It seemed like the logical place to start, but of course logic doesn't always prevail in reality, especially what with sailing from A to B (most probably via Y), feeding ourselves, and making the most of the opportunities to learn from the people we meet enroute. It has therefore taken a little while to get round to answering the first of our series of questions, but here is what we have discovered...
How much plastic is there in the sea?
“...we really don’t have an absolute number but I think everyone is pretty clear that there’s more than we want and we need to move towards a reduction.” Prof. Richard Thompson
Sometimes the questions we ask don’t always lead us to the place from where we can find conclusions or solutions. And the act of searching for the solution to the problem is actually the act of searching for the right question to ask; ask any research student. In retrospect this is what I have found and so our first question of how much plastic is in the sea is a rather moot one. Why? Well because we don’t really need to know exactly how much there is, we already know that there’s enough to be causing a variety of problems.
There we are then, and if that’s all you have time for, then do stop scrolling now: we have a problem and we need to turn off the tap.
If you are still with me, then we’ll delve into the estimates and impacts. Prof. Richard Thompson has been researching microplastic for 20 years, and we were lucky enough to interview him, armed with his reusable coffee flask, on the deck of Amelie Rose when we visited Plymouth.
He is also the author of a very concise and accessible report written for the UK Government Office for Science, which presents scientific evidence for the Prime Minister and cabinet in a way that is easy to grasp. It outlines the impacts for the UK, but also quotes a global figure estimating that 4.8-12.7 million tonnes of coastally mismanaged plastic enters our oceans from the land annually.
That is a big number and rather difficult to imagine; the excellent articles in the National Geographic 06.18 edition quote Jambeck who equates 8 million metric tonnes as the equivalent of 5 shopping bags full for every square foot of the global coastline. This estimate comes from the per-person waste production rates from 192 coastal countries in 2010, applying the percentage of that which was plastic, and then the percentage of that which was mismanaged (ended up as litter or dumped on the land) gave the estimated loss per person. Applying this figure to the population in a 50km coastal strip in each country gave the overall estimate. Why a 50km strip? Coastal populations generate more of the land based waste which ends up in the sea. These estimates so far do not include estimates of how much plastic is introduced to the sea from fishing, aquaculture, water processing etc.
It is even trickier to estimate how much will be added in a number of years time, but around a two-fold increase is expected by 2025 as waste production, population and plastic use continues to rise.
So you may ask, why not just count what is found on beaches, and from plankton net trawl surveys. Firstly, the ocean is a big place, you can’t count every piece of plastic so inevitably you’d need to sample in a number of locations, count and then multiply up. Yet the selected locations may not be representative locations of the average, maybe they are areas where the current concentrates the plastic, maybe the location collects mainly one size of plastic and so forth. Some plastics float and some do not. There is also plastic locked up in sea ice. Therefore we need to go to each environment where plastic is present and sample each.
We are left with a top down method to calculate how much: how much plastic did we make, how much plastic did we responsibly manage into the waste stream; and a bottom up method: take samples from the ocean and multiply up. Which is the more accurate? Again, maybe it doesn’t always matter and time spent debating would detract from time spent seeking solutions. The effects are either already being felt, and have been proved or are very strongly believed on the basis of supporting evidence.
What happens to plastic when it enters the sea?
Well, that kind of depends on what type of plastic it is and its shape, some will float, some will not. Plastic is not a uniform substance, it is a range of polymers with different additives. Having studied marine renewable energy I could start quoting archimedes and buoyancy, but for those of you who are sailors I’ll just make reference to the difference between floating line used for towing dinghies, which is specially used because it won’t wrap around your propellor and well, the other stuff. Universally, its the density of the material and its displaced volume of water which determines if it floats. PET, which is used for many plastic bottles has a density of 1300 to 1400 kg/m3 as opposed to around 1025 kg/m3 for seawater. Lidded empty PET bottles contain lots of air and so float nicely.
Those which float will likely get the greatest impact of UV, and the wind, waves and tides will carry it around the sea. Depending on the plastic, some will be more resistant than others to UV taking longer to break down e.g. HDPE may be made with UV stabilizers. UV degradation will cause plastic to become brittle and the waves will likely cause mechanical strain on the plastic which will break it into pieces, bacteria will also cause it to fragment and maybe seals will play with it, thinking it a fun toy. By whatever combination of actions, it will break down into smaller and smaller pieces. Some of it will be predated, some of it will sink to the seabed, some of it will be washed up onto our coastlines and some will be carried with the currents to be concentrated in the ocean gyres we all now recognise exist.
