PATTERNS OF HERBICIDE CONTAMINATION IN SELECTED VERMONT STREAMS DETECTED BY ENZYME-IMMUNOASSAY AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

The patterns of contamination of the heavily used herbicide atrazine were determined in four Vermont streams. Over two seasons, 600 streamwater samples were collected following rain events and analyzed for atrazine content using a low-cost enzyme immunoassay (EIA). To ensure the accuracy of the EIA and to determine the concentration patterns of five other herbicides commonly used in Vermont (alachlor, cyanazine, metolachlor, pendimethalin, and simazine), 30% of the water samples were also analyzed using standard gas chromatography/mass spectrometry (GC/MS) techniques. Fifty stream sediment samples were also analyzed by GC/MS. The atrazine concentrations detected in the water samples varied from less than 1 to over 7 mu g/L, depending on the rainfall patterns during the season, the location of the sampling site within the watershed, and the intensity of the agricultural activity surrounding the sites. Combined water concentrations of all six herbicides were often several times higher than atrazine concentrations. Except in the largest stream, herbicide contamination usually occurred in pulses that dissipated within a few days after each rain event. Only trace amounts of two of the six herbicides were found in stream bottom sediment samples.