Gaps in aquatic toxicological studies of microplastics.

The contamination of aquatic environments with microplastics (MPs) has spurred an unprecedented interest among scientific communities to investigate their impacts on biota. Despite the rapid growth in the number of studies on the aquatic toxicology of MPs, controversy over the fate and biological impacts of MPs is increasingly growing mainly due to the absence of standardized laboratory bioassays. Given the complex features of MPs, such as the diversity of constituent polymers, additives, shapes and sizes, as well as continuous changes in the particle buoyancy as a result of fouling and defouling processes, it is necessary to modify conventional bioassay protocols before employing them for MP toxicity testings. Moreover, several considerations including quantification of chemicals on/in the MP particles, choice of test organisms, approaches for renewing the test solution, aggregation prevention, stock solution preparation, and units used to report MP concentration in the test solution should be taken into account. This critical review suggests some important strategies to help conduct environmentally-relevant MP bioassays.