Pyrethroid Pesticides and Anthelmintic Drugs in Amazonian River Sediment: Occurrence, Environmental Drivers, and Ecotoxicological Risks

Knowledge about the occurrence of currently used pesticides and pharmaceuticals in the Amazon Basin is very limited. Therefore, we collected sediment samples from Amazonian Rivers near Manaus (Brazil) and measured concentrations of selected pyrethroid pesticides and anthelmintic drugs. Concentrations of Σpyrethroids and Σanthelmintics ranged between 19–180 and <0.093–0.28 ng/g dw in sediments, respectively. Sediment concentrations of pyrethroids were significantly positively correlated to total organic carbon (TOC) (p < 0.05), with 56% of the variance explained, indicating a hydrophobicity-driven accumulation process of pyrethroid distribution modulated by TOC, while the significant negative correlation between anthelmintic concentrations in sediments and pH (p < 0.05) implied a distribution process of anthelmintics mainly driven by pH (explaining 75% of the variance). The lack of statistical significance between sediment concentrations of either pyrethroids or anthelmintics and anthropogenic activities (p > 0.05) reduced the relevance of local anthropogenic inputs and further highlighted the dominance of environmental drivers. Both exposure-based (using predicted no-effect concentration (PNEC) values for sediment) and effect-based (using sediment LC50 to Hyalella azteca and Chironomus dilutus) risk assessments consistently highlighted the high ecotoxicological risks presented by cyfluthrin, deltamethrin, and esfenvalerate, which also indirectly indicated potential risks to aquatic organisms (e.g., fish), despite their limited biomagnification potential.