‘Mermaid’s tears’: the terrifying scale of microplastic pollution
Beach-combers have long-known about the tiny beads of plastic of plastic, the brittle multicoloured fragments, like polystyrene crumbs, that litter the high-tide line amongst the bladderwrack. They call them ‘mermaid’s tears’. Scientists call them microplastics, now universally dispersed across the oceans, and even found in the stomachs of organisms at the bottom of the Mariana Trench. As the anti-plastic revolution gets underway, it’s worth analysing the global problem of these microscopic particles. In doing so, we’ll discover why microplastics are scariest part of plastic pollution, and why plastic-free supermarkets are just a drop in the ocean in solving the problem.
Microplastics are loosely defined as pieces of plastic with a diameter less than 5 mm. Currently, the cosmetic industry is the scapegoat for governments looking to tackle microplastics: the tiny micro-abrasive beads have been used since the 1980s in everything from defoliants (replacing pumice and ground almonds) to facial cleansers and shampoos. According to a paper briefing UK government ministers last year, though, the cosmetic industry’s contribution to the global microplastic total is as little as 0.01-4.1%: rather than exculpating the cosmetic industry, it highlights the sheer size of the problem. A single shower can release 100,000 plastic particles to the marine ecosystem, and a 150ml of bottle of cosmetic can contain up to 3 million of theme. The industry is now removing all microbeads from its products, with a complete US ban beginning in 2018.
left: plastic microbeads in a shower gel; right: ‘mermaid’s tears’, plastic nurdles combed from a beach
Air blasting technology is also an important source of primary microplastics: tiny acrylic beads are fired at boat hulls and machinery to remove rust and paint. Secondly, lentil-sized plastic nurdles – from which all plastics are melted and moulded – can often be spilt from factories or in transportation, washing up on beaches as ‘mermaid’s tears’. In one Swedish study, which used an 80 µm mesh to filter seawater next to a plastic-producing factory, researchers found that the concentration of microplastics were 102,000 nurdles per m3. The average harbour measured was 2400/m3, still staggering though. Moreover, a 2008 study found a 600% increase in estuarine microplastic concentrations following a storm, perhaps suggesting that microplastic usage in fertilizers must also be banned.
Secondary microplastics – the largest source
But even by banning all microbeads – as Obama did in 2015 – the problem is not solved: microplastic fibres are released when clothes are washed. One study cites a weight of 1.7g of microfibres per garment per wash. Another suggests more than 1900 microfibres are released in every washing cycle.
Yet despite all this – the prevalence of microbeads and microfibres that escape water filtration – the majority of microplastic fragments are not released domestically. Instead, they come from weathered macro-plastics: the plastic bags, packaging and bottles blown offshore or carried by rivers, the detritus which collects in the ocean’s five gyres.
Here, UV-light can cause the photodegradation of plastic: the atoms within the bonds of the polymer dissociate at a similar frequency to UV light, causing them to break free of the polymer, and become highly reactive free radicals. When the polymer is disrupted, the plastic loses structural integrity; weathered, brittle, and yellowing, fragmenting into microplastics by the turbulence and abrasion of waves. As well as UV light, thermal oxidation can also disintegrate the plastic, a process in which the additives to the polymer oxidize when exposed to high temperatures and the air, forcing open the polymer.
Although the majority of macro-plastic floats on the sea-surface layer, the majority of this degradation takes place on beaches. Sand has a low heat capacity: in summer, it can easily heat to 40oC, as anyone who has gingerly picked their way across sand in summer will know. According to one review, a 10% rise in temperature doubles the rate of thermal oxidative degradation, exposing the whole plastic debris to UV solar radiation at the high tide line, before being washed away by neap tides. Luckily, however, as the author points out, this makes beach cleaning the most viable option for reducing the toll of microplastics.
