Decline of Phorate and Dimethoate Residues in Treated Soils Based on Toxicity to Drosophila melanogaster

Abstract

Dimethoate and phorate were studied as soil treatments in the field and laboratory, using toxicity to Drosophila melanogaster (Meigen) to determine the rate of breakdown. Initial recoveries of surface treatments with both insecticides in the field were significantly greater than the amount applied. The high dimethoate recoveries were confirmed in laboratory surface treatments of moistened soil. Surface treatment of air dry soils and soil insecticide mixtures produced recoveries lower than applied. The high recoveries of phorate field surface treatments were not confirmed by laboratory surface treatments, but are thought to be associated with the significantly higher re-coveries obtained throughout the laboratory study when phorate-soil mixes were held in a 3-in. layer. These phorate soil mixes gradually increased in toxicity lor 28 days, when they were equivalent to 4 times the phorate applied.Following the high initial recoveries, the surface treatments of both insecticides declined in a conventional manner. Phorate breakdown was greatest during the first week and almost complete at the end of 1 month. Dimethoate declined more slowly, with about 30% remaining at the end of 1 month.

Synergistic Phytotoxicities of Herbicide-Insecticide Combinations in Soil

“…Under the conditions of the experiments reported herein diuron was not as persistent as reported by Lee (3) and Sheets (7) when o~ts, corn, and cotton were usef or bioassay. However, dlsulfoton and phorate or theIr degradation products were more persistent than pre-viously reported (5) when insects were the bioassay. Persistence of the combined diuron-insecticide phytotoxic effects corresponded closely to the individual pesticide phytotoxic effects in the experiments reported herein.…”

“…of herbicides under various rainfall conditions in different types of soils. The downward movement of a number of herbicides in soil columns has been determined by bioassays (3,5,6,8), radioactivity measurements (7,9), and chemical analysis (2,10) of the different soil layers after leaching with water. When comparing herbicides in regard to their leaching characteristics, some bioassay methods including the slotted tube test (8) have the drawback that the herbicidal activity on the assay plant varies from one compound to another.…”

“…L.) stands occurred with either disulfoton and phorate soil treatments at planting, but these losses were attributed to increased soil microbial infections and not to phytotoxicity (6). Phorate toxicity to flies (Drosophila melanogaster Meigen) increased nearly five times after 28 days in a moist stony silty loam soil (5). Chloroform extraction of a sand, clay loam, and muck 7, 14, and 28 days after radio active phorate treatment contained 12, 8, and 6% phorate, 61, 34, and 7% as oxidation products, 2, 7, and 5% as hydrolysis products, and 25, 51, and 82% radioactivity bound to soil, respectively (1).…”

Insecticidal Activity and Persistence of Phorate, Phorate Sulfoxide, and Phorate Sulfone in Soils

“…Nevertheless although more strongly inactivated in soil than phorate, p. sulfoxide and p. sulfone were intermediate in toxicity between carbofuran and fensulfothion, two commonly used soil insecticides. The biological activity of phorate in soil was, as suggested by others (Parker and Dewey 1965;Dewey and Parker 1965;Suett 1971), due to the joint action of phorate, p. sulfoxide, and p. sulfone.…”

“…It is volatile and volatilization is probably a major factor in its dissipation from soil (Getzin and Chapman 1960; Harris and Lichtenstein 1961; Getzin and Shanks 1970). In addition it is oxidized in soil to the sulfoxide and sulfone (Getzin and Chapman 1960;Parker and Dewey 1965; Dewey and Parker 1965; Bache and Lisk 1966; Getzin and Shanks 1970;Menzer et al 1970; Suett 1971Suett , 1974Suett , 1975; Schulz et a l . 1973; Lichtenstein et a l .…”