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EVALUATION OF THE JOINT TOXIC ACTION OF MIXTURES OF HALOACETIC ACIDS CONSTRUCTED USING ENVIRONMENTAL CONCENTRATION/EXPOSURE DATA
Citation:
SIMMONS, J. E., E. D. WAGNER, AND M. J. PLEWA. EVALUATION OF THE JOINT TOXIC ACTION OF MIXTURES OF HALOACETIC ACIDS CONSTRUCTED USING ENVIRONMENTAL CONCENTRATION/EXPOSURE DATA. Presented at International Society of Exposure Analysis Meeting, Durham, NC, October 14 - 18, 2007.
Impact/Purpose:
assessment of mixtures
Description:
Disinfection byproducts (DBPs) are formed by reactions between chemicals used to disinfect water and organic compounds present in source water. The composition of DBP mixtures varies based on a number of factors, including treatment scenario, with different DBP mixtures containing chemicals of the same class but at varying concentrations. The objective of the present study was to examine the influence of the mixing ratio (the concentrations of chemicals relative to one another) on toxic outcome across a wide range of mixture dose levels. Haloacetic acids (HAAs) are prevalent in disinfected drinking waters. Mixtures of HAAs, containing some or all of the 5 HAAs (bromo/chloro) regulated by the U.S. EPA, plus 4 HAAs (bromo/chloro) commonly measured and one HAA (idoacetic acid, IA) recently identified in water disinfected by chloramine, were tested at equimolar mixing ratios and at mixing ratios representing disinfection by either postchlorination or preozonation/postchlorination. The toxicity of the 10 individual HAAs and 7 HAA mixtures was evaluated in a Chinese Hamster Ovary cell chronic cytotoxicity assay. Based on the concentration that resulted in a 50% decrease in cell density (%C½), the toxicity of the 7 mixtures varied over a 7.5-fold range. The specific HAAs included in a mixture and their mixing ratio affected the overall cytotoxicity of the resulting mixture. Because the toxicity of HAA mixtures is influenced by the mixing ratio, toxicological assessment of mixtures benefits from assessment of mixtures constructed based on environmental exposure data. In conclusion, improved knowledge of the influence of mixing ratio on mixture toxicity is crucial for understanding the risk associated with chemicals regulated as mixtures. (This abstract does not reflect EPA policy.)