Tons of plastic waste enters the Great Lakes every year. So where does it end up?

The Chicago shore of Lake Michigan. Image: J. Crocker/Wikimedia Commons.

Awareness is rising worldwide about the scourge of ocean plastic pollution, from Earth Day 2018 events to the cover of National Geographic magazine. But few people realise that similar concentrations of plastic pollution are accumulating in lakes and rivers. One recent study found microplastic particles – fragments measuring less then five millimeters – in globally sourced tap water and beer brewed with water from the Great Lakes.

According to recent estimates, over 8m tons of plastic enter the oceans every year. Using that study’s calculations of how much plastic pollution per person enters the water in coastal regions, one of us (Matthew Hoffman) has estimated that around 10,000 tons of plastic enter the Great Lakes annually. Now we are analysing where it accumulates and how it may affect aquatic life.

No garbage patches, but lots of scrap on beaches

Plastic enters the Great Lakes in many ways. People on the shore and on boats throw litter in the water. Microplastic pollution also comes from wastewater treatment plants, stormwater and agricultural runoff. Some plastic fibres become airborne – possibly from clothing or building materials weathering outdoors – and are probably deposited into the lakes directly from the air.

Sampling natural water bodies for plastic particles is time-consuming and can be done on only a small fraction of any given river or lake. To augment actual sampling, researchers can use computational models to map how plastic pollution will move once it enters the water. In the ocean, these models show how plastic accumulates in particular locations around the globe, including the Arctic.

When plastic pollution was initially found in the Great Lakes, many observers feared that it could accumulate in large floating garbage patches, like those created by ocean currents. However, when we used our computational models to predict how plastic pollution would move around in the surface waters of Lake Erie, we found that temporary accumulation regions formed but did not persist as they do in the ocean. In Lake Erie and the other Great Lakes, strong winds break up the accumulation regions.

Three-dimensional transport simulations of particle movement in Lake Erie, based on water current models developed by the National Oceanic & Atmospheric Administration.

Subsequent simulations have also found no evidence for a Great Lakes garbage patch. Initially this seems like good news. But we know that a lot of plastic is entering the lakes. If it is not accumulating at their centers, where is it?

Using our models, we created maps that predict the average surface distribution of Great Lakes plastic pollution. They show that most of it ends up closer to shore. This helps to explain why so much plastic is found on Great Lakes beaches: in 2017 alone, volunteers with the Alliance for the Great Lakes collected more than 16 tons of plastic at beach cleanups. If more plastic is ending up near shore, where more wildlife is located and where we obtain our drinking water, is that really a better outcome than a garbage patch?

Average density of simulated particles in the Great Lakes from 2009-14. Notice that there are no patches in the middle of the Lakes, but more of the particles are concentrated near the shores. Image: Matthew Hoffman/creative commons.

Searching for missing plastic

We estimate that over four tons of microplastic are floating in Lake Erie. This figure is only a small fraction of the approximately 2,500 tons of plastic that we estimate enter the Lake each year. Similarly, researchers have found that their estimates of how much plastic is floating at the ocean’s surface account for only around 1 per cent of estimated input. Plastic pollution has adverse effects on many organisms, and to predict which ecosystems and organisms are most affected, it is essential to understand where it is going.

We have begun using more advanced computer models to map the three-dimensional distribution of plastic pollution in the Great Lakes. Assuming that plastic simply moves with currents, we see that a large proportion of it is predicted to sink to lake bottoms. Mapping plastic pollution this way begins to shed light on exposure risks for different species, based on where in the lake they live.

According to our 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.

Three-dimensional transport simulation in Lake Erie. Particle color represents depth below the water surface: the bluer the particle, the deeper it is.

In a real lake, plastic does not just move with the current. It also can float or sink, based on its size and density. As a particle floats and is “weathered” by sun and waves, breaks into smaller particles, and becomes colonised by bacteria and other microorganisms, its ability to sink will change.

Better understanding of the processes that affect plastic transport will enable us to generate more accurate models of how it moves through the water. In addition, we know little so far about how plastic is removed from the water as it lands on the bottom or the beach, or is ingested by organisms.

Prediction informs prevention

Developing a complete picture of how plastic pollution travels through waterways, and which habitats are most at risk, is crucial for conceiving and testing possible solutions. If we can accurately track different types of plastic pollution after they enter the water, we can focus on the types that end up in sensitive habitats and predict their ultimate fate. The Conversation

Of course, preventing plastic from entering our waterways in the first place is the best way to eliminate the problem. But by determining which plastics are more toxic and also more likely to come into contact with sensitive organisms, or end up in our water supply, we can target the “worst of the worst”.

With this information, government agencies and conservation groups can develop specific community education programmes, target cleanup efforts and work with industries to develop alternatives to products that contain these materials.

Matthew J. Hoffman, Associate Professor of Mathematical Sciences, Rochester Institute of Technology and Christy Tyler, Associate Professor of Environmental Science, Rochester Institute of Technology.

