Understanding the Source, Behaviour, and Fate of Nanoplastics in Aquatic Environments

It is well-established that the presence of plastics in the aquatic environment is near ubiquitous, and it has been proposed that larger plastics entering the environment may break down into micro- and nano-scale plastic particles. It has equally become apparent that there is an increasingly large quantity of plastic nanoparticles entering the hydrosphere; this is a particularly concerning suggestion, as there is emerging evidence that nanoplastics may have the potential to traverse the blood-brain barrier and enter the vital organs. Despite the attention that this topic has garnered over recent decades, there remains a significant lacuna in our understanding of the behaviour of these materials in the aquatic environment. This includes the processes they undergo and, most notably, their ultimate fate and impacts upon the health of the environment. There is, additionally, much disagreement in the literature as to the very categorization of nanoplastics. In this contribution, we endeavour to compile what is known to date on the fate and behaviour of nanoplastics in the hydrosphere. We touch upon a number of emerging trends, such as the potential trophic transfer of these contaminants and the mechanisms by which they may enter the food chain. We examine the potential impacts of organic matter on the toxicity of nanoplastics, as well as the possibility that nanoplastics may act as vectors for pathogens and other contaminants in the environment. Finally, we offer a number of recommendations for the direction of future study in this area. We identify the underappreciated risk posed by plastic additives and complexation mechanisms and propose a realignment of priorities towards understanding mechanisms and nano-specific processes, rather than standard toxicological approaches.