Determination of Residues and Degradation Kinetics of Oryzalin in Different Soils of Soybean Ecosystem

Abstract

ABSTRACT Dinitroanilines group are persistent pesticides and important pollutants of soil and water. Their dissipation is needed to accurately predict the environmental risk entailing its use in different ecosystems. Degradation kinetics is not reported under subtropical conditions thus, kinetics of oryzalin under soybean field conditions at two application rate in texturally different Pantnagar soils were investigated for two cropping years. Oryzalin was extracted with acetone: methanol from soils followed by florisil SPE cleanup and residues were identified by HPLC-UV. Oryzalin persisted for more than 120 days in soils and slowly dissipated with biphasic first order kinetics. Dissipation was faster in sandy loam compared to silty clay loam soil. At 1.5 & 3.0 kg ha−1 initial half-life in silty clay loam and sandy loam soils were 5.892 & 5.675 and 6.015 & 5.770 days, while, in later phase it were 49.500 & 52.105 and 37.459 & 40.290 days, respectively. Recovery in soil, plant straw, seed husk, soybean oil, deoiled cake, and water samples varied from 77.50–88.85%, 79.50–89.25%, 78.05–88.20%, 75.45–83.92%, 77.40–84.75% and 81.75–93.75%, respectively. Minimum detection limit was 0.001 μg mL−1 and quantitation limit for soil, straw, oil, cake, husk and water were 0.007, 0.01, 0.04, 0.05, 0.03 µg g−1 and 0.005 µg mL−1, respectively. At harvest the oryzalin residues were below detection & MRL in all samples. Study revealed that under subtropical conditions oryzalin is safe for weed control in soybean fields and at harvest soybean crop could be used safely for human/animal consumption and would not create any residual/environmental problem.