Take in the fireworks this Fourth of July weekend and youll 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.
Its 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 productstwo in duplicateand 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 co-author 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 isnt the pyrotechnic danger most of us have in mindburns, 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 chamberoutside, 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 super high 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 theyre 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 theyre 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 4 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.