Like most of us who read this headline, I was aghast.
On face value it appears to be incredible because: a) there must be a lot of fish in the sea, and b) plastic is really dangerous stuff particularly when it is in the World’s oceans.
Then I asked myself a couple of questions:
- How many fish are in the sea?
- How dangerous is plastic when it is in the sea?
With the help of Google I found out that:
- There are between 800,000,000 and 2,000,000,000 tonnes of biomass in the World’s oceans (http://phys.org/news/2009-01-first-everworldwide-fish-biomass-impact.html).
- The surface area of the World’s seas is an amazing 335,228,000 km² (http://www.eoearth.org/view/article/154984/).
- This gives between 2.386 and 5.966 tonnes of plastic per km², or between 2.386 and 5.966 grams of plastic per m².
- The estimated average depth of the ocean is 4,000 m (http://www.mbgnet.net/salt/oceans/data.htm).
- If the plastic becomes evenly distributed there will be between 0.000596555 and 0.001491389 grams per m³, or between 0.597 and 1.491 mg per m³.
- If we take the average density of plastics in the ocean to be about 1g per mm³ the concentration of plastic would equate to between 0.597 and 1.491 parts per million (ppm) using the correlation of mg per m³ to ppm at the same density.
Now that we have the amount in some sort of perspective let’s consider the second question. Whilst the raw materials for plastics might be considered to be potentially harmful and also some of the other ingredients used in the manufacture of plastics may also be considered as potentially dangerous most chemists would agree that in their polymerised state, plastics are inert and stable and that typically additives are effectively encapsulated within that stable polymer matrix. So what are the issues with plastics in the sea?
Probably there are three areas of concern:
- Plastics waste as a physical hazard to wildlife and we are all too familiar with the pictures of birds and sea creatures that have either become entangled with, or ingested plastic items.
- Plastics waste as floating litter often washed up on beaches and shore lines or accumulating in so called gyres (https://en.wikipedia.org/wiki/Ocean_gyre).
- Plastics becoming a ‘media’ that attracts other pollutants and as plastic articles physically breakdown into smaller particles, which are then ingested by sea creatures with the risk that they become contaminated or affected by these other pollutants.
Of course all of the above are most concerning and we must do everything that we can to prevent contamination of the oceans be it by plastics or indeed other matter that we, as the human race, are putting there.
However, I would suggest that we need to acknowledge the following:
- There is already a lot of plastic in the oceans and it is probably going to be there forever.
- Almost no matter what we do to prevent plastics entering into watercourses, a proportion of that plastic will continue to be deposited in the ocean. Wear and tear occurs to our synthetic (plastic) soled shoes, our car tyres degrade and as we wash our clothes made from synthetic fibres (plastics) we directly discharge particles into the watercourses.
- We need to keep the problem in perspective as illustrated by the numbers above.
- Plastics are very inert.
- Life without plastics is not sustainable.
- Plastics have many positive environmental and health benefits.
- The impact of plastics in the sea needs to be better understood.
- Other forms of contamination in the ocean may be much more significant.
- Plastics are an incredibly valuable resource and efforts must focus on reducing per capita consumption, reusing plastic items, recycling plastics waste and recovery of energy from plastics at the end of their useful life.
Finally I wish the Ellen McArthur Foundation success in its quest to encourage us all towards a circular economy.