Potential Regulatory Problems Associated with Atrazine, Cyanazine, and Alachlor in Surface Water Source Drinking Water

Abstract

Post-application seasonal (May-July) average concentrations of atrazine, cyanazine, and, to a lesser extent, alachlor sometimes exceed their Maximum Contaminant Levels (MCLs) (3 ug/L for atrazine and 2 ug/L for alachlor) or Maximum Contaminant Level Goal (MCLG) (1 ug/L for cyanazine) in surface waters of the Mississippi and Great Lakes Basins. These three chemicals are among the primary pre-emergent herbicides applied to corn. MCLs and MCLGs are compared to annual average concentrations for regulatory purposes. However, annual average concentrations are much less frequently reported than post-application seasonal averages. In most cases, both seasonal and annual average concentrations are substantially less than the MCLs or MCLG. However, actual and estimated annual mean concentrations occasionally exceed the MCLs or MCLG. Actual or estimated exceedences occur more frequently for atrazine and cyanazine than for alachlor, and may occur more frequently in lakes or reservoirs with long retention times than in streams and rivers. Additional year round data, and data for lakes and reservoirs, are needed to determine the extent to which such exceedences occur throughout the corn belt. The American Water Works Association (AWWA) believes that substantial numbers of Community Water Systems (CWSs) within the corn belt are currently, or will be, in violation of the revised Safe Drinking Water Act (SDWA) with respect to atrazine and cyanazine. They are concerned that such violations could result in numerous CWSs having to implement expensive tertiary treatment systems such as granular activated carbon to decrease herbicide concentrations. The United States Environmental Protection Agency, (US EPA) is continuing to review data on the pesticide concentrations in reservoirs and lakes that registrants have been submitting over the last 18 mo under the 6(a)(2) adverse impact provision of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The US EPA is also currently using computer modeling and other methods to evaluate potential alternative and/or supplemental herbicides to reduce atrazine use. In June 1992, the US EPA approved revised labeling that is designed to reduce indirect atrazine loadings to surface waters. Additional mitigation methods have been proposed and are being considered.

Factors Affecting Atrazine Fate in North Central U.S. Soils

“…Many studies have shown atrazine movement from the point of application in runoff water (see Nelson and Jones 1994, and references cited therein) (Table 4). Amounts detected for surface runoff studies range from < 0.1 010 to 7.20/0 of applied atrazine (Gaynor et al 1992.…”

KIH-485 and S-metolachlor Efficacy Comparisons in Conventional and No-Tillage Corn

“…Best management practices (BMPs) have been developed to reduce pesticide movement into nontarget areas and reduce contamination of water. BMP guidelines include conservation tillage, buffer strips and setbacks, crop rotation, between-row cultivation, herbicide incorporation, application timing, split applications, reduced rates, and alternative herbicides (Baker and Mickelson 1994;Devlin and Regehr 1996;Donald et al 2004;Nelson and Jones 1994;Wright et al 1993). Off-target movement is also influenced by the physical properties of the herbicides used.…”

Zone herbicide application controls annual weeds and reduces residual herbicide use in corn

“…New best management practices are needed to reduce offsite herbicide, nutrient, and sediment movement in runoff (Logan et al 1987;Logan 1993;Nelson and Jones 1994) and minimize herbicide contamination of surface and ground water (Fawcett 1998) without compromising farmers' economic or soil conservation goals. Moreover, if best management practices are to be adopted and used, they must be practical and acceptable to farmers (Rikoon et al 1996).…”