How to Accurately Predict the Fate and Effects of Engineered Nanomaterials

RecommendationsE ngineered nanomaterials (ENMs) challenge risk assess- ment because their environmental fate and toxicity cannot be predicted from manufactured properties alone.After release, ENMs transform under pH, ionic strength, redox conditions, dissolved organic matter, and surrounding phases.Dissolution, aggregation, sulfidation, corona formation, and mineral interactions alter particle size, surface chemistry, speciation, and bioavailability, changing the magnitude and mechanisms of impact. 1 Consequently, organisms may encounter forms substantially different from the original material.For example, in a pilot wastewater treatment plant, silver nanoparticles (AgNPs) rapidly associated with biosolids, transforming into Ag 2 S. 2 Sulfidation reduced AgNP-mediated inhibition of Escherichia coli in vitro.3 Similarly, Huo et al. showed that AgNPs participate in a dynamic transformation network involving AgNPs, Ag + and secondary Ag 0 nanoparticles.The relative contributions of these species to toxicity changed over time, with Ag + contributing strongly to early effects and particulates increasingly contributing during prolonged exposure.4 A toxicity value for pristine AgNPs may therefore not represent the evolving species generated after release.Copper oxide (CuO) and zinc oxide (ZnO) engineered nanoparticles (ENPs) provide complementary examples.Sulfidation and protein-corona formation altered the composition, morphology, surface chemistry, aggregation, dissolution and toxicity of CuO ENPs, with effects depending on transformation pathway and biological end point.5 In plants, transformed CuO nanoparticles produced different patterns of Cu uptake, translocation, ionomic disruption and stress responses from pristine particles.Similarly, transformation and protein-corona formation altered ZnO morphology, Zn 2+ release, aggregation and toxicity, with transformed particles exhibiting lower toxicity than pristine ENPs.These findings demonstrate that ENM transformations alter toxicity, highlighting the need to identify the resulting forms, their persistence, abundance, and associated risks.Natural organic matter (NOM) can form eco-coronas that alter ENM fate and biological interactions, reducing the aquatic ecotoxicity of metal-based ENMs but increasing the toxicity of nanoscale plastics in gastrointestinal models.ENMs can also carry cocontaminants; TiO 2 ENMs increased heavymetal accumulation in organisms, creating exposure scenarios not captured by assessing pristine substances individually.