The adverse effects of virgin microplastics on the fertilization and larval development of sea urchins

Over the last decade, laboratory experiments have revealed a wide range of adverse effects in marine organisms following exposure to microplastics. This study investigated the working hypothesis that the observed effects of two types of virgin micro polymers ((polystyrene (PS) and high density polyethylene (HDPE)) might be, at least in part, due to the leaching of co-contaminants. For this purpose, the toxicity of these two polymeric materials and their leachates was tested on gametes and zygotes of the sea urchin Paracentrotus lividus following validated procedures. Zygotes were exposed for 48 hours to virgin and aged microspheres and leachates of fluorescent PS (10^3, 10^4 and 10^5 particles/mL) and agranular HDPE fluff (0.005, 0.5 and 5 g/L). Additionally, sea urchin eggs were exposed for 10 minutes to virgin fluorescent PS microspheres (10^3, 10^4 and 10^5 particles/mL). After exposure, the fertilization rate and percentage of larval abnormalities as well as larval growth were determined and compared to control groups. Overall, toxic effects on embryonic development and larval growth of the sea urchin were found for all treatments (untreated and weathered particles and leachates) with both polymeric materials. Furthermore, the highest toxicity (% abnormalities and reduction of the larval growth > 50%) was found after exposure to the lowest concentrations of leachate solutions for both types of polymeric materials. Microplastic ingestion was observed in the gastric cavity of the larvae in a dose- dependent manner, but not in a toxicity-dependent manner. Furthermore, eggs pre-exposed to concentrations of PS microspheres (10^3, 10^4 and 10^5 particles/mL) showed a toxic effect on the fertilization rate and on subsequent larval development as well as growth in a dose-dependent manner. These findings demonstrate that virgin microplastics are toxic to sea urchins through the leaching of chemicals, e.g., additives, residual monomers and other co-contaminants, which has been confirmed by chemical analysis elsewhere. The results of this study highlight the necessity to wash or weather microplastics before they are used in experimental laboratory studies to allow a more realistic extrapolation of the results to field conditions.