The fate and transport of microplastics in aquatic ecosystems: Synthesis and directions for future research

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About the project

Plastics are durable, lightweight and cheap to manufacture, making them suitable candidates for use in a wide spectrum of products. Despite their benefits, challenges related to the end-of-life of these materials remain to be addressed. It is estimated that 4.8 to 12.7 million tonnes of plastic waste entered the ocean in 2010. In the past decade, plastic particles sized smaller than 5 millimetres, known as microplastics, have emerged as a hazardous pollutant due to their impact on aquatic animals and human health. Plastics are considered relatively recalcitrant in aquatic systems as their decomposition and degradation can take up to several centuries, if not millennia.

Microplastics are spread and found globally, even in the deepest sea sediments and remote arctic areas. The distribution of microplastics in such environments is closely associated with hydrodynamic conditions. Some of the physical processes responsible for the mobilization of nutrients, oxygen and sediments, which are vital to aquatic ecosystems, are also capable of transporting microplastics. Hydrodynamic processes play significant roles in the dispersal and deposition of aquatic microplastics. However, our knowledge of the geographical and temporal distribution of microplastics and their accumulation is limited. Our objectives are to identify (i) microplastic characteristics and (ii) hydrodynamic parameters that shape the distribution of microplastics in aquatic environments.

Key findings

Following an extensive review and analysis of peer-reviewed scholarly literature, our key findings are:

• Microplastics found in marine and freshwater environments have diverse characteristics. These characteristics are influenced by plastic properties (e.g., density, rigidness) and the deterioration of plastic in the environment. They are found in various shapes, ranging from microbeads and pellets, which are virgin primary microplastics manufactured in micro size, to fragments, sheets and films, which are by-products of larger plastic created during weathering and fragmentation processes. 
• These characteristics are unique to microplastics and different from those of other contaminants or sediments. Therefore, physical and numerical modelling of the spread and dispersal of microplastic pollution has to account for such characteristics. 
• Plastics have a wide range of density. Some are positively buoyant and in a static fluid float; others are negatively buoyant and sink. Accumulation of floating plastic debris in the subtropical gyres has drawn attention over the last decade. However, while positively buoyant plastics account for a large portion of plastic production, floating microplastics found on the surface account for a small portion of the total aquatic plastic budget. Numerous peer-review articles have reported high quantities of buoyant microplastics in the sediment and water column. This highlights that the distribution of microplastic particles is governed by features beyond their density. 
• Microplastics' dispersal is controlled by hydrodynamic processes, such as sinking, windage, in-depth and surface currents, and gravity currents. Several studies have attributed the presence of these contaminants in remote areas to the global ocean's recirculation patterns created due to salinity and temperature variations of seawater across the world. Due to their size, microplastics can be easily transported in-depth and long-distance, making them prevalent in all corners of both freshwater and marine systems.

Policy implications

• Reduction in overseas transport and production: The majority of plastic input and waste mismanagement originates from Asia. Therefore, putting in place regulations and legislation to control and limit the use and demand for overseas products will greatly impact Canadians' plastic footprint.
• Development of microplastics-related water quality monitoring programs: Canada has an abundance of rich freshwater ecosystems, unique in the world, with a diverse array of plants and animals. They provide Canadians with drinking water, food supplies, tourism and recreational opportunities. Despite widespread monitoring and water quality surveillance in Canada, in some areas—for example, the Great Lakes—surveillance for microplastics is not included in such programs. The design, development and implementation of surveillance programs help identify the hot spots and accumulation of these emerging contaminants in freshwater across Canada.
• Support of interdisciplinary research: Microplastics research is often complex, especially in areas regarding their emission, long-term presence and transport, toxicology, and risk assessment and mitigation. In recent years, the Canadian government has supported research on plastic pollution. Continued immediate support of interdisciplinary co-operation is necessary to tackle complex issues around microplastics pollution.

Further information

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Contact the researchers

Shooka Karimpour, Assistant Professor, Lassonde School of Engineering, Civil Engineering; Shooka.karimpour@lassonde.yorku.ca

Satinder K. Brar, Professor and Love Chair in Environmental Engineering, Lassonde School of Engineering, Civil Engineering; Satinder.Brar@lassonde.yorku.ca