MOVEMENT AND DEGRADATION OF TRIAZINES, ALACHLOR, AND METOLACHLOR IN SANDY SOILS

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 foamy sand soil that had a w ater 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 betwee n 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 d rinking water standard of two parts per billion. In the fourth experim ent, all five herbicides moved below the root zone after a simulated r ainfall (75 mm) five days after they were applied. Alachlor was detect ed more frequently in the lysimeters and groundwater than the other fo ur herbicides. The research indicates pesticides may move to shallow g roundwater by macropore flow in the sandy soils of the Mid-Atlantic st ates if more than 30 mm of rainfall occurs shortly after they are appl ied. There are very few management practices available that will reduc e the leaching of certain pesticides to groundwater in loamy sand and sandy loam soils of the Coastal Plain. Regulations may have to be adop ted to limit the application of highly leachable pesticides in areas w here the risk for groundwater contamination and human health effects a re high.