Plastic oceans

Figure 3. Bacteria and ocean plastic. Artwork: Mark W. Slater

You may have heard, lately, that fish stocks are rapidly declining. I thought this was something new, as in general knowledge in the last couple of years. Well, its not. In 2003, the National geographic published an article stating that fish stocks had declined by 90%. 90%. An article in 2011 by Juan-Jordá et al, (1) looked at tuna and its relatives and show a 60% decline in the last 50 years. Clearly, dear Readers, there is a problem and its pretty much slamming us in the face. Apart from overfishing, our old frenemy plastics has a large part to play.

What happens to plastic that enters the ocean? That plastic beach ball I let go of on holiday when I was 10 and that bobbed out to sea before we could get a hold on its slippery surface. Plastic used by the fishing industry, plastic accidentally or purposely dumped in the ocean, plastic from land use that finds it way from rivers to the ocean, dumping from commercial liners (to name a few) all make up the debris. The plastic that floats is swept around by the oceans currents and collects in gigantic slow moving pools including the 5 major oceanic gyres. The orgnanisation "5 gyres" has a great website showing the location of the gyres and how the plastic gets there. The debris is not visible from space as it is dispersed and often below the surface of the water but the concentration of plastic, chemical sludge and other debris in the open sea (also called the pelagic zone) is much higher than in non-gyre areas.

Figure 1. Potential pathwys of transportation of microplastics and its biological interactions (6)

Once in the water, numerous evils result (Figure 1). First plastic is weakened and broken down by several types of degradation: biodegradation, photodegradation (action from sunlight), thermooxidative degradation (slow oxidative breakdown at moderate temperatures) and hydroysis through reaction with water (2). It ends up breaking down further and further until it reaches sandsized and then microscopic particles. At this point it is in the neuston layer of the ocean which is the region at the surface and just below the surface of the water. Neuston can also be used to describe organisms that live in this region. For example, a water strider (UK: skater) is a neustonic organism. Neustonic plastic in the garbage patches reaches densities up to 7 fold higher than zooplankton - the small organims that drift in the ocean and are found at the start of the food chain.


You can easily imagine the danger to wild life of entangling fishing line or an ingested bottle cap. Study of birds, fish and other aquatic organisms find that they are loaded with plastic (Figure 2)(3,4,5). If this is the consequence of larger organisms eating plastic we can see by eye, what happens to the broken down plastic that we need a magnifying glass or microscope to see?  Microplastics are defined as plastic particles less than 5mm in size (6) and of course even small organisms can eat these. The authors of the article in (7) have conducted a study on the size, mass and type of plastic they found in testing 748 samples from the western North Atlantic Ocean and 88% was less then 10mm long. Smaller organisms can eat these particles and they in turn can be eaten by organisms further up the food chain. What happens to the eaten plastic? For the larger organisms such as fish, birds and even whales it can be lethal [Figure 2, (1-6)]. But what about  microplastics and  - wouldn't they just pass straight through?  As we've seen in the previous posts, during plastic manufacture, chemicals are added to change the properties of the the plastic to suit their end products or to make them more biodegradeable. Additionally, monomers that were not properly incorporated during polymer production, chemicals that result from breakdown and chemicals unrelated to the manufacture of the plastic but included as part of the product (e.g. detergents in household cleaners, engine oil etc) will also end up in the water - they are known as persistent organic pollutants (POPs) and can by highly toxic (2). Some of these chemicals have been found to adsorb to microplastics and therefore will also end up in organisms and probably become part of their cellular make up and work their way up the food chain [5 gyres website; (2)] and eventually, one would assume getting passed on to us.

Figure 2. Dead Laysan albatross chick with plastic in its stomach (1).

I'm only scratching the surface of this topic and since my topic in this blog has so far been micro-organsims but lets get back on task: do micro-organisms have anything to do with  microplastics? The straight answer is yes but not much. Of the 4 types of degradation mentioned above, biodegradation is the least contributory. It is certain that microplastics are colonized by micro-organisms (Figure 3) but they have little impact on their generation and how much they have to do with their further breakdown has not been studied - as far as I can see. They could of course feed off POPs that adsorb to the plastics and contribute to the chemical status of these as they exist in the oceans or are eaten by other organisms. There is some suggestion that the bacteria that colonize ocean plastic come from the Vibrio Genus (see this link for a summary and reference), which is also the Genus that causes cholera. Whether or not the species of Vibrio is pathogenic remains unknown.   

Considering how much plastic we use for the amount of time we have used it and our careless manners with regard to our planet, there must be a quite a bit of plastic in the ocean. I haven't been able to get a substantiated figure but according to CBS, Jim Oswald of the Marine Mammal Center in San Francisco, California, USA says 300 billion pounds or 150 million tons (or 43 million elephants!).

Is it all doom and gloom and no fish and chips? Is there anything we can do about it? YES - try to use less plastic! Much easier said then done but think about it. The best form of being green is to reduce consumption. Recycling is good but if there's no demand for your recycle material, it will still end up in a landfill or incinerator. Reusing is good too but reducing is best. I am starting to consider how I can reduce my plastic consumption. For example instead of buying a plastic tub of hummus to take to a gathering, I could make it myself with cans (tins) of garbanzo beans. I don't need to put my fruit and veggies in little plastic bags at the supermarket I shop at. I can search out farmers markets and bring my own reusable bag.  I was searching the internet and came across Beth Terry who blogs about living without or very little plastic on her my plastic free life. Would you take a look and adopt some strategies for reducing the plastic in your life and maybe, just maybe reducing your chances of being part of marine life destruction. All life is linked - if they suffer, we suffer, even if you only feel it as no tuna in the supermarket.

References.
1. Juan-Jordá MJ, Mosqueira I, Cooper AB, Freire J, Dulvy NK. 2011 Global population trajectories of tunas and their relatives. Proc Natl Acad Sci USA. Dec 20; 108(51): 20650-5
2. Andrady L. Microplastics in the marine environment, 2011, Marine Pollution Bulletin, 62, 1596-1605.
3. Young LC, Vanderlip C, Duffy DC, Afanasyev V, Shaffer SA (2009) Bringing Home the Trash: Do Colony-Based Differences in Foraging Distribution Lead to Increased Plastic Ingestion in Laysan Albatrosses. PLoS ONE 4(10)
4. Mrosovsky, N, Ryan GD, James MC, Leatherback turtles: the menace of plastic. 2011 Proc Natl Acad Sci U S A. Dec 20;108(51):20650-5.

5. Boerger CM, Lattin GL, Moore SL, Moore CJ. 2010 Mar Pollut Bull. Plastic ingestion by planktivorous fishes in the North Pacific Central Gyre. Dec; 60(12):2275-8

6. Wright S.L, Richard C. Thompson RC, Galloway TS. 2013 The physical impacts of microplastics on marine organisms: A review. Environmental Pollution. In press.
7. Morét-Ferguson S, Law KL, Proskurowski G, Murphy EK, Peacock EE, Reddy CM. 2010. The size, mass, and composition of plastic debris in the western North Atlantic Ocean. Mar Pollut Bull. 2010 Oct;60(10):1873-8.

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Lifestyle magic: Reduce your plastic use.
Use reusable shopping bags (stash extra's in your car/backpack/briefcase, refill water bottles - metal, refill coffee cup (metal), buy from bulk bins for rice, grains etc, don't bag your fruit, go to farmer's markets if possible and bring your own bag. Write to your supermarket to reduce packaging.