Mapping the dawn of nanoecotoxicological research

Some researchers consider nanotechnology the next industrial revolution, and consumer products and a variety of industries increasingly use synthetic nanoparticles. In this Account, we review the initial accomplishments of nanoecotoxicology, a discipline that is just a decade old. This new subdiscipline of ecotoxicology faces two important and challenging problems: the analysis of the safety of nanotechnologies in the natural environment and the promotion of sustainable development while mitigating the potential pitfalls of innovative nanotechnologies. In this Account, we provide a snapshot of the publicly available scientific information regarding the ecotoxicity of engineered nanoparticles. We pay special attention to information relevant to aquatic freshwater species commonly used for risk assessment and regulation. Just as the development of ecotoxicology has lagged behind that of toxicology, nanoecotoxicological research has developed much more slowly than nanotoxicology. Although the first nanotoxicolology papers were published in 1990s, the first nanoecotoxicology papers came out in 2006. A meta-analysis of scientific publications covering different environmental impacts of nanomaterials showed that the importance of research into the environmental impact of nanotechnology has gradually increased since 2005. Now the most frequently cited papers in the environmental disciplines are often those that focus on synthetic nanoparticles. The first nanoecotoxicology studies focused on adverse effects of nanoparticles on fish, algae and daphnids, which are ecotoxicological model organisms for classification and labeling of chemicals (these model organisms are also used in the EU chemical safety policy adopted in 2007: Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH)). Based on our experience, we propose a multitrophic battery of nanoecotoxicological testing that includes particle-feeding and a priori particle-"proof" prokaryotic and eukaryotic organisms at different food-chain levels. Using this battery of selected test organisms, we demonstrated that TiO₂ nanoparticles were toxic to algae and that ZnO and CuO nanoparticles were toxic to several aquatic invertebrate test species. Thus, one single biotest cannot predict the ecotoxicological effects of chemicals/nanoparticles, and researchers should use several tests instead. Moreover, produced nanoparticles usually vary in features such as size, shape, and coating; therefore, a single nanoparticle species may actually include many entities with different physicochemical properties. An ecotoxicity analysis of all these variants would require a huge number of laboratory tests. To address these issues, high throughput bioassays and computational (QSAR) models that serve as powerful alternatives to conventional (eco)toxicity testing must be implemented to handle both the diversity of nanomaterials and the complexity of ecosystems.