Environmental distribution of acetochlor, atrazine, chlorpyrifos, and propisochlor under field conditions

The environmental behavior, movement, distribution, persistence, and runoff by rainfall of the pesticides acetochlor, atrazine, chlorpyrifos, and prop isochlor were studied under field conditions during a five-month period at normal weather conditions. The pesticide concentrations in soil depths of 0 -5 and 5-20 cm, and in sediment and runoff water samples (collected from an artificial reservoir built in the lower part of the experimental plot) wer e measured every second week and following every runoff event. The contamin ation of a stream running across the lowest part of the plot was also monit ored. The weather conditions were also recorded at the experimental site. T he pesticide residues were quantified by a capillary gas chromatograph equi pped with a nitrogen phosphorus selective detector (GC-NPD). There was a co nsistent decrease in pesticide residues in the 0-5 cm soil layer with time after spaying. At 140 days after treatment only atrazine and chlorpyrifos w ere present; acetochlor and propisochlor were not detected in this soil lay er. Atrazine and chlorpyrifos in the soil at a depth of 5-20 cm. were detec table during the whole experimental interval, whereas acetochlor and propis ochlor concentrations were below the limit of detection. Pesticide losses b y the surface runoff process and the contamination of the stream were close ly related to the time of rainfall elapsed after treatment and amount of ra in at the experimental plots. Losses were primarily dependent on surface ra infall volume and intensity. The maximum detected residues of atrazine and acetochlor in streamwater were 1 order of magnitude higher than the maximum residue limit specified by the European Union (EU) for environmental and d rinking water (0.1 mug/L for individual compounds and 0.5 mug/L for total p esticides). Chlorpyrifos and propisochlor were not detected in this matrix.