Pollution Characteristics of Typical Pesticides and Multi-Level Ecological Risk Assessment in the Jiujiang Port Basin

Pesticides have attracted widespread attention as significant factors affecting aquatic ecosystem diversity. Jiujiang Port, located at the confluence of the Yangtze River and Poyang Lake, is the largest hub port in Jiujiang City and also an important agricultural production area. However, the characteristics and ecological risks of pesticide pollution in this basin have rarely been reported. In this study, we investigated the contamination profiles of 49 typical pesticides in surface waters in the Jiujiang Port area and conducted a multi-level ecological risk assessment using the Risk Quotient (RQ) method, semi-probabilistic risk assessment (RQf), and Joint Probability Curve (JPC) approach. The results showed that the average concentrations of triazine, carbamate, neonicotinoid, and organophosphorus pesticides were 3.063 ng·L−1, 0.321 ng·L−1, 3.752 ng·L−1, and 1.554 ng·L−1, respectively. Among them, hexazinone was the most predominant contaminant, with an average concentration of 19.209 ng·L−1. Twenty pesticides were detected at frequencies exceeding 80%, and the overall pollution level was higher in the wet season than in the dry season. The RQ assessment indicated that 11 pesticides posed low or higher risks in either the wet or dry season, with imidacloprid, simazine, and terbutryn presenting moderate risks and hexazinone, chlorpyrifos, and diazinon posing high risks. The RQf values of hexazinone, chlorpyrifos, diazinon, imidacloprid, simazine, and terbutryn all exceeded 1 in both seasons, indicating substantial ecological risks to aquatic organisms in the Jiujiang Port basin. The JPC evaluation suggested that hexazinone may pose a moderate risk to 0.3–6% of aquatic species, while chlorpyrifos, imidacloprid, and terbutryn were associated with a low risk. This study elucidates the contamination characteristics, spatiotemporal distribution, and ecological risks of pesticides in surface water, providing a scientific basis for the protection of aquatic biodiversity and the management of pesticide pollution in the Jiujiang Port basin.