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

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Abstract
Chlorpyrifos and chlorfenvinphos persistences (10 .mu.g/g) were examined 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.degree. C. Chlorpyrifos was fairly stable in sterile soils, with .apprx. 50% remaining at the end of 24 wk. In natural soils, chlorpyrifos disappeared most rapidly from air-dry soil and 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-(.apprx. 10% of the technical material) and trans-chlorfenvinphos disappeared at the same rate in sterile soils. In natural soils the cis-isomer disappeared .apprx. 2-fold as fast, suggesting specific microbial degradation.