Trihalomethanes and maximum contaminant levels: the significance of inhalation and dermal exposures to chloroform in household water.

Our review of the literature on the importance of inhalation and dermal exposures to volatile organic compounds in household water relative to ingestion exposures sought to answer two questions. First, how well do the inhalation and dermal doses predicted by simple models, complex simulations, and measurements agree with one another? And second, what are the implications for the cancer risk from chloroform in household water? The literature yields a coherent and credible range of dose estimates: the ratio of lifetime inhalation dose to lifetime ingestion dose is probably in the range of approximately 0.6 to approximately 1.5, but may be as high as approximately 5.7; and the ratio of lifetime dermal dose to lifetime ingestion dose is probably about approximately 0.3, but may be as high as approximately 1.8. However, because the U.S. Environmental Protection Agency's (EPA's) Cancer Potency Factor (CPF) for inhalation of chloroform is much higher than the CPF for ingestion, the ratios of incremental lifetime cancer risk from inhalation of chloroform to risk from ingestion are much larger than the corresponding ratios for dose. The incremental lifetime cancer risk from chloroform by all three pathways is probably approximately 9 to approximately 21 times the ingestion risk and may be as much as approximately 79 times the ingestion risk. As the EPA reviews the drinking water standard for total trihalomethanes, it is essential that the Agency take account of all exposure pathways in estimating cancer risk.