Take in the fireworks this Fourth of July weekend and you’ll witness the results of centuries of chemical innovation. Gunpowder goes boom, sure, but modern fireworks use a wide range of metals to produce all those colors. Metals naturally oxidize when exposed to air, but they oxidize rapidly and intensely when gunpowder supplies a sudden burst of oxygen, making the burning metals throw off light. In an exploding firework, lithium makes red, sodium makes yellow, and aluminum makes silver.
It’s all fun and games until a firework manufacturer starts tossing in illicit metals that make toxic smoke, like lead. Tainted pyrotechnics may be more common than you think: Writing yesterday in the journal Particle and Fibre Toxicology, researchers showed that the smoke from some common consumer fireworks is toxic to both human respiratory tract cells and to mouse test subjects. They sampled 10 different products—two in duplicate—and found that smoke from two of the 12 fireworks contained lead. Five of the 10 different products produced smoke that caused the human cells significant oxidative stress, a common theory as to how particles damage the lung.
“I was surprised by the level of metals in the particles,” says coauthor Terry Gordon, who studies respiratory health at the NYU School of Medicine. “One had a super high level, 40,000 [parts per million] lead, which was just totally unexpected, very high.”
This probably isn’t the pyrotechnic danger most of us have in mind—burns, sure, but done safely, fireworks are good, clean American fun. “We joked, actually, when we turned the paper in,” Gordon adds. “We put three titles, and one was something like ‘The Most Unpatriotic Toxicology Study Ever Undertaken.’”
Gordon and his colleagues began by igniting off-the-shelf fireworks in a ventilation chamber—outside, of course. They collected the air after each ignition and filtered out the smoke particles. Back in the lab, they exposed cultured human respiratory cells and live mice to these particles, and watched for cellular damage. They found that the smoke from the firework with those superhigh lead levels was 10 times more damaging to the human cells than a saline solution, which is considered benign. Its smoke also caused severe inflammation in the lungs of the lab mice.
Mammalian lungs have evolved to expel particulate matter by way of mucus: That goopy cough is your body evicting invaders to keep your respiratory system clean and unobstructed. Coughing keeps tiny particles of metals like lead from working their way deeper into the lower lung, where they’re more likely to stick around. This is because cells called macrophages, which grab particles and carry them away, have to travel farther to get the foreign objects out of this part of the lung and to the back of the throat, where they’re swallowed into the stomach.
Down in the lower lung, “is the residence time of the particle so long that they start to dissolve and the metals can go into the cells?” asks Gordon. “Or worse yet, the toxic particles get out of the lung and get into the circulation and then go to other organs like the brain.” For this reason, an inhaled toxin like lead can cause problems all over the body, including neurological issues.
Metals of all kinds are spewing from your neighborhood fireworks show. Gordon and his colleagues analyzed over a decade of Environmental Protection Agency data and found that levels of metals like barium in the air spike around July Fourth and New Years Eve; 19 of the 22 highest-recorded peaks of airborne strontium, which produces red in fireworks, occurred around those holidays. Copper, which produces blue, also spikes around these times. The researchers note that the firework smoke that tested for 40,000 parts per million lead also tested for 12,000 parts per million copper.
The holiday pyrotechnic smoke can be so thick, in fact, that historically, epidemiologists studying ambient levels of metal in the air actually throw out the data around these two dates. Those aberrations are just too big. But perhaps that’s not surprising, as Americans bought 249 million pounds of fireworks in 2019, according to the American Pyrotechnics Association.
So why is lead showing up in fireworks? A nonprofit called the American Fireworks Standards Laboratory is trying to prevent just that. The group does what its name suggests, developing and maintaining what their website calls “voluntary safety and quality standards for each classification of fireworks” and assisting “manufacturers in improving safety and quality in the design, manufacture and performance of fireworks.”
