Analytical Determination of Atrazine, Alachlor and Their Selected Degradation Products in Contaminated Groundwater: Implication for Wisconsin Groundwater Standards

Abstract: Little is known of the occurrence of pesticide degradation products in groundwater. Therefore, methods were developed for the analysis of degradation products of atrazine and alachlor in water. Atrazine and alachlor were targeted because they are among the most widely used herbicides in Wisconsin. Two breakdown products of alachlor (2,6- diethylaniline (DEA), and 2- Cl-2′,6′-diethylacetanilide) and two of atrazine (deethylatrazine and deisopropylatrazine) were focused upon. These were selected based upon a) their likelihood to occur in groundwater as determined by literature review, b) the existing toxicological information on the products, and c) the availability of analytical standards. Samples were collected from four sites in Wisconsin known to have groundwater contaminated by atrazine or alachlor. These samples were analyzed for atrazine, alachlor, and their targeted breakdown products using the study methods. The data indicate that neither DEA or 2-Cl-2′,6′-diethylacetanilide are important groundwater breakdown products of alachlor. Deethylatrazine was detected in all 32 of the study wells where atrazine was detected, and in three wells where atrazine was below the detection limit. Deisopropylatrazine was detected in 11 of the wells with atrazine detections and in two wells where atrazine was below the detection limit. The data was used to develop a mathematical model to predict atrazine breakdown product levels as a function of the concentration of atrazine in groundwater. If this model was used to adjust the enforcement standard to account for the presence of atrazine breakdown products in atrazine contaminated groundwater, the Enforcement Standard in Wisconsin for atrazine would decrease from 3.5 – to 1.1 μg/l.