UC Davis

With climate change, water shortages, and high anthropogenic activity, California faces many water quality challenges. One challenge includes the formation of disinfection by-products (DBPs) in drinking water due to reactions between disinfectants, natural organic matter, and ions present in source waters. While only a few compounds are regulated, significantly more toxic unregulated DBPs are emerging. In addition, DBPs can have significant variability within a given distribution system due to changes in demand, different water ages, changes in formation kinetics, and transformations. Thus, a better understanding on the occurrence, variability, and toxicity of DBPs in California drinking water is needed. As a component of the Drinking Water Project funded by the California Breast Cancer Research Program (CBCRP), the purpose of this study was to (1) investigate disinfection by-product formation potential (DBP–FP) in household drinking water across different water systems in California; (2) examine DBP variability within each distribution system; and (3) identify compounds that may be contributing to breast cancer toxicity. The results of this study indicate that regulatory monitoring approaches may not provide an accurate representation of household DBP exposure due to high variability and higher toxicity associated with unregulated compounds including dibromoacetonitrile (dBAN), bromochloroacetonitrile (BCAN), and iodoacetic acid (IAA). Due to their occurrence and role in driving toxicity, these specific compounds are recommended for prioritization in future research on long term exposure and breast cancer risks. In addition, higher unregulated DBP concentrations and toxicity were observed in public water systems that utilize complex water sources including high salinity water, brackish groundwater, and indirect potable reuse of recycled water. Potentially higher DBP exposures in these public water systems raises concern because such complex water sources are an increasingly important component of the California drinking water supply.