Significant decline of Daphnia magna population biomass due to microplastic exposure

Even though microplastics are intensively studied, the focus of the research is mainly on relatively short term effects at high doses. Therefore there is a need to shift the focus toward more realistic, longer-term endpoints. Studies with a range of chemicals have shown that the response of populations often differs from studies in which a single organism is exposed in an individual container (as often described within standard ecotox screening assays). Here we investigate the impact of primary microplastics (1-5 μm in size) on a population of Daphnia magna. We first allowed a stable population of D. magna to develop over 29 d, after which the populations were exposed to microplastics for three weeks (concentrations ranging from 10² to 10⁵ particles mL^-1 and a control). We found a significant impact of microplastics on the total population of D. magna, with a reduction in the amount of adult daphnids. Importantly, when expressed as total biomass, exposure to 10⁵ microplastics mL^-1 resulted in a 21% reduction in total biomass compared to control. These results indicate that exposure to microplastics can result in significant adverse effects on the population of D. magna, including a reduction in the number of individuals as well as total biomass. Given the importance of D. magna in freshwater food webs, both as a grazer as well as a food source, this can potentially impact the functioning of the ecosystem.