Exposure to the Herbicides Atrazine and Simazine in Drinking Water

A population-linked database was used to assess exposure to the herbicides atrazine and simazine in drinking water provided by community water systems (CWS) in 21 major use states. Herbicide concentration and population data from 1993 through 1995 were paired for each CWS and aggregated for all CWS to construct state and multi-state exposure profiles. The assessed populations were 110 million for atrazine and 107 million for simazine. The majority of the CWS population had no detectable exposure to atrazine and simazine. All simazine and 99.9% of atrazine populations had exposure below their respective drinking water MCLs. Thirteen of 13,688 CWS had atrazine multi-year mean concentrations above the MCL ranging from 3.06 to 6.19 ppb. Exposures to atrazine and simazine both corresponded to a margin of safety of at least 10,000 for 94% and 96% of the assessed population. Ciba Crop Protection (Ciba) is continuing this monitoring program at least through 1997 to provide a 5-year database, and will update this assessment with 1996 and 1997 data.