INFLUENCE OF MOISTURE ON THE PERSISTENCE OF CHLORPYRIFOS AND CHLORFENVINPHOS IN STERILE AND NATURAL MINERAL AND ORGANIC SOILS

Chlorpyrifos and chlorfenvinphos persistences were examined (concentration - 10 pg/g) in sterile and natural mineral (sandy loam) and organic (muck) soils at 4 moisture levels; air-dry, and 20, 40 and 60% of moisture holding capacity at 28°C. Chlorpyrifos was fairly stable in sterile soils, with ca. 50% remaining at the end of the 24 wk experiment. In natural soils, chlorpyrifos disappeared most rapidly from air-dry soil; slightly less rapidly from the 3 moist soils. Chlorfenvinphos was fairly stable in sterile soils, with >50% remaining at 24 wk at all moisture levels. In natural soils chlorfenvinphos, in contrast to chlorpyrifos, was more stable in air-dry soils. In moist loam the disappearance rates of chlor-fenvinphos were similar for all 3 moisture levels; but in moist muck its disappearance was proportional to the moisture content, “Cis” (ca 10% of the technical material) and “trans” chlorfenvinphos disappeared at the same rate in sterile soils. In natural soils the “cis” isomer disappeared about twice as fast, suggesting specific microbial degradation. Copyright © 1984 by Marcel Dekker, Inc.