Response of reservoir atrazine concentrations following regulatory and management changes

Since the early 1990s, atrazine concentration exceeding the drinking water standard of 3 μg L−1 (parts per billion) in US drinking water supplies has been identified as a costly and major water quality concern. Atrazine levels in Columbus, Ohio, tap water reached 8.74 μg L−1 in the early 1990s, leading to a watershed-based approach aimed to reduce elevated atrazine concentrations. In 1999, a special Environmental Quality Incentives Program (EQIP) was implemented in the watershed that feeds Hoover Reservoir, the primary drinking water supply for Columbus, Ohio. Through EQIP, the Natural Resource Conservation Service (NRCS) offered financial incentives to farmers and operators to apply alternative pesticide management practices in an effort to reduce atrazine concentrations in the reservoir and maintain the concentrations below the drinking water standard. Monthly reservoir atrazine concentrations measured from 1985 through 2005 represent three distinct time periods with respect to atrazine management: no label restrictions (1985 to 1992), post label restrictions (1993 to 1998), and post label restrictions plus EQIP implementation (1999 to 2005). Significant (p < 0.05) reductions in mean monthly reservoir atrazine concentrations were noted between all three time periods: no label restrictions (2.27 μg L−1) > post label restrictions (1.99 μg L−1) > post label restrictions plus EQIP implementation (1.18 μg L−1). Regression analyses indicated that May through June precipitation and hectares enrolled in the EQIP pest management practice (Natural Resource Conservation Service Practice 595) were the two most important predictors of reservoir atrazine concentration. Additionally, for every dollar spent on the NRCS 595 pest management practice cost shared through the EQIP program, a US$2.73 benefit for the City of Columbus was realized through reduced drinking water treatment costs to remove atrazine. For farmers and operators, atrazine is an economically viable and effective herbicide for corn production. This study indicates that annually eliminating atrazine application on approximately 16% of the crop production acres may reduce and maintain reservoir atrazine concentrations below drinking water thresholds.