Seasonal Disparities and Risk Evaluation of EOCs in Pearl River Delta Water Sources

Emerging organic contaminants (EOCs) are extensively employed for disease control and agricultural yield enhancement. However, EOCs can enter aquatic environments through multiple pathways, constituting a potential threat to both human health and aquatic ecosystems, particularly drinking water sources. This study investigated the residual levels of two typical classes of biocides-antibiotics and pesticides-in five drinking water sources within the Pearl River Delta (PRD) region. The average total concentrations of antibiotics and pesticides were 102.50 and 103.13 ng/L during the dry season, 112.13 and 74.94 ng/L during the wet season, and 169.62 and 133.40 ng/L during the normal-flow season, respectively. Between 2023 and 2024, pesticide contamination exhibited a general declining trend, whereas antibiotic contamination displayed a gradual increase. PCA suggested seasonal/site-specific co-variation patterns that were consistent with influences from domestic wastewater, livestock/aquaculture activities, and mixed inputs when interpreted together with land use information. An ecological risk assessment revealed that clothianidin and imidacloprid posed high risks to the aquatic ecosystem. This study elucidates the contamination characteristics and potential risks of antibiotics and pesticides in the drinking water sources of the PRD region, thereby providing a scientific basis for water pollution prevention and water quality safeguarding in the area.