On a mild December evening in 2017,  Southern California’s powerful Santa Ana winds fueled a massive wildfire after smashing power lines together and carrying molten bits of metal onto the dry ground. 

The Thomas Fire, California’s largest at the time, ultimately torched 440 square miles and cost Ventura and Santa Barbara counties’ $3.5 billion agricultural industry nearly $200 million in damaged crops and buildings. 

Researchers are still tallying the impacts on farmworkers, who were especially hard hit by the smoke and falling ash, the stress of working near a raging fire and, in some cases, lost workdays. 

Exposure to wildfire smoke is a growing threat to farmworkers, many of whom are forced to toil through fires that are not just more frequent and severe but more toxic than ever. And as each year brings bigger and more destructive fires, scientists are scrambling to identify all the chemicals in smoke and the risks they pose. 

What’s in the smoke and how different chemical constituents harm health remain largely unknown, said Ilona Jaspers, director of the Center for Environmental Medicine, Asthma and Lung Biology at the University of North Carolina. 

“There’s a lot of research to be done to understand how climate change, wildfires and emissions mixtures really affect public health,” Jaspers said. “Every fire will have a slightly different emission profile because of what’s  burning and how it’s burning.”

Making matters worse, heat waves now coincide with the height of the California wildfire season, between summer and early fall—when the greatest number of farmworkers are out in the fields. Both smoke and heat exposures are expected to increase, adding urgency to researchers’ efforts to understand how these combined insults amplify workers’ risks.

But even when there’s not a heat wave or fire, farm work is one of the most dangerous and deadly jobs in America, said Lucas Zucker, policy and communications director for the advocacy group Central Coast Alliance United for a Sustainable Economy, or CAUSE. “It doesn’t require a disaster for a day working in the fields to result in injury or even death.”

Every day, about 100 agricultural workers sustain injuries that force them to miss work, according to the Centers for Disease Control and Prevention. 

To understand how climate-driven disasters affect farmworkers’ already precarious working conditions, Zucker and his colleagues interviewed workers after the Thomas Fire for a study published last year in Geoforum. 

As expected, the fire proved disastrous for many of these farmworkers, thanks to multiple factors that make them especially vulnerable. 

Most farmworkers in Ventura and Santa Barbara counties, like those in the rest of California, are undocumented, have no health or unemployment insurance and live paycheck to paycheck. Plus, more than 54,000 workers in the region speak only Mixteco, Zapoteco or other Indigenous languages with no written form, making them reliant on peers and community organizers to translate safety warnings about air quality, heat and pesticides.

Most also go home to crowded, substandard housing with no air conditioning, live in constant fear that they’ll get deported and worry about making enough to feed their families on “extremely low poverty wages,” Zucker said. 

Unable to afford to lose even a day’s pay, many worked without protective gear like N95 respirators, in dangerously unhealthy air, because heavy smoke lingered over the fields for several weeks. Others lost wages when farms temporarily ceased operations, then resumed work as soon as they could.

“When you’re paid $2 for a box of strawberries,” he said, “you work hard and fast, even at the cost of your own safety.”

One worker told Zucker she suffered from headaches and watery eyes because she worked without a mask as the Thomas Fire continued burning. Another told him, “We all got sick. Our throats closed in from breathing too much smoke.”

Getting a Handle on Smoke

The greatest health risk from wildfires comes from inhaling fine particles in smoke made up of burned materials. Fine particulate matter, or PM2.5, causes a range of harmful effects: It irritates the eyes, nose and lungs, aggravates asthma and other respiratory illnesses and increases the risk of death from lung cancer and heart disease. 

Fires are increasingly burning not just vegetation but everything from pesticides stored in sheds to houses, garages and all they contain. When a fire burns a house, said Jaspers of the University of North Carolina, it also burns plastic, fiberglass, plywood and often tires on cars. 

“All of a sudden, that’s potentially a lot more harmful than if you just had emissions from a burning brushfield,” she said. 

