ATRAZINE - ITS USE IN CORN PRODUCTION AND ITS LOSS TO STREAM WATERS IN SOUTHERN ONTARIO, 1975-1977

In a farm-to-farm survey of 11 agricultural watersheds averaging 4279 ha, it was found that on average 18% of the watersheds were devoted to corn production and 73% of this production was treated with atrazine at a mean rate of 1.7 kg/ha. Flow volumes in the 11 streams were gauged and waters were monitored for atrazine and its metabolite desethylatrazine between May 1975 and April 1977. These two compounds were detected in 80% of the stream waters at a mean concentration of 1.4 μg/l. Seasonal variations in concentration were observed. Peak residues occurred in streams shortly after the main spray period and after a secondary fall spray period. During the winter season, concentrations declined below 1 μg/l. Losses of applied atrazine were greatest on clay and least on sandy soils. The highest losses (60%) were caused by storm runoff events and especially in the January to April period. Spills accounted for 20% of the atrazine loss and the major period when this occurred was May to August. Losses due to base flow associated with drainage accounted for 20% and varied little over the year. © 1979.