Environmentally relevant concentrations and sizes of microplastic do not impede marine diatom growth

The current knowledge about the ecological effects of microplastic (MP) remains limited, and to-date ecotoxicity tests often utilize standard microplastic with one or two distinct size classes and expose the organisms to unrealistically high MP concentrations. We exposed the marine diatom Phaeodactylum tricornutum to microplastic particles of a mimicked realistic size frequency distribution complemented with serial experiments with distinct size classes. To do so, we exposed this diatom to a concentration series of different sized polyethylene (PE) microbeads (sizes: 10-106 mu m; 1.25 x102-1.25 x107 particles/L) in a 72-h growth inhibition test. No effect on the growth of P. tricornutum by virgin PE microbeads up to 1.25 x 107 particles/L (or 499 mg/L), indicating environmentally relevant concentrations and sizes of MP does not alter the growth of marine diatoms. Results of smaller sized MPs (10-20 mu m) did not differ from those obtained with larger MPs (90-106 mu m) and mix sized MPs (10-106 mu m), i.e. no impact on the microalgae growth. As a pioneer work, our results contribute with high quality dose-response data to an improved risk assessment of microplastic under realistic present and future marine MP pollution.

Automated summary

The study found that microplastic at environmentally relevant concentrations and sizes does not alter the growth of marine diatoms like Phaeodactylum tricornutum. The results provide high quality dose-response data for improved risk assessment of microplastic pollution in present and future marine environments.