Our beloved Laurentian Great Lakes, which make up roughly one fifth of the world’s fresh surface water and support 1000s of species of wildlife, have become contaminated by our plastic waste. In fact, researchers estimate that roughly 10,000 tonnes of plastics enter the Great Lakes every year, polluting all five of our Great Lakes and their surrounding watersheds. Each year, approximately one million pieces of plastic litter are collected by community scientists as part of the International Coastal Cleanup, which includes the Great Canadian Shoreline Cleanup. And that’s not all (!) – beyond what the eye can see are tiny pieces of plastics called microplastics (<5 mm in size - as large as your pinky nail or as small as the width of a strand of your hair). Microplastics are found in surface water, sediment and in wildlife within and around the Great Lakes, reaching as high as 1.25 million particles/km2 – a concentration on par with what is found in the ocean’s garbage patches – in surface waters. Even our drinking water, despite water treatment, has been shown to contain plastic particles.
Plastic picked up as part of the International Coastal Cleanup for years 2016 – 2018. Figure made by Arielle Earn from U of T Trash Team.
Plastic debris, of all types, shapes and sizes, enter our lakes from various sources (e.g., litter from land, debris from vessels, tire dust in road runoff, pellets from industry, or microfibers from washing our clothing entering via wastewater treatment plants). Understanding these sources is a key part of the solution.
The Great Lakes Plastic Cleanup is capturing and removing plastic litter from our Great Lakes. In addition, we are also capturing data! Our large network of community scientists, spread across the Great Lakes, are measuring how much we collect by mass, and also characterizing the litter by product type (e.g., straw, pre-production pellet, foam take-out container) and material (e.g., plastic, metal, paper). Combined, this data will allow us to understand the effectiveness of our network in removing plastic litter, and allow us to make predictions about the sources of litter entering our waterways. For example, if we find a lot of plastic pellets in the bins, we may link this to plastic industry upstream. If we see many plastic straws and food wrappers, we may attribute the material to the littering of single-use plastic items. This information will inform policy-makers about effective solutions to prevent litter, including both upstream and downstream.
the impacts of plastic
There are many different types of plastic, and plastic litter comes in a variety of shapes and sizes. All this plastic can interact with the environment in different ways and have a range of potential impacts on aquatic ecosystems. While data specific to the Great Lakes is relatively limited, field and laboratory studies suggest that plastic pollution is common in freshwater food webs. These studies point to plastic having potential immediate and long-term environmental impacts.
A recent study found that macroalgae in the Great Lakes contain large quantities of synthetic microfiber pollutants including polyethylene terephthalate (PET) and polyethylene, both entangled and adsorbed into the algae strands. These microfibers could find their way into the food web and affect ecological communities in the lakes. PET has been found to degrade faster than other polymers as it has fewer additives, so there is less opportunity for aquatic organisms to interact with it.
There is evidence of the damage that plastic can do when it does make its way into aquatic food webs. A laboratory study demonstrated the transfer of nano-sized polystyrene in a freshwater food chain, including algae, water fleas, and two levels of fish. Potential impacts on freshwater fish included damage to liver tissue, altered metabolism, disturbance to embryos, and changes in locomotive activity. Polystyrene has been shown to adsorb other contaminants, such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), which can be passed on to other organisms through ingestion.
Polyethylene and polypropylene plastic has been found in the gastrointestinal tract of double-crested cormorant chicks in the Great Lakes, with studies suggesting that this may be due to parent cormorants consuming prey (like fish) which have themselves consumed plastic before being captured, and then feeding this prey to their chicks. Another study supports this, having found microplastics, including fibres, in the digestive tracts of fish in three major tributaries of Lake Michigan.
Fish larvae and invertebrates are also at risk: in laboratory studies, chronic exposure to polyethylene particles and polypropylene microfibers was found to significantly decrease freshwater amphipod growth and reproduction, and exposure to polyvinyl chloride (PVC) significantly inhibited weight gain and growth of common carp larvae. In the Grand River watershed, which flows into Lake Erie, freshwater mussels were found to be ingesting microplastic fragments, including those made of polypropylene.
A double-crested cormorant in Oakville, Ontario swallowing a fish still attached to a fisherman's line.
© Gavin Edmondstone on Flickr