Microplastic exposure in aquatic invertebrates can cause significant negative effects compared to natural particles -...

Many studies have now reported adverse effects of exposure to microplastics in aquatic organisms. Still, relatively few studies have compared the effects of MPs with those of natural particle controls, which makes it difficult to separate particle effects from chemical effects. In this study, we carry out a meta-analysis of 26 studies to compare the effects of MPs and natural particles on aquatic animals using three different endpoints - growth, reproduction, and mortality. This analysis showed that MPs have the capacity to induce more adverse effects on growth, reproduction, and mortality for some taxonomic groups. However, the effects of exposure to MPs are not consistent across each endpoint or between taxonomic groups. We were not able to clearly discern differing impacts resulting from exposure to specific polymer types or shapes, though more negative effects were associated with polylactic acid and polyethylene, as well as fragments as opposed to beads or fibres. Additionally, meta-regression indicated that larger MP sizes, higher experimental temperatures, and longer exposure periods were all generally associated with more adverse effects. Future studies should continue to make use of negative particle controls to allow for better risk assessment of microplastics and nanoplastics in aquatic ecosystems.