This November, the world will convene in Busan, South Korea for the final round of negotiations on the Global Plastics Treaty, a legally binding instrument to help countries address plastic pollution at source. One point of discussion that has evolved between 2022, when the agreement was signed, and now is the addressing of microplastics.
During initial meets, countries largely focused on microplastics, a term used for plastics with a diameter of up to 5 mm, as a component of marine plastic pollution since they are often generated through degradation of larger plastic waste discarded into aquatic environments. But by the fourth round of negotiations in April this year, focus shifted to clear measures to reduce their generation and release, with particular emphasis on reducing intentionally produced microplastics. These include the raw materials used in plastic fabrication and processing, as well as small microbeads added to toothpaste and other personal care products as an exfoliating agent. According to “Microplastics–Occurrence, Fate and Behaviour in the Environment”, a chapter published in the 2017 book Comprehensive Analytical Chemistry, approximately 6 per cent of liquid skin-cleaning products sold in the EU, Switzerland and Norway contain microplastics.
The greater focus on microplastics and their reduction comes amid increasing scientific research and evidence on their all-pervasive nature. According to the UN, the world produces 430 million tonnes of plastic per year, two-thirds of which are only used for a short time. This means as plastic production and waste grows, microplastics will grow exponentially as well and eventually end up in agricultural soil, the air we breathe, the water we drink, the food we eat, and even our own bodies. The UN Environment Programme (UNEP) had already warned against this, by labelling microplastics as an emerging contaminant that could potentially threaten the health of humans and other organisms in the “UNEP Year Book 2014: emerging issues in our global environment”.
Scientific research also provides greater clues on the potential health impacts of microplastics. For several years, governments have debated whether the presence of these tiny, inert particles can pose a major threat. Even the World Health Organization said in 2022 that there was insufficient evidence to determine the risk microplastics pose to human health. But new research is increasingly providing more clues.
In a recent preprint, a team of researchers led by the University of New Mexico, US, show that microplastics appear to have invaded the brain. The preprint, which was posted online in May 2024 but is yet to be peer reviewed, shows significant accumulation of microplastics and nanoplastics (particles less than 1 μm in diameter) or MNPs in the human brain. For the study, the team analysed liver, kidney and brain samples from deceased individuals in Albuquerque, New Mexico, US. The samples available were from 2016 and 2024. “MNP concentrations in decedent brain samples ranged from 7-to-30 times the concentrations seen in livers or kidneys,” they say. Some 24 brain samples collected by the team in early 2024 were nearly 0.5 per cent plastic by weight.
Other research also shows that the particles are present in human lungs, kidneys, placenta, reproductive organs, and even blood. While not every detection is linked with specific health impacts, some clues have been found. A 2022 review paper published in Marine Pollution Bulletin explains that exposure to the particles can induce oxidative stress or cytotoxicity in cerebral and epithelial cells. The paper highlights other impacts like decreased immune response, inflammation, DNA damage, disruption of metabolism and impaired reproductive activity.
In March 2024, a study published in the New England Journal of Medicine also confirmed presence of microplastics in the heart by analysing the carotid artery plaque (a buildup of fatty deposits in the carotid arteries that supply oxygenated blood to the brain) of 304 patients. The researchers detected MNPs in nearly half the patients. Among the 257 patients that came for follow-up after 34 months, those with MNPs had a higher risk of myocardial infarction (heart attack), stroke as well as death. Microplastics exposure also reduces lipid digestion in simulated human gastrointestinal systems, due to the formation of oil droplets, and inhibits enzyme activity during the digestion process, says a 2020 paper in Environmental Science and Technology.
How do microplastics enter the human system? One way is through inhalation; microplastics are deposited in the air as atmospheric fallout from industries, construction, urban dust and residues of synthetic textiles and tyre erosion. In a 2023 review paper published in Groundwater for Sustainable Development, Indian researchers note that in one day, Dongguan City in China sees about 36 micro-plastics per sq m deposited into its atmosphere, Paris, France sees about 110 microplastics per sq m, while London, UK sees as many as 575-1,008 microplastics per sq m. Even remote areas of the Pyrenees mountain range on the France-Spain border see considerable microplastic deposition into the atmosphere, at 365 particles per sq m. But analysing whether these deposition rates are harmful is difficult, given that the world is yet to set standards on safe exposure levels to microplastics.
The review highlights that compared to the outdoors, indoor concentrations of microplastics are higher (1,600–11,000 particles per sq m per day). “The high detected concentrations of microplastics in indoor environments might be attributed to the higher flux of indoor microplastics sources and fewer particles being removed by dispersion processes than in outside environments,” it says.
Earlier in 2020, a study published in the journal Environment International analysed indoor dust samples from 12 countries and detected presence of polyethylene terephthalate-based microplastics (PET-based MPs) ranging from 38 to 120,000 μg per g. It also says that children may take in more microplastics than adults, based on body weight (bw). “The median daily intake of PET-based MPs calculated for infants was in the range of 4,000-150,000 ng/kg-bw/day,” it says, adding that these values are tenfold higher than those for adults.
The food chain also plays a role. On land, microplastics have been found in terrestrial organism wastes like earthworm cast and chicken faeces, with concentrations ranging from 14.8 to 129.8 particles per g, says the 2023 review paper. Among marine organisms, molluscs show the highest concentration (up to 10.5 microplastics per g), followed by crustaceans (up to 8.6 microplastics per g) and fish (up to 2.9 microplastics per g), according to a 2020 study published in the journal Environmental Health Perspectives.