Earlier this year, Jaspers and her colleagues published what she called a “very introductory” analysis to identify mixtures of chemical emissions in smoke and link them to harmful effects through experiments in mice. 

The study, published in Science of the Total Environment, found that the temperature of a fire changes not just the degree of combustion but the chemical profiles and toxicity of the smoke. 

A controlled, smoldering fire appears to present far less risk than a roaring blaze, Jaspers said. “The problem starts when it’s no longer controlled, and it starts burning things you don’t want to have in there, like household materials.”

Understanding the health impacts of burning all these different materials is a major research focus now, Jaspers said. 

Wildfire smoke exposures have gotten so bad, so quickly, that the science is lagging behind the urgency to protect public health, she said. “We don’t know enough about the mixtures. We don’t know enough about the toxicity. We don’t know what the health effects are.”

What’s more, she said, current air quality regulations for smoke reflect only the levels of PM2.5, but not their contents. 

And, it turns out, the assumption that all PM2.5 sources carry the same risk is wrong.

The first study to assess how PM2.5 from wildfire smoke affects public health, published in Nature Communications in March, analyzed respiratory hospitalizations in Southern California over 14 years between September and May, when the Santa Ana winds typically fuel the biggest wildfires.

Respiratory hospitalizations attributed to wildfire smoke were 10 times higher than those attributed to “regular” bad air days, the researchers found, suggesting that wildfire particle pollution is substantially more harmful than particulates from other sources.

Scientists are just beginning to figure out why, but emerging evidence suggests that wildfire particulates are especially toxic to immune cells in the lungs.

Farmworkers routinely wear cloth masks or bandannas to keep out dust and pesticides. But they don’t protect against the fine particles in smoke. 

Two years after the Thomas Fire, California passed an emergency regulation that established new requirements to protect workers from wildfire smoke. Employers must make N95 respirators available to workers when the air quality index, or AQI, for PM2.5 exceeds 150 on a 500-point scale, a level considered “unhealthy.” But the state requires their use only when the levels are more than three times those deemed unhealthy. 

Though farmworkers are routinely exposed to high levels of toxic pesticides that often drift from fields to nearby communities, so far no studies have looked for pesticides and their derivatives in smoke. 

Occupational health expert Anne Katten is less worried about fires burning pesticide residues on crops than, say, igniting a pesticide storage shed. Even more troubling, said Katten, who directs the Pesticide and Worker Safety Project for the California Rural Legal Assistance Foundation, would be if workers inhaled wildfire smoke and pesticides that harm the airways at the same time. That would likely compound the health impacts, she said.

That may be why wildfire smoke triggered more severe disease in people exposed to the coronavirus. Fine particulate pollutants from smoke from last year’s wildfires, the worst in California’s history, may have led to thousands more cases and deaths from the disease, Harvard University researchers reported in August. 

The high levels of particle pollution produced by the wildfires, the researchers wrote, “substantially exacerbated the health burden of Covid-19.”

California’s Latino food and agricultural workers, who were deemed “essential” and continued working during the pandemic, had a nearly 60 percent increased risk of dying from Covid-19 compared to other residents, researchers from the University of California, San Francisco, reported in June. 

The study did not consider whether exposure to wildfire smoke contributed to their risk.

Boosting Resilience

A warming world will become an ever more dangerous world for farmworkers.

Agricultural workers face a 20- to 35-fold risk of heat-related deaths compared to other occupations. Hotter temperatures also greatly increase the risk of injury on the job, researchers with the Institute of Labor Economics reported in July. 

A warming world is also proving more costly for farmworkers.

Federico Castillo, an environmental and agricultural economist at the University of California, Berkeley, has been interviewing farmworkers about the ways heat has disrupted their lives. He found that, on average, workers lost about 12 days of work a year to dangerous heat. “Twelve days of work translates into 12 days that they don’t earn money,” Castillo said. 

That, in turn, translates into less money to feed their kids, pay bills and send to relatives in Mexico or Central America.