John Rogers, the group’s executive director, notes that 98 or 99 percent of fireworks in the US market are imported from China. The slice of the fireworks manufacturing market in the US is “very, very, very little,” Rogers says. “The United States used to have, years ago, a fairly significant manufacturing market. China basically put us out of business in terms of manufacturing. In terms of labor, fireworks is a very labor intensive product. It’s handmade.”
US importers partner with the AFSL, agreeing to only import from Chinese manufacturers that also belong to the group. Workers at the standards laboratory take samples from batches of fireworks and test them for chemical composition, as well as the effectiveness of the fuse (making sure they burn at least 3 seconds and no longer than 9 seconds) and whether they’re prone to tipping over and firing into crowds. In a given year, the group tests around 25,000 batches. If one fails, it’s barred from sale to AFSL member importers in the US.
All told, Rogers says, the AFSL oversees about 85 percent of the US market. The feds also do some oversight via the Consumer Product Safety Commission, looking at samples from ports of entry and testing fireworks off the shelf.
Still, tainted fireworks are slipping through the regulatory cracks. And Gordon says that being able to buy some of them for his study is only proof of that. “Obviously, when I bought these several years ago, two out of 12 with high lead levels means they weren’t doing too good in the breadth of their sampling,” says Gordon. “It’s all there for color and noise. And to me, the main point of this is for the manufacturers to straighten up and do more testing.”
That’s all well and good, but some of the less ethical manufacturers probably don’t want more testing. Roger Schneider, vice president and secretary of the International Symposium on Fireworks Society, which hosts gatherings of pyrotechnics industry experts, says that some of those manufacturers may even be deliberately adding lead. Those little explosive, crackling stars that spew out of fireworks? In the old days, lead-based compositions made that happen, but the industry switched to an alternative: bismuth oxide.
“The bismuth oxide works just fine, and it doesn’t carry with it the kind of toxicity that we associate typically with lead compounds,” says Schneider. “But sometime down the road—I don’t know, maybe there’s a shortage of bismuth oxide—what the Chinese manufacturer will do to meet the manufacturing demand, they’ll freely substitute, and they go back to employing some compounds that are not authorized.”
The authors of this new paper finding such high levels of lead in a firework, then, is alarming, but perhaps not surprising. Still, it’s particularly aggravating because the world long ago recognized the threat lead poses to human health, and acted to mitigate it. In the 1980s, the EPA forced oil companies to phase it out of gasoline, for instance. “The lead in the air has decreased by 98 percent over the ensuing 30 years, so that’s a huge victory for the EPA,” says Brian Christman, a volunteer medical spokesperson for the American Lung Association and vice chair at Vanderbilt Medicine. “But we also know that lead in paint leads to really significant brain damage and cognitive impairment and decreased IQ in children. The idea of blowing up fireworks and blowing lead all over children is really terrible.”
A critical component in calculating how risky fireworks are to human health is the number of exposures a person can tolerate before they get sick. Is a night of fireworks OK for your lungs long-term? What about repeated exposure, like years upon years of July Fourth and New Years pyrotechnics? “Like most things, a small exposure is probably insufficient to warrant cause for concern,” says W. Graham Carlos, who studies respiratory health at the Indiana University School of Medicine and Eskenazi Health, but wasn’t involved in the study. “A large or repeated exposure may be. We need more research to help us understand how much is too much. Until we have it, the best advice is to remain careful around fireworks and do your best to avoid direct inhalation of smoke.”
Prepare for more of the Most Unpatriotic Toxicology Studies Ever Undertaken, folks.
More Great WIRED Stories
- My friend was struck by ALS. To fight back, he built a movement
- Poker and the psychology of uncertainty
- Retro hackers are building a better Nintendo Game Boy
- The therapist is in—and it’s a chatbot app
- How to clean up your old social media posts
- ? Is the brain a useful model for AI? Plus: Get the latest AI news
- ??♀️ Want the best tools to get healthy? Check out our Gear team’s picks for the best fitness trackers, running gear (including shoes and socks), and best headphones