Spatiotemporal variations and risk assessment of fungicides in the Dongjiang River Basin: tributaries as contamination hotspots

Although considerable research has explored fungicide patterns in major rivers, the role of tributaries remains overlooked. This study investigated the spatiotemporal distribution, and ecological risks of seven target fungicides in the Dongjiang River Basin of southeastern China, focusing on both the main stream and tributaries. All fungicides were detected in 100% of water samples, with total concentrations ranging from 7.72–476.52 ng/L (median, 106.35 ng/L) in autumn and 1.86–501.68 ng/L (median, 59.91 ng/L) in spring. Carbendazim, tebuconazole, and tricyclazole were the dominant fungicides. Higher concentrations were observed in autumn compared to spring, driven by increased agricultural activity and precipitation-driven runoff. Tributaries generally exhibited higher fungicide concentrations than the main stream, largely due to weaker dilution effects and proximity to intensive cropland use, particularly in upstream regions. Environmental factors such as electrical conductivity, total phosphorus, and land-use patterns correlated with fungicide distribution. Ecological risk assessments indicated that while acute toxic risks to aquatic organisms were negligible, the chronic risks posed by prolonged exposure, particularly to carbendazim, were significant at most sampling locations. These results highlighted the critical role of tributaries as contamination hotspots and emphasized the need for stricter regulatory policies and improved agricultural practices to mitigate fungicide pollution.