The real issue, though, is that it’s too late to stem the issue; microplastics are too small to remove from the oceans, floating for 1000 years before their carbon atoms are finally unchained. A 2011 review of literature cites microplastics washed up on beaches from the mid-Atlantic eco-paradise of Fernando de Noronha, to Plymouth estuaries, Malta, Hawaii, even Antarctica. It is suggested that trans-oceanic currents transport plastic pollution worldwide, but inner shore currents trap them, habitually returning them to the beach to further degrade. Another study dissected 90 organisms from the seven deep-sea Pacific trenches: every single organism from the bottom of the Mariana trench contained microplastic pollution in their gut. An unknown percentage of microplastics sink to the benthic zone, or hang in limbo in the deep pelagic zone.
Microplastics and toxins
The scariest thing about microplastics, though, is that they concentrate persistent organic pollutants (POPs), which are toxins that resist degradation. Being hydrophobic, they refuse to dissolve in water, instead attaching themselves to microplastics, which can concentrate these chemicals over a million times higher than the ambient sea. The chemical additives which leach out of the plastics as they degrade add to the problem, by concentrating themselves on the surface of the plastic.
These chemicals then act as a vector, carrying carcinogens and toxins (such as dioxins, DDT, and insecticides) between continents, and between prey and predator. What’s more, many marine insects use microplastics as a site for their eggs; eventually, the particles can play host to entire microbial communities, attached to a biofilm of algae. Studies have shown microplastics be a pathogenic vector for the Vibrio bacterium (which spreads cholera and gastroenteritis) and its ilk. The huge relative surface area of microplastics magnifies their danger as a vector, as high concentrations of POPs are delivered straight to the stomachs of biota.
Interactions with the marine ecosystem
Zooplankton, drifting on the ocean currents, indiscriminately feed on microplastics, expecting them to be their phytoplankton or algal food, swept along in the dark. In one study, Pacific krill had no ‘foraging bias’ between polyethene beads and algae; the Internet is awash with images of translucent plankton contaminated with plastic. Overall, few studies have investigated the bioaccumulation of POPs within organisms, but the picture is unlike to be optimistic.
Despite the similar size of microplastics to ingested inorganic sediment, studies have shown them to be a mechanical hazard, with metabolic consequences. A study cited by the National Geographic found the reproduction of oysters fed in microplastic-contaminated water to be halved. They explain that oysters must expend more energy passing the plastic through their gut, hence digesting more algae, which harms their reproductive potential. It’s a similar story for crabs, leading researchers to conclude that the energy budgets of indiscriminate feeders are being fundamentally altered by plastic.
The UK Parliamentary report cites that over 280 species which have been found with ingested microplastics, extending to seabirds, such as puffins, fulmars and shearwaters, which mistake the coloured plastic fragments for fish eggs, with consequent weight loss and malnutrition. Who can forget the images of the dead albatross in Blue Planet II, overwhelmed by plastic fragments in its stomach.
It affects us too…
It even affects us. Apparently, for the average European shellfish consumer, 11,000 microplastic pellets will pass through their body a year, the mussel beds carpeting the North Sea duly contaminated. Whilst a shocking statistic, there is little concern for human health at present. What all scientists agree on, though, is that a paucity of research exists in the field, particularly surrounding biotic effects and predation. Crucially, despite the prevalence of the problem, there is not even a common size definition for the term ‘microplastic’, a sign of how quickly this field has been pushed into the limelight.
As world media wakes up to plastic pollution, and gives daylight to the once-obscure field of microplastics, the Guardian reports that, on average, 83% of drinking water samples across the world are contaminated with microplastics, 94% in the USA, 72% in the EU. Microplastics have even been found in bottled water.
This is the extent of the pollution that we face. This is the terrifying, global scale of these microscopic fragments of plastic. When Margret Atwood was asked the one thing she would get rid of, she chose not the oil companies, or climate change, but plastic pollution: “the modern equivalent of a universal religion”.
All images, apart from those attributed, are in the public domain