Images of plastic debris choking estuarine systems or spreading insidiously across the surface of the sea are commonly used to represent the issue of marine pollution – and for good reason. It is estimated that the world’s oceans are contaminated with approximately 100,000,000 metric tons of plastic trash – including bottles, wrappers, discarded fishing gear and plastic bags. Because plastics take centuries to degrade, they may be transported many thousands of miles from their original source by ocean gyres. They leave a trail of devastation in their path, causing injury and death to all kinds of marine species through entanglement or ingestion.
The Microplastic Problem
In recent years, scientists have become increasingly aware of the threat posed by microplastics – tiny plastic fibres that measure no more than a millimetre in length and are invisible to the naked eye. Despite their small size, microplastics are capable of causing considerable damage. Each tiny fibre collects toxins, either absorbing them or adsorbing them from the water around it. When microplastics are ingested by primary organisms like phytoplankton and zooplankton, these toxins are introduced into the marine food chain at the lowest level. When those species are preyed upon by those higher up the food chain, the toxins carried by the microplastics are transferred from one animal to the next, accumulating exponentially at each stage.
Although the specific consequences of microplastic ingestion are as yet little understood, a 2013 study that exposed small fish species to a mixture of contaminated polyethylene particles proved that the fish suffered acute liver damage as a result. Coral reefs may also be affected, as polyps confuse the tiny particles for food and are then unable to digest the plastic fibres or take on further sustenance thereafter. Additionally, as plastics sink towards the seafloor, they are exposed to low temperatures that may cause them to degrade and release their toxins into the water column. Microplastic pollution almost certainly impacts on human health, as seafood species contaminated with harmful toxins make their way onto our plates.
Sources of Microplastic – Washing Machines
Until recently, scientists believed that microplastics were caused by the degradation of larger plastic debris. However, we now know that they come from their own, entirely separate sources. In 2011, Dr. Mark Browne of University College Dublin led a study that investigated the sources and sinks of microplastic. His team collected sediment samples from 18 beaches across six continents, including sites in Australia, Oman, South Africa, Japan, the Philippines and the United States. Each sample showed varying levels of microplastics, with those sites nearest areas of large development proving to be the most contaminated.
In total, Browne and his team found that microplastics accounted for 85% of the plastic waste found on all 18 beaches. Determined to find out where the fibres were coming from, the team analysed samples and found that the majority of fibres were synonymous with those used to make synthetic clothing. Eventually, after comparing samples of the wastewater produced by washing machines used to clean synthetic clothing with the contaminated beach samples, Browne and his team were able to establish the former as a major source of microplastic pollution.
According to the team’s findings, a single item of synthetic clothing can generate as many as 1,900 microplastic fibres per wash. Too small to be captured by the washing machine’s filtration system, the fibres flow with the resulting wastewater into aquatic systems, and subsequently into the sea. Human population density has increased by 250 percent in the last 50 years, and in that time the use of synthetic materials in clothing, as well as the number of people who have access to washing machines, has also grown. Therefore, the potential impact of washing-machine wastewater as a source of marine microplastic pollution is huge.
Sources of Microplastic – Hygiene Products
Laundry-generated wastewater is not the only major source of microplastic pollution. A recent report published in the journal Environmental Science & Technology claims that tiny plastic particles added to cosmetics including toothpaste, exfoliating creams and shower gel also contribute significantly to the problem. Using figures from previously published papers, the authors of this study estimate that in the United States alone, 8 trillion of these particles (known as microbeads) make their way into lakes, rivers and estuaries every day.
The estimate published in this report is based upon U.S. wastewater treatment plants operating at half capacity, and as such lead author Chelsea Rochman warns that 8 trillion microbeads per day is a conservative figure. In reality, microbead pollution may be taking place on a much larger scale, particularly as those microbeads thought to enter aquatic systems directly represent just 1% of those washed down the sink every day. Treatment plants separate solid and liquid waste, using settling tanks to divide the two. The vast majority of microbeads settle into the resulting sludge, some of which is later used as fertiliser.
When it rains, fertiliser enters rivers and lakes as run-off, before making its way to the ocean – carrying the microbeads with it. This means that instead of the 8 trillion microbeads cited in the study, as many as 800 trillion microbeads could potentially enter the marine ecosystem every day – enough to cover 30,000 tennis courts. Like synthetic clothing fibres, microbead pollution stems from the fact that the plastic particles are simply too small to be effectively filtered out by wastewater treatment plants.
The solution to microbead pollution is simple. Legislation banning the inclusion of microbeads in hygiene products needs to be introduced globally, and indeed has already been introduced in certain American states. In the meantime, organic exfoliants like crushed nut shells and salt are available as an environmentally-friendly alternative, and conscientious shoppers should make sure to choose products containing these over those that use microbeads.
The solution to microplastics generated by washing machine wastewater is harder to find, because in modern society, synthetic clothing is considered a necessity rather than a luxury. Scientists like Browne are working towards the development of textiles that shed fewer fabrics, and washing machine filtration systems capable of capturing even the tiniest clothing fibres. Until such inventions are perfected, consumers can help limit the damage by reducing the frequency with which they wash their clothes, and opting for those made from natural materials wherever possible.
Article by Jessica Vyvyan-Robinson