Movement and degradation of triazines, alachlor, and metolachlor in sandy soils

Abstract

Four experiments conducted over a nine‐year period are summarized. The movement of alachlor, atrazine, simazine, cyanazine, and metolachlor were studied in a Coastal Plain, Evesboro loamy sand soil that had a water table near the surface. In two experiments atrazine and simazine were detected more frequently in the groundwater than metolachlor and cyanazine. There was no large difference in pesticide transport between conventional tillage and no‐tillage. In another experiment alachlor was detected in approximately 20% of the groundwater samples from May to July over a three‐year period. Several samples were above the EPA drinking water standard of two parts per billion. In the fourth experiment, all five herbicides moved below the root zone after a simulated rainfall (75 mm) five days after they were applied. Alachlor was detected more frequently in the lysimeters and groundwater than the other four herbicides. The research indicates pesticides may move to shallow groundwater by macropore flow in the sandy soils of the Mid‐Atlantic states if more than 30 mm of rainfall occurs shortly after they are applied. There are very few management practices available that will reduce the leaching of certain pesticides to groundwater in loamy sand and sandy loam soils of the Coastal Plain. Regulations may have to be adopted to limit the application of highly leachable pesticides in areas where the risk for groundwater contamination and human health effects are high.