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Zinc Hazards to Fish, Wildlife, and Invertebrates: a Synoptic Review

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Zinc Hazards to Fish, Wildlife, and Invertebrates: a Synoptic Review Biological Report 10 Contaminant Hazard Reviews April 1993 Report 26 Zinc Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review by Ronald Eisler U.S. Department of the Interior Fish and Wildlife Service Patuxent Wildlife Research Center Laurel Maryland 20708 Abstract Sources and Uses Chemical and Biochemical Properties General Chemical Properties Metabolism Interactions Carcinogenicity, Mutagenicity, Teratogenicity General Carcinogenicity Mutagenicity Teratogenicity Background Concentrations General Nonbiological Biological Zinc Deficiency Effects General Terrestrial Plants and Invertebrates Aquatic Organisms Birds Mammals Lethal and Sublethal Effects General Terrestrial Plants and Invertebrates Aquatic Organisms Birds Mammals Recommendations Acknowledgments References TABLES Number 1 Estimated annual zinc input to U.S. coastal marine ecosystems; study area comprised 116,000 km2 (Young et al. 1980 2 Some properties of zinc, zinc chloride, and zinc sulfate (PHS 1989) 3 Zinc concentrations (milligrams of zinc per kilogram fresh weight [FW] or dry weight [DW]) in representative nonbiological materials 4 Zinc concentrations (milligrams of zinc per kilogram fresh weight [FW] or dry weight [DW) in field collections of representative plants and animals 5 Effects of zinc on representative terrestrial plants and invertebrates 6 Effects of zinc on representative aquatic plants and animals. Concentrations are in micrograms of zinc per liter of medium 7 Effects of zinc on representative birds 8 Effects of zinc on representative mammals 9 Proposed zinc criteria for the protection of natural resources and human heath 2 Zinc Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review by Ronald Eisler U.S. Department of the Interior Fish and Wildlife Service Patuxent Wildlife Research Center Laurel Maryland 20708 Abstract. Ecological and toxicological aspects of zinc in the environment are reviewed with emphasis on natural resources. Subtopics include sources and uses; chemical and biochemical properties; carcinogenicity, mutagenicity, teratogenicity; background concentrations in biological and nonbiological compartments; effects of zinc deficiency; toxic and sublethal effects on terrestrial plants and invertebrates, aquatic organisms, birds, and mammals; and recommendations for the protection of sensitive resources. The estimated world production of zinc is 7.1 million metric tons; the United States produces about 4% of the total and consumes 14%. Zinc is used primarily in the production of brass, noncorrosive alloys, and white pigments; in galvanization of iron and steel products; in agriculture as a fungicide and as a protective agent against soil zinc deficiency; and therapeutically in human medicine. Major sources of anthropogenic zinc in the environment include electroplaters, smelting and ore processors, mine drainage domestic and industrial sewage, combustion of solid wastes and fossil fuels, road surface runoff corrosion of zinc alloys and galvanized surfaces, and erosion of agricultural soils. Zinc has its primary effect on zinc-dependent enzymes that regulate RNA and DNA. The pancreas and bone are primary targets in birds and mammals; the gill epithelium is a primary target site in fish. Dietary zinc absorption is highly variable in animals; in general, it increases with low body weight (BW) and low zinc status and decreases with excess calcium or phytate and by deficiency of pyridoxine or tryptophan. Low molecular weight proteins called metallothioneins play an important role in zinc homeostasis and in protection against zinc poisoning; zinc is a potent inducer of metallothioneins. Zinc interacts with many chemicals to produce altered patterns of accumulation, metabolism, and toxicity; some interactions are beneficial to the organism and others are not depending on the organism, its nutritional status, and other variables. Knowledge of these interactions is essential to the understanding of zinc toxicokinetics. 