K. A. Zh. Vsesoyuzn. Khim. O-va im. D. I. Mendeleeva, 1972, no. 2, pp. 197–201. — Vrochinsky K. K. Gig. i San., 1973, no. 11, pp. 76–78. — Gaidamaka V. V. In: Issues in Environmental Sanitary Protection, Occupational Hygiene, and Disease Prevention. Leningrad, 1972, pp. 31–32. — Dyson G., May P. Chemistry of Synthetic Medicinal Substances. Moscow, 1964. — Ershova K. P., Konunnikova L. S. Gig. i San., 1973, no. 9, pp. 89–90. — Zabarilo A. B., Repetyuk L. Ya., Goronovsky I. T. In: Water Preparation and Industrial Wastewater Treatment. Information Bulletin on New Technology. Kiev, 1968, pp. 12–21. — Kandzas P. F., Mokina A. A. Vodosnabzhenie i Kanalizatsiya, 1973, no. 3, pp. 7–10. — Kearney P. (ed.). Degradation of Herbicides. Moscow, 1971. — Korolev A. A., Egorova N. A. In: Hygiene Science in Practice. Moscow, 1972, pp. 49–51. — Korolev A. A., Shigan S. A., Vitvitskaya B. R. Gig. i San., 1972, no. 8, pp. 99–101. — Kulsky L. A., Kalinichuk E. M. Drinking Water Conditioning. Moscow, 1964. — Kustov V. V., Tiunov L. A. In: Problems of Space Biology. Nauka, 1969, vol. 11. — Kulsky L. A., Nedoshepa G. N. Khim. Prom. Ukrainy, 1966, no. 4, pp. 21–25. — Lastochkina K. O. Gig. i San., 1972, no. 11, pp. 109–110. — Melnikov N. N. Chemistry of Pesticides. Moscow, Khimiya, 1968. — Nekhamkina G. S. In: Collected Scientific Works of the Kuibyshev Research Institute of Epidemiology, Microbiology and Hygiene, 1972, issue 7, pp. 40–43. — O’Brien R. Toxic Phosphorus Esters. Moscow, Mir, 1964. — Rubinsky N. D. Acetonitrile and Succinonitrile: Their Sanitary and Toxicological Characteristics and Conditions of Entry into Water Bodies. Candidate’s dissertation. Kharkov, 1969. — Rudenko A. A. Malononitrile, Malonic Ester, and Malonamide: Their Sanitary and Toxicological Characteristics and Conditions of Entry into Water Bodies. Candidate’s dissertation. Kharkov, 1970. — Sanotsky I. V. et al. Zh. Vsesoyuzn. Khim. O-va im. D. I. Mendeleeva, 1974, vol. 19, no. 2, pp. 146–155. — Svetlakova M. N. Gig. i San., 1955, no. 2, pp. 11–16. — Sopach E. D., Boltromenyuk L. P. Ibid., 1974, no. 7, pp. 10–13. — Styazhkina A. A. Study of the Hygienic Effectiveness of the Biological Method for Treating Industrial Wastewater from Organic Synthesis Plants. Abstract of candidate’s dissertation. Moscow, 1967. — Timokhina V. I. Toxicology of MK-6 Adhesive Based on Ethoxyethyl Cyanoacrylate, Intended for Sutureless Joining of Body Tissues. Abstract of candidate’s dissertation. Moscow, 1972. — Trofimovich E. M. Hygienic Studies on Protecting Water Bodies from Pollution by Dye-Manufacturing Products (ortho- and para-Aminophenols). Candidate’s dissertation. Novosibirsk, 1967. — Tsipriyan V. I. et al. Gig. i San., 1974, no. 9, pp. 14–17. — Cherkinsky S. N., Krasovsky G. N. In: Industrial Pollution of Water Bodies. Moscow, 1967, issue 8, pp. 7–9. — Cherkinsky S. N. et al. Gig. i San., 1970, no. 11, pp. 15–18. — Cherkinsky S. N. In: Sanitary Protection of Water Bodies from Pollution by Industrial Wastewater. Moscow, 1949, issue 1, pp. 5–111. — Chekhovskaya E. V. A Biochemical Method for Detoxifying Toxic Substances in Wastewater from Acrylonitrile Production. Abstract of candidate’s dissertation. Kharkov, 1970. — Shevchenko M. A. Organic Substances in Natural Water and Methods for Their Removal. Kiev, 1966. — Shtannikov E. V. Gig. i San., 1972, no. 9, pp. 97–99. — Adamson J. Y. R., Weeks J. L. Arch. environm. Hlth., 1973, vol. 27, pp. 69–73. — Brebion G. et al. Techn. Sci. munic., 1972, vol. 64, pp. 179–184. — Eaton J. W., Kolpin C. F. Science, 1973, vol. 181, pp. 463–464. — Faust S. D., Gomaa H. Environm. Letters, 1972, vol. 3, pp. 171–201. — Jensen S., Jernelov A. Nature, 1969, vol. 223, pp. 753–754. — Jouama J. Wld. med. J., 1971, vol. 18, pp. 81–91. — Leclerc H. Evolut. Med., 1973, vol. 17, pp. 237–250. — Malaney G. W., Davis T. J. Am. J. publ. Hlth., 1967, vol. 57, pp. 2194–2198. — Haeger L. L., Leibman K. C. Toxicol. appl. Pharmacol.,

1972, vol. 22, pp. 517–527. — Northidton C. W., Chang S. L., McCabe L. S. — In: Water Quality Improvement. Austin, Tex., 1970, pp. 49–56. — Ottoboni A., Greenberg A. E. — J. Water Pollut. Control. Fed., 1970, vol. 42, pp. 493–499. — Salquain I. — Teintex, 1962, vol. 27, pp. 615–629. — Sander J., Burkle G. — Z. Kresbsforsch., 1969, Bd. 73, S. 54–66.

Received February 6, 1975.

1. The term “transformation” encompasses all possible changes in the chemical structure, behavior, and biological activity of toxic substances in the aquatic environment under the influence of various factors. ↩