Plastic pollution in our oceans: what we know, what we don’t and what we can do
This post is by Erik van Sebille, lecturer in oceanography and climate change at Imperial College London’s Grantham Institute, Alyssa Gilbert, head of policy and translation at the Grantham Institute and Dustin Benton, head of energy and resources at Green Alliance.
Plastic is a great material. It’s lightweight, durable, cheap, and over the past 50 years it has become embedded in every part of modern life. Unfortunately, it’s now embedding itself in the earth’s largest ecosystem, the ocean. The visibility of plastic pollution has put it onto the agenda of campaigners, scientists and policy makers alike. But, unlike climate change, air pollution or deforestation, we don’t yet have a grasp of many of the basic questions about marine plastic pollution.
What we know
We do know, at least roughly, the total amount of plastic going into the ocean: a recent inventory estimated that around ten million tonnes of plastic entered the ocean in 2010 alone. We think that the vast majority of the plastic comes from land based sources.
We know that plastics fragment and can absorb ecotoxins. We know that plastics are commonly found in filter feeders, like mussels; have been found in fish and marine mammals, including in the stomachs of bluefin tuna in the Mediterranean; and that more than 90 per cent of seabirds have swallowed plastics.
We know that plastics spread far and wide. For example, ocean current modelling shows that most of the plastic from the UK that stays afloat ends up in the Arctic, taking between two and five years to get there. Observations from the Arctic confirm that plastics are pervasive even in this remote and heretofore pristine environment.
Finally, we know that cleaning the ocean up is going to be very difficult, and that, if we decide to skim off the plastic floating on the surface, the best place to do it is near coastlines.
What we don’t know
Perhaps the biggest mystery about marine plastic pollution is where it’s all hiding. While ten million tonnes is estimated to get into the sea per year, just 100,000 tonnes can be found bobbing around on the surface. This means that more than 99 per cent of the plastic is missing.
We think a lot of it sinks to the ocean floor, with unknown ecological consequences; quite a lot of it washes up on beaches; and a fair amount ends up being consumed by marine life. The problem is we don’t even have ballpark figures of how much plastic is in these places.
We also don’t know the full ecological impacts of plastic yet. While we find many marine animals with plastic in their gut, it is unclear whether that plastic harms them. Only very recently have two studies on oysters and small fish found that the concentrations of plastics they are experiencing in some areas may be seriously harmful to them.
We have a few estimates of the costs associated with marine plastics pollution, but the data are fragmentary and highly location specific: for example, it’s estimated that the costs of plastic pollution to affected Scottish fisheries are already equal to around five per cent of their annual turnover. Similarly, the cost of litter clean up to UK local authorities rose by 37 per cent between 2004 and 2014. But we have no idea of the total cost, just a suspicion that it’s very high indeed.
What we should do
With so many unknowns, the temptation is to wait and gather more data. After all, plastics are a complex problem: they come from a huge range of sources and perform widely different functions. But we know enough about the damage done by oceanic plastic pollution to act now. With the European Commission set to consult on its plastics strategy in the autumn, here are some easy wins they should include.
First, we can ban products that are almost certain to become pollution. Take microbeads in cosmetics. It’s hard to imagine a product that’s better designed to enter the marine foodchain: microbeads are tiny, used for seconds, intentionally washed down drains and efficiently deposited into coastal waters. Products like cigarette filters and polystyrene packaging could be subject to similar restrictions (highly biodegradable alternatives for both exist).
Second, we can support redesign. Cotton buds that use plastic sticks can use paper instead; plastic bottles can include a tether to prevent their caps from becoming litter; even genuinely biodegradable plastics might have a role in on-the-go food packaging (though we should be wary of accidentally encouraging litter, of the carbon emissions associated with biodegrading plastic and of the potential land use impacts of bioplastic feedstock crops).
Third, we shouldn’t shy away from liability. Nurdles, plastic pellets used in manufacturing, end up in the marine environment in vast quantities. Industry is starting to tackle the problem, but this is industrial waste, and we shouldn’t tolerate it.
Finally, we can improve end-of-pipe plastics capture. Evidence from the United States shows that sand filters in wastewater treatment plants appear to capture microplastics which come from washing synthetic clothing. End-of-pipe will always be a last resort, but it’s smarter than cleaning up once plastics are in the ocean.
These actions won’t solve the problem alone, but they would make a good start. With marine plastic pollution projected to double within a decade, we don’t have time to wait.
This post draws on a recent briefing paper from the Grantham Institute on ocean plastic pollution.