Health & Medicine

Tiny particles of plastic have been found everywhere — from the deepest place on the planet, the Mariana Trench, to the top of Mount Everest. And now more and more studies are finding that microplastics, defined as plastic pieces less than 5 millimeters across, are also in our bodies.

“What we are looking at is the biggest oil spill ever,” says Maria Westerbos, founder of the Plastic Soup Foundation, an Amsterdam-based nonprofit advocacy organization that works to reduce plastic pollution around the world. Nearly all plastics are made from fossil fuel sources. And microplastics are “everywhere,” she adds, “even in our bodies.”

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In recent years, microplastics have been documented in all parts of the human lung, in maternal and fetal placental tissues, in human breast milk and in human blood. Microplastics scientist Heather Leslie, formerly of Vrije Universiteit Amsterdam, and colleagues found microplastics in blood samples from 17 of 22 healthy adult volunteers in the Netherlands. The finding, published last year in Environment International, confirms what many scientists have long suspected: These tiny bits can get absorbed into the human bloodstream.

“We went from expecting plastic particles to be absorbable and present in the human bloodstream to knowing that they are,” Leslie says.

The findings aren’t entirely surprising; plastics are all around us. Durable, versatile and cheap to manufacture, they are in our clothes, cosmetics, electronics, tires, packaging and so many more items of daily use. And the types of plastic materials on the market continues to increase. “There were around 3,000 [plastic materials] when I started researching microplastics over a decade ago,” Leslie says. “Now there are over 9,600. That’s a huge number, each with its own chemical makeup and potential toxicity.”

Though durable, plastics do degrade, by weathering from water, wind, sunlight or heat — as in ocean environments or in landfills — or by friction, in the case of car tires, which releases plastic particles along roadways during motion and braking.

In addition to studying microplastic particles, researchers are also trying to get a handle on nanoplastics, particles which are less than 1 micrometer in length. “The large plastic objects in the environment will break down into micro- and nanoplastics, constantly raising particle numbers,” says toxicologist Dick Vethaak of the Institute for Risk Assessment Sciences at Utrecht University in the Netherlands, who collaborated with Leslie on the study finding microplastics in human blood.

Nearly two decades ago, marine biologists began drawing attention to the accumulation of microplastics in the ocean and their potential to interfere with organism and ecosystem health (SN: 2/20/16, p. 20). But only in recent years have scientists started focusing on microplastics in people’s food and drinking water — as well as in indoor air.

Plastic particles are also intentionally added to cosmetics like lipstick, lip gloss and eye makeup to improve their feel and finish, and to personal care products, such as face scrubs, toothpastes and shower gels, for the cleansing and exfoliating properties. When washed off, these microplastics enter the sewage system. They can end up in the sewage sludge from wastewater treatment plants, which is used to fertilize agricultural lands, or even in treated water released into waterways.

What if any damage microplastics may do when they get into our bodies is not clear, but a growing community of researchers investigating these questions thinks there is reason for concern. Inhaled particles might irritate and damage the lungs, akin to the damage caused by other particulate matter. And although the composition of plastic particles varies, some contain chemicals that are known to interfere with the body’s hormones.

Currently there are huge knowledge gaps in our understanding of how these particles are processed by the human body.

How do microplastics get into our bodies?

Research points to two main entry routes into the human body: We swallow them and we breathe them in.

Evidence is growing that our food and water is contaminated with microplastics. A study in Italy, reported in 2020, found microplastics in everyday fruits and vegetables. Wheat and lettuce plants have been observed taking up microplastic particles in the lab; uptake from soil containing the particles is probably how they get into our produce in the first place.

Sewage sludge can contain microplastics not only from personal care products, but also from washing machines. One study looking at sludge from a wastewater treatment plant in southwest England found that if all the treated sludge produced there were used to fertilize soils, a volume of microplastic particles equivalent to what is found in more than 20,000 plastic credit cards could potentially be released into the environment each month.

