Abstract
Due to their high surface reactivity engineered nanomaterials (ENMs) can interact with other anthropogenic contaminants, potentially influencing their environmental distribution, bioavailability and toxicity. Suggested mechanisms behind those altered toxic effects include changes of contaminant bioavailability caused by contaminant adsorption to ENMs, or an altered toxicity due to interactive toxic effects of mixture exposures. Here we want to summarise results from a range of experiments investigating the effects of several ENM-contaminant mixtures: carbon nanotubes (CNTs)-phenanthrene; titanium nanoparticles (TiO2NP)-benzo(a)pyrene; silver nanoparticles (AgNP)-water soluble faction of crude oil (WSF); and AgNP-17?-ethinylestradiol. Studies included different aquatic organisms, reaching from the unicellular freshwater algae Pseudokirchneriella subkapitata to the marine flatfish Scophthalmus maximus. The ENMs were characterised and their behaviour in the tested environmental matrices was determined. ENM-contaminant interactions, their uptake in organisms and effects on contaminant bioavailability were investigated. To determine potential changes in toxic effects, suitable endpoints or biomarkers were analysed for each test species. All tested nanomaterials were found to be taken up or to be associated to organisms' surfaces; however interaction between ENM and contaminants and effects on bioavailability and toxicity varied. Adsorption of hydrophobic PAHs was observed to CNT and TiO2NP. Undergoing aggregation, both CNTs and TiO2NPs reduced dissolved PAH concentrations. However, both dissolved and ENM-associated appeared to remain bioavailable to varying extends. Similarly, both, single and mixture exposures of AgNP and the WSF of North Sea crude oil, caused activation of oxidative stress related biomarkers in calanoid copepods. The presence of AgNP did not significantly change 17?-ethynylestradiol bioavailability to juvenile turbot. Impacts on steroid hormone concentrations in mixed exposures followed 17?-ethynylestradiol single contaminant effects, however, impacts on some hormones were slightly increased in mixed exposures. ENM-contaminant mixture effects do not follow a general mechanism. Their interaction and mixture toxicity depends on multiple factors, including ENM material and contaminant properties. Further research is needed in order to provide sound data for ENM environmental risk assessment, which needs to include risks from ENM-contaminant mixtures.