Parathion

CAS RN:56-38-2

Soil Adsorption / Mobility

Parathion had a mobility 0.01 compared to that of water in a French soil(2) and ranked 36 and 40 in a ranking of 41 pesticides by attenuation factor and retardation factor respectively, in 2 sandy soils(5). Some reported Koc values are: 674 (average for 8 Israeli soils) and 1538 (average for 4 Israeli sediments)(1); 10454 for 4 soils(3); 314 to 15860 for unspecified number of soils(4); 2000 average(6); 1310 to 4490 in 6 soils from India(7); 4800(8); 965 to 1700 in 4 soil types with percent organic carbon ranging from 0.41 to 43.7%(9); 1600 to 6200 for 4 Israeli soils(11); 602 to 805 in 5 sterilized Iowa soils(12). The fraction of parathion leached from soil by 10 successive 200 ml applications of water to a soil column was 1.24 and 4.36 for an organic soil and sand, respectively(9). Only a small fraction of parathion adsorbed to a sandy loam, 10%, was found to undergo diffusion (diffusion constant in soil with highest moisture content 0.03 sq cm/day)(10). In soil columns of Nacodoches clay subsoil, parathion leached to 60 inches when 230 inches of rainfall was simulated, while in Houston black clay, 1725 inches of rain were required to produce leaching to 60 inches(13). In field studies, little leaching occurred in 16 yr after 4 annual applications of parathion despite 42 inches of precipitation per year(13). Little parathion was found below 9 inches, 6 yr after 30,000 to 95,000 ppm was applied to the soil(14). In a 15-yr study of residues in a light sand soil, no parathion was found below 8 inches(13). In an 8 mo persistence test under experimental conditions with 20 cm of simulated rain, no parathion was found below 1 inch. In cases where small amounts of parathion penetrated into the soil, it was believed to be the result of the movement of particulate or microparticulate matter containing sorbed parathion(13). In a field study involving the application of parathion to a peach orchard providing watershed for a 2.7 acre pond, no residue was found below 6 inches and there appeared to be little desorption of the insecticide from the bottom sediment of the pond(15). According to a classification scheme(16), these Koc values suggest that parathion is expected to have moderate to no mobility in soil.
In wet soils, parathion sorbed to soil by complexing with water, whereas in dehydrated soil saturated with cations, complexation was direct(1). Koc values of 38,000, 3,086, and 6,404 were determined in batch adsorption experiments using sediments from the Windrush river catchment(2).
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