On top of that, fertilizers are coated with plastic for controlled release, plastic mulch film is used as a protective layer for crops and water containing microplastics is used for irrigation, says Sophie Vonk, a researcher at the Plastic Soup Foundation.

“Agricultural fields in Europe and North America are estimated to receive far higher quantities of microplastics than global oceans,” Vonk says.

A recent pilot study commissioned by the Plastic Soup Foundation found microplastics in all blood samples collected from pigs and cows on Dutch farms, showing livestock are capable of absorbing some of the plastic particles from their feed, water or air. Of the beef and pork samples collected from farms and supermarkets as part of the same study, 75 percent showed the presence of microplastics. Multiple studies document that microplastic particles are also in fish muscle, not just the gut, and so are likely to be consumed when people eat seafood.

Microplastics are in our drinking water, whether it’s from the tap or bottled. The particles may enter the water at the source, during treatment and distribution, or, in the case of bottled water, from its packaging.

Results from studies attempting to quantify levels of human ingestion vary dramatically, but they suggest people might be consuming on the order of tens of thousands of microplastic particles per person per year. These estimates may change as more data come in, and they will likely vary depending on people’s diets and where they live. Plus, it is not yet clear how these particles are absorbed, distributed, metabolized and excreted by the human body, and if not excreted immediately, how long they might stick around.

Babies might face particularly high exposures. A small study of six infants and 10 adults found that the infants had more microplastic particles in their feces than the adults did. Research suggests microplastics can enter the fetus via the placenta, and babies could also ingest the particles via breast milk. The use of plastic feeding bottles and teething toys adds to children’s microplastics exposure.

Microplastic particles are also floating in the air. Research conducted in Paris to document microplastic levels in indoor air found concentrations ranging from three to 15 particles per cubic meter of air. Outdoor concentrations were much lower.

Airborne particles may turn out to be more of a concern than those in food. One study reported in 2018 compared the amount of microplastics present within mussels harvested off Scotland’s coasts with the amount of microplastics present in indoor air. Exposure to microplastic fibers from the air during the meal was far higher than the risk of ingesting microplastics from the mussels themselves.

Extrapolating from this research, immunologist Nienke Vrisekoop of the University Medical Center Utrecht says, “If I keep a piece of fish on the table for an hour, it has probably gathered more microplastics from the ambient air than it has from the ocean.”

What’s more, a study of human lung tissue reported last year offers solid evidence that we are breathing in plastic particles. Microplastics showed up in 11 of 13 samples, including those from the upper, middle and lower lobes, researchers in England reported.

Perhaps good news: Microplastics seem unable to penetrate the skin. “The epidermis holds off quite a lot of stuff from the outside world, including [nano]particles,” Leslie says. “Particles can go deep into your skin, but so far we haven’t observed them passing the barrier, unless the skin is damaged.”

What do we know about the potential health risks?

Studies in mice suggest microplastics are not benign. Research in these test animals shows that lab exposure to microplastics can disrupt the gut microbiome, lead to inflammation, lower sperm quality and testosterone levels, and negatively affect learning and memory.

But some of these studies used concentrations that may not be relevant to real-world scenarios. Studies on the health effects of exposure in humans are just getting under way, so it could be years before scientists understand the actual impact in people.

Immunologist Barbro Melgert of the University of Groningen in the Netherlands has studied the effects of nylon microfibers on human tissue grown to resemble lungs. Exposure to nylon fibers reduced both the number and size of airways that formed in these tissues by 67 percent and 50 percent, respectively. “We found that the cause was not the microfibers themselves but rather the chemicals released from them,” Melgert says.

“Microplastics could be considered a form of air pollution,” she says. “We know air pollution particles tend to induce stress in our lungs, and it will probably be the same for microplastics.”

