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

The persistence of chlorpyrifos and chlorfenvinphos was examined (concentration ‐ 10 μg/g) in sterile and natural mineral (sandy loam) and organic (muck) soils at 3°, 15° and 28°C for 24 wk. In sterile soils, chlorpyrifos was least stable at 28°, with 67% remaining in muck, and 38% in sandy loam after 24 wk. Chlorfenvinphos had similar stability in muck, but in sterile sandy loam it was more stable with 86% remaining after 24 wk at 28°. In the natural (non‐sterile) soils there were marked differences in persistence at 3°, 15° and 28°. Chlorpyrifos in muck had half‐lives of >24, 15 and 6 wk, and in loam 16, 6 and 2.5 wk, respectively at 3°, 15° and 28°. Chlorfenvinphos had half‐lives in muck of >24, 11 and 3 wk, and in sandy loam 14, 6 and 2.5 wk respectively at 3°, 15° and 28°. The implications of temperature effects on the rate of microbial degradation, insecticide efficacy and persistence are discussed.