Correlation between the stability and toxicity of PFAS-nanoplastic colloids

The interaction between per- and polyfluoroalkyl substances (PFASs) and nanoplastics (NPLs) in the environment is a growing concern due to their possible combined toxicity and potential impacts on ecosystems and human health. In aqueous compartments, their common migration strongly depends on the colloidal stability of the particles. Here, a clear relation between the toxicity and aggregation stage of colloids containing positively charged polystyrene NPL and perfluorohexanoic acid (PFHxA) PFAS was established. PFHxA adsorption on NPL altered the particle charge leading to unstable dispersions at the charge neutralization point and stable ones away from this condition. Toxicity studies on zebrafish embryos shed light on the synergistic mortality effect of the NPL-PFHxA adducts, and such a synergy strengthened with the increase in the dispersion stability highlighting the importance of environmental conditions like the NPL-to-PFAS ratio. The findings unambiguously demonstrate that high colloidal stability of environmental samples polluted with both NPL and PFAS leads to remarkable synergistic toxicity on living ecosystems, while the individual particles are expected to migrate faster in the environment than their aggregated counterparts.