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I Toxicity of Selected Contaminants in Drinking Water The health effects of 21 contaminants found in drinking water are evalu- ated in this chapter. The substances are discussed in alphabetical order: aldicarb, carbofuran, carbon tetrachloride, chlorobenzene, o-dichloro- benzene, p-dichlorobenzene, 1,2-dichloroe~ane, 1,1-dichloroethylene, cis- and ~ans-1,2-dichloroethylene, dichloromethane, dinoseb, hexachlo- robenzene, methomyl, picloram, rotenone, tetrachloroethylene, 1,1,1-tri- chloroethane, trichloroethylene, vinyl chloride (monochloroethylene), and uranium. For each one, the committee reviewed data from studies of me- tabolism, health effects in humans and laboratory animals, mutagenicity, carcinogenicity, and teratogenicity. When there were sufficient data, it calculated numerical estimates of cancer risk. It also calculated suggested no-adverse-response levels (SNARL's) for chronic exposures to chemicals that were not known or suspected to be carcinogens. The descriptions of some of the contaminants are limited to data gener- ated since the last four volumes of Drinking Water and Health were pub- lished. Other contaminants and their health effects are evaluated for the first time in this report. This is one reason why no significance should be attached to the length of the discussion devoted to each contaminant. 9

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10 DRINKING WATER AND HEALTH ALDICARB propanal, 2-methyl-2-(methylthio), [(methyl amino) carbonyl]oxime CASNo.11606-3 CH2 o 11 CH3S-CCH = NOCNHCH3 1 CH2 Aldicarb was evaluated in the first volume of Drinking Water and Health (National Research Council, 1977, pp. 635-643~. The following material, which became available after the 1977 report was prepared, updates and, in some instances, reevaluates the information contained in the previous review. Also included are some references that were not assessed in the earlier report. METAL O LI SM Preliminary studies by Hurst and Dorough (1978, abstract) indicate that aldicarb, which is an inhibitor of acetylcholinesterase, inhibits certain car- boxyesterases that play a role in the hydrolytic detoxification of this pesti- cide. Such anticarboxyesterase activity could enhance the toxicity of this agent. By administering radiocarbon-labeled aldicarb to bile-cannulated rats, Marshall and Dorough (1979) demonstrated that an oral dose is com- pletely absorbed. In their experiment, approximately 28~o of the dose ap- peared in the bile within 24 hours; 64~o was excreted in the urine. Reduced acetylcholinesterase activity was observed in the brain and liver of rat fetuses for as long as 24 hours after doses of 0.01 or 0.10 mg/kg body weight (bw) were administered orally to the dams (Cambon et al., 1979~. REALTH ASPECTS Observations in Humans Peoples et al. (1978) reviewed 38 reports of occupational illnesses that ap- parently resulted from exposure to aldicarb. These reports were obtained from the registry for the State of California, where the product is available only as a granular formulation. The symptoms described in the documents were consistent with those expected for a carbamate insecticide: dizziness, blurred vision, constricted pupils, nausea, and abdominal pain. Virtually all incidents involved employees who handled, loaded, or applied aldicarb.