Microplastics: the ocean’s biggest problem
Most of you probably recognise that plastic pollution in the marine environment is a major problem. Anyone who owns a TV or computer cannot avoid coming across images of seabirds caught in six-pack rings, turtles feeding on plastic bags, or drinks bottles floating in the open ocean.
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Since the 1970s, research has uncovered this macroplastic pollution (size >25mm) to be the
primary cause of plastic entanglement, which can harm marine life through suffocation, laceration,
drowning and general reduced fitness. As 80% of marine plastic debris originates from land-based
sources, greater public and legal attention has thankfully now led to macroplastics being covered – at least in developed countries – by many international regulations and beach clean-up operations, which aim to reduce plastic waste inputs into the marine environment. Unbeknownst to most, however, the ocean is hiding an even more worrying, and less obvious, plastic pollutant: microplastics.
Microplastics are generally defined as plastic particles smaller than 5mm, and are therefore incredibly difficult to see with the naked eye, and even harder to control. They're also a double-threat; entering our oceans through both primary and secondary sources. Primary microplastics are manufactured specifically to be of microscopic size, such as the microbeads often added as
exfoliants to cosmetics, toothpastes and facial scrubs. Microbeads can be small enough to pass
through water filtration processes at waste treatment plants, and so ultimately end up in our natural systems. To put the problem into perspective, a 2015 study in the US estimated that 19 tonnes of microbeads were washed down the drain each year in the state of New York alone. The sheer amount means that even if 99% are successfully filtered out, the number that could potentially be released in the other 1% is still staggering. However, headway has now been made to tackle primary microplastics, as strong scientific evidence combined with public campaigns that gained significant momentum on social media earlier this year have led to microbeads being banned in the US and Canada, with the UK (hopefully) set to follow suit in 2017.
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So what about secondary microplastics? Well, whilst the properties of plastics lend them to persist
for centuries, they don't tend to persist in their original form. After entering the marine environment, large macroplastics become brittle and break down into smaller pieces through
fragmentation and photodegradation (where UV radiation from the sun breaks the chemical bonds
within the plastic). This then renders the plastic susceptible to further fragmentation through
biodegradation and wave action; generating hundreds of tiny fragments from one large macroplastic item.
Microplastics are described by scientists as ubiquitous and persistent in the world's oceans, and the terrifying reality is that there is estimated to be over 5.25 trillion pieces of floating plastic debris in the ocean, weighing an enormous 268,940 tonnes (or almost 45,000 African elephants for comparison). A large number of the floating particles are transported by currents into the open ocean and accumulate in the convergence zones of the Earth's five subtropical gyres, which are large systems of rotating ocean currents. Others remain trapped near land-based industrial plastic hotspots, such as coastal areas of Indonesia and China, where 75-90% of land- based plastic waste is inadequately disposed of. The seabed can also become final resting place for even previously buoyant plastics, as the development of microbial films on the particles can increase their density relative to seawater, causing them to sink.
With this much plastic in our oceans, you can see why we are being described as in the Plastic Age.
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The dangers of both primary and secondary microplastics manifest in all levels of the marine food
chain, and can even return to affect us back on land. At the base of the food chain, microplastics
resemble tiny zooplankton, and are often accidentally consumed by molluscs, larger crustaceans and zooplanktivorous fish (where the incidence of ingested plastic can reach a worrying 35%). Plastic fragments eaten by small fish will either sink to the seabed with the bodies of dead fish, be
defecated, or be transferred to larger predators. Fragments of plastic have therefore been found
within the digestive tracts of a wide variety of predatory species; including marine mammals, seabirds, and even fish species commonly consumed by humans. Yes, the plastic you throw away
could end up back on your plate.
Aside from the obvious obstructive harm that may be caused by ingested plastic, which can lead to gastrointestinal blockage and reduced food consumption, plastics can have hidden chemical effects on organisms. Firstly, they often contain additives intended to enhance the materials performance, which can leach into an organism's tissues and have adverse effects on reproduction, metabolism, hormone function and behaviour. Secondly, microplastic fragments can also absorb waterborne chemical pollutants called POPs; which are toxic, persistent in the environment and could potentially be transported long distances on contaminated plastic particles. POPs pose an additional threat to humans and marine life if a contaminated particle is consumed, as high concentrations have been found to cause hormone disruption and toxicity of the liver and kidney.
At the end of the day, plastic is something we all use, and no-ones going to start telling you to throw away all your lunch boxes. However, there are so many simple changes that the average person can make to help reduce plastic waste, which will inevitably limit the available plastic that could enter our oceans. Here are a few:
1. Avoid products containing microbeads. You don't even need to go around scouring ingredients lists – beatthemicrobead.org have produced some handy country-specific product lists to bring with you shopping, and even a scanning app for your phone.
2. Buy a reusable water bottle. Did you know that over 25% of bottled water is actually bottled, purified, municipal water?! Plus let's face it – no-one wants to spend a pound every time they want to hydrate, anyway. BPA-free (or bisphenol A – a chemical property of certain plastics that is feared to be correlated with various health issues) water bottles, and now even filter bottles, can be bought online for under a tenner – thus increasing your pennies in the long term while decreasing your plastic waste.
3. Recycle. Most people don't realise that nearly all plastics can be recycled. The extent to which this occurs through domestic recycling really depends on the logistical capacities of the local council, as some types of plastics cant be mixed. If your council only accepts a few types, check online for local drop-offs at big stores like supermarkets, so you can get rid of your recycling while you do your shopping.
4. Reduce your use of single-use plastics. It might be nice to sip your drink through a straw, or separate your veggies in plastic bags at the supermarket (heaven forbid someone touches your carrots), but such single-use plastics are easy to cut out of your day to day life. Many single-use items now have reusable or biodegradable alternatives, such as compostable picnic cutlery or plastic-free teabags (yes, teabags contain plastic too...).
If we change our thinking to consider if we truly need to use a plastic item, we can reduce plastic inputs into the marine environment and focus on eradicating the existing microplastic particles using new technologies – keeping our oceans simply full of life.
References
Cózar, A., Echevarría, F., González-Gordillo, J.I., Irigoien, X., Úbeda, B., Hernández-León, S., Palma, Á.T., Navarro, S., García-de-Lomas, J., Ruiz, A. and Fernández-de-Puelles, M.L., 2014. Plastic debris in the open ocean. Proceedings of the National Academy of Sciences. 111(28), pp.10239-10244.
Eriksen, M., Lebreton, L.C., Carson, H.S., Thiel, M., Moore, C.J., Borerro, J.C., Galgani, F., Ryan, P.G. and Reisser, J., 2014. Plastic pollution in the world's oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea. PloS one. 9(12), p.e111913.
Jambeck, J.R., Geyer, R., Wilcox, C., Siegler, T.R., Perryman, M., Andrady, A., Narayan, R. and Law, K.L., 2015. Plastic waste inputs from land into the ocean. Science. 347(6223), pp.768-771.
Li, W.C., Tse, H.F. and Fok, L., 2016. Plastic waste in the marine environment: A review of sources, occurrence and effects. Science of The Total Environment.566, pp.333-349.
do Sul, J.A.I. and Costa, M.F., 2014. The present and future of microplastic pollution in the marine environment. Environmental Pollution. 185, pp.352-364.
Vegter, A.C., Barletta, M., Beck, C., Borrero, J., Burton, H., Campbell, M.L., Costa, M.F., Eriksen, M., Eriksson, C., Estrades, A. and Gilardi, K.V., 2014. Global research priorities to mitigate plastic pollution impacts on marine wildlife. Endangered Species Research. 25(3), pp.225-247.
