I’ve been trying really hard to write posts about other stuff that I feel is more important or interesting, but it looks like marine plastic is just so much at the front of people’s minds at the moment it’s difficult to blog about anything even tangentially related without the debate going sideways. And as with most debates played out on social media, there’s a lot of emotion, and not a lot of evidence. So, I have spent my evening finding data and reading up on the problem.
Where is the data from?
The best sources of information I’ve found on this are:
- Jambeck et al. (2015). Plastic waste inputs from land into the ocean. 10.1126/science.1260352
- European Commission (2016). Harm caused by marine litter. JRC Technical report.
- UNEP (2016). Marine plastic debris and microplastics. Global lessons and research to inspire action and guide policy change.
- Niaounakis (2017). Managing of marine plastic debris. [I’ve not read this, but would be delighted to hear from anyone that had]
I would encourage you to read the first one by Jambeck, which is simple yet elegant. The next two reports amount to almost 400 pages, and assuming you get out more than I do, I would suggest you read the next 2000 words of this and then do something more fun.
The two main sources of marine plastic are from land (largely as municipal solid waste), and from the fishing industry. Beach littering, aquaculture and shipping are minor in terms of numerical totals, although they can cause local hotspots and beach litter is a problem from an aesthetic perspective.
Marine plastics from land
The study by Jambeck estimates the total burden of plastic from land-based sources entering the oceans each year. This is a difficult thing to do with any great certainty, but given that it’s been published in Science (a highly regarded peer reviewed journal), I’m happy to assume that the authors have a better idea of what reasonable assumptions consist of than the rest of us would do. For the 192 countries with coastal populations their approach was to a) work out the population within 50km of the coast, b) find data on per capita waste production and the percentage of that which is plastic, c) estimate the percentage of that countries waste that is mismanaged. From this, they calculated the likely quantities of plastic entering the ocean in 2010. They estimated that 275 million tonnes of plastic waste was generated by these countries, and that between 4.8 million and 12.7 million tonnes of this ended up in the ocean in 2010. The 10 worst offenders based on these assumptions are shown in the table below (the paper itself lists the 20 worst, and includes the quantities).
The only high income country on the list (coming in at 20th) is the US. Significantly, 16 of the 20 worst offenders are middle income countries; countries whose economies are growing faster than their infrastructure can cope with. We should be wary of criticising these countries; they are going through exactly the kind of dirty growth phase that the UK itself went through.
The next question to ask is whether or not this 4.8 – 12.7 million tonnes of waste plastic entering the ocean is a big number. The World Bank estimates that in 2012, municipal waste production was 1.3 billion tonnes. If we were to combine these figures (which I think is methodologically pretty dodgy) we could then say that 1% of total world municipal waste production is plastic that ends up in the ocean each year. But as I say, that’s not a great method, and I think the situation is rather worse than 1% suggests.
As part of their calculations, Jambeck et al made some assumptions on the percentage of waste that was mismanaged in the 192 countries included (how they arrived at these is detailed in the supplementary information, rather than the paper itself). Amongst the top 10 worst offenders in the table above, this percentage ranged from 57% to 89% (this compares to the US, where a 2% mismanaged waste fraction was assumed, sadly the authors don’t present data for the UK). Shockingly high amounts of waste are therefore going completely untreated. I don’t think we have a problem with plastic waste per se, I think we have a problem with all waste. And I think that one of the consequences of this is that we should focus on waste management in a more holistic way, rather than simply worrying about plastic.
Marine plastics from fishing
Having looked at plastics from land, let’s move on to plastic waste from the fishing industry. According to this EU technical report, 640,000 tonnes of fishing gear is discarded or lost at sea each year. Obviously much of this is nets, and these abandoned nets entangle and kill significant quantities of marine animals, in a phenomenon known as ‘ghost fishing’. Another interesting snippet from the same source, relates to the fragments of orange and blue rope that you see on beaches; ‘dolly rope’. This is sacrificial rope that is attached to bottom trawl fishing nets. It’s designed to protect the net itself from damage, but it’s estimated that 10-25% of the 100,000kg of dolly rope used each year in the EU ends up as marine plastic waste. Is there a better solution to the problem than dolly rope? Apparently not (or at least not one I could find via google).
Derelict fishing gear removal programmes do exist, but whether or not they operate at anything like the scale required to put a dent in the problem I haven’t been able to determine. However, given that plastic waste from fishing doesn’t travel as far as smaller plastics, targetting removal at particular hotspots may well be a worthwhile approach. Obviously not dropping it into the sea in the first place would be better, and it should be a relatively easy problem to legislate against. And as you’ll see below, whilst the amount of plastic from fishing is relatively low compared to that from land, it is responsible for most of the harm done by entanglement.
What harm does marine plastic do?
This is dealt with very well by the EU report ‘harm caused by marine litter’. I’ve tried to summarise the main points below.
- Affects marine mammals, sea birds, turtles.
- Numbers of fish species affected impossible to determine.
- Recorded at a rate that impacts on total populations in many larger species (including whale, turtle, shark and seal species).
