Target and Nontarget Analyses Reveal Similar Dissolved Organic Contaminant Patterns Relative to Quantified Catchment Characteristics along Two German Rivers

River water quality is compromised by diverse organic contaminants from human activities. However, it is not well characterized how the mixture of dissolved organic contaminants in rivers evolves longitudinally from source to mouth or how it is related to river catchment characteristics. We collected dry-weather water samples along two large, anthropogenically impacted German rivers, the Neckar and Spree, and used target and nontarget analyses to assess the concentration patterns of individual organic contaminants as well as the peak area patterns of nontarget anthropogenic features and the remaining nontarget "other" features. 81% of the target contaminants, 66% of the anthropogenic features, and 56% of the "other" features were detected in at least 50% of sites in both river catchments, indicating a high degree of chemical similarity despite catchment spatial separation. Contaminant concentrations and feature peak areas increased within and downstream of urbanized regions. Pharmaceuticals correlated most strongly with the annual volume of treated wastewater effluent in a catchment, whereas polymer-related chemicals correlated most strongly with urban land covers linked to industry and transportation. Feature-based molecular networks of sartans, hexa(methoxymethyl)melamine derivatives, and polyethylene glycols revealed a multitude of contaminants in the rivers that would be overlooked if relying on target or nontarget annotation methods alone. This study highlights the importance of better understanding the occurrence of chemicals related to rivers' catchment characteristics to inform water quality management and pollution source control.