Trends, risks and opportunities in environmental nanotechnology

Engineered nanomaterials (ENMs), intentionally synthesized materials with sizes less than 100 nm in at least one dimension, have numerous potential environmental applications, such as pollution remediation and water treatment. However, concerns regarding their potential health and environmental impacts have been raised. In this Review, we assess the opportunities of ENMs in environmental applications versus their potential public and environmental health risks, focusing on water treatment and reuse, and identify strategies for their responsible use. Life-cycle analyses indicate that the highest potential environmental and health impacts of ENMs used in commercial products are associated with production rather than incidental release during use. Typically, the detected or predicted ENM concentrations are 1 to 4 orders of magnitude lower than their respective predicted no-effect concentrations. In addition, ENMs often undergo passivating transformations, such as agglomeration and oxidation, reducing risks after release. Therefore, the environmental and health risks of ENMs are relatively low. However, some point sources under extreme scenarios, such as sewage effluent, can potentially increase localized risks. Adopting green chemistry and immobilization strategies can further limit the release of ENMs, minimizing their potential discharge into the environment. Such strategies to reduce toxicity and exposure enable sustainable application of ENMs, such that the environmental benefits could outweigh the risks if managed properly.