Microplastics Are Everywhere

Feature WILL PARSON/CHESAPEAKE BAY PROGRAM BAY WILL PARSON/CHESAPEAKE Microplastics collected from the Magothy River in Maryland. end,” says Tamara Galloway, an ecotoxicologist at the University of Exeter, UK. “I think it is fair to say the potential risk might be high,” says Li, choosing his words carefully. MICROPLASTICS ARE Researchers have been worried about the potential harms of microplastics for almost 20 years — although most studies have focused on the risks to marine life. Richard Thomp- son, a marine ecologist at the University of EVERYWHERE — BUT Plymouth, UK, coined the term in 2004 to describe plastic particles smaller than 5 mil- limetres across, after his team found them on British beaches. Scientists have since seen ARE THEY HARMFUL? microplastics everywhere they have looked: in deep oceans; in Arctic snow and Antarctic Scientists are rushing to study the tiny plastic ice; in shellfish, table salt, drinking water and beer; and drifting in the air or falling with rain specks that are in marine animals — and in us. over mountains and cities. These tiny pieces could take decades or more to degrade fully. By XiaoZhi Lim “It’s almost certain that there is a level of exposure in just about all species,” says Galloway. The earliest investigations of microplastics focused on microbeads found in personal-care unzhu Li used to microwave his reported last October1. If parents prepare baby products, and pellets of virgin plastic that lunch each day in a plastic con- formula by shaking it up in hot water inside a can escape before they are moulded into tainer. But Li, an environmental plastic bottle, their infant might end up swal- objects, as well as on fragments that slowly engineer, stopped when he and lowing more than one million microplastic erode from discarded bottles and other large his colleagues made a disturbing particles each day, the team calculated. debris. All these wash into rivers and oceans: discovery: plastic food containers What Li and other researchers don’t yet in 2015, oceanographers estimated there were shed huge numbers of tiny specks know is whether this is dangerous. Everyone between 15 trillion and 51 trillion microplastic — called microplastics — into hot eats and inhales sand and dust, and it’s not particles floating in surface waters worldwide. Dwater. “We were shocked,” Li says. Kettles and clear if an extra diet of plastic specks will harm Other sources of microplastic have since been baby bottles also shed microplastics, Li and us. “Most of what you ingest is going to pass identified: plastic specks shear off from car other researchers, at Trinity College Dublin, straight through your gut and out the other tyres on roads and synthetic microfibres shed 22 | Nature | Vol 593 | 6 May 2021 ©2021 Spri nger Nature Li mited. All ri ghts reserved. ©2021 Spri nger Nature Li mited. All ri ghts reserved. from clothing, for instance. The particles blow disrupting cellular activity. But most of these exhausts and forest fires called PM10 and PM2.5 around between sea and land, so people might particles are too small for scientists even to — particulate matter measuring 10 μm and be inhaling or eating plastic from any source. see; they were not counted in Koelmans’ diet 2.5 μm across — are known to deposit in the From limited surveys of microplastics in the estimates, for instance, and California will not airways and lungs, and high concentrations air, water, salt and seafood, children and adults try to monitor them. can damage respiratory systems. Still, PM10 might ingest anywhere from dozens to more One thing is clear: the problem will only levels are thousands of times higher than the than 100,000 microplastic specks each day, grow. Almost 400 million tonnes of plastics concentrations at which microplastics have Albert Koelmans, an environmental scientist are produced each year, a mass projected to been found in air, Koelmans notes. at Wageningen University in the Netherlands, more than double by 2050. Even if all plastic The larger microplastics are more likely to reported this March2. He and his colleagues production were magically stopped tomor- exert negative effects, if any, through chemi- think that in the worst cases, people might be row, existing plastics in landfills and the envi- cal toxicity. Manufacturers add compounds ingesting around the mass of a credit card’s ronment — a mass estimated at around 5 billion such as plasticizers, stabilizers and pigments worth of microplastic a year. tonnes — would continue degrading into tiny to plastics, and many of these substances are Regulators are taking the first step towards fragments that are impossible to collect or hazardous — for example, interfering with quantifying the risk to people’s health — meas- clean up, constantly raising microplastic lev- endocrine (hormonal) systems. But whether uring exposure. This July, the California State els. Koelmans calls this a “plastic