Persistence and Movement of Diuron and 3,4-Dichloroaniline in an Orchard Soil

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Abstract
The movement and persistence of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and its degradation product, 3,4-DCA (3,4-dichloraniline) were studied in an orchard soil which had received diuron annually at the rate of 4.5 kg/ha for 7 yr. Accumulation of residues was not observed at significant levels although carry-over of the herbicide occurred between years. The bulk of the herbicide residue was confined to the upper 15 cm of soil. The degradation rate of diuron generally followed first-order kinetics and the residual levels of diuron in the soil were highly phytotoxic to oat (Avena sativa L.) plants during the 3 yr after the last application. The levels of 3,4-DCA were low in all soil samples (< 21 ppb) and its relative distribution in the soil profile was similar to that of diuron.