THE DEETHYLATRAZINE ATRAZINE RATIO AS AN INDICATOR OF THE ONSET OF THE SPRING FLUSH OF HERBICIDES INTO SURFACE-WATER OF THE MIDWESTERN UNITED-STATES/

The ratio of deethylatrazine to atrazine (DAR) may be used to record t he first major runoff of herbicides from non-point-source corn fields to surface water in the Midwestern United States. The DAR dramatically decreases from similar to 0.5 to < 0.1 upon application of herbicide and the first major runoff event of a basin. The DAR then gradually in creases to values of approximately 0.4-0.6 during the harvest season. Furthermore, the DAR may be used in studies of surface water movement to give a temporal indicator of water moving into reservoirs for possi ble storage of herbicides. It is hypothesized that deethylatrazine, wh ich accounts for only 6% of the degradation of atrazine, becomes a sig nificant metabolite in surface water (similar to 50% of parent compoun d) because of its selective removal from soil. This removal process ma y be an important concept for consideration in studies of herbicide co ntamination of rivers and reservoirs.