The abundance of plastic debris in the environment is an increasing concern since this contamination is ubiquitous and found in habitats as remote as the mid-Atlantic archipelagos and Antarctica. Notably, the prevalence of microplastics (MPs), defined as plastic particles <5 mm, in aquatic systems has captured the attention of the scientific community and general public because of the limited knowledge on the prevalence and potential impact that these pollutants may have on biota and humans.
Depending on their origin, MPs are generally classified as primary or secondary. Primary sources consist of two main groups: beads contained in cleaning and cosmetic products and pellets used in plastic manufacturing. In these, polyethylene, polypropylene, and polystyrene are the most common polymeric constituents. Secondary MPs result from the breakdown of larger macromolecules and this may occur either before release into the environment or afterwards as the by-products of weathering. Within this category, fibres made of polyester, acrylic and polyamide are the most prevalent.
Microplastics impact living communities and also alter the physical/chemical properties of habitats. Ingestion is the most common way by which MPs and organisms interact. In marine environments, MPs have been found to be assimilated by all trophic levels from zooplankton to mammals. Ingested plastics may act as stressors and damage organs. Furthermore, MPs and their breakdown products can move up the food chain with the potential bioaccumulation effect for predators. In addition, because of their hydrophobic nature, MPs can interfere with the dynamic distribution of chemicals in the water bodies.
Despite MPs having not been regularly monitored and the lack of available baseline information, evidence of plastic litter in fresh waters has been found in England (Solent estuary and River Thame); Europe (Garda and Geneva Lakes, Danube, Elbe, Mosel, Necktar and Rhine rivers); and North America (Great Lakes, Los Angeles basin, North Shore Channel Chicago, St. Lawrence River). In most of these locations, the presence of MPs was linked to effluents from wastewater works or discharges from plastic manufacturing factories. These studies also provided valuable insight into primary and secondary MPs in terms of size, polymer composition, transformation/weathering degree and concentration. Nevertheless, comparison and synthesis of the data was difficult because of the lack of consistency across the studies. Principally this is because the analysis of MPs is very inconsistent since researchers follow ad hoc methods rather than validated protocols. Inconsistency is also noticed on the role that potable treatment plants play in MPs management. Contradictory arguments can be found in the literature on the physical prevalence or removal of MPs in wastewater treatment processes. When it comes to drinking water quality and treatment, the lack of data is even more striking with only a few studies having been conducted on bottled water.
At Cranfield Water Science Institute, we are conducting research to provide insight into the occurrence, fate and transport of MPs in water bodies used for human consumption. Our project reviews the different analytical methods applied for the characterisation of MPs in the aquatic environment as well as the current knowledge on the exposure routes of MPs to humans. We are also carrying out experiments to clarify the removal profile of MPs during water treatment. Based on the experimental results and the literature findings, a monitoring plan will be proposed in order to learn about the presence and removal of MPs in final waters and across full scale water treatment systems.