Vrisekoop is studying how the human immune system responds to microplastics. Her unpublished lab experiments suggest immune cells don’t recognize microplastic particles unless they have blood proteins, viruses, bacteria or other contaminants attached. But it is likely that such bits will attach to microplastic particles out in the environment and inside the body.

“If the microplastics are not clean … the immune cells [engulf] the particle and die faster because of it,” Vrisekoop says. “More immune cells then rush in.” This marks the start of an immune response to the particle, which could potentially trigger a strong inflammatory reaction or possibly aggravate existing inflammatory diseases of the lungs or gastrointestinal tract.

A study reported last year identified microplastic particles in 11 of 13 samples of human lung tissue (examples shown). The plastics were found throughout the lungs, and their presence suggests that inhalation is one route for the particles to enter the body.L.C. JENNER ET AL/SCIENCE OF THE TOTAL ENVIRONMENT 2022

Some of the chemicals added to make plastic suitable for particular uses are also known to cause problems for humans: Bisphenol A, or BPA, is used to harden plastic and is a known endocrine disruptor that has been linked to developmental effects in children and problems with reproductive systems and metabolism in adults (SN: 7/18/09, p. 5). Phthalates, used to make plastic soft and flexible, are associated with adverse effects on fetal development and reproductive problems in adults along with insulin resistance and obesity. And flame retardants that make electronics less flammable are associated with endocrine, reproductive and behavioral effects.

“Some of these chemical products that I worked on in the past [like the polybrominated diphenyl ethers used as flame retardants] have been phased out or are prohibited to use in new products now [in the European Union and the United States] because of their neurotoxic or disrupting effects,” Leslie says.

What are the open questions?

The first step in determining the risk of microplastics to human health is to better understand and quantify human exposure. Polyrisk — one of five large-scale research projects under CUSP, a multidisciplinary group of researchers and experts from 75 organizations across 21 European countries studying micro- and nanoplastics — is doing exactly that.

Immunotoxicologist Raymond Pieters, of the Institute for Risk Assessment Sciences at Utrecht University and coordinator of Polyrisk, and colleagues are studying people’s inhalation exposure in a number of real-life scenarios: near a traffic light, for example, where cars are likely to be braking, versus a highway, where vehicles are continuously moving. Other scenarios under study include an indoor sports stadium, as well as occupational scenarios like the textile and rubber industry.

Melgert wants to know how much microplastic is in our houses, what the particle sizes are and how much we breathe in. “There are very few studies looking at indoor levels [of microplastics],” she says. “We all have stuff in our houses — carpets, insulation made of plastic materials, curtains, clothes — that all give off fibers.”

Vethaak, who co-coordinates MOMENTUM, a consortium of 27 research and industry partners from the Netherlands and seven other countries studying microplastics’ potential effects on human health, is quick to point out that “any measurement of the degree of exposure to plastic particles is likely an underestimation.” In addition to research on the impact of microplastics, the group is also looking at nanoplastics. Studying and analyzing these smallest of plastics in the environment and in our bodies is extremely challenging. “The analytical tools and techniques required for this are still being developed,” Vethaak says.

Vethaak also wants to understand whether microplastic particles coated with bacteria and viruses found in the environment could spread these pathogens and increase infection rates in people. Studies have suggested that microplastics in the ocean can serve as safe havens for germs.

Alongside knowing people’s level of exposure to microplastics, the second big question scientists want to understand is what if any level of real-world exposure is harmful. “This work is confounded by the multitude of different plastic particle types, given their variations in size, shape and chemical composition, which can affect uptake and toxicity,” Leslie says. “In the case of microplastics, it will take several more years to determine what the threshold dose for toxicity is.”

Several countries have banned the use of microbeads in specific categories of products, including rinse-off cosmetics and toothpastes. But there are no regulations or policies anywhere in the world that address the release or concentrations of other microplastics — and there are very few consistent monitoring efforts. California has recently taken a step toward monitoring by approving the world’s first requirements for testing microplastics in drinking water sources. The testing will happen over the next several years.