time bomb”. ingesting microplastics significantly raises our Water Resources Control Board, a branch of “If you ask me about risks, I am not that exposure to these chemicals depends on how the state’s environmental protection agency, frightened today,” he says. “But I am a bit con- quickly they move out of the plastic specks and will become the world’s first regulatory cerned about the future if we do nothing.” how fast the specks travel through our bodies authority to announce standard methods for — factors that researchers are only beginning quantifying microplastic concentrations in Modes of harm to study. drinking water, with the aim of monitoring Researchers have several theories about how Another idea is that microplastics in the water over the next four years and publicly plastic specks might be harmful. If they’re environment might attract chemical pollut- reporting the results. small enough to enter cells or tissues, they ants and then deliver them into animals that Evaluating the effects of tiny specks of plas- might irritate just by being a foreign pres- eat the contaminated specks. But animals tic on people or animals is the other half of the ence — as with the long, thin fibres of asbestos, ingest pollutants from food and water any- puzzle. This is easier said than done. More than which can inflame lung tissue and lead to can- way, and it’s even possible that plastic specks, 100 laboratory studies have exposed animals, cer. There’s a potential parallel with air pollu- if largely uncontaminated when swallowed, mostly aquatic organisms, to microplastics. tion: sooty specks from power plants, vehicle could help to remove pollutants from animal But their findings — that exposure might lead guts. Researchers still can’t agree on whether some organisms to reproduce less effectively pollutant-carrying microplastics are a signif- or suffer physical damage — are hard to inter- icant problem, says Jennifer Lynch, a marine pret because microplastics span many shapes, biologist affiliated with the US National sizes and chemical compositions, and many “It’s almost certain Institute of Standards and Technology in of the studies used materials that were quite that there is a level of Gaithersburg, Maryland. unlike those found in the environment. Perhaps the simplest mode of harm — when The tiniest specks, called nanoplastics — exposure in just about it comes to marine organisms, at least — might smaller than 1 micrometre — worry researchers all species.” be that organisms swallow plastic specks of no most of all (see ‘Microplastics to scale’). nutritional value, and don’t eat enough food to Some might be able to enter cells, potentially survive. Lynch, who also leads the Center for Marine Debris Research at Hawaii Pacific Uni- MICROPLASTICS TO SCALE versity in Honolulu, has autopsied sea turtles Biological objects Micro- and nanoplastics are of similar size to many that are found dead on beaches, looking at plas- Non-biological particles biological organisms, and become harder and more tics in their guts and chemicals in their tissues. expensive to analyse as they get smaller. Tools for analysis In 2020, her team completed a set of analyses Nanoplastics Microplastics for 9 hawksbill turtle hatchlings, under 3 weeks 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 10 mm old. One hatchling, only 9 centimetres long, had 42 pieces of plastic in its gastrointestinal Particles may cross blood–brain barrier Fish eggs and larvae tract. Most were microplastics. Unicellular marine algae “We don’t believe any of them died spe- , 1012–1047 (2020). , 1012–1047 May cross into cells 74 . cifically from plastics,” Lynch says. But she Human Alveoli Copepod (type macrophage of zooplankton) wonders whether the hatchlings might have Asbestos flakes struggled to grow as fast as they need to. “It’s Sand and sediment a very tough stage of life for those little guys.” APPL. SPECTROSC PM2.5* PM10 >1 mm . <1 m Naked eye Marine studies ET AL Py-GCMS‡ >100 µm ($200,000–300,000) Optical microscope ($700–3,000) Researchers have done the most work on >10–20 µm FTIR† (>$25,000) microplastic risks to marine organisms. >1 m Zooplankton, for instance, among the small- Micro-Raman spectroscopy (>$50,000) est marine organisms, grow more slowly and (Black or dark-coloured particles can’t be identified) reproduce less successfully in the presence of microplastics, says Penelope Lindeque, 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 10 mm a marine biologist at the Plymouth Marine Size Laboratory, UK: the animals’ eggs are smaller *Particulate matter less than 2.5 micrometres (PM2.5) or less than 10 µm (PM10) in diameter, often from soot, vehicle exhaust or dust; † ‡ SOURCE (TOOLS AND COSTS): S. PRIMPKE COSTS): AND (TOOLS SOURCE FTIR, Fourier-transform infrared spectroscopy; Py-GCMS, pyrolysis–gas chromatography–mass spectrometry. and less likely to hatch.

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