CAS RN: 333-41-5

Soil Adsorption / Mobility

The Koc for diazinon ranged from 40-432, and averaged 191 for 3 soils(1); in one sediment, the Koc was 250(1). For sandy loam(2.0% OM, pH 5.4), silt loam(1.4% OM, pH 7.0), silt loam(1.8% OM, pH 6.5) and sand(1.4% OM, pH 7.0), the Kocs were 1,539, 1,007, 1,653, and 1,842, respectively, with a recommended value of 1520(2). The Koc for diazinon was found to be 1589 in an Hungarian brown forest soil(3). The Koc for diazinon in two New Zealand topsoils was 165.22 and 324.49(4); the Koc in a New Zealand subsoil was 1447.47(4). According to a classification scheme(5), these experimental Koc values suggest that diazinon is expected to have moderate to low mobility in soil(SRC). Diazinon was given a leaching index of 2.0 (<20 cm movement/yr with 150 cm of annual rainfall)(6). Diazinon is reported to be fairly strongly adsorbed onto soil with low mobility(7).
Soil sorption constants based on the organic carbon content of 15 pesticides were measured using 2 soils (clay loam and high clay) at 0.01, 0.1 and 1.0 ppm pesticide. The soil sorption coefficients ((ug pesticide/g soil)/(ug pesticide/g water)) for diazinon were 13.9 in clay loam and 2.4 in high clay soil. The soil sorption constants were 327 and 175 respectively, with a mean of 251. Significant correlations were found between organic carbon content and water solubility, octanol/water partition coefficient, retention time in reversed phase high pressure liquid chromatography and molecular wt(1). In sediment-water partition studies, the sorption of diazinon was found to increase with time over a 28-day test period(1); in sediments from Bonita Creek (Orange County CA), the calculated Koc increased from 46 (on day 0) to 497 (on day 28); in sediments from the San Diego Creek (Orange County CA), the calculated Koc increased from 113 (on day 0) to 777 (on day 28)(2).
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