As the plastic breaks down into smaller and smaller pieces, the sizes of plastic range from whatever size it entered the ocean down to microns (0.000001m) across. It is likely that nanoscale particles exist but we just can't prove this yet as our measurement techniques can't prove particles at these scales are polymers. There are also now conventions over the definitions of microplastic for the purposes of policy, so whereas micro used to mean at miron scale, its now any particle less than 5mm across.
What are the impacts on marine species?
Seven hundred species including marine mammals, birds, fish and invertebrates are known to encounter marine plastics. The marine species become entangled or ingest the plastic depending on the type and size of debris. Those encounters result in a range of impacts of severe physical harm or death through to sub-lethal effects such as on behaviour and ecological interactions such as the ability to feed, escape predators or migrate, although other sub-lethal effects such as the result of exposure
to chemicals are expected.
Fishing gear does very well what it was designed for, to entangle and catch marine creatures. When lost, ejected or cut free due to being caught, it is not managed and it drifts. These lost nets, also known as ghost gear, are globally known to cause harm or death to many species and so far 250 species are recorded to have been entangled including 50 species of marine mammal, over 100 species of seabird, many species of fish and all 7 species of marine turtle. In the South West of the UK, in a single year spanning 2016-2017, 102 different grey seals in the area were entangled at 15 different locations, mostly in monofilament net. When we at Clean Seas Odyssey visited Scilly, we heard of the Scilly based fishermen who cut free a leatherback turtle from nets drifting off Cape Cornwall.
Plastic cups in Falmouth which don't fit into the bins so some end up in the sea - next year they plan to introduce a deposit scheme on reusable cups which is great news.
Our consumer items such as bottle tops, balloons, sewage debris and small fragments pose a threat to marine life when they are eaten (ingested): 300 species are known to ingest litter, from small planktonic and benthic invertebrates to fish, birds and animals. Haven't we all seen Chris Jordan's image of dead albatross decaying with stomachs full of plastic fragments?
It is not just bigger species. In lab tests, it has been proven that ingestion adversely affects the ability of plankton to feed and the ability of marine worms and fish to gain energy from food. As the owner of a cat who has recently had surgery for fur balls which were stopping the proper flow of digestion, I can anecdotally hold testament to the resulting lethargy and miserable nature of such an untreated creature.
Anyway, back to the sub-lethal effects that are not so obvious and not so heart wrenching in photographs, and therefore perhaps a little less appreciated yet with potentially wider ranging effects. There is concern that microplastics might facilitate the transfer of organic and inorganic chemicals to biota.
It has been proven that when plastics enter seawater they accumulate man-made chemicals which are present, especially those which are hydrophobic and within a week there can be orders of magnitude greater concentrations. Through laboratory tests it has also been proven that these chemicals can transfer out in a solution which mimics the guts of organisms, especially warm blooded ones. However, no need to panic yet, the dose in comparison to other means of marine creatures accumulating these chemicals is likely to be low. Think of fish who are swimming for all the hours of the day and exchanging chemicals through their gills.
Biota - animal or plant life of a specific region, habitat or geological period.
The other area of concern is from the transfer of chemicals, such as plasticisers and flame retardants, which are added during manufacture and therefore exist in higher concentrations in any sea plastic particles, but precisely whether these types of plastics are entering the ocean is as yet unknown. This remains an area of ongoing research, as does investigation into whether nanoparticles of plastic could transfer across cell membranes and become present in the bodies of creatures.
So what next?
A similar quantity of plastic will be produced in the next 8 years as the whole of the 20th century.
This is an oft quoted figure, and provides part of the input for that twofold increase Jambeck and the team predict. I have no reason to think that this isn’t going to be true...
...except that we make the future.
The future is not foisted on us, and so we can change the figures on how much is produced and how much leaks into the environment through our choices. As Professor Richard Thompson so correctly suggests, the benefits of plastic to society are not directly linked with plastic being emitted to the environment, and so if only we could manage this potentially dangerous substance, we could benefit without harm.
Rebecca
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