A Microplastic Marine Mystery

By Juliet Boddington

Scientists have known for a long time that the human race is polluting the world – land, atmosphere and sea – and one of the worst examples is the disposal of plastic waste in the form of polymer chains of carbon and hydrogen atoms that are not biodegradeable. Now an international research project based at the University of Manchester has revealed the highest levels of microplastic ever recorded on the seafloor, with up to 1.9 million pieces in a thin layer covering just 1 square metre.

Microplastics are a type of plastic fragment less than five millimetres in size. For those of you who like to imagine just how small, they are between one and a thousand micrometres wide, bearing in mind there are 1,000 micrometres in a millimetre. If particles cannot be seen with the naked eye, they are measured in nanometres, there being 1,000 in one micrometre, and are referred to as nanoplastic. Not surprisingly, these dust-like particles are very difficult to separate from the atmosphere to measure and quantify.

Microplastics are divided into two groups: primary microplastics are produced as pellets or fibres and used in industrial manufacturing, textiles and personal care products; secondary microplastics occur when larger pieces of plastic get into the environment and break down into smaller pieces over time, as a result of weathering when exposed to sunlight and any form of friction.

Microplastics are found everywhere: in rainwater on the Rocky Mountains, for instance, and even in places where there are no humans. It is thought that particles found on the snow in the Arctic were blown there by the wind. They can enter our water systems from runoff because we dispose of plastics in landfills, from the plastic in rubber tyres and from hundreds of thousands of tons of dust, from shoes, tennis balls, artificial turf, paint markings on roads, glitter, sewage sludge and agricultural plastic in mulching. Many daytrippers dump their rubbish in the countryside. Cigarette butts shed microfibres and high levels of toxins including nicotine.

Microplastic is also the ‘invisible enemy’ at the bottom of the sea, according to a research paper published in the journal Science. The team from Manchester found that ocean currents distribute plastics on the seafloor, where they gather in huge sediment accumulations, which the scientists call ‘microplastic hotspots’. These hotspots appear to be the deep-sea equivalents of the infamous ‘garbage patches’ formed by currents on the ocean surface.

Over 10 million tons of plastic waste enter the oceans each year. Floating plastic waste at sea has caught the public’s interest, thanks to the ‘Blue Planet Effect’, which has resulted in moves to discourage the use of plastic drinking straws and carrier bags. Yet the trash we can actually see on the seafloor accounts for less than 1% of the plastic that enters the world’s oceans.

The missing 99% is instead thought to occur in the deep ocean, but until now it has been unclear where it actually ended up. The new research shows that microplastic can be transported rapidly in the ocean by episodic turbidity currents – powerful underwater avalanches – that travel down submarine canyons to the deep seafloor.

Once in the deep sea, microplastics are readily picked up and carried by continuously flowing seafloor currents (‘bottom currents’) that can preferentially concentrate fibres and fragments within large drifts of sediment. Microplastics on the seafloor mostly consist of fibres from textiles and clothing. These get into the system because washing synthetic clothing releases millions of microplastic fibres: through microbeads in personal products like shower gel (banned in the UK since 2018); and through things like cotton buds, wet wipes and sanitary towels wrongly flushed away. They are not effectively filtered out in treatment plants for domestic waste water but easily enter rivers and oceans.

Even things like ‘pods’ of washing machine powder, triangular teabags, plastic coverings on dishwasher tablets, washing drying on the line, plastic sheeting degrading on construction sites, all contribute to the problem.

So much waste is dumped in the seas and oceans from fishing nets and gear. Rubbish is left on beaches, alongside waste from ships and household sewage. The tides, thermal currents and winds moving the microplastics make this pollution a global issue rather than one that any single country can tackle alone. It has been found that microplastics get into the food chain through the digestive system and muscles of fish, crustaceans and zooplankton, and of course then into their predators like larger fish and mammals and birds until they end up on dinner plate. It is particularly worrying because zooplankton play a crucial role in the marine food chain and in regulating the global climate.

When plastic is broken down into smaller pieces, the toxic chemicals added during its manufacture escape into the air, water, earth and life forms. These chemicals vary depending on the type of plastic, but it has been shown that they can cause a number of health risks such as the induction of pro-inflammatory cytokines (toxicity to cells – chemotherapy causes this), hypersensitivity (undesirable reactions produced by the normal immune system such as allergies) or autoimmunity (immune response to one’s own healthy cells and tissues) and acute responses such as hemolysis, which is a rupture or destruction of red blood cells.

Research on animals shows the effect of microplastics on fertility and growth, even survival, but the scientific study of human exposure to microplastics is still at an early stage, and it is uncertain whether ingested fragments are a danger to health in the long term. However, a study has shown that we eat at least 50,000 particles of microplastics a year through food and water and swallow a similar amount again from the air. Only a small number of foods and drinks have been analysed to produce these figures so the real numbers are likely to be much higher.

It may be impossible to eliminate the problem of microplastics but it is important to be aware that they can be found in sea salt, drinking water (and 22 times more so in bottled water), in food packaging, in the air, in bread, processed products, meat, dairy, vegetables, sugar, beer and seafood. Nanoparticles are particularlydangerous because they can pass through our tissues to our brains and nervous systems.

Apart from campaigning to raise awareness of the negative impact of microplastics on the environment, we must think carefully, as individuals, and try to reduce our reliance on plastics. Washing machines need to be fitted with very fine filters. Avoid buying food and cleaners wrapped in plastic – and don’t store food in plastic bags or containers. Don’t give children or babies plastic toys or buy single-use plastic cutlery – and if you do, recycle all your plastics appropriately.

It is important to recognise that changes away from plastics have consequences. For example, organic cotton production needs more land and water than artificial fabrics. Some countries don’t have water-purifying systems like ours and dealing with waterborne infections takes priority. Using glass containers makes imported goods heavier and more expensive and so on.

Juliet Boddington is the membership officer of the AGS

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