ET-4G1 (2/10/05 version)
Chemical Integrity: Pesticides

Why is this a Surface Water Quality Problem?

Ohio community and non-transient, non-community, public water systems are required to monitor for a number of pesticides in their treated drinking water. Monitoring results are compared to federally derived health limits for treated drinking water, known as Maximum Contaminant Levels (MCLs). MCLs are based on the Safe Drinking Water Act (SWDA), and are enforceable standards.

An Ohio EPA study to assess pesticide threats to Ohio drinking water most frequently detected atrazine, alochlor and simazine in treated drinking water. Similar results are documented in USGS reports for the East Fork Little Miami River and the Great and Little Miami basins. The MCLs for atrazine and simazine are 3.0 ug/l and 4.0 ug/l, respectively.

Because some public water systems using surface water sources now provide advanced treatment to remove pesticides from their source water, the public water system monitoring data for treated water does not show the complete distribution and occurrence of elevated pesticide levels in Ohio streams and lakes. Fortunately, from 1999-2003 there were no pesticide MCL violations (based on an annual running quarterly average) issued to Ohio public water systems based on treated water monitoring results.

However, elevated (above the MCL) pesticide levels, occur seasonally in many Ohio surface waters. Currently, more frequent monitoring is required when this occurs. Twenty three (29%) of the 78 public water systems using inland streams or Lake Erie as source water have had atrazine levels exceed the MCL of 3 ug/l and 7 public water systems have measured individual samples of over 4 times the MCL in their treated water. Approximately 60 percent of all public water systems using surface water sources have detected lower levels (below MCL) of atrazine, simazine, alachlor, or metolachlor in their treated water during the past five years.

Priority Areas: Public surface drinking water sources with seasonally elevated pesticide (above MCL) levels that have not yet caused, but at are risk of causing, future MCL violations; Lake Erie.