Mixed-Solvent Sorption and Moisture-Regime-Dependent Degradation of Chlorpyrifos in Selected Tropical Soils

Abstract

Chlorpyrifos (CPF) is strongly hydrophobic, adsorbing on container walls used in analysis in aqueous systems. The study investigated the aqueous sorption kinetics and equilibria parameters for CPF in Teflon Lined Centrifuge Container walls and tropical soils, as well as the persistence of CPF in the soils. Batch sorption kinetics experiments were conducted by varying methanol fractions, and the Solvophobic theory was employed to predict the sorption coefficients K W and KOC indirectly. Degradation experiments were conducted on ten soils to study the effect of biotic and abiotic processes under flooded and field capacity moisture conditions. The Groundwater ubiquity index was calculated to determine the leaching potential of CPF in soils. Sorption coefficients decreased exponentially with increasing methanol fraction, while the mass transfer coefficient increased with methanol content, with equilibrium attained after 4-8 hours. The K W value for container walls was 0.19 mL/g, while soil K W values ranged from 46.53 to 56.71 mL/g. The KOC values ranged from 1551 -1890, which were lower than literature KOC values in experiments conducted in aqueous systems. The degradation rates were in order sterilized flooded > unsterilized flooded > sterilized field capacity > unsterilized field capacity soils, with calculated half-lives ranging from 18 to 52 days, 30 to 132 days, 18 to 21 days, and 32 to 33 days for sterilized flooded, unsterilized flooded soils, sterilized field capacity, and unsterilized field capacity soils, respectively. The Groundwater ubiquity index range was 1.013 and 1.536, showing that CPF does not leach in the selected soils.