Many Americans are looking forward to the upcoming 4th of July fireworks show. But the dazzling lights and thundering cracks may come at a cost to our health — and I don’t mean the risk of contracting COVID-19 from the surrounding crowds.

According to a new study led by researchers at New York University’s Grossman School of Medicine, the same metals that cause fireworks to explode in vibrant colors are also highly toxic and could potentially damage human cells and lungs. These metals include lead, copper, and other toxic materials.

Out of 12 types of commercially-available fireworks that were sampled as part of the study, two had harmful levels of lead.

Particle emissions from five types of fireworks significantly increased oxidation in rodent and human tissue during experiments. This suggests that some firework fumes can pose significant health risks to the lungs.

“While many are careful to protect themselves from injury from explosions, our results suggest that inhaling firework smoke may cause longer-term damage, a risk that has been largely ignored,” says study senior author Terry Gordon, a professor in the Department of Environmental Medicine at NYU Langone Health.

Aside from performing experiments with tissue samples in the lab and with live mice, Gordon and colleagues also analyzed air quality data taken at dozens of sites across the United States in the last 14 years.

Compared to any other time of the year, levels of toxic metals in the air skyrocketed during Independence Day and New Year’s Eve, both fireworks-intensive celebrations.

Although some might think inhaling toxic metals two days a year isn’t such a big deal, the researchers urge people to be cautious. Metals like lead, titanium, strontium, and copper can cause much more damage than the regular pollution we’re exposed to on a daily basis.

For some Americans, exposure to firework smoke can be quite common. You see it not only on the 4th of July or the end of the year, but also at concerts, sports venues, and even birthday parties.

According to the  American Pyrotechnics Association, more than 258 million pounds of fireworks are sold every year in the country.

This is the first study to examine the effects of firework fumes in human cells and living animals (mice). However, the experiments only address the potential impact of one-time exposure to firework metals. As such, Gordon cautions that repeated exposure is likely much more worrisome.

The findings were published in the Particle and Fibre Toxicology Journal.