Toxicity assessment of trifluralin and its transformation products in soil: Bioassay response, and ecotoxicity of by-products

Evaluating pesticide residues in soil requires approaches that capture both phytotoxicity and ecological risk, particularly because degradation can generate transformation products that remain hazardous. This study presents an integrated experimental-modeling framework to assess the toxicity of trifluralin and its degradation by-products formed during hydroxyl radical-driven oxidation in loam soil. Trifluralin-spiked soils (initially ۱۰۰ mg kg-¹) were oxidized for different durations to create a concentration gradient (C₁-Cs; ۹.۵-۱۰۰ mg kg-¹), while an uncontaminated control (Co) was maintained. Residual trifluralin was quantified by HPLC, and transformation intermediates were identified using LC-MS/MS. Phytotoxicity was evaluated using Lepidium sativum (garden cress) bioassays (n=۴), measuring germination percentage, germination index, seedling length, and vigor index after ۱۰ days. Germination declined from ۹۰% (Co) to ۳۴% (Cs), while growth-related endpoints showed stronger discrimination among intermediate treatments, indicating that germination alone can underestimate sublethal toxicity. To complement bioassay findings, ecotoxicity of trifluralin and detected intermediates was estimated with U.S. EPA ECOSAR for fish, Daphnia magna, and green algae. Trifluralin was predicted to be highly toxic, and several early-stage intermediates exhibited toxicity comparable to or greater than the parent compound, highlighting that contaminant degradation does not necessarily reduce environmental risk. Overall, this combined bioassay-QSAR approach improves soil toxicity characterization and supports more reliable risk-informed management of herbicide-contaminated soils.

کلیدواژه ها:

Soil contamination ، Herbicides ، Trifluralin ، Germination ، ECOSAR