Transport and spatial distribution of microplastics and byproducts, and associated risks to freshwater ecosystems.

Biofouling, the unintentional accumulation of sediments, chemicals, microbes and other organisms on submerged substrates, is exacerbated by the ubiquitous presence of microplastics (MPs) in freshwaters. The transportation of pristine and befouled MPs in water increases contamination and infection risk resulting in unexpected ecological consequences to aquatic and human health. This interdisciplinary project will explore how aquatic microplastics and their byproducts are transported. The relationship of microplastics with farming activity, public sewerage network and wastewater treatment will be examined with specific emphasis on the effectiveness of constructed wetlands and reed beds to treat wastewater and MP. This will be achieved using Dwr Cymru's existing network of online monitors in the Taff/Ely catchments and at a downstream constructed wetland treatment site which routinely measure pH, conductivity, DO, temperature, ammonia, nitrate and phosphate. These datasets will be augmented by spot-MP sampling at the same locations of MPs, metal and pathogen load to examine the dispersion and spread of pollutants and whether existing water monitoring can act as a proxy for other pollutants. In addition, pristine and bioaccumulated MP transport experiments will be conducted in the hydraulics laboratory at Cardiff University.

Microplastics have been found in all riverbed substrates despite these particles having lower densities than water; byproduct attachment on MPs (biofouling) can increase density and this may be a possible reason. The current understanding of the transport and fate of pristine and biofouled microplastics in freshwater systems is lacking. The varying size, density and shape of MPs in the environment impacts their buoyancy, settling velocity, and critical bed shear stress, making it challenging to predict their transport and distribution (Waldschläger and Schuttrumpf, 2019b; Khatmullina and Chubarenko, 2020; Waldschläger et al., 2022). This research will help our understanding of how MPs are transported in turbulent flow (e.g. rivers) as well as low velocity systems (e.g. constructed wetlands) so that we can understand travel time and wastewater treatment capabilities. This will benefit freshwater ecosystem health, human health and help water companies optimise wastewater treatment methods.