Plastiglomerates in the Great Lakes

Great Lake Shoreline and Plastic Confetti. Text: Plastiglomerates in the great lakes

Geology and plastics are two areas of study that wouldn’t often be thought of as interconnected; the former focuses on natural objects, some that are billions of years old while the latter has only really existed for under a century. But increasingly, we can see how human-made, or anthropogenic, materials such as plastics are gradually forming a part of the current rock stratum. In the next age, this plastic deposition will be a distinguishing feature of the future rock record. Perhaps the quintessential method in unravelling geologic history is by analyzing cross-sections of rock to see what secrets are locked into the layers which form over distinct periods of time; millennia from now, geologists will almost certainly find significant plastic deposits embedded in the rock of the Anthropocene – the name often associated with our current geologic age.

Making up almost any human-made object within arm’s reach, plastics – or more specifically plastic pollution – has become an environmental scourge. The effects of the pollution are evident at any scale, from large macroplastics to micro- and even nano-plastics; their widespread accumulation negatively impacts animal life in water bodies and on land. Large and small plastic debris are often inadvertently ingested by wildlife and microplastics can build up in the tissues of affected organisms. Plastic fragments are also a source of chemical exposure as many toxic compounds adhere to the surface of the plastic or leach out during plastic decomposition. Beyond environmental devastation, the chemicals associated with plastics are a major cause of concern to human health; plastic and chemical accumulation in the seafood we consume can have increasing toxic

The costs of plastic pollution on the environment and economy are staggering. In Canada, 10,000 tonnes of plastic end up in the Great Lakes every year and comprehensive estimates of global costs are in the trillions of dollars. Moreover, the problem is pervasive – bodies of water around the world, and the marine life we consume living within them, are becoming increasingly polluted by plastic fragments and associated chemical compounds. Plastic-associated chemicals exist in almost all humans in measurable quantities; notorious compounds, like BPA are known hormone disruptors in humans, with links to issues in fertility and thyroid function.

“With the wholesale introduction of plastics to our waters, riverbeds, and shorelines, plastics and ‘plastiglomerates’ are becoming recognizable features of sediment layers.” - Patricia Corcoran

Patricia Corcoran and her research group in the Department of Earth Sciences at Western University are studying the abundance and distribution of plastic pollution in and around the Great Lakes. Centres of plastic pellet production, are among the sources of widespread release of plastic pollution in the surrounding waters; the pellets they produce are buoyant, meaning that they can easily end up hundreds, or even thousands of kilometers away on shorelines.


Corcoran’s group has found plastic pellets at nearly 70 locations surveyed around all five Great Lakes, with the highest concentration around major production centres near Sarnia. These pellets, which are shipped around the world to be melted and formed into other plastic goods, are only a few millimeters in size, meaning they are easily ingested by birds and fish. Any chemicals coating these pellets become introduced into the food chain, including the fisheries of the Great Lakes watershed.

The Corcoran group’s characterization and long-term monitoring of plastic deposition in the Great Lakes basin are unparalleled and provide significant steps forward in mitigating the effects of plastic pollution.

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Communities all over Canada have iron-bound ties to fishing, whether it be remote northern communities who have long relied on fish for their subsistence or the millions of Canadians who fish recreationally, regardless of the season. Many people are aware of the risks of consuming too much tuna sushi – high levels of mercury accumulate in the tissues of large fish and can have health effects on humans. But in the Canadian context, consumers of freshwater fish from our own lakes sometimes must be cautious of elevated levels of mercury due to the pollutant’s global footprint.