The widespread use and storage of volatile organic compounds (VOCs) in the United States has led to releases of these chemicals into the environment, including groundwater sources of drinking water. Many of these VOCs are commonly found in public drinking water supplies across the nation and are considered by state or federal agencies to be potentially carcinogenic to humans. In this paper, we evaluate the detection frequencies, detected concentrations, and relative cancer risks of six VOCs in drinking water sources in California from 1995 to 2001. We find that, during this 7-year period, the most frequently detected VOCs in sampled drinking water sources were chloroform (12-14), PCE (11-13), and TCE (10-12). Detection frequencies in water were lower for 1,1-DCE (36), MTBE (1-3), and benzene (<1). Mean detected concentrations were also consistently above California's primary maximum contaminant level for some VOCs, including benzene, PCE, and TCE. Although none of the six VOCs necessarily poses a significant public health threat from drinking water exposures, 1,1-DCE and benzene were found to pose the greatest cancer risk relative to the other VOCs. However, after adjusting for the occurrence of each voc in drinking water, chloroform and PCE were found to pose the greatest relative cancer risk. Despite media reports about significant MTBE contamination of drinking water supplies in California, MTBE detections were infrequent, and this chemical was found to pose the least cancer risk relative to the other VOCs.
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