Soils Isofenphos

A pure culture of Arthrobacter sp. was capable of degrading isofenphos at different soil concentrations (10, 50, and 100 ppm) in less than 6 h. In previously treated soils, isofenphos could be mineralized to carbon dioxide by indigenous microorganisms (Racke and Coats, 1987). Hydrolyzes in soil to salicylic acid (Somasundaram et al., 1991). 

Both isofenphos and fonofos were much less persistent in the history versus the nonhistory soils. A major difference between these insecticides and the carbamates was that considerable mineralization of the aromatic ring portion of the organophosphorus compounds occurred. For Isofenphos, considerable quantities (15.2/0 of isofenphos oxon accumulated only in the nonhistory, whereas no such accumulation was noted in the isofenphos-history soil. Several reports of the reduced persistence of isofenphos in field plots following repeated use have appeared (29.30). and isofenphos was withdrawn from the rootworm insecticide market after widespread experiences of control failure following second year applications. This is especially ironic because upon first application to soil isofenphos behaves as one of the most persistent organophosphorus insecticides (31). 

CASRN 25311-71-1 molecular formula C15H24NO4PS FW 345.40 Soil. Rapidly degraded by microbes via oxidative desulfuration in soils forming isofenphos oxon (Abou-Assaf et al, 1986 Abou-Assaf and Coats, 1987 Somasundaram et al., 1989), isopropyl salicylate, and carbon dioxide (Somasundaram et al., 1989). The formation of isofenphos oxon is largely dependent upon the pH, moisture, and temperature of the soil. The degradation rate of isofenphos decreased with a decrease in temperature (35 °C >25 °C >15 °C), moisture content (22.5% >30% >15%), and in acidic and alkaline soils (pH 6 and 8). After isofenphos was applied to soil at a rate of 1.12 kg ai/ha, concentrations of 8.3, 7.2, 5.1, and 1.0 ppm were found after 5, 21, 43, and 69 d, respectively. Following a second application, 4.9, 1.55, 0.25, and 0.10 ppm of isofenphos were found after 5, 21, 43, and 69 d, respectively (Abou-Assaf and Coats, 1987). 

Racke, K.D. and Coats, J.R. Enhanced degradation of isofenphos by soil microorganisms, / Agric. Food Chem., 35(l) 94-99, 1987. 

Conventional control of termites is heavily reliant upon prophylactic application of liquid insecticides to form a soil barrier around and beneath a structure to termite entry. These barriers, designed to repel or kill termites, degrade over time and must be reapplied every 5-10 years. A barrier termiticide application requires significant quantities of active ingredient, 5-10 kg, carried in 300 to 600 liters of water. Conventional products used as soil termiticides include organophosphates such as chlorpyrifos and isofenphos. 

A 25-g portion of each soil was placed in a glass Jar and treated with C-insectlclde at 5 (ig/g. Insecticides used for this assay Included those for which fields with some treatment histories could be identified C-carbonyl-carbofuran, C-ring-isofenphos,... 

The second component of the laboratory methodology for study of enhanced degradation involved a more intense investigation of the soil degradation of insecticides identified as suspect from the rapid degradation assay (carbofuran, isofenphos, fonofos) as well as 2 additional insecticides (cloethocarb, chlorpyrifos). The degradation... 

For this study 100 samples of soil were placed in glass Jars auid treated with either T[Pg.74]

Chapman,R.A., Harris, C.R. unpublished results) provided an opportunity to observe the persistence of enhanced activity in the absence of further treatment. E-factors observed at times ranging from 52 to 164 weeks following the third annual treatment are listed in Table IX. Soils previously treated with carbofuran, isofenphos and trimethacarb were tested by the aqueous incubation procedure mentioned previously (16) and are assessed as either active or slightly active. 

Isofennhos. Exposure of soils to salicylic acid, the secondary hydrolysis product of isofenphos, resulted in enhanced degradation of isofenphos (Table IV). Nearly two-thirds of the applied isofenphos was converted to soil-bound residues in soil pretreated 3 and 4 times with salicylic acid. Seventy-eight percent of the applied isofenphos was recovered at the end of the 3-week incubation in the control treatment as compared with 34 to 65% in soils pretreated with salicylic acid. The ability of microbes to metabolize structurally similar compounds such as 3,5-dichlorosalicylate, 3,6-dichlorosalicylic acid (24), and 5-chlorosalicylate (25) to their benefit has been reported. The low microbial toxicity, relative availability (as discussed later in this chapter), and nutritive value of salicylic acid may contribute to its potential to condition soils for enhanced degradation of isofenphos. 

Mobility in Soils. Chlorpyrifos was not mobile in any of the soils studied, but its hydrolysis product trichloropyridinol was mobile, especially in loamy sand and silt loam soils (Table VI). Parathion, diazinon, and isofenphos were slightly mobile (Rf < 0.25), and their hydrolysis products were significantly more mobile than the respective parent compounds (p < 0.01). Carbofuran phenol was more mobile in all soils studied (Rf 0.33 to 0.68). 2,4-D was mobile in... 

Figure 1. Recovery of 14CC>2 from 14C-carbonyl-labeled carbofuran in soil 11 pretreated with carbofuran, isofenphos, or rotations of carbofuran and isofenphos. See text for treatment codes.

Isofenphos Metabolite Assay. Racke and Coats (22) discovered a new metabolite of isofenphos, isopropyl salicylate, in cultures of isofenphos-degrading microorganisms isolated from enhanced soil. Since isopropyl salicylate is closely related to aspirin, we investigated methods currently used in the medical diagnostics field. The method of Sunshine (23.) is used by coroners for... 

Table V. Preliminary Results of Isopropyl Salicylate Detection Four Days After Soil Amendment with Isofenphos...

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