Acute and partial life-cycle toxicity of a tri-polymer blend of microplastics in the copepod Acartia tonsa

Microplastics are a prolific environmental contaminant that pose a risk to marine organisms. Ecotoxicological studies have identified microplastics can cause sub-lethal harm to aquatic biota. However, prior studies often lack comparability and environmental relevance, for example focussing upon monodisperse beads at extremely high concentrations. Copepods are keystone marine taxa that play vital roles in the marine food web and biogeochemical cycling. In this study, we adapted ISO methods to conduct acute and partial life-cycle toxicity tests exposing adult and juvenile life stages of the copepod Acartia tonsa to a fully characterised tri-polymer microplastic blend comprising cryoground polyethylene, polypropylene, and nylon particles (5-100 μm) at concentrations ranging 0-1000 μg L^-1. The tests considered the toxicity of microplastics on a wide number of endpoints including adult survival, algal ingestion rates, egg production and size, larval development ratio and juvenile survival. Mortality, egg size and larval development ratio proved to be the most sensitive endpoints. The tri-polymer blend had an LC50_72h value of 182 μg L^-1 providing a baseline for future toxicity testing using this method.