Temporal and Spatial Changes in Bromine Incorporation into Drinking Water–Disinfection By-Products in Pennsylvania

Abstract

Bromide concentrations have been changing in rivers in Pennsylvania. Elevated bromide in source waters at drinking water treatment plant intake locations is expected to increase the formation and bromine incorporation of disinfection by-products (DBPs) that present health risks to consumers. Results from major drinking water distribution systems in southwestern and southeastern Pennsylvania taken during a national sampling effort (1997-1998) were compared with more recent data from these same systems (2012-2016). Sample sets were compared both temporally, across the nearly 20-year span between the first and final sampling periods, and spatially, comparing southwestern and southeastern Pennsylvania. Total trihalomethanes (TTHM) and bromine incorporation data show little change in southeastern Pennsylvania. In southwestern Pennsylvania, TTHM decreased significantly, likely as a result of treatment modifications designed to comply with more stringent regulations. However, fractional bromine incorporation in THMs increased, indicating TTHM reductions were associated with reduced chloroform alone. Risk metrics prioritizing brominated species indicated no change in southwestern Pennsylvania despite the decline in the surrogate, TTHM, which is used for regulatory compliance.