Sophia A. Salomon, Eric Grubmüller, Philipp Kropf, Elisa Nickl, Anna Rühl, Selina Weigel, Felix Becker, Ana L. Antonio Vital, Matthias Schott, Magdalena M. Mair 

Significant quantities of micro- and nanoplastic particles (MNP) end up in the
environment, either due to larger plastic debris breaking down or by entering directly
as MNPs. Effects of MNPs on organisms have been increasingly reported in recent
years, 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 the
environment 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 an
ecocorona influences MNP toxicity is still uncertain. While some studies suggest that
ecocorona formation can mitigate the negative effects of MNP on organisms, other
studies did not find such associations. In addition, it is unclear whether the ecocorona
itself is attenuating the effects of MNP or whether dissolved organic matter (DOM)
affects toxicity indirectly such as by increasing Daphnia‘s resilience to stressors in
general. To draw more solid conclusions about the direction and size of the mediating
effect of DOM and ecocorona formation on MNP-associated immobilization in Daphnia
spp., we synthesized evidence from the published literature and compiled 305 data
points from 13 independent studies. The results of our meta-analysis show that the
toxic effects of MNP are likely reduced in the presence of certain types of DOM. We
observed similar mediating effects when MNP were incubated in media containing
DOM before the exposure experiments, although to a lesser extent. Future studies
designed to disentangle the effects of the ecocorona itself from the general effects of
DOM will contribute to a deeper mechanistic understanding of MNP toxicity in nature
and enhance the reliability of MNP risk assessment.