Multicriteria Prioritization of Emerging Contaminants in Agricultural Ditch Systems across China

Agricultural ditches play an underappreciated role in accumulating or attenuating waterborne emerging contaminants (ECs) from farmlands to downstream aquatic ecosystems. Here, we present the first nationwide assessment of ECs in ditches across major agricultural regions of China, through analyzing over 300 compounds at 183 sampling sites. A multicriteria assessment framework was applied to prioritize contaminants along the farmland ditch-river continuum by integrating scenario-specific occurrence patterns, transferable environmental fate properties, and toxicological profiles covering cytotoxicity, ecotoxicity, and human health endpoints. Principal component analysis was used to derive data-driven weights from the nationally representative data set, enabling objective synthesis of commonly used risk dimensions while reflecting the agricultural ditch context, avoiding the subjectivity of expert-assigned scoring. The prioritization identified per- and polyfluoroalkyl substances (PFASs) as the highest-priority pollutants owing to their extreme persistence, bioaccumulation potential, and human health risks, followed by several pesticides (notably tebuconazole and fipronil), bisphenol A, di-n-octyl phthalate, and natural hormones. Cluster analysis revealed two distinct pathways to high priority: source-intensive contaminants driven by continuous agricultural inputs and legacy-type persistent chemicals attributed to intrinsic molecular stability. Over 60% of the top-ranked substances appear on international regulatory watch lists, including those of China, the EU, and the US EPA, confirming the framework's practical relevance. Beyond providing priority rankings for agricultural ditch management, our methodology offers a transparent and adaptable template for contaminant prioritization in other environmental settings.