Influence of moisture on the persistence of chlorpyrifos and chlorfenvinphos in sterile and natural mineral and organic soils

Abstract

Abstract Chlorpyrifos and chlorfenvinphos persistences were examined (concentration ‐ 10 μg/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 chlorfenvinphos 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.