Insights on persistent herbicides in cropland soils in northern China: Occurrence, ecological risks, and phytotoxicity to subsequent crops.

Herbicides are essential inputs in agriculture, but their long-term persistence creates underappreciated risks in intensive cropping systems. While previous studies focused on single-herbicide persistence, the cumulative ecological and agronomic impacts of multi-herbicide residues remain poorly understood, particularly in phytotoxicity to subsequent crops. This study investigated the occurrence, ecological risk, and phytotoxicity of six persistent herbicides in cropland soils in northern China. Herbicide contamination was widespread, with at least one herbicide detected in 90.9 % of soil samples. The most frequently detected herbicides were atrazine (54.6 %), deethylatrazine (41.1 %), fomesafen (47.3 %), and nicosulfuron (54.3 %), with mean concentrations of 9, 7, 41, and 99 μg/kg dw, respectively. Clomazone and imazethapyr were detected in 5.5 % and 0.8 % of samples, with mean concentrations of 8 and 4 μg/kg dw, respectively. Risk quotient (RQ) values indicated that clomazone (0.004), fomesafen (0.001), and imazethapyr (0.00006) pose low ecological risk (RQ<0.01), whereas nicosulfuron (26.95) and atrazine (2.54) present high ecological risk (RQ≥1). Phytotoxicity risks to subsequent crops, including tobacco, were identified for atrazine (28.6 % of soils), nicosulfuron (26.4 % of soils), and fomesafen (14 % of soils). Most subsequent crops, like soybean and wheat, were unaffected by atrazine residues in over 99 % of the soils. These findings provide key data for agricultural management.