Review: Do engineered nanoparticles pose a significant threat to the aquatic environment?

Nanotechnology is a rapidly growing industry of global economic importance, exploiting the novel characteristics of materials manufactured at the nanoscale. The properties of engineered nanoparticles (ENPs) that make them useful in a wide range of industrial applications, however, have led to concerns regarding their potential impact on human and environmental health. The aquatic environment is particularly at risk of exposure to ENPs, as it acts as a sink for most environmental contaminants. This paper critically evaluates what is currently known about sources and discharge of ENPs to the aquatic environment and how the physicochemical characteristics of ENPs affect their fate and behaviour and thus availability for uptake into aquatic organisms, and assesses reported toxicological effects. Having reviewed the ecotoxicological information, the conclusion is that whilst there are data indicating some nanoparticles have the potential to induce harm in exposed aquatic organisms, there is insufficient evidence for harm, for known/modelled environmental concentrations for almost all ENPs considered. This conclusion, however, must be balanced by the fact that there are significant gaps in our understanding on the fate and behaviour of ENPs in the aquatic environment. Greater confidence in the assessments on ENP impacts in aquatic systems to enable effective comparisons across studies urgently requires more standardised approaches for ENP hazard identification, and critically, more thorough characterisations on the exposed particles. There is also an urgent need for the advancement of tools and techniques that can accurately quantify and visualise uptake of nanoparticles into biological tissues.