This article was originally published on The Conversation. Read the original article.


What’s killing northerners?

The Angel of the North. Image: Getty.

There is a stark disparity in wealth and health between people in the north and south of England, commonly referred to as England’s “north-south divide”. The causes of this inequality are complex; it’s influenced by the environment, jobs, migration and lifestyle factors – as well as the long-term political power imbalances, which have concentrated resources and investment in the south, especially in and around London.

Life expectancy is also lower in the north, mainly because the region is more deprived. But new analysis of national mortality data highlights a shockingly large mortality gap between young adults, aged 25 to 44, living in the north and south of England. This gap first emerged in the late 1990s, and seems to have been growing ever since.

In 1995, there were 2% more deaths among northerners aged 25 to 34 than southerners (in other words, 2% “excess mortality”). But by 2015, northerners in this age group were 29% more likely to die than their southern counterparts. Likewise, in the 35 to 44 age group, there was 3% difference in mortality between northerners and southerners in 1995. But by 2015, there were 49% more deaths among northerners than southerners in this age group.

Excess mortality in the north compared with south of England by age groups, from 1965 to 2015. Follow the lines to see that people born around 1980 are the ones most affected around 2015.

While mortality increased among northerners aged 25 to 34, and plateaued among 35 to 44-year-olds, southern mortality mainly declined across both age groups. Overall, between 2014 and 2016, northerners aged 25 to 44 were 41% more likely to die than southerners in the same age group. In real terms, this means that between 2014 and 2016, 1,881 more women and 3,530 more men aged between 25 and 44 years died in the north, than in the south.

What’s killing northerners?

To understand what’s driving this mortality gap among young adults, our team of researchers looked at the causes of death from 2014 to 2016, and sorted them into eight groups: accidents, alcohol related, cardiovascular related (heart conditions, diabetes, obesity and so on), suicide, drug related, breast cancer, other cancers and other causes.

Controlling for the age and sex of the population in the north and the south, we found that it was mostly the deaths of northern men contributing to the difference in mortality – and these deaths were caused mainly by cardiovascular conditions, alcohol and drug misuse. Accidents (for men) and cancer (for women) also played important roles.

From 2014 to 2016, northerners were 47% more likely to die for cardiovascular reasons, 109% for alcohol misuse and 60% for drug misuse, across both men and women aged 25 to 44 years old. Although the national rate of death from cardiovascular reasons has dropped since 1981, the longstanding gap between north and south remains.

Death and deprivation

The gap in life expectancy between north and south is usually put down to socioeconomic deprivation. We considered further data for 2016, to find out if this held true for deaths among young people. We found that, while two thirds of the gap were explained by the fact that people lived in deprived areas, the remaining one third could be caused by some unmeasured form of deprivation, or by differences in culture, infrastructure, migration or extreme weather.

Mortality for people aged 25 to 44 years in 2016, at small area geographical level for the whole of England.

Northern men faced a higher risk of dying young than northern women – partly because overall mortality rates are higher for men than for women, pretty much at every age, but also because men tend to be more susceptible to socioeconomic pressures. Although anachronistic, the expectation to have a job and be able to sustain a family weighs more on men. Accidents, alcohol misuse, drug misuse and suicide are all strongly associated with low socioeconomic status.

Suicide risk is twice as high among the most deprived men, compared to the most affluent. Suicide risk has also been associated with unemployment, and substantial increases in suicide have been observed during periods of recession – especially among men. Further evidence tells us that unskilled men between ages 25 and 39 are between ten and 20 times more likely to die from alcohol-related causes, compared to professionals.

Alcohol underpins the steep increase in liver cirrhosis deaths in Britain from the 1990s – which is when the north-south divide in mortality between people aged 25 to 44 also started to emerge. Previous research has shown that men in this age group, who live in the most deprived areas, are five times more likely to die from alcohol-related diseases than those in the most affluent areas. For women in deprived areas, the risk is four times greater.

It’s also widely known that mortality rates for cancer are higher in more deprived areas, and people have worse survival rates in places where smoking and alcohol abuse is more prevalent. Heroin and crack cocaine addiction and deaths from drug overdoses are also strongly associated with deprivation.

The greater number of deaths from accidents in the north should be considered in the context of transport infrastructure investment, which is heavily skewed towards the south – especially London, which enjoys the lowest mortality in the country. What’s more, if reliable and affordable public transport is not available, people will drive more and expose themselves to higher risk of an accident.

Deaths for young adults in the north of England have been increasing compared to those in the south since the late 1990s, creating new health divides between England’s regions. It seems that persistent social, economic and health inequalities are responsible for a growing trend of psychological distress, despair and risk taking among young northerners. Without major changes, the extreme concentration of power, wealth and opportunity in the south will continue to damage people’s health, and worsen the north-south divide.

The Conversation

Evangelos Kontopantelis, Professor in Data Science and Health Services Research, University of Manchester

This article is republished from The Conversation under a Creative Commons license. Read the original article.