Effects of Dissolved Organic Matter on Residues of Chlorpyrifos in Soil and on Plant Uptake

Dissolved organic matter (DOM) is comprised of a myriad of macromolecules with specific physical and chemical properties that may influence the fate of hydrophobic pesticides in the soil-plant system. A pot experiment was conducted to evaluate the effect of dissolved organic materials derived from green manure (GM) and pig manure (PM) on Chlorpyrifos dissipation in Typic Ferri-Udic Argosols (Chinese Soil Taxonomy 2001) and Chlorpyrifos uptake by Chinese Cabbage (Brassica chinensis). Chlorpyrifos was added to soil with an initial concentration equivalent to 5 mg.kg^-1. Following the pesticide application, DOM (100 mg.L^-1) was applied to the plants by surface irrigation during growing season. The degradation of Chlorpyrifos in soil was calculated by fitting the data to a first-order equation C_t=C₀e^-kt. In the presence of GM and PM effluent, the dissipation of Chlorpyrifos is faster; the final Chlorpyrifos residue in soil is 5.8% and 37.3% less than that in DOM free soil. Furthermore, DOM application diminished Chlorpyrifos phytoavailability and bio-concentration significantly, total uptake of Chlorpyrifos by Chinese Cabbage in the absence of DOM was 61.4% and 20.8% more than those irrigated with GM and PM effluent, respectively. However, the extent to which the residue was influenced differs according to the DOM type; the GM exhibited higher reductions than PM. Our findings indicate the use of organic waste-derived effluents for irrigation may be applied to provide means to reduce Chlorpyrifos residue in soil-plant systems.