U.S. farmworkers are expected to see double the average number of unsafe conditions from extreme heat by midcentury, University of Washington researchers warned last year. Heat extremes will be highest in California’s Imperial County, near the Mexican border, exceeding 115 degrees Fahrenheit, which federal regulators consider a “very high/extreme” risk level.

Even without climate change, there are already problems with lack of access to drinking water and shade in the fields, said Zucker. “Add in more and more extreme heat waves, and those kinds of inadequate safety measures at facilities become much more deadly.”

In the Salinas Valley, known as the nation’s salad bowl for its fields of lettuce and leafy greens, workers are taking matters into their own hands.

“Workers are starting earlier and earlier in the day because of the heat, trying to make good use of the early morning hours, so they’re not working in the peak periods of sunshine,” said Brenda Eskenazi, emeritus professor of maternal and child health and epidemiology at the University of California, Berkeley, School of Public Health. 

But Eskenazi, a pioneer in documenting health risks to farmworkers and their families, is worried about how such adjustments are affecting workers’ children.

If mothers and fathers have to leave at three in the morning to get to the fields, Eskenazi said, who takes care of the kids? “I’m really concerned about that, but I don’t know anybody who’s studied that.”

Researchers have only just started to look at combined exposures to heat and wildfire smoke, but early results are worrying. In a study of agricultural workers in Washington State, published last year, the highest concentrations of wildfire PM2.5 tended to coincide with high heat in counties with the largest farmworker populations, during peak harvest season. 

That’s especially concerning, advocates for farmworkers say, because extreme heat makes wearing N95 masks even more uncomfortable.

Imagine doing hard manual labor outdoors for 10 hours in severe wildfire smoke, even when it’s not hot, said CAUSE’s Zucker. “That mask is drenched in sweat in an hour.”

A lot of people take off their masks because they’re just trying to get through the day, he said. “They’re not thinking about the long-term impacts of cancer or respiratory illness. They may not even know about that.”

When workers are paid by how many boxes of strawberries or crates of parsley they pick, their main focus tends to be on working as quickly as possible.

“Paying by the piece is conducive to all kinds of what we might think is irrational behavior, like spending too long in the fields when it’s hot,” said UC Berkeley’s Castillo. “But that in the end is rational given that the payment is piece-rate.”

Climate change has laid bare the injustices we expect farmworkers to endure, Zucker said.

“When people lose work, there’s a huge part of the population that has nothing to fall back on, no unemployment benefits, no safety net to keep a roof over their head or their kids fed,” he said.

Extreme weather crises, combined with no safety net, Zucker said, encourages workers who are already living on the edge to take more risks to do whatever they have to do to survive.

“The exclusion of undocumented people from the safety net in this country is one of the most dangerous problems that we have in terms of climate resilience,” he said. 

Undocumented workers need unemployment insurance so they can make ends meet when working conditions are too dangerous, or there’s nothing to harvest in the winter. He pointed to New York, which in April became the first state to offer the equivalent of unemployment benefits to undocumented workers affected by the pandemic.

“That would make our communities more resilient to climate change,” Zucker said, “and just more resilient in general.”

Castillo worries that the public and policymakers will accept extreme weather as the new normal, just as they did with housing conditions.

For years advocates have fought to reform minimal standards that allow farmworkers to live in dilapidated, crowded heat traps, with lead paint and subpar plumbing, Castillo said. Overcrowding also contributed to workers’ heightened risk of dying from Covid-19.

Improving living conditions would be a game changer for their health, Castillo said, yet they’re as deplorable as ever. 

“I’m afraid the same thing might happen with climate change and heat waves and wildfires,” Castillo said.

For Eskenazi, the biggest priority right now is making sure workers get Covid-19 booster shots. She hopes the pandemic has made people more aware of the plight of farmworkers.
“I’m an eternal optimist,” she said. “I’m hoping that it’s managed to pull back the curtain on everything that’s been wrong up till now, and that people who may not have cared so much are caring more now.”