Pieters is very pragmatic in his outlook: “We know ‘a’ and ‘b,’” he says. “So we can expect ‘c,’ and ‘c’ would [imply] a risk for human health.”

He is inclined to find ways to protect people now even if there is limited or uncertain scientific knowledge. “Why not take a stand for the precautionary principle?” he asks.

For people who want to follow Pieters’ lead, there are ways to reduce exposure.

“Ventilate, ventilate, ventilate,” Melgert says. She recommends not only proper ventilation, including opening your windows at home, but also regular vacuum cleaning and air purification. That can remove dust, which often contains microplastics, from surfaces and the air.

Consumers can also choose to avoid cosmetics and personal care products containing microbeads. Buying clothes made from natural fabrics like cotton, linen and hemp, instead of from synthetic materials like acrylic and polyester, helps reduce the shedding of microplastics during wear and during the washing process.

Specialized microplastics-removal devices, including laundry balls, laundry bags and filters that attach to washing machines, are designed to reduce the number of microfibers making it into waterways.

Vethaak recommends not heating plastic containers in the microwave, even if they claim to be food grade, and not leaving plastic water bottles in the sun.

Perhaps the biggest thing people can do is rely on plastics less. Reducing overall consumption will reduce plastic pollution, and so reduce microplastics sloughing into the air and water.

Leslie recommends functional substitution: “Before you purchase something, think if you really need it, and if it needs to be plastic.”

Westerbos remains hopeful that researchers and scientists from around the world can come together to find a solution. “We need all the brainpower we have to connect and work together to find a substitute to plastic that is not toxic and doesn’t last [in the environment] as long as plastic does,” she says. More

The lungs’ immune defenses can wane with age, leaving older adults more susceptible to lung damage and severe bouts of respiratory infections. New research reveals one reason why this might happen: Inhaled particulate matter from pollution gunks up the works over time, weakening the lungs’ immune system, researchers report online November 21 in Nature Medicine.

Air pollution is a major cause of disease and early death worldwide and disproportionately impacts poor and marginalized communities (SN: 7/30/20). Particulate matter — a type of pollution emitted from vehicle exhaust, power plants, wildfires and other sources —  has been tied to health harms including respiratory, cardiovascular and neurological diseases (SN: 9/19/17).

In the new study, researchers from Columbia University analyzed lung immune tissue from 84 organ donors, ranging in age from 11 to 93 years old. The donors were nonsmokers or had no history of heavy smoking. With age, the lungs’ lymph nodes — which filter foreign substances and contain immune cells — became loaded with particulate matter, turning them a deep onyx, the research team found.

“If the [lymph nodes] build up with so much material, then they can’t do their job,” says Elizabeth Kovacs, a cell biologist who studies inflammation and injury at the University of Colorado Anschutz Medical Campus in Aurora.

The lymph nodes are home to an array of immune cells, including macrophages. These cellular Pac-Mans gobble up pathogens and other debris, including the particulate matter. Filled with the pollutant, the macrophages’ production of cytokines, proteins the cells secrete to activate other immune cells, decreased. The cells also showed signs of having a diminished capacity for more gobbling.

The new study indicates that older people have accumulated so much debris, “they may not be able to accumulate more,” impairing their ability to deal with inhaled material, says Kovacs, who was not involved in the research.

Pollution “is an ongoing and growing threat to the health and livelihood of the world’s population,” the research team writes. Their work finds that threat includes “a chronic and ubiquitous impact” on respiratory immunity with age. More

After a relaxing day at the Jersey Shore last July, Jessica Reeder and her son and daughter headed back home to Philadelphia. As they crested a bridge from New Jersey into Pennsylvania, they were greeted with a hazy, yellow-gray sky. It reminded Reeder of the smoky skies she saw growing up in Southern California on days when fires burned in the dry canyons.

