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Effect of Soil Treatments on Losses of Two Chloronitrobenzene Fungicides¹

ABSTRACT

PCNB (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.

Key Words: flooded soils • pesticides • microbial degradation

¹ Contribution from the Department of Soils and Plant Nutrition, Univ. of California, Davis 95616.

² Former Graduate Research Assistant and Professor of Soil Microbiology, respectively. The senior author is presently Soil Specialist, IRI Research Institute, Inc. Caixa Postal 258, Belem-Para.

Received for publication February 23, 1973.