Polystyrene microplastics ingestion induced behavioral effects to the cladoceran Daphnia magna

Microplastic (μPs) contamination represents a dramatic environmental problem threatening both aquatic and terrestrial organisms. Although several studies have highlighted the presence of μPs in aquatic environments, the information regarding their toxicity towards organisms is still scant. Moreover, most of the ecotoxicological studies of μPs have focused on marine organisms, largely neglecting the effects on freshwater species. The present study aimed at exploring the effects caused by 21-days exposure to three concentrations (0.125, 1.25 and 12.5 μg/mL) of two differently sized polystyrene microplastics (PμPs; 1 and 10 μm) to the Cladoceran Daphnia magna. The ingestion/egestion capability of daphnids (<24 h) and adults, the changes in individual growth and behavior, in terms of changes in swimming activity, phototactic behavior and reproduction, were investigated. Both particles filled the digestive tract of daphnids and adults within 24 h of exposure at all the tested concentrations. Ingested PμPs remained in the digestive tract even after 96 h in a clean medium. For both particles, an overall increase in body size of adults was noted at the end of the exposure to the highest tested concentrations, accompanied by a significant increase in swimming activity, in terms of distance moved and swimming velocity, and by an alteration of the phototactic behavior. A significant increase in the mean number of offspring after the exposure to the highest PμPs concentrations of different size was recorded. Polystyrene μPs can affect behavioral traits of D. magna leading to potentially harmful consequences on population dynamics of this zooplanktonic species.