New Approaches to Regulating Disinfection Byproduct Exposures.

Regulations to mitigate disinfection byproduct (DBP) exposure have relied on in vivo toxicological studies to set limits on ∼10 of the ∼1,000 DBPs identified to date. This chemical-by-chemical focus is ill-suited to the rapid pace of novel DBP discovery and does not consider that DBPs occur in mixtures. Focusing on these DBPs can encourage changes to disinfection methods that minimize their formation while promoting the formation of other DBPs. This perspective discusses alternative approaches. Acknowledging consumer exposure to DBP mixtures, Calculated Additive Toxicity measures DBP exposure as the sum of DBP concentrations, each weighted by metrics of toxic potency, including from in vitro assays. Bioassays incorporate the effects of uncharacterized DBPs and avoid assuming that mixture toxicity is additive. The Multiple Barrier Approach combines treatment requirements for precursor removal with limits on indicator DBPs that represent the broader array of DBPs associated with each disinfectant. Combining the three approaches could efficiently mitigate DBP exposures.