- Impossible to estimate for fish and small species.
- Majority of entanglement recorded (>80%) is from fishing industry plastic.
- Risks to birds are particularly high in species that are attracted to plastic as nest building material (e.g. gannets).
- Affects at least half of marine mammal species, all turtle species, half of sea bird species studied.
- Certain seabirds seem attracted to plastic (e.g. fulmar, shearwater).
- Numbers of fish species affected impossible to determine.
- Only detectable by post mortem, and even then highly dependent on digestive system (e.g. less easy to detect in animals that regurgitate undigested matter).
- Impacts on the animal are unclear; could result in malnourishment (plastic taking up space in the digestive tract), blockage of the intestine, difficulty in regurgitating.
Poisoning from constituents of plastic:
We have strict limits on the types of chemicals allowed in food grade plastics, because of the risk to human health. Clearly, non-food plastics end up in the marine environment, and can contain much more toxic constituents. In addition to the constituents of the plastic, other materials can be adsorbed onto the surface of the plastic, which then acts as a vector when ingested. Sub-lethal effects are possible but have not been proven.
Plastic acts as a vector for transfer of biological material into regions it’s not been found before (organisms quite literally hitching a ride on floating plastic waste). It’s not clear whether this mechanism of species transfer has yet resulted in serious consequences, and there certainly aren’t any numbers on it, but it’s another potential source of harm.
What else is in the ocean that we need to worry about?
The thing that worries me most about the marine plastic issue is that it is quite literally, the tip of the iceberg. We are only really aware of stuff that is floating (i.e. very buoyant), or in midwater (i.e. moderately buoyant). We simply have no idea what there is that has sunk to depth, although estimates suggest that over 90% of plastic sinks. It might be that at least some of the ocean floor is so deep that anything down there is effectively inert, or at least very slow to break down, but there are probably also significant areas of much shallower ocean floor that are biologically much more important. And obviously, a lot of what isn’t so buoyant is not plastic. The countries discharging massive amounts of plastic into the ocean aren’t just discharging plastic; they are countries with poorly developed municipal waste infrastructure, so all their other municipal wastes are also being discharged without treatment. It’s true to say that stuff that is buoyant is more likely to find it’s way into the ocean than stuff that immediately sinks, but I think we need to be very careful about assuming that the ‘marine plastic problem’ is really about plastic.
What do we do about it?
Maybe I’m missing something, but the answer is a lot simpler than I was expecting it to be when I first started reading up on the subject. It seems to be largely a question of actions needed by government rather than individuals. Whilst the fishing industry is a relatively minor source of marine plastic on a tonnage basis, it causes a disproportionately high number of entanglements. This should be relatively easy to combat with legislation.
As discussed above, thanks to the study done by Jambeck et al., we have a good idea of the countries where waste plastic is coming from. It then becomes a question of how to support these countries in developing their waste infrastructure. Just 20 countries are responsible for 83% of the plastic entering the oceans each year. Developing waste infrastructure is something that the World Bank is heavily involved in, although how rapidly progress is being made, I don’t know.
China is the biggest source of marine plastic in the world, but since it is no longer accepting waste plastic from other countries, we can but hope that this is being mirrored with investments in waste infrastructure. China’s decision is certainly causing a lot of headaches in the UK waste management industry. What I’d hope would happen next is that we invest in waste infrastructure in the EU that allows us to treat this material somewhere with a well developed regulatory regime. In the interim, this is likely to be incineration. What I fear will happen next is that we will simply start sending our plastic waste to a country without decent waste management infrastructure, quite probably one on the list of 20 worst offenders detailed by Jambeck et al. The best way of stopping this happening is to ensure that waste management legislation has diligence checks that are stringent enough to effectively prevents us exporting waste at all. At present, the UK is the largest exporter of notifiable waste in Europe; we alone were responsible for 24% of the total in 2015.
What I haven’t found is any scientific quantification of the cumulative volumes of plastic; Jambeck et al have done an excellent job of calculating what is happening at present, but it would be interesting to read a similar study using backcasting of historic waste management practices, combined with estimated rates of plastic breakdown (which is very slow). Whilst most high income countries are not major contributors to marine plastic now, we may well have been in the past, and it would be interesting to have some idea of who is responsible for what is already there (and this should influence who pays for any clean up operations).
It’s an emotive subject. The infamous Blue Planet episode which resonated with so many people also included a significant segment on ocean acidification caused by rising CO2, and another on the impacts of climate change on ocean temperatures. Somehow, these don’t resonate in the same way that an image of an entangled seabird does.
I think I’ve learnt two things from all of this. Firstly, we live in a country where perhaps 1-2% of municipal solid waste is mismanaged, but this is not how most of the world works. I had no idea that in countries like China, Indonesia and the Philippines, upwards of 80% of waste isn’t treated properly. The second thing I’ve learnt is that we simply don’t know what damage waste is doing to the marine environment and the organisms that live in it, as it’s such a difficult environment to study.
But the thing that strikes me most about all of this is that it isn’t just about plastic.