Despite
many studies on the toxicity of nanoplastic particles (NPPs)
to aquatic invertebrates, the effects of ecological constituents such
as humic substances (HSs) are often neglected. In our study, Daphnia magna was used to evaluate the effects of
three HSs, natural organic matter (NOM), fulvic acid (FA), and humic
acid (HA), on NPP toxicity and corona formation. Acute toxicities
of NPPs were reduced by all HSs at environmentally relevant concentrations.
NPPs elicited the upregulation of all genes related to detoxification,
oxidative stress, and endocrine activity after 7 days of exposure.
The presence of NOM or HA resulted in the mitigation of gene expression,
whereas significantly higher upregulation of all of the genes was
observed with FA. The presence of FA led to increased protein adsorption
on NPPs in D. magna culture medium
(eco-corona, EC) and homogenates (protein corona, PC), while there
was less adsorption in the presence of HA. The highly abundant proteins
identified in EC are involved in immune defense, cell maintenance,
and antipredator response, while those in PC are responsible for lipid
transport, antioxidant effects, and estrogen mediation. Our findings
revealed the key influence of HSs on the toxicity of NPPs and provide
an analytical and conceptual foundation for future study.