Smelling smoke and worried about her asthma and her kids, Reeder flipped the switch to recirculate the air inside the car instead of drawing from the outside. At home, the family closed all the windows and turned their air purifiers on high.

The smoke had traveled from fires raging on the other side of the continent, in the western United States and Canada. Although air quality in Philadelphia didn’t come close to the record-bad air quality that some western cities experienced, it was bad enough to trigger air quality warnings — and not just for people with asthma or heart problems.

Most large U.S. wildfires occur in the West. But the smoke doesn’t stay there. It travels eastward, affecting communities hundreds to thousands of kilometers away from the fires. In fact, the majority of asthma-related deaths and emergency room visits attributed to fire smoke in the United States occur in eastern cities, according to a study in the September 2021 GeoHealth.

Smoke poured into the eastern United States and Canada from wildfires in the West on July 21, 2021 (darker red is denser smoke). Residents of eastern cities received code orange and code red warnings that air quality was unhealthy.Joshua Stevens/NASA Earth Observatory

The big problem is fine particulate matter, tiny particles also known as PM2.5. These bits of ash, gases and other detritus suspended in smoke are no more than 2.5 micrometers wide, small enough to lodge in the lungs and cause permanent damage. PM2.5 exacerbates respiratory and cardiovascular problems and can lead to premature death. The particles can also cause asthma and other chronic conditions in otherwise healthy adults and children.

Over the last few decades, U.S. clean air regulations have cut down on particulate matter from industrial pollution, so the air has been getting cleaner, especially in the populous eastern cities. But the regulations don’t address particulate matter from wildfire smoke, which recent studies show is chemically different from industrial air pollution, potentially more hazardous to humans and increasing significantly.

So far, a lot of the research on how wildfire PM2.5 can make people sick has been based on people living or working near fires in the West. Now, researchers are turning their attention to how PM2.5 from smoke affects the big population centers in the East, far from the wildfires. One thing is clear: With the intensity and frequency of wildfires increasing due to climate change (SN: 12/19/20 & 1/2/21, p. 32), people across North America need to be concerned about the health impacts, says Katelyn O’Dell, an atmospheric scientist at George Washington University in Washington, D.C.

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Bad air travels

Air pollution regulations limit PM2.5 from exhaust-emitting cars and trucks and fossil fuel–burning factories and power plants. These regulations have done “a really good job” reducing anthropogenic air pollution in the last couple of decades, says Rosana Aguilera, an environmental scientist at the Scripps Institution of Oceanography in La Jolla, Calif. In the United States, concentrations of six of the most common air pollutants have dropped by 78 percent since the Clean Air Act of 1970, according to the U.S. Environmental Protection Agency. PM2.5 concentrations have come down as well — at least until recently.

Western wildfires, which are growing more frequent, more severe and larger, are erasing some of the gains made in reducing industrial pollution, says Rebecca Buchholz, an atmospheric chemist at the National Center for Atmospheric Research in Boulder, Colo.

Fires in the Pacific Northwest are “driving an upward trend” in particulate matter air pollution, Buchholz and colleagues wrote April 19 in Nature Communications. Such smoke pollution peaks in August when fires in the region tend to spike and the atmosphere’s ability to clean itself through, say, rain, is limited. This spike of late-summer air pollution is new, Buchholz says. It’s especially noticeable since 2012.

New York City, visible through hazy skies in September 2020, and many places in the East have seen some of the worst air quality in decades due to fires burning in the U.S. West and in Canada. Such fires are increasing in intensity and frequency.Gary Hershorn/Getty Images plus

And, as Reeder and her family experienced last year, transported wildfire pollution is causing substantial particulate matter spikes in the central United States and northeastern North America, Buchholz and colleagues found. Pacific Northwest wildfires thus “have the potential to impact surface air quality, even at large distances downwind of the wildfires,” the team wrote, putting some 23 million people in the central United States and 72 million in northeastern North America at increased risk of health impacts from the imported wildfire smoke.

