Uncovering ecological risks of pesticides: From parent compounds to unknown transformation products in soils from Dongting Lake Basin.

Transformation products (TPs) of pesticides have gained substantial attention due to their potential greater persistence and ecological risks than parent compounds. Nevertheless, given to the variety of pesticides and complex of TPs, the effective identification of unknown TPs presents a considerable challenge. Herein, we employed a target quantitative approach to quantify twelve insecticides, twenty-three fungicides, nine herbicides and nine commercialized TPs in soils from Dongting Lake Basin, with total concentrations ranged from 4.39 to 3012 ng/g dw (median range: n.d.- 5.98 ng/g dw). Nineteen unknown TPs were tentative identified through suspect/non-target analysis by high resolution mass spectrometry (HRMS), some of which were firstly observed. Reactions through dechlorination, hydroxylation, dealkylation, and methylation were the main transformation pathways for these pesticides. Further evaluation of ecological risks for these TPs by the Toxicity Estimation Software Tool (TEST) and the US EPA Toxicity Evaluation Software Tool (ECOSAR) was conducted. Some TPs exhibited higher toxicity than their parent pesticides, whereas others demonstrated reduced toxicity. Hydroxylation, and sulfonation were considered as detoxification pathways, and methylation is a potential ecological risk enhancement process for organic pollutants, which warrant further attention. These findings highlight the critical necessity to include the TPs for risk assessment and toxicity evaluation.