How Much is Too Much?

When it comes to plastic pollution, are we crossing thresholds for risk?

I began researching plastic pollution in 2008 in graduate school. My interest in the subject was piqued while studying abroad in Australia in 2006. There, we traveled to North Stradbroke Island to visit a research station run by the University of Queensland. While walking on a beach, I noticed a lot of marine debris. I wondered, where could all this be from? Inside the research station’s rehabilitation centre, I saw sea turtles who had ingested plastic and were on site to excrete and regurgitate as much plastic as possible before they could be returned home to the ocean. I have always been interested in the environment, our oceans, and pollution, but it was thanks to this visit, and my professors in Australia, that I discovered my career.

I chose to become a scientist to help increase our understanding of plastic pollution and help facilitate informed change. Back then, we knew much less than we know today. We knew for decades that large pieces of plastic pollution, macroplastics, were harming marine mammals, seabirds and sea turtles through entanglement and ingestion. The compelling images of these animals suffering from plastic pollution initiated cleanup programs all over the world, including the International Coastal Cleanup in 1986 by Ocean Conservancy  (then called the Delta Organization). We also knew that small pieces of plastic pollution, now referred to as microplastics, were contaminating remote parts of the oceans and coastlines. But, we did not know how plastic pollution was interacting with all wildlife, and what amount could harm wildlife populations, communities, and ecosystems –i.e., how much is too much?

How much plastic is too much?

Now, you might find yourself thinking – isn’t any plastic waste in our oceans too much? Plastic pollution is an eyesore, it is killing wildlife, and it simply should not be there. This is all true. However, it is a monumental task to keep ALL plastic out of the ocean, especially with the multitude of sources. For example, plastic nets, buoys and ropes are accidentally lost from fishing vessels or aquaculture farms. Single-use plastic bags, bottles, and straws leak from overflowing garbage bins or those without lids, and are then carried by wind to bodies of water. Large durable plastics, including furniture and refrigerators and cars, enter the oceans as a consequence of natural disasters – e.g., tsunamis and mudslides. Microplastics are especially sneaky, leaking from land as tire dust crumbling off our tires when we drive, paint flecks wearing from buildings and roads, and microfibers shedding from our clothing while wearing and washing them.

In theory, all sources and pathways of plastics to the environment are preventable, but to make a serious dent toward reducing plastic pollution we need policy. In the eyes of policymakers, knowing how much plastic pollution is too much is essential to make change. This means we must predict risk thresholds, or in other words, estimate what level of plastic pollution has the potential to cause significant harm to wildlife. In response to this need, scientists have begun building risk assessment frameworks for all sizes of plastic pollution.

There is too much plastic pollution in our oceans and lakes

We have learned that in some parts of our oceans and freshwater systems (i.e., lakes and rivers), the amount of plastic pollution we currently observe is above levels that can cause harm to animals. These locations tend to be where plastic pollution is abundant, and therefore animals have a greater likelihood of encountering it.

In a recent groundbreaking study led by Dr. Erin Murphy at Ocean Conservancy, we predicted risk thresholds for macroplastics. We synthesized data from >10,000 observations of seabirds, sea turtles, and marine mammals that had washed up on beaches. For each of these animals, there was data on the amount of plastic they ingested and their cause of death. In total, 35% of the seabirds, 47% of the sea turtles, and 12% of the marine mammals had plastic in their digestive tracts. Of the animals that ingested plastic, roughly 3% of the seabirds, 8% of the turtles and 5% of the marine mammals died because of the plastic they ate. From this data, we estimated that if a seabird eats 23 pieces of plastic pollution (equivalent to a volume of plastic just under three sugar cubes) they are 90% likely to die. For turtles this number is 405 pieces (or just over two baseballs by volume), and for marine mammals it is 29 pieces (or the volume of a soccer ball). Why the difference? Well, each group of taxa varies in body size and tends to eat plastic pollution of different sizes due to the variability in the size of their mouth. For example, sea turtles (generally smaller than marine mammals) tend to eat plastic the size of a pea and marine mammals tend to eat plastic the size of a tennis ball.

Risk assessment frameworks for microplastics were recently developed by Dr. Albert Koelmans’ research group in the Netherlands. These risk assessment frameworks synthesize data across many laboratory toxicology studies where small algae, invertebrates, and fish are exposed to microplastics at different concentrations. This synthesized data is then used to predict the concentration where negative effects are observed for several species. These frameworks can be used to set thresholds, and can be paired with local management frameworks, as they have in the State of California and here at home in the Laurentian Great Lakes region.

Within the Laurentian Great Lakes, two thresholds for risk were proposed by a Microplastic Work Group I co-chaired within the International Joint Commission (IJC), a bi-national organization that helps manage our shared waters. The risk assessment was paired with the management framework used to assess the state of the Great Lakes under the Great Lakes Water Quality Agreement (GLWQA), and with guidance from a diverse group of expert stakeholders.

Here, each threshold is tied to a condition status ranging from good to poor. When microplastic concentrations exceed threshold 1, that sample suggests fair conditions, and when they exceed threshold 2, the sample suggests poor conditions. The status of the Great Lakes measured through this framework is used to inform the urgency of policies to protect them. We found that several concentrations reported in Lakes Michigan and Ontario exceed thresholds 1 and 2. These findings are not unique, in California concentrations reported in the San Francisco Bay also exceed locally proposed thresholds.

Too much plastic signals it is time to act

Since my time studying abroad in Australia, we have learned a lot about the risks associated with plastic pollution. Today, we understand that the amount of plastic pollution in some locations is alreadytoo much. It is time for policymakers to act.Policies need to prioritize prevention. Prevention includes reducing plastic waste, such as producing less plastic and increasing the circularity (i.e. reusability and recyclability) of what we produce. We also need to prevent the continuous leakage of plastics into our environment through accidental loss (e.g., pellet spills during production and transport, construction foam leaking from build sites, overflowing garbage bins) and the wear and tear of products (e.g., microfibers, tire dust, paint). To increase the success of new policies, we need to increase awareness – increasing waste literacy among members of the public, our governments, industry, and the next generation. Moreover, we need to continue to clean up the legacy plastic pollution currently putting animals at risk. Cleanup removes harmful plastics from our environment and can be used to collect monitoring data to inform local solutions and increase awareness. After all, if you remove just 23 pieces of plastic pollution from your local shoreline, you reduce the risk to a seabird that may choose to eat them.