Parathion: toxicity to sheep and persistence on pasture and in soil

Abstract

The acute oral MLD of parathion to ewe and ram lambs of 20 kg body weight was approximately 40-50 mg a.i.jkg body weight. The insecticide was not markedly cumulative in its toxic effects.Pastures were topdressed with granules of 20% parathion at the rates of 3.4 kg and 6.7 kg a.i.zha and groups of four sheep were grazed on the pastures after withholding periods of 0, 7, 14, and 28 days. Sheep in the O-day groups developed slight scouring and their blood cholinesterase activity was severely depressed. None of these sheep died and their subsequent recovery was uneventful. In the other groups the only evidence of exposure to parathion was depression of blood cholinesterase activity, which was progressively less as the length of the withholding period increased. No parathion was detectable in the fat of the sheep that had the highest exposure to parathion on the treated pastures.Over a 3-month period parathion residues in topsoil (0-2.5 em) decreased from 6.5 ppm to 4.7 ppm and from 10.7 ppm to 8.5 ppm for application rates of 3.4 kg and 6.7 kg parathion/ha, There was little penetration of insecticide below the top 2.5 em of soil, and no parathion was found in the soil 8 months after treatment.Residues of parathion on pasture were more persistent in this grazing trial than in a subsequent ungrazcd plot trial. Parathion was not systemic in pasture, as residues were present apparently only on the plant surfaces.

Parathion: Residues in soil and water

“…Bioassay of field soils treated with a granular formulation of parathion at the rate of 1.12 kg/ha showed less than 20% bioactivity after six weeks of application (BURKHARDT and F AmCHILD 1967). Parathion disappeared completely from the soils within eight months after top dressing the soils at 3.4 and 6.7 kg/ha with a 20% granular formulation (MOL et al 1972). When applied to the soil at the rate of 112 kg/ha, the insecticide persisted for 325 days (KASTING and WOODWARD 1951).…”