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Environmentally Realistic Mixtures of Haloacetic Acids Exhibit Concentration-Dependent Departures from Dose Additivity (Presentation)
Citation:
SIMMONS, J. E., C. Dingus, E. D. Wagner, L. K. TEUSCHLER, G. E. RICE, AND M. J. PLEWA. Environmentally Realistic Mixtures of Haloacetic Acids Exhibit Concentration-Dependent Departures from Dose Additivity (Presentation). Presented at Society for Risk Analysis Annual meeting, Salt Lake City, UT, December 05 - 08, 2010.
Impact/Purpose:
We assessed the validity of an assumption of dose addition for 7 HAA mixtures.
Description:
Disinfection byproducts (DBPs), including haloacetic acids (HAAs), are formed when oxidizing disinfectants react with inorganic and organic matter in water. Drinking water is assayed routinely for 9 HAAs (HAA9): chloro-, dichloro-, trichloro-, bromo-, dibromo-, tribrorno-, bromochloro-, bromodichloro-, dibromochloro-acetic acid. The first 5 (HAA5) are regulated by EPA as a mixture at 60 ug/L. Recently, iodoacetic acid (IA) was identified as a DBP. We assessed the validity of an assumption of dose addition for 7 HAA mixtures: environmentally relevant mixtures of HAA5 and HAA9 at mixing ratios representing disinfection by postchlorination or preozonation/postchlorination, and equimolar (EQ) mixtures of HAA5, HAA9 and HAAI0 (comprised of HAA9 + IA). Individual HAAs and HAA mixtures were evaluated in a Chinese Hamster Ovary cell chronic cytotoxicity assay at a minimum of 10 concentrations each, ranging from 1 -31,000 uM based on toxicity. Data were expressed as percent of the concurrent negative control. Individual HAA data were used to develop a smooth additivity model consistent with Berenbaum's definition of additivity. The slope of the fitted dose-response curve for each individual HAA and HAA mixture was negative and statistically significant, indicating that cell density decreased significantly with increasing concentration. The overall Wald test for departure from dose additivity was significant (p