Some use is being made of nanoparticles to remediate polluted groundwater. However the incomplete science base underpinning such deployments is resulting in both inefficient remediation and in hindering the deployment of new nanoparticles with low potential environmental hazard. This session will bring together geoscientists working on various aspects of understanding the fate, transport, toxicity and efficacy of nanoparticles to provide a step change in remediation of recalcitrant contaminants.