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MIXING RATIO INFLUENCES HALOACETIC ACID (HAA) MIXTURE TOXICITY
Citation:
SIMMONS, J. E., E. WAGNER, AND M. J. PLEWA. MIXING RATIO INFLUENCES HALOACETIC ACID (HAA) MIXTURE TOXICITY. Presented at 45th Annual Society of Toxicology Meeting 2006, San Diego, CA, March 05 - 09, 2006.
Description:
Mixtures of the same type (for example, disinfection byproduct mixtures) often contain the same chemicals, but at varying concentrations. The objective of the present study was to examine the influence of mixing ratio (the concentrations of chemicals relative to one another) on toxic outcome across a wide range of mixture dose levels. HAAs are formed during chemical disinfection of water. Mixtures of HAAs, containing some or all of the 5 HAAs (bromo/chloro) regulated as a mixture by the U.S. EPA, 4 additional HAAs (bromo/chloro) commonly measured in drinking water and one HAA (idoacetic acid, IA) recently identified in water disinfected by chloramination, 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 (%C1/2), the toxicity of the individual HAAs varied across 3 orders of magnitude, with IA and bromoacetic acid (BA) the most toxic and dichloroacetic acid (DCA) the least toxic. The toxicity of the HAA mixtures was profoundly influenced by mixing ratio. Based on the %C1/2 values, mixture toxicity was not correlated (r = 0.60, p < 0.15) with the concentration of BA, one of the most toxic HAAs. In contrast, there was a significant correlation (r = 0.90, p < 0.006) between the concentration of DCA (the least toxic HAA) and mixture toxicity. These results indicate that mixing ratio has a significant impact on HAA mixture toxicity. Further, HAA mixture toxicity cannot be predicted from the concentrations of the most toxic individual HAAs. 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. When conducting risk assessments of mixtures from the same mixture class, the effect of mixing ratio on toxicity should be considered. (This abstract may not reflect EPA policy.)