It’s not just living organisms that contain microplastics. Sea salt can have up to 1,674 particles per kg, which is higher than the concentration in rock salts and lake salts, says a 2018 study published in Environmental Science and Technology. A 2019 study published in the same journal said a single tea bag releases about 11.6 billion microplastics and 3.1 billion nanoplastics into a cup of tea. Other items where microplastics have been detected include take-out food containers and cigarette butts, which also facilitate ingestion.
Other forms of exposure include dermal contact, or through items such as medical implants. A 2021 study in the Journal of Hazardous Materials by researchers from Iran and the UK retrieved traces of microplastics from human washes and found 16,000 particles from 2,000 individuals. The largest number of microplastics were found in head hair (more than 7,000) and the least in saliva (about 650 particles). Men had almost twice the amount of microplastics as women. But gauging the exact impact of these concentrations remains a challenge until the safe exposure limits and standardised risk assessments are established.
Microplastics also impact the environment that they invade. After air, soil is the second-largest reservoir of the particles, majorly deposited through agricultural practices like mulching with low-density plastic. Studies in China, cited in the 2023 review, found average concentration of 310 particles per kg in agricultural sites near Hangzhou Bay, with mulched soils having 571 particles per kg. Landfills and industries also contribute to soil microplastic levels.
Effluents from wastewater treatment plants are a significant source as well. While larger particles are typically cap-tured during the various stages of wastewater treatment, smaller microplastics often pass through. Some of these parti-cles get trapped in activated sludge, which is then applied as fertiliser in agriculture, potentially releasing microplastics into soil.
“Once accumulated in soil, microplastics may naturally breakdown and bioaccumulate in plants, soil organisms, and biodiversity,” says the 2023 review paper. The bioaccumulation has been shown to hamper soil quality and nutrient cycles, alter soil chemical characteristics and reducing water and nitrate-holding capacity, as well as microbial activity crucial for plant growth. A 2020 study in the journal Plants shows that irrigation water contaminated with microplastics results in reduced shoot and root length in Lepidium sativum (garden cress). The study suggests that chemicals leaching in the water from the particles may be impacting the grass’s germination.
Another 2020 study, published in the journal Plants, People, Planet, notes that concentrations of the microplastic ethylene propylene diene monomer rubber, used in artificial sport turfs, may have negative effects on plant growth.
Like soil, water is also heavily contaminated by microplastics. “Exposed agricultural soil surfaces could be significant contributors of microplastics to the atmosphere or rivers (through runoff),” says the review paper. Plastic waste can also enter rivers through domestic and industrial drainage systems, it adds. In fact, says UNEP, about 19-23 million tonnes of plastic waste leaks into aquatic ecosystems, such as lakes, rivers, and seas every year. Without action to reduce plastic pollution, emissions of plastic waste into aquatic ecosystems will triple by 2040. Rivers in regions as remote as Antarctica and Arctic already show microplastic traces.
In the water, microplastics interact differently with various aquatic organisms. For instance, the presence of certain nu-trients on the surface of microplastics attracts microbial organisms, which bind to the particles to form biofilms. These biofilms are a food source for aquatic organisms, which may ingest them and thus bring microplastics into the aquatic food chain, explains the 2023 review paper. When they accumulate in large aquatic organisms, microplastics laden with chemical contaminants leach additives and release toxins, causing endocrine disruption and mutations, it adds. Further, the review paper says that zooplankton exposed to microplastics experience reduced growth, increased mor-tality, and disrupted reproduction. And in algae, larger-sized microplastics can reduce the photosynthesis mechanism by blocking the sunlight, whereas smaller particles affect their cell wall and destroy their internal structure.
Clearly, microplastics cannot just be considered inert contaminants. But many of their impacts are still being understood, which has made it difficult to fix policies and measures to remove or limit their deposition. The Global Plastics Treaty, however, has begun discussions on some aspects such as production of microbeads.
Countries have already imposed their own restrictions on these; like the Netherlands introduced a ban on microbeads in cosmetic products in 2014. The UK imposed similar restrictions in 2018, even banning microbeads made of so-called biodegradable plastic. China, US and Canada have also imposed bans on microbeads in the cosmetics indus-try. The EU has also taken some comprehensive regulatory measures. In 2019, the European Chemicals Agency proposed extensive restrictions on intentionally added microplastics in products placed on the EU market. The Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulation that came into effect in October 2023, bans microplastics in intentionally added to products like cosmetics and detergents.
The treaty discussions also include addressing microplastics during wastewater treatment using newer technologies. Microplastics removal in wastewater treatment plants primarily relies on screening, sedimentation and filtration methods, which show varying suc-cess depending on type of technology used and particles targeted, says the 2023 review. It cites other recent technologies that show more promising results, such as electrocoagulation, which involves using electricity to separate pollutants from wastewater, or the sol-gel process, a chemical technique in which microbeads are trapped in a silica gel for removal.
Apart from this, several countries including India have imposed restrictions on overall plastic production and use, which would indirectly reduce microplastic generation as well. The measures that countries will have to put in place in the future to meet the eventual obligations under the Global Plastics Treaty will also help in this regard. Apart from this, investing in research to detect, monitor and understand the environmental risks of microplastics is also necessary. This requires standardised scientific protocols for microplastic sampling, extraction, and analysis in various sectors, including food. As the world moves toward finalising the Global Plastics Treaty, it is imperative for governments, industries, and individuals to collaborate on reducing microplastic pollution from invading the entire ecosystem.
This was first published in the 1-15 October, 2024 print edition of Down To Earth