Micro- and nanoplastic effects on the reproduction of Daphnia spp. - a meta-analysis

Several traits of micro- and nanoplastic particles (MNPs), including among others, polymer type, size, and shape, have been shown to influence MNP toxicity. The direction and size of these moderating effects are however often unclear and generalizations from single studies are difficult to establish. Meta-analyses, which quantitatively aggregate data on a specific topic, can be used to increase generalizability of results and derive more accurate and precise effect size estimates by combining measurements from published studies. We conducted a meta-analysis to investigate the effects of MNP exposure on the reproductive output of water fleas of the genus Daphnia by aggregating 369 data points from 64 published studies. We show that Daphnia individuals exposed to MNP produce on average 13.6 less neonates, which represents a reduction of 20.8% compared to the particle free controls (control mean = 65.37 neonates). This effect is moderated by the particles’ concentration and shape category, exposure duration, experimental temperature, and size category with microplastic particles eliciting a stronger negative effect than nanoplastic particles. Species, age of the test organisms, polymer type, size (as continous), fluorescence, modification type, presence of surfactant and DOM present did not influence effect sizes significantly. Based on the high residual heterogeneity in the data, we suggest that additional factors likely influence observed effects and discuss how a better characterization of particles could improve our understanding of the drivers of MNP toxicity.