Polyethylene microplastics increase the toxicity of chlorpyrifos to the marine copepod Acartia tonsa

Abstract Ingestion of microplastics by marine organisms has been well documented, but their interaction with chemical pollutants has not been sufficiently addressed. The aim of this study was to determine the individual and combined effects of chlorpyrifos (CPF) and polyethylene microplastics (MP) on the survival, fecundity, feeding and egg viability of Acartia tonsa, a calanoid copepod widely distributed in planktonic communities. The median lethal concentration obtained for CPF was higher (LC50 = 1.34 μg/L) than for the combination with MP (LC50 = 0.37 μg/L), or CPF-loaded MP (LC50 = 0.26 μg/L). Significant effects were also observed for feeding and egg production (EC50 = 0.77 and 1.07 μg/L for CPF, 0.03 and 0.05 μg/L for CPF combined with MP, 0.18 and 0.20 μg/L for CPF-loaded MP). No significant effects were observed in the exposure to ‘virgin’ MP. This study confirms the role of MP as vectors of pollutants to marine organisms and supports the increased availability of certain toxicants carried out by MP. The effects observed in fitness-related responses suggest potential damage to A. tonsa populations. The comparison of the results obtained here with environmental concentrations indicates that the combined exposure to CPF and MP could constitute a risk to A. tonsa in the natural environment.