Drinking Water and Health, Volume 9 Selected Issues in Risk Assessment (1989) / Chapter Skim
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4 Assessment of Exposure to Organophosphorus Conpounds, Carbamates, and Volatile Organic Chemicals
4 Assessment of Exposure to Organophosphorus Conpounds, Carbamates, and Volatile Organic Chemicals
Pages 133-145
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From page 133... ...
Failure to detect a pesticide of the organophosphate or carbamate class known to be a potential contaminant of a specific water supply might not signify its absence; the pesticide might have hydrolyzed or undergone other chemical changes to other toxic substances, or the detection limit used in the analysis might have been too high. An EPA method (EPA, 1986)
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From page 134... ...
. OCCURRENCE OF ORGANOPHOSPHORUS COMPOUNDS AND CAR BAMATES I N OR I N Kl NG WATER Several surveys have compiled data on concentrations of organophosphorus compounds and carbamates in surface waters, groundwaters, and, in some cases, completely treated ("finished'')
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201. Methy' parathion Methyl parathion has been found in 1,402 of 29,002 surface-water samples and 25 of 2,878 groundwater samples in 22 states (EPA, 1987e)
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From page 136... ...
The highest concentrations were 2.3 ~g/liter in surface water and 3 ~g/liter in groundwater. OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER There have been several surveys of THMs and VOCs in surface waters, groundwater, and finished water supplies.
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One can conclude that VOCs other than THMs are normally found at concentrations of less than 10 ~g/liter- and often less than 1 ~g/liter in finished groundwater supplies. ROUTES OF HUMAN EXPOSURE TO CHEMICALS IN DRINKING WATER The usual estimates of exposure to contaminants in drinking water are based on ingestion and are calculated from the standard of 2-liters/day ingestion of water by a 70-kg man.
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'~Surface-water and groundwater sources. ''Tentative identification by single-column gas chromatography.
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From page 139... ...
is about 104 times that of water. How quickly and how completely a pesticide or other contaminant in TABLE 4-2 Summary of Occurrences of Volatile Organic Chemicals at 186 Randomly Sampled Groundwater Sites Serving More Than 10,000 Persons Eacha Quantitation Occurrences Median of Limit, Positives.
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From page 140... ...
and chlordane volatilized from water surfaces at about 20%30% of the rate of oxygen in reaeration studies, but dieldrin, which has a substantially lower H value, volatilized at only 1%-5% of the oxygen reaeration rate (Atlas et al., 19821. The H values of specific organophosphorus and carbamate compounds vary, but many are low.
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From page 141... ...
When human toxicity associated with exposure through water is assessed, combined exposures through other media have the potential for raising an apparently low exposure through water to the point where a toxic threshold is exceeded or, in the case of a carcinogen, a risk is increased. An early multimedia-exposure analysis for some of the chemicals considered here addressed the multiple routes and variability of uptake of chloroform and carbon tetrachloride (NRC, 19781.
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From page 142... ...
CONCLUSIONS AND RECOMMENDATIONS If joint exposure to THMs or to all VOCs with roughly equivalent potency could be considered to have additive toxic effects, it would be useful to have an analytic method for monitoring purposes that could be used as a measure of the total concentration of members of the group. For example, the sum of the volatile organohalide concentrations could be measured with a single instrument, even though it would measure a group of compounds such as vinyl chloride, carbon tetrachloride, 1,2-dichloroethane, trichloroethylene, p-dichlorobenzene, 1,1-dichloroethylene, and 1, 1,1-trichloroethane with widely varied toxic effects.
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Environmental Protection Agency.
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Cincinnati, Ohio: Environmental Monitoring and Support Laboratory, U.S. Environmental Protection Agency.
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From page 145... ...
1983. Mass transfer of volatile organic contaminants from aqueous solution to the atmosphere during surface aeration.
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