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Guidelines for Chemical Warfare Agents in Military Field Drinking Water 7 Guidelines for Cyanide INTRODUCTION Hydrogen cyanide has been known as a potent toxicant for over 200 years. It was used as a chemical warfare agent during World War I by France. Although it is highly volatile (and was later considered “militarily useless” because of its volatility), no deaths from its military use during World War I were ever reported (Haber, 1986). There are also reports of hydrogen cyanide being used as a war gas during the Iran–Iraq war in the 1980s (Lang et al., 1986; Heylin, 1988). However, because hydrogen cyanide can be detoxified rapidly by humans and because it is very volatile, massive amounts of the gas are needed for it to be effective as a chemical warfare agent. Cyanide is primarily an environmental contaminant of industrial processes and usually enters the drinking water as industrial waste. It is used in the metal-processing industry for electroplating, heat treating, and metal polishing (California State Water Resources Control Board, 1963; Jenks, 1979) and can be found in waste waters from many mining operations that use cyanide compounds in the extraction of metals, such as gold and silver, from ore (Towill et al., 1978; Jenks, 1979). Microbial metabolism of nitrogenous compounds can also be responsible for the presence of cyanide in water (Knowles, 1976; Leduc, 1981). Among the various chemicals that contain the cyanide moiety and that
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Guidelines for Chemical Warfare Agents in Military Field Drinking Water can be found in water, hydrogen cyanide is the form that is of the most toxicological consequence (Scofield et al., 1988). Chlorination of water containing hydrogen cyanide results in the formation of cyanogen chloride, which is highly toxic but not as toxic as hydrogen cyanide (Cotton and Wilkinson, 1980), and other less toxic cyanates (California State Water Resources Control Board, 1963). Cyanogen chloride has limited solubility in water, persists for more than 24 hr, and slowly hydrolyzes to the cyanate ion. All cyanates are able to persist in aerobic water at pH 7 at 20°C for 10 days (Resnick et al., 1958). TOXICITY The acute toxicity of cyanide has been well documented in humans and experimental animals. Symptoms of toxicity in humans include headache, breathlessness, weakness, palpitations, nausea, giddiness, and tremors (Gupta et al., 1979). Death results from respiratory arrest (Smith, 1980). Chronic exposure to cyanide can result in neuropathies, goiter, and diabetes (Hardy et al., 1950; El Ghawabi et al., 1975). The mode of action that leads to cyanide toxicity is to block electron transport, thus inhibiting enzymes in the cytochrome oxidase chain and, in turn, blocking oxygen use in metabolizing cells. That action can be rapidly lethal at high doses. Blood cyanide concentrations are correlated with various health effects. The most reliable data are the measurements of cyanide concentrations in blood drawn from patients who received infusions of sodium nitroprusside (a cyanide-releasing drug) during surgery. Table 7-1 lists the whole-blood cyanide concentrations at which health effects occur in animals and humans.1 In the table, the first six entries are examples of “background” concentrations of cyanide measured in healthy people. They show that a measurable concentration of cyanide is normally present in human blood. The concentrations reported by Symington et al. (1978) are mean values; individual values range up to 0.32 1 The remainder of this section is a slightly modified excerpt from the Lawrence Livermore National Laboratory's report to the Army (Scofield et al., 1988).
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Guidelines for Chemical Warfare Agents in Military Field Drinking Water TABLE 7-1 Whole-Blood Cyanide Concentrations and Health Effects Cyanide Conc., mg/L Population Health Effect References Background level: <0.086 Nonsmoker None Chandra et al., 1980; <0.094 Smoker None Background level: 0.016 Nonsmoker None Ballantyne, 1977 0.041 Smoker None Background level: 0.08 Nonsmoker None Symington et al., 1978 0.18 Smoker None Occupational level: 0.18 Nonsmoker Complaintsa Chandra et al., 1980 0.56 (0.23)b Smoker Complaintsa Gupta et al., 1979 0.20 Humans Suggests toxic reaction Berlin, 1977 0.22 SNPc-treated humans None Pasch et al., 1983 0.51 SNP-treated humans Threshold for metabolic effects Aitken et al., 1977; Schulz et al., 1982 0.90 SNP-treated humans Metabolic acidosis Aitken et al., 1977 1.0-10.0 Human poisonings Toxicity and lethality Niyogi, 1973 1.82d Mice Lethal Smith and Kruszyna, 1974 2.00 Dogs No effects Michenfelder and Tinker, 1977 2.9-28.7 Humans Lethal Bogusz et al., 1979 7.0-10.0 Dogs Lethal Michenfelder and Tinker, 1977 aHeadache, weakness, palpitation, nausea, breathlessness, and tremors. bMean concentration if the highest concentration measured for one of eight subjects (2.2 mg/L) is not included. cSNP, sodium nitroprusside. dBlood concentration after a lethal dose (intraperitoneal administration); represents 50% of a population of laboratory mice. Source: Scofield et al., 1988.
