Plastic Waste

On March 10 this year the Province of Ontario announced that it was considering a ban on plastic waste as part of a broader strategy to send less waste to landfill sites. Almost one tonne of waste per person is generated annually in Ontario and only 30 per cent is diverted from landfills by composting and recycling. According to the government this rate of diversion has not changed over the last thirty years. The Environment Minister Rod Phillips has said, “Plastics is a priority from our government’s point of view, particularly as we talk about plastics in our waterways.” The government estimates that almost 10,000 tonnes of plastic debris enter the Great Lakes each year.

In a February 2017 report by the International Joint Commission (IJC), the Canada/USA body that manages the lakes, studies have documented the occurrence of plastic debris, including plastic bags, bottles, boxes, fibres, micro-beads, and cigarette butts, in marine and fresh waters including the Great Lakes. Larger plastic debris degrades into smaller micro-plastics, and it is these smaller particles that are of particular concern. Micro-plastics generally refer to particles 5 mm or less in size and include; micro-beads from personal care products; fibres from synthetic clothing; pre-production pellets and powders; as well as degraded pieces from larger plastic products. Little is known about the fate of these smaller plastic particles and the IJC is concerned about their potential impacts on environmental and human health.

Plastic enters the Great Lakes in many ways. Most egregiously, people on the shore and on boats throw litter in the water but micro-plastic pollution also comes from wastewater treatment plants, storm water and agricultural runoff. Some plastic fibres become airborne, possibly from clothing or building materials weathering outdoors and these are probably deposited into the lakes directly from the air.

The IJC made 10 recommendations, one of which was to develop a model to determine the sources and fate of micro-plastics. In their Aug 20 2018 issue, The Conversation, an independent, not-for-profit media outlet, reported on the work of two scientists, from the Rochester Institute of Technology, Matthew J. Hoffman and Christy Tyler, who have developed a computer model to track the movement of micro-plastics in the lakes.

They found that, while plastics often accumulate in large floating garbage patches in the oceans, in the Great Lakes there may be temporary accumulation patches but they do not persist as they do in the ocean. In Lake Erie and the other Great Lakes, strong winds break up the accumulated patches and there was no evidence for a Great Lakes garbage patch. This appears to be good news except that we know that a lot of plastic is entering the lakes so if it is not accumulating in large patches, where is it?

Hoffman and Tyler’s computer model shows that most of it ends up closer to shore (see map below.) This helps to explain why so much plastic is found on Great Lakes beaches. In 2017 alone, one group of volunteers collected more than 16 tons of plastic at beach cleanups. Thus, the plastic is ending up near shore, where more wildlife is located and where we obtain our drinking water.

Average density of simulated particles in the Great Lakes from 2009-2014. Notice that there are no patches in the middle of the Lakes, but more of the particles are concentrated near the shores. Credit: Matthew HoffmanCC BY-NC-ND

The scientists estimate that over four tons of micro-plastic are floating in Lake Erie. This figure is only a small fraction of the approximately 2,500 tons of plastic that they estimate enters the Lake each year. According to their initial simulations, much of the plastic is expected to sink. This prediction is supported by sediment samples collected from the bottom of the Great Lakes, which can contain high concentrations of plastic. You can see the computer simulation of the dispersal of micro-plastics in Lake Erie here.

Another IJC recommendation was to assess the potential ecological and human health impacts of micro-plastics in the Great Lakes. One such recent study – available here.

The researchers found micro-plastic particles – fragments measuring less then five millimetres – in tap water and beer brewed with water from the Great Lakes. Since many studies indicate risks to human health when plastic particles such as synthetic polymers are ingested, clearly more needs to be known about the presence and abundance of micro-plastic particles in human foods and beverages. The PLOS study investigated the presence of micro-plastic particles in 159 samples of globally sourced tap water, 12 brands of Great Lakes beer, and 12 brands of commercial sea salt. Of the tap water samples analyzed, 81% were found to contain micro-plastic particles. The majority of these particles were fibres (98.3%) between 0.1–5 mm in length and there was an average of 5.45 particles per litre. Plastic debris was also found in each brand of beer and salt. Of the extracted particles, over 99% were fibres. The average number of particles found in beer was 4.05 particles per litre and the average number of particles found in each brand of salt was 212 particles per kg. Based on consumer guidelines, the study indicated that the average person ingests over 5,800 particles of synthetic debris from these three sources annually, with the largest contribution coming from tap water (88%).

The IJC also recognized that it is vital to change peoples’ behaviour and the only way to do that is through education. They recommended that Canada and the USA increase their funding of education programs, particularly for grades K to 12.

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