Abstract
AbstractPCNB (pentachloronitrobcnzene) and DCNA (2,6‐dichloro‐4‐nitroaniline) are widely used as soil fungicides and have been found to be quite persistent in soils at field moisture capacity. Laboratory experiments were conducted to determine the effects of flooding, sterilization, addition of organic matter, atmosphere composition, free or combined oxygen, and soil temperature on pesticide decomposition.Known quantities of fungicides were added to three different California soils and analyzed for residual concentrations after incubation under controlled conditions. Samples were extracted with acetone and analyzed by gas‐liquid chromatographic analysis (GLC).Both fungicides were rapidly lost from soils made anaerobic by flooding or exclusion of oxygen. Losses were mainly due to microbial degradation. Loss rates were inversely related to organic matter content. Pentachloroaniline and possibly pentachlorothioanisole were found to be degradation products of PCNB.Organic amendments increased the rate of fungicide loss under flooded conditions, but not at field capacity, Degradation in flooded soils was retarded by free oxygen or combined oxygen in nitrate form. Rates of loss varied directly with temperature from 15 to 35C.
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