Effects of dissolved organic matter and ecocorona formation on the toxicity of micro- and nanoplastic particles to Daphnia - A meta-analysis

Significant quantities of micro- and nanoplastic particles (MNP) end up in theenvironment, either due to larger plastic debris breaking down or by entering directlyas MNPs. Effects of MNPs on organisms have been increasingly reported in recentyears, with a large number of studies conducted on water fleas of the genus Daphnia.Most of the available studies used pristine particles that have not been exposed to theenvironment or to organic substances. In natural environments, however, proteins,organic substances and, if the particles are large enough, bacteria attach to MNP,forming an ecocorona or biofilm on the particles’ surface. How the formation of anecocorona influences MNP toxicity is still uncertain. While some studies suggest thatecocorona formation can mitigate the negative effects of MNP on organisms, otherstudies did not find such associations. In addition, it is unclear whether the ecocoronaitself is attenuating the effects of MNP or whether dissolved organic matter (DOM)affects toxicity indirectly such as by increasing Daphnia‘s resilience to stressors ingeneral. To draw more solid conclusions about the direction and size of the mediatingeffect of DOM and ecocorona formation on MNP-associated immobilization in Daphniaspp., we synthesized evidence from the published literature and compiled 305 datapoints from 13 independent studies. The results of our meta-analysis show that thetoxic effects of MNP are likely reduced in the presence of certain types of DOM. Weobserved similar mediating effects when MNP were incubated in media containingDOM before the exposure experiments, although to a lesser extent. Future studiesdesigned to disentangle the effects of the ecocorona itself from the general effects ofDOM will contribute to a deeper mechanistic understanding of MNP toxicity in natureand enhance the reliability of MNP risk assessment.