The amount of plastic in the oceans is in the news again, this week following a journal paper in Nature Scientific Reports on the Great Pacific Garbage Patch. In an earlier post on marine plastics, I looked at data on the scale of the total problem, but this new data is interesting because of its emphasis on studying a specific geographical area of ocean. This type of work is important for several reasons.
Firstly, environmental damage from a particular substance is often dose-dependent. So whilst my last post on the subject talked about the overall amounts of plastic going into the ocean, the nature of ocean currents means that plastic accumulates in specific areas rather than being evenly distributed. This means that environmental damage is likely to be particularly pronounced in these areas.
The second reason that studies of specific areas are important is that the regularity of ocean currents makes it relatively easy to establish where the majority of plastics in a particular area originate from. We might then consider specific investments in waste management infrastructures in countries whose plastics end up in particularly vulnerable areas of ocean. Obviously it would be preferable to manage waste properly in all countries across the world, but action targetting countries whose plastic affects particularly delicate ecosystems might be a good starting point for investments.
The Great Pacific Garbage Patch is between California and Hawaii.
The authors in the study reported this week used a combination of trawl nets to catch smaller plastic and aerial imagery (which is more reliable for larger plastic given its much lower prevalence). The study reports the detail of what sort of plastic was found (chemical type, sizes of pieces, nature of product, and likely origin countries). They then developed a computer model which was based on the way plastics move on the ocean surface (principally via currents, waves, and wind-induced drag). They ran the model with data on sources of plastic over time from other studies, in order to estimate the location, size, variability and growth in the Great Pacific Garbage Patch.
“Our model estimates that this 1.6 million km2 accumulation zone is currently holding around 42k metric tons of megaplastics (e.g. fishing nets, which represented more than 46% of the GPGP load), ~20k metric tons of macroplastics (e.g. crates, eel trap cones, bottles), ~10 k metric tons of mesoplastics (e.g. bottle caps, oyster spacers), and ~6.4 k metric tons of microplastics (e.g. fragments of rigid plastic objects, ropes and fishing nets).”
The authors note that their estimates are a lot larger than those from previous studies; as always, assumptions are key, particularly when it comes to modelling. However the authors also suggest that the higher estimate might reflect the impact of the 2011 Japanese tsunami, which is believed to have resulted in about 4.5 million tonnes of debris entering the ocean. Whilst this is a staggeringly large number, it’s perhaps callous to dwell on waste management impacts of tsunamis given the estimated 16,000 deaths that resulted.
Are there more of these garbage patches?
Yes. There are 5 main ocean gyres (areas of ocean where water currents are fairly circular) and plastics accumulate in all of them.
There is a great visualisation tool here which allows you to see where plastic released from a particular location travels to over a 10 year period. The underpinning method and data is hideously complicated (and is detailed here), but the front end tool just requires a mouse click on the map of the world. If you run the tool for plastic released from the UK coastline, you see that some of it stays in the North Sea for a while, with some ending up in the Arctic. Depending on where in the UK you release it from, some of it seems to end up in the North Atlantic gyre. I live in Wales, and it looks like beach litter from the Welsh coast spends a lot of time in the Irish sea, then carries on down to the Channel, and then ends up in the North Atlantic.
It’s not surprising that plastic in the ocean tends to accumulate in gyres. Unfortunately whilst they’re significant accumulations, they’re mostly fairly remote from land and not at a sufficient density that would allow a focussed clean up to occur. The plastic in these areas will still be there in hundreds of years time. Whilst we cannot necessarily do huge amounts to reduce the size of the garbage patches, we should at least try to prevent the leakage of plastic into oceans. As stated in my earlier post on the subject, my view on how we do that is to; a) to invest in waste management infrastructure in the countries contributing to the marine plastic problem, and b) to properly regulate the fishing industry in order to prevent dumping of fishing nets at sea; this plastic is disproportionately responsible for entanglements of wildlife. The fact that ocean plastic is still in the news is a good thing, and it will hopefully result in resources being chanelled into developing alternatives to plastics in the long term.