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

Abstract Chlorpyrifos (CPF) is a widely used organophosphate insecticide, yet its ecological effects on Latin American marine species, both alone and in combination with other pollutants, remain poorly characterized. Here, we assessed the acute toxicity of CPF alone and in mixtures with low (100 µg L − 1 ) and high (1000 µg L − 1 ) concentrations of polyethylene nanoplastics (NPs) in the marine amphipod Parhyale hawaiensis . Neonates were exposed under laboratory conditions, and mortality and immobility were evaluated over a 96-h period. CPF induced acute toxicity in P. hawaiensis at concentrations within the environmental range. The mixture CPF+NPs100 µg L − 1 showed the highest toxicity for mortality (LC50 = 0.25 µgL − 1 ) and immobility (EC50 = 0.06 µgL − 1 ), compared with CPF+NPs1000 µgL − 1 mixture (LC50 = 0.57 µgL − 1 ; EC50 = 0.11 µgL − 1 ) and CPF alone (LC50 = 0.32 µgL − 1 ; EC50 = 0.1 µgL − 1 ). Additionally, acute toxicity data for CPF in marine species were compiled by geographic origin (Latin America vs. non-Latin America) to construct species sensitivity distributions (SSDs) and support a region-specific ecological risk assessment (ERA). SSD analysis showed lower HC 5 values for Latin American species (0.064 µgL − 1 ) than for non-Latin American species (0.113 µgL − 1 ), which coincides with the limited data available for the former. Risk Quotients (RQ) indicated high ecological risk for Latin American species (RQ = 23.5) and moderate risk for non-Latin American species (RQ = 0.8). Overall, P. hawaiensis showed high sensitivity to CPF across both experimental assays and the Latin American dataset. The increased CPF toxicity observed under co-exposure to low concentrations NPs (100 µgL − 1 ) underscores the need to incorporate mixture scenarios into ERA, as risks might be underestimated.