Adsorption and degradation of triazophos, chlorpyrifos and their main hydrolytic metabolites in paddy soil from Chaohu Lake, China

Triazophos and chlorpyrifos are organophosphorus pesticides (OPs), and their primary hydrolytic metabolites are 1-phenyl-3-hydroxy-1,2,4-triazole (BZC) and 3,5,6-trichloro-2-pyridinol (TCP). In this study, the adsorption and degradation of triazophos, chlorpyrifos, BZC and TCP were investigated in paddy soil from Chaohu Lake, China. Adsorption tests demonstrated that the adsorption of these compounds to soils could be described by the Freundlich equation. Moreover, chlorpyrifos displayed the highest affinity for adsorption, followed by triazophos, BZC and TCP. Degradation of these compounds in non-sterile soil followed first-order exponential decay kinetics, and the half-life (t(1/2)) of these contaminants ranged from 8.40 to 44.34 d. Sterilization of soil decreased the degradation rate, indicating that microorganisms played a significant role in the degradation of these compounds. The values of t(1/2) and K(oc) were fitted to obtain models that could predict the leaching potential of the contaminants from soil. Compared to their parent compounds, BZC and TCP showed high potential for leaching into groundwater. The inoculation of OPs-degrading bacterium (Diaphorobacter sp. GS-1) removed 95.38%, 100% and 100% of triazophos, chlorpyrifos and BZC in paddy soil after 21 d, respectively. The pollution risk of triazophos, chlorpyrifos and BZC could be greatly decreased by inoculating soil with Diaphorobacter sp. GS-1, which decreases the t(1/2) of the contaminants.