PARTITIONING AND FATE OF ACEPHATE AND ITS METABOLITE, METHAMIDOPHOS, FROM WHITE SPRUCE CONES INTO SOIL AND WATER

An aqueous solution of acephate, an organophosphate systemic insecticide, was painted onto the injured bark of clipped branch tips of white spruce containing fresh cones, at dosage rates of 5 and 10 mg in 0.2 mL. Twelve days later the cones were harvested for residue analysis. Acephate was taken up by the cones from the treated region, and was partly converted into its major metabolite, methamidophos. Contaminated cones were then placed in moist sandy loam and clay loam soils, and also in pond and river water. All samples were incubated for 48 h with gentle agitation. Residues of acephate and methamidophos were measured in soil and water at different intervals up to 45 d, to study persistence. Both compounds underwent considerable partitioning from the cones into soil and water. The amounts partitioned were higher and persisted longer in the clay loam containing high organic matter than in the sandy loam. Partitioning occurred more in the turbid pond water than in the relatively clear river water. Both compounds dissipated more slowly in the sterile soil and water than in the non-sterile samples, indicating the role of microbes on dissipation. In all cases, both chemicals persisted longer in water than in soil, and acephate persisted longer than methamidophos.