How far and where PM2.5 travels depends on weather patterns and how high wildfire smoke reaches — the stronger the fire, the longer it can last and the farther smoke can go, and thus the farther particulate matter can reach. Last year, far-away wildfires created unhealthy air quality conditions in locations from the Great Plains to New York City and Washington, D.C.

New York City saw some of its worst air quality in two decades. Philadelphia had two “code red” days — meaning air quality was unhealthy for all — because of the U.S. West and Canadian fires. In 2019, 2020 and 2021, those fires pushed PM2.5 to unhealthy levels in much of Minnesota. In fact, a 2018 study showed that wildfire smoke plumes now waft above Minnesota for eight to 12 days per month between June and September.

Human impacts

Smoke in the West is already having a tangible effect on human health in the East, says O’Dell, lead author of the 2021 GeoHealth study.

Reviewing smoke and health data from 2006 to 2018, O’Dell and colleagues found that more people visit emergency rooms and are hospitalized in the East than in the West from asthma problems attributable to smoke PM2.5. Asthma-related ER visits and hospitalizations were higher east of the Rockies in 11 of the 13 years.

Over the study period, an average of 74 percent of asthma-related deaths and 75 percent of asthma ER visits and hospitalizations attributable to smoke occurred east of the Rockies. Of the estimated 6,300 excess deaths from asthma complications due to smoke PM2.5 that occurred annually over the study period, more than 4,600 were in the East.

Smoke affects so many more people in the East primarily because more people live there, O’Dell notes. Her team defined “West” as west of the Rockies, with a population of 64 million, and “East” as east of the Rockies, home to 226 million people. In the West, smoke PM2.5 causes a higher portion of regional asthma deaths. In the East, it’s a lower portion of the total population, but a far higher total number of people affected.

“We may be already seeing the consequences of these fires on the health of residents who live hundreds or even thousands of miles downwind,” Buchholz said in a press release.

Vulnerable youth

“Asthma is a very widespread, common health condition,” says Yang Liu, an environmental scientist at Emory University in Atlanta. In the United States, about 25 million people have asthma, or 8 percent of adults and 7 percent of children, according to the U.S. Centers for Disease Control and Prevention.

Fine particulate matter can spark asthma attacks, but it can also be a danger to people without the condition. Children are especially vulnerable primarily because of physiology. Children breathe faster so they end up taking in more particulate matter, plus their lungs are smaller so more of their lung surface is likely to be damaged when they breathe in particulate matter. And their lungs are still developing, says Jennifer Stowell, an environmental epidemiologist at Boston University School of Public Health.

Stowell led a study, reported in the January Environmental Research Letters, estimating how much wildfire smoke will exacerbate asthma attacks in the West. Stowell, Liu and colleagues estimate that, in the 2050s, there will be an additional 155,000 asthma-related ER visits and hospitalizations per wildfire season in the West just from smoke PM2.5. The biggest concern, Stowell says, is for children and younger adults.

Aguilera, of Scripps, and her colleagues found associations between wildfire-specific PM2.5 and pediatric respiratory-related ER and urgent care visits. In San Diego County from 2011 to 2017, wildfire-specific PM2.5 was 10 times as harmful to respiratory health in children 5 and younger as ambient PM2.5, the researchers reported in 2021 in Pediatrics. In fact, the same increase in levels of PM2.5 from smoke versus ambient sources caused a 26 percent higher rate of ER or urgent care visits. The researchers didn’t note whether the children had preexisting asthma.

And even when a wildfire increased PM2.5 by a small amount, respiratory ER and urgent care visits in kids 12 and under increased, Aguilera and colleagues reported in 2020 in the Annals of the American Thoracic Society. “Even relatively smaller wildfires can still generate quite an impact on the pediatric population,” Aguilera says. “And really, any amount of PM or air pollution is harmful.”

