Chemical Fact Sheet

Chemical Abstract Number (CAS #) 115902
CASRN 115-90-2
Phosphorodithioic acid, O,O-diethyl O-[4-(methyl sulfinyl)phenyl] ester
Analytical Method EPA Method 8141A
Molecular FormulaC11H17O4PS2

Link to the National Library of Medicine's Hazardous Substances
Database for more details on this compound.

Use INSECTICIDE AGAINST SOIL INSECTS; MOSQUITO LARVICIDE INSECTICIDE & NEMATOCIDE PRINCIPALLY FOR TOBACCO, CORN, AND VARIOUS OTHER CROPS Nematocide-Insecticide that kills by contact action. Effectively controls insects inhabiting soil and controls in a limited manner attacking insects.
Boiling Point 138-141 DEG C @ 0.01 MM HG
Molecular Weight 308.35
Density 1.202 @ 20 DEG C/4 DEG C
Environmental Impact Fensulfothion is a commercially produced insecticide and nematocide. The dominant source of its release to the environment is likely its application as a pesticide. If released to soil, fensulfothion will be transformed by microbial degradation and chemical hydrolysis. Adaptation of soil microbes has been demonstrated to be important which significantly shortens the persistence of fensulfothion upon annual reapplication. The estimated Koc values of 77 and 105 suggest that fensulfothion may be susceptible to significant leaching in many soil types. A correlation between increased adsorption with increasing soil organic content has been demonstrated. In soils of very high organic content (65%), such as onion fields in which fensulfothion has pesticidal use, fensulfothion has been shown to be retained in the upper soil layers. Volatilization from soil is not expected to be significant. The initial persistence half-life of fensulfothion in soil which has not received previous fensulfothion treatment has been observed to vary from less than one week to several weeks. If released to the aquatic environment, fensulfothion will hydrolyze; the measured hydrolysis half-life in pure water at 25 deg C is 58-87 days over the pH range of 4.5 to 8.0. Microbial degradation in natural water may also be important, especially under anaerobic conditions. Fensulfothion is not expected to volatilize, bioconcentrate in aquatic organisms, or adsorb to sediments significantly in natural waters. If released to the atmosphere, vapor-phase fensulfothion will react rapidly with a resultant estimated half-life of 7.03 hours at 25 deg C in atmosphere with a typical average concentration of 8X10 5 hydroxyl radicals/cu m. However, fensulfothion will not react with ozone. If released to air in solid-phase, such as dusts or mists generated by pesticidal application, fensulfothion is likely to be removed from the air by dry deposit. Localized removal by rainfall washout may be possible. Occupational exposure by inhalation and dermal routes related to the use of fensulfothion as a pesticide may be significant.
Environmental Fate AFTER APPLICATION TO PASTURE PLOTS, IN ADDITION TO UNCHANGED FENSULFOTHION, FENSULFOTHION SULFONE & FENSULFOTHION OXYGEN ANALOG SULFOXIDE & SULFONE WERE ALSO FOUND. TERRESTRIAL FATE: Fensulfothion degraded rapidly in a sandy loam soil to the moderately persistent metabolite fensulfothion sulfone . Field application of 50 ppm fensulfothion was reduced to 5 ppm after 120 days in the first year of application; however, in the second year of application, less than 0.2 ppm remained after 60 days, which was attributed to microbial adaptation . In laboratory studies, the initial half-life of fensulfothion in a sandy loam soil (organic matter 2.9%) and in an organic soil (organic matter 48.7%) was less than one week and one week, respectively, but was greater than 24 weeks in the same soils which had been sterilized by autoclaving . Initial fensulfothion concn of 50-175 ppm persisted for 50-60 days in a laboratory soil, whereas initial concn of 250-500 ppm persisted for up to 900 days . In a greenhouse study using an organic soil containing 65% organic matter, the initial half-life of fensulfothion applied at normal insecticidal concn was about 3-5 weeks with a slightly faster disappearance exhibited in wetter soil . Persistence of fensulfothion (as measured by