Herbicides in Karst Groundwater in Southeast West Virginia

A field study was conducted to determine the karst groundwater impact of herbicide application to feed crops in support of livestock production in southeast West Virginia. Grab samples were taken on a weekly/biweekly schedule at three resurgences for two agriculturally intensive karst watersheds. Two surface water sites were also sampled. The samples were analyzed for the presence of 12 different analytes: atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), its two metabolites, desethylatrazine (2-chloro-4-ethylamino-6-amino-1,2,5-triazine) and desisopropylatrazine (2-chloro-4-amino-6-isopropylamino-1,3,5-triazine), and nine additional triazine herbicides. Little impact was detected at the two surface water sites. In contrast, 6 of the 10 herbicides were detected in at least two of the three resurgences. Three of them, atrazine (ATR), metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], and simazine [2-chloro-4-6-(ethylamino)-s-triazine], were detected in more than 10% of all samples at all three resurgences. ATR and desethylatrazine (DES) were detected in more than 50% of samples at all three resurgences; median ATR values were 0.060, 0.025, and 0.025 µg/L. DAR*, the ratio of DES to ATR plus DES, was used to differentiate atrazine leaching following storage for long periods in the soil, from transport that bypassed deethylation in the soil through sinkholes and other solutionally developed conduits. DAR* was low (median of <0.5) and highly varied during the periods immediately following ATR application, indicating that significant quantities of ATR were present. In the winter, a release of ATR metabolites from the soil was evidenced by a steadier, and higher DAR* (median of 0.64). The maximum detected ATR concentration was 1.20 µg/L, which is within the USEPA maximum contaminant level of 3 µg/L.