Water-extractable organic matter from tropical soils and biochar amendment tailors the colloidal behavior of nanoparticles and mitigates their toxicity through molecular eco-corona formation

Abstract

Understanding the interactions between nanoparticles and organic matter is crucial for environmental nanoscience and agricultural innovation, whether from intentional applications (fertilizers and agrochemicals) or unintentional release through widespread commercial use in many products. Molecular eco-corona formation on nanoparticle surfaces is a key element governing nano-bio interactions. Here, we investigated how water-extractable organic matter (WEOM) from tropical soils (i.e., oxisol and Amazonian dark earth) and biochar-amended oxisol affects eco-corona formation on copper oxide nanoparticles (CuONP) and how this impacts their colloidal stability and modulates their toxicity in a zebrafish model. Fluorescence spectroscopy, cryogenic electron transmission microscopy and ultrahigh-resolution mass spectrometry showed that the molecular structure and functionality of carbon compounds from WEOM are the main drivers of eco-corona rather than carbon content. Small, highly functionalized conjugated aromatic compounds exhibited the highest potential to form a strong eco-corona, which was positively correlated with nanoparticle stability. The interaction between CuONP and WEOM from Amazonian soil effectively inhibited nanoparticle aggregation at higher ionic strengths, thereby avoiding agglomeration and resulting in no significant impact on the embryo hatching rate. A correlative microscopy approach enabled the identification of different deposition patterns of nanoparticle association with the chorion membrane of zebrafish embryos. The mitigation of CuONP toxicity by strong eco-corona highlights the decisive role of the organic matter source and carbon chemistry in modulating nano-bio interactions and eco-corona composition, with implications for biological membrane attachment (i.e., chorion binding) linked to toxicological effects (i.e., embryotoxicity). These findings carry significant implications for risk assessment, safety, and the regulation of nanoparticles in tropical environments.