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Microplastics do not affect standard ecotoxicological endpoints in marine unicellular organisms
Summary
Bacteria and marine diatoms were exposed to polyethylene microplastics of 1–500 μm at concentrations above environmental levels, finding no acute toxicity on bioluminescence inhibition or algal growth by standard ISO endpoints. The results suggest that standard ecotoxicological endpoints are insufficiently sensitive to detect microplastic effects on marine microbial primary producers and decomposers.
In this study, the acute toxicity of microplastics (MPs) on unicellular organisms as marine decomposers and microalgae was assessed, by evaluating standards endpoints included in International Standard Organization (ISO) protocols. The bacteria Vibrio fischeri and the diatom Phaeodactylum tricornutum were exposed to different sizes (1-500 μm) of polyethylene MPs in order to evaluate bioluminescence inhibition and microalgal growth. No acute toxicity was found on bacteria or microalgae in an order of magnitude above environmentally relevant concentrations, suggesting that tested MPs did not affect the investigated biological processes. In conclusion, standard ecotoxicological endpoints are not sufficiently sensitive to assess the potential effects of MPs on decomposers and primary producers, conversely to nanoplastics. These findings highlight that the current approach for MP risk assessment in unicellular species should be revised, by providing alternative endpoints to be included in standardized protocols, able to monitor the fate and biological effects of MPs.