POINT AND NONPOINT-SOURCE LEACHING OF ATRAZINE FROM A CORN FIELD - EFFECTS ON TILE DRAINAGE WATER-QUALITY

Atrazine concentrations in tile drainage waters emanating from a conti nuously cropped, commercial corn field (silt to clay loam) were monito red for 30 consecutive months, March 1989 to September 1991. Water sam ples were collected approximately every two weeks from three independe nt tile drainage plots within the field. Excluding the effects of an a ccidental spill, atrazine concentrations in the tile water ranged from 0.1 to 29 mu g/L. Concentrations declined with time after application to approximately 0.1 mu g/L prior to planting the following spring. I n June 1990, approximately 60 g of active ingredient were accidently d ischarged in one of the plots followed by a 71 mm rainfall (in 12 h) s everal days later. Subsequent auto-sampling of the drainage waters eve ry 4 hours revealed atrazine + deethylatrazine concentrations to 150 m u g/L. Concentrations de creased to less than the maximum acceptable c oncentration for drinking water (MAC) within six days of the initiatio n of tile flow. As a result of this storm, about 18 g of atrazine leac hed from the soil into the tile drainage water. This was in contrast t o simulation results for a uniform porosity soil that indicated no atr azine would be transported to drain depth. Atrazine + deethylatrazine concentrations declined to <1.0 mu g/L by May 1991, similar to concent rations in the other plots where atrazine was properly applied. Docume nted case histories of this nature are helpful in assessing the degree and duration of hazard resulting from accidental release of atrazine in a field crop setting.