larvae mortality) varied from 3-10 weeks in greenhouse and field studies of a sandy loam soil(6). Based on the available data, microbial degradation appears to be a major transformation process for fensulfothion in soil; chemical hydrolysis in moist soils may also contribute to its transformation. The estimated Koc value of 77 and 105 suggest that fensulfothion may be susceptible to significant leaching in many soil types; however, in soils of very high organic content (65%), fensulfothion has been shown to be tightly retained in the upper soil layers . A correlation of stronger adsorption of fensulfothion to soils of increasing organic content has been demonstrated(7). Based on a calculated vapor pressure of 6.82X10-7 mm Hg at 25 deg C (8) and an expectation of tight adsorption in high organic matter soils, fensulfothion is not expected to volatilize significantly from soil. AQUATIC FATE: The persistence of fensulfothion in both sterile and non-sterile natural water at 20 deg C was approximately the same with a half-life of about 16 weeks; under anaerobic conditions, the fensulfothion disappeared from the non-sterile natural water in 8-12 weeks with almost complete conversion to fensulfothion sulfide . The hydrolysis half-life of fensulfothion in pure water at 25 deg C has been measured to be 58 to 87 days over the pH range of 4.5 to 8.0. Based on estimated Koc values of 77 and 105, fensulfothion adsorption to aquatic sediment is not expected to be significant. Volatilization and bioconcentration are also not expected to be significant process in water. Based on the available data, hydrolysis and biodegradation are expected to be the important aquatic removal mechanisms for fensulfothion. ATMOSPHERIC FATE: Vapor-phase fensulfothion will react rapidly with photochemically produced hydroxyl radicals with a resultant estimated half-life of 7.03 hours at 25 deg C, but will not react with ozone. Fensulfothion dusts or mists released to the air by insecticidal applications are likely to be removed from the air by dry deposition, with the time required for deposition dependent on particle size and climate. Localized removal by rainfall wash-out may be possible. Fensulfothion is among the most persistent nematocides, but significant carry-over in soil from year to year is unlikely. Persistence in soil at 10 ppm initial concentration was 50% in > 24 weeks for sterile sandy loam and organic soil; 5% in about 5 weeks for non-sterile sandy loam and organic soil. One year after fensulfothion application, the residues of both fensulfothion and its oxidative metabolite had disappeared. Laboratory studies were conducted to assess fensulfothion persistence in soil. Persistence varied from 50-60 days with concentrations of 50-175 ppm. At concentrations of 250 ppm or more, fensulfothion persisted for more than 900 days in soil. Greenhalgh R; Read DC; Persistence of Fensulfothion in a Sand-Loam Soil and Uptake by Rutabagas, Carrots and Radishes Using Microplots; Field microplots were treated with 141 and 282 ppm fensulfothion (FSO) and 37.1 and 74.2 ppm fensulfothion sulfone (FSO2). The soil in the microplots consisted of 67.1% sand, 25.1% silt, 7.8% clay, and 2.6% organic matter. The pH of the soil was 5.7. The water content of the air-dried soil samples ranged from 0.9 to 1.8%. The calculated half-life values for FSO were 35 and 39 days, respectively for the 8.48 and 16.96 kg AI/ha treatments in 1978, and 31 and 30 days in 1979. A calculated half-life of 14-23 days was found for FSO2, which was less than that of the parent insecticide.
Drinking Water Impact GROUNDWATER: No residues of fensulfothion were detected at the minimum detectable level of 5.0 ppb in 27 wells sampled in areas of agricultural usage in California . Methods (gas chromatog and HPLC) were developed for the detn of >50 pesticides in wastewaters. A detection limit of apprx 1.5 ug/l was achieved for Fensulfothion/. EFFL: Fensulfothion has been detected (no concentration available) in run-off water from agricultural fields treated with the insecticide .

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