Environmental assessment of solid sorbents towards 'Safe by Design'

Owing to their specific material properties, solid sorbents engineered at the nano-scale have been subject to increasing attention. Whilst bulk materials exhibiting nano-scale structures are less likely to find their way into the environment, nano-sized particulate materials (NMs) are known to be released at different stages of their life cycle (e.g. production, application and waste processing). Many NMs elicit negative impacts on a range of freshwater, marine and soil organisms. However, understanding NM environmental fate and behaviour is necessary to assess the potential for exposure and risk. A simple strategy for the assessment of NM fate and behaviour in freshwater environments, and how this can be used for selecting relevant species for further toxicity (hazard) evaluation towards risk assessment, is presented. Ten carbon nanotubes (CNTs) and 3 TiO₂ NMs representing candidate solid nano-sorbent materials for potential application in CO₂ capture technology were selected. Studies have been conducted to investigate how physicochemical properties influence NM dispersability (concentration) and dispersion stability in aqueous media relevant to freshwater environments. A standard method for the dispersion of NMs in aquatic media has been developed to permit reproducible and comparable conditions for different test materials. A basic strategy for using such environmental data in a 'Safe by Design' approach to material development and selection will also be outlined.