Studies of nonhuman primates have also shown permanent effects of smoke on the young — results researchers expect would also apply to humans, given genetic similarities. In 2008, a group of infant rhesus macaques at the California National Primate Research Center at the University of California, Davis was exposed to high PM2.5 levels from a series of devastating wildfires in Northern California. Researchers have been comparing those monkeys with macaques born a year later that weren’t exposed to smoke.

At the California National Primate Research Center, rhesus macaques that were exposed to wildfire smoke early in life have immune disorders, nervous system changes and weakened lungs. © 2014 Kathy West/California National Primate Research Center/UC Davis

At around age 3, macaques exposed to smoke displayed immune disorders and reduced lung capacity, lung function and lung volume, says Hong Ji, a molecular biologist at UC Davis and the primate center who wasn’t involved with this study. The lungs look like they had fibrosis, Ji says. “Early life smoke exposure … changed the trajectory of lung development,” and it doesn’t appear to be reversible, she says.

The monkeys exposed to wildfire PM2.5 also have important changes to how their DNA works, Ji and colleagues reported in the January Environment International. Exposure to wildfire smoke in infancy can cause life-altering, long-term changes to the monkeys’ nervous and immune systems, as well as brain development, Ji says. Even worse, she says, the DNA changes are the type that can be passed down and may result in generational damage.

Even macaques born after in utero exposure to wildfire smoke can suffer cognitive, immune and hormone problems, primate center researchers reported April 1 in Nature Communications.

Now, Ji and colleagues have teamed with Rebecca Schmidt, a molecular epidemiologist at UC Davis who’s leading a study on the effects of wildfire smoke exposure on pregnant women and young children. This research group, as well as other teams, is also looking into whether PM2.5 is causing genetic changes to babies exposed to smoke in utero, Ji says. The more results gathered on the effects of wildfire PM2.5 on babies and children — and even in pregnancy — the more dangerous we realize it is, Ji says.

Chemical differences

Particulate matter changes as it travels through the atmosphere, both in volume and in chemistry. Some PM2.5 is emitted directly from fires, and some is born from chemicals and trace gases emitted from fires that get chemically processed in the atmosphere, Buchholz says. Reactions that happen in the smoke plume, combined with sunlight, can create even more PM2.5 downwind of the fires. How these particulates change chemically — through interactions between the atmosphere and the particulate matter, and between fire pollution and human pollution — and what that means for human health “is a really active area of research right now,” she says. “It’s super complicated.”

Epidemiological and atmospheric chemistry studies indicate that wildfire PM2.5 is more hazardous to human health than ambient PM2.5, says Stowell, the Boston epidemiologist. One such study compared particulate matter from Amazonian fires with urban sources such as vehicle exhaust in Atlanta. Nga Lee Ng, an atmospheric chemist at Georgia Tech, and colleagues found that smoke particulate matter is more toxic than urban particulate matter, “inducing about five times higher cellular oxidative stress,” Ng says. Oxidative stress damages cells and DNA in the body.

In addition, as smoke travels through the atmosphere and ages, it seems to become even more toxic, Ng says. Reactions between the particulate matter and sunlight and atmospheric gases change the particulate matter’s chemical and physical properties, rendering it even more potentially harmful. So, even though particulate matter dissipates over time and distance, “the health effects per gram are greater,” says Daniel Jaffe, an atmospheric chemist at the University of Washington Bothell.

That means that the studies of health effects near wildfires in the West may not represent the full story of how smoke from distant fires affects people in the East.

Liu, at Emory, hopes to see the U.S. government revisit policies related to what PM2.5 levels are dangerous, since they’re based on ambient and not wildfire-related PM2.5. In March, an EPA advisory panel recommended just that. In a letter to the agency, the Clean Air Scientific Advisory Committee wrote: “Regarding the annual PM2.5 standard, all CASAC members agree that the current level of the annual standard is not sufficiently protective of public health and should be lowered.” The committee added, “There is substantial epidemiologic evidence from both morbidity and mortality studies that the current standard is not adequately protective.”