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Guidelines for Chemical Warfare Agents in Military Field Drinking Water mg/L of whole blood for nonsmokers and 0.52 mg/L for smokers. These values are much higher than the concentrations reported by Chandra et al. (1980) and Ballantyne (1977). The variation might be due to the use of a different analytical method, or it might be due to the long interval between the time the blood samples were taken and the time the samples were analyzed. The storage conditions for the blood samples in the study by Symington et al. (1978) can result in cyanide formation. Workers exposed to cyanide gas and alkali cyanide salts via inhalation had mean blood cyanide concentrations of about 0.23 mg/L (Chandra et al., 1980). The high mean value (i.e., 0.56 mg/L) for smokers is primarily due to one very high value (2.2 mg/L); if that one value is excluded, the mean is 0.23 mg/L. Symptoms and signs reported for the workers include headache, palpitation, nausea, breathlessness, weakness, dizziness, and tremors—typical symptoms of cyanide poisoning (Gupta et al., 1979). According to the authors, those symptoms and signs were probably due to elevated inhalation exposures and associated high blood cyanide concentrations. Therefore, mean blood cyanide concentrations are not necessarily indicative of toxicity. Other symptoms noted for the workers—including pain and irritation in the throat and eyes—are attributable to the irritating properties of the alkali cyanide salt aerosols rather than to cyanide itself (NIOSH, 1976). Berlin (1977) found that whole-blood cyanide concentrations above 0.2 mg/L might cause cyanide intoxication in humans. In measurements of cyanide concentrations in patients administered sodium nitroprusside, Pasch et al. (1983) determined that a whole-blood cyanide concentration of 0.22 mg/L would be safe for patients. Metabolic effects were not detected until about 1 mg/L. For example, Aitken et al. (1977) detected metabolic disturbances in patients administered sodium nitroprusside when whole-blood cyanide concentrations were above 0.9 mg/L. The threshold cyanide concentration was found to be 0.51 mg/L of whole blood. Pasch et al. (1983) indicated that cyanide concentrations above 2.2 mg/L of whole blood in patients administered sodium nitroprusside can produce severe clinical symptoms, and concentrations above 4.4 mg/L are lethal. Concentrations as low as 1 mg/L have been associated with cyanide poisonings (Niyogi, 1973), but such concentrations are often due to blood measurements taken after toxicity is observed or post mortem and
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Guidelines for Chemical Warfare Agents in Military Field Drinking Water are not reliable indications of the blood cyanide concentrations actually causing the toxicity. Based on the totality of acute-toxicity data in humans, Scofield et al. (1988) concluded that a blood cyanide concentration of 0.5 mg/L is a reasonable threshold concentration for changes in blood chemistry and that clinical symptoms of cyanide intoxication are likely above a concentration of approximately 2 mg/L. CONCLUSIONS AND RECOMMENDATIONS A blood cyanide concentration of 0.5 mg/L is considered nontoxic. By using a pharmacokinetic model and assuming that the blood cyanide concentration of 0.5 mg/L is nontoxic, the Army proposed field drinking-water standards for cyanide of 2 mg/L and 6 mg/L, assuming a water consumption of 15 L/day and 5 L/day, respectively. The subcommittee is in agreement with the Army's proposed standards. Therefore, the subcommittee's recommended field drinking-water guidelines for cyanide are the same as the Army's proposed standards.
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