Combined toxicity of chlorpyrifos and nanoplastics in the marine amphipod Parhyale hawaiensis: implications for chlorpyrifos risk assessment in Latin American coasts.

Chlorpyrifos (CPF) is a widely used organophosphate insecticide, yet ecotoxicological evidence for marine organisms in Latin America, particularly under co-exposure with other pollutants, remains limited. We assessed the acute toxicity of CPF alone and in mixtures with low (100 µg/L) and high (1000 µg/L) concentrations of polyethylene nanoplastics (PE-NPs) in the marine amphipod Parhyale hawaiensis. Neonate mortality and immobility were evaluated over 96-h exposures. The CPF+NPs_Low mixture showed the highest toxicity for mortality (LC50 = 0.25 µg/L) and immobility (EC50 = 0.06 µg/L), compared with CPF+NPs_High (LC50 = 0.57 µg/L; EC50 = 0.11 µg/L) and CPF alone (LC50 = 0.32 µg/L; EC50 = 0.1 µg/L). Acute CPF toxicity data for marine organisms of Latin American origin were also compiled to develop a regional SSD and a preliminary ecological risk assessment (ERA), alongside a broader non-Latin American dataset for comparison. The analysis revealed substantial uncertainty across estimates, reflecting important gaps in the quantity, quality, and representativeness of regional ecotoxicological data. Overall, P. hawaiensis showed high sensitivity to CPF, and co-exposure to NPs modified its toxicity. These findings highlight the need to address regional ecotoxicological data gaps and to consider mixture effects in the CPF ERA for Latin American coastal ecosystems.