2+ In natural waters, dissolved zinc speciates into the toxic aquo ion [Zn(H2O)6] , other dissolved chemical species, and various inorganic and organic complexes zinc complexes are readily transported. Aquo ions and other toxic species are most harmful to aquatic life under conditions of low pH, low alkalinity, low dissolved oxygen, and elevated temperatures. Most of the zinc introduced into aquatic environments is eventually partitioned into the sediments. Zinc bioavailability from sediments is enhanced under conditions of high dissolved oxygen, low salinity low pH, and high levels of inorganic oxides and humic substances. Zinc and its compounds induce testicular sarcomas in birds and rodents when injected directly into the testes; however zinc is not carcinogenic by any other route. Growth of animal tumors is stimulated by zinc and retarded by zinc deficiency. Under some conditions, excess zinc can suppress carcinoma growth, although the mechanisms are imperfectly understood. Organozinc compounds are effective mutagens when presented to susceptible cell populations in an appropriate form; the evidence for the mutagenic potential of inorganic zinc compounds is incomplete. Zinc deficiency can lead to chromosomal aberrations, but excess zinc was not mutagenic in the majority of tests. Excess zinc is teratogenic to frog and fish embryos, but conclusive evidence of teratogenicity in higher vertebrates is lacking. In mammals, excess zinc may protect against some teratogens. Zinc deficiency may exacerbate the teratogenic effects of known teratogens, especially in diabetic animals. Background concentrations of zinc seldom exceed 40 µg/L in water 200 mg/kg in soils and sediment, or 0.5 µg/m3 in air. Environments heavily contaminated by anthropogenic activities may contain up to 99 mg Zn/L in 3 water, 118 g/kg in sediments, 5 g/kg in soft, and 0.84 µg/m3 in air. Zinc concentrations in field collections of plants and animals are extremely variable and difficult to interpret. Most authorities agree on six points: (1) elevated concentrations (i.e., >2 g Zn/kg fresh weight [FW]) are normally encountered in some species of oysters, scallops, barnacles, red and brown algae, and terrestrial arthropods; (2) concentrations are usually <700 mg Zn/kg dry weight (DW) tissue in fish, <210 mg Zn/kg DW tissue in birds, and <210 mg Zn/kg DW tissue in mammals; (3) concentrations are higher in animals and plants collected near zinc-contaminated sites than in the same species collected from more distant sites; (4) zinc content in tissue is not proportionate to that of the organism's immediate surroundings; (5) for individual species, zinc concentration varies with age, sex, season, tissue or organ, and other variables; and (6) many species contain zinc loadings far in excess of immediate needs, suggesting active zinc regulation. The balance between excess and insufficient zinc is important. Zinc deficiency occurs in many species of plants and animals and has severe adverse effects on all stages of growth, development, reproduction, and survival. In humans, zinc deficiency is associated with delayed sexual maturation in adolescent males; poor growth in children; impaired growth of hair, skin, and bones; disrupted vitamin A metabolism; and abnormal taste acuity, hormone metabolism, and immune function. Severe zinc deficiency effects in mammals are usually prevented by diets containing >30 mg Zn/kg DW ration. Zinc deficiency effects are reported in aquatic organism at nominal concentrations between 0.65 and 6.5 µg Zn/L of medium and in piscine diets at <15 mg Zn/kg FW ration. Avian diets should contain >25 mg Zn/kg DW ration for prevention of zinc deficiency effects and <178 mg kg DW for prevention of marginal sublethal effects. Sensitive terrestrial plants die when soil zinc levels exceed 100 mg/kg (oak and maple seedlings), and photosynthesis is inhibited in lichens at >178 mg Zn/kg DW whole plant. Sensitive terrestrial invertebrates have reduced survival when soil levels exceeded 470 mg Zn/kg (earthworms), reduced growth at >300 mg Zn/kg diet (slugs), and inhibited reproduction at >1,600 mg Zn/kg soil (woodlouse). The most sensitive aquatic species were adversely affected at nominal water concentrations between 10 and 25 µg/L, including representative species of plants, protozoans, sponges, molluscs, crustaceans, echinoderms, fish, and amphibians. Acute LC50 (96 h) values were between 32 and 40,930 µg/L for freshwater invertebrates, 66 and 40,900 µg/L for freshwater teleosts, 195 and >320,000 µg/L for marine invertebrates, and 191 and 38,000 µg/L for marine teleosts. Acute toxicity values were markedly affected by the age and nutrient status of the organism, by changes in the physicochemical regimen, and by interactions with other chemicals, especially copper salts. Pancreatic degeneration occurred in ducks fed diets containing 2,500 mg Zn/kg ration. Ducks died when fed diets containing 3,000 mg Zn/kg feed or when given single oral doses >742 mg Zn/kg BW. Domestic poultry are routinely fed extremely high dietary levels of 20 g Zn/kg ration as a commercial management technique to force the molting of laying hens and the subsequent improvement of long-term egg production that molting produces. However, poultry chicks died at 8 g Zn/kg diet, had reduced growth at 2-3 g Zn/kg diet, and experienced pancreas histopathology when fed selenium-deficient but zinc-adequate (100 mg Zn/kg) diets. Mammals are comparatively resistant to zinc, as judged by their tolerance of extended periods on diets containing >100 times the minimum daily zinc
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