Analytical approaches to support current understanding of exposure, uptake and distributions of engineered nanoparticles by aquatic and terrestrial organisms

Initiatives to support the sustainable development of the nanotechnology sector have led to rapid growth in research on the environmental fate, hazards and risk of engineered nanoparticles (ENP). As the field has matured over the last 10 years, a detailed picture of the best methods to track potential forms of exposure, their uptake routes and best methods to identify and track internal fate and distributions following assimilation into organisms has begun to emerge. Here we summarise the current state of the field, focussing particularly on metal and metal oxide ENPs. Studies to date have shown that ENPs undergo a range of physical and chemical transformations in the environment to the extent that exposures to pristine well dispersed materials will occur only rarely in nature. Methods to track assimilation and internal distributions must, therefore, be capable of detecting these modified forms. The uptake mechanisms involved in ENP assimilation may include a range of trans-cellular trafficking and distribution pathways, which can be followed by passage to intracellular compartments. To trace toxicokinetics and distributions, analytical and imaging approaches are available to determine rates, states and forms. When used hierarchically, these tools can map ENP distributions to specific target organs, cell types and organelles, such as endosomes, caveolae and lysosomes and assess speciation states. The first decade of ENP ecotoxicology research, thus, points to an emerging paradigm where exposure is to transformed materials transported into tissues and cells via passive and active pathways within which they can be assimilated and therein identified using a tiered analytical and imaging approach.