Local communities throughout the country need to determine when to close schools or at least keep kids inside, Liu says, as well as when to advise people to close windows and turn on air purifiers. Good masks — N95 and KN95 — can help too (yes, masks that block viruses can also block particulate matter).

City, county and state governments also need to prepare the health care system to respond to increased asthma issues, Liu says. Some states are starting to respond. In 2017, for example, the Minnesota Pollution Control Agency increased its air quality monitoring stations around the state from two to 18. The agency is also working with the National Weather Service, the Minnesota Department of Health and the Minnesota Department of Transportation to better communicate air quality warnings.

Minnesota, after experiencing a rise in smoky summer days, has added extra air quality monitoring stations to improve local forecasts.Minnesota Pollution Control Agency

In the meantime, much more research is needed into the human health implications of increasing wildfire smoke, Buchholz says, as well as the chemical interactions in the atmosphere, how climate is changing fires, how fires change year after year, and how they impact the atmosphere, not to mention how different trees, buildings and other fuels affect particulate matter.

“Wildfires are perhaps one of the most visible ways that [climate change] is linked to health,” Stowell says. And the reality is, she says, “we’re going to see it remain as bad or worse for a while.” More

Not all air is created equal. 
While air quality has improved across the United States in recent decades, significant disparities persist in terms of who breathes the worst air. Communities exposed to the most air pollution in the 1980s — often poor and with high proportions of Black and Hispanic residents — are largely in the same position today, researchers report in the July 31 Science.
Lots of different pollutants can clog the air, but scientists are especially interested in particulate matter less than 2.5 microns in diameter. Called PM2.5, the tiny particles are associated with myriad health problems, including cardiovascular disease, respiratory illness, diabetes and neurological problems (SN: 9/19/17). 
Marginalized communities, often closer to factories or major roadways than whiter, wealthier communities, bear the brunt of PM2.5 pollution. That exposure contributes to stark racial health inequities in the United States. “There hasn’t been clear documentation of how these disparities have evolved over time,” says Jonathan Colmer, an economist at the University of Virginia in Charlottesville. The U.S. Environmental Protection Agency only began measuring PM2.5 in 1999. Addressing current inequities requires an understanding of the past, Colmer says.

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He and colleagues estimated annual average PM2.5 levels for each square kilometer in the country from 1981 to 2016 using published data derived from satellites and simulations of pollutant movement through space. The team then mapped those estimates onto about 65,000 census tracts to rank neighborhoods from most to least polluted annually, and noted how rankings changed over time. 
Whereas average PM2.5 concentrations decreased by 70 percent across the entire country, the relative ranking of neighborhoods hardly budged.
On average, whiter, more affluent neighborhoods were less polluted throughout the 36-year time frame. Disadvantaged neighborhoods with more Black or Hispanic people remained more polluted, despite experiencing a larger absolute drop in PM2.5 levels.
“It’s really good news that air pollution is dropping for everyone,” says Anjum Hajat, an epidemiologist at the University of Washington in Seattle who wasn’t involved in the research. But even relatively low levels of pollution pose significant health risks, and the reductions might not translate to improved health for the hardest-hit communities. “To me, the take-home message is that inequity is very stubborn.”
The study wasn’t designed to address why these inequities persist, though a move away from manufacturing or coal production was associated with air quality improvements in certain neighborhoods. 
More important, Hajat says, is power structure. “The communities that were the most marginalized and had the least political power in the 1980s are likely the same communities that continue to have the least power today.”
White, wealthy communities have been able to prevent polluting facilities from being placed in their communities, she says, while marginalized communities often haven’t had this power. To see real change, “marginalized communities need to be included in discussions about their future,” she says, for instance through community members holding decision-making roles. More