Some of the fireworks that will be used tomorrow to celebrate Independence Day in the US emit lead, copper and other toxins, according to a new study. These metals, which are what gives fireworks their beautiful colors, are also harmful for humans and animals, damaging their cells and lungs.

The study, carried out by researchers at New York University, found harmful levels of lead in two of the 12 types of commercially-available fireworks analyzed. Subsequent experiments using live rodents and human cells also showed that five of them released particle emissions that could damage humans and animals.

“You or your family is setting off a ton of fireworks, and you’re doing it safely as far as a physical injury is concerned, but people ignore that they’re inhaling high levels of toxic metals,” Terry Gordon, senior author of the study, told CNN. “Inhaling firework smoke may cause longer-term damage, a risk that has been largely ignored.”

Gordon and his team also looked at air quality samples of the last 14 years taken at a dozen sites across the country. The findings showed that the levels of toxic metals increased in the samples taken near celebrations such as Independence Day or New Year’s Eve. Lead, titanium, strontium, copper were some of the toxic metals that they found.

Americans buy more than 258 million pounds (117 million kilograms) of fireworks every year, according to the American Pyrotechnics Association. They aren’t used only for holidays but also during concerts, sports events, and even at parks. The metals are exposed to high temperatures to create bright colors.

The new study is the first to examine the effects of firework exposure in human cells and living animals, as well as the first to study the particles of common firework metals thrown into the atmosphere. “They are much more toxic than the pollutants we breathe every day,” said Gordon.

The team collected emissions from a dozen types of fireworks commonly sold in the United States, including Black Cuckoo, the Color Changing Wheel, and the Blue Storm. The fireworks were detonated in a chamber in the lab and then exposed human lung cells and several dozen mice to the captured particles.

The most toxic of the group was the Black Cuckoo, a fountain-style firework. It was 10 times more damaging to human cells than a non-toxic saline solution. The study only looked at one-time exposure to the fireworks, as Gordon explained. Repeated exposure is probably a larger concern.

The study didn’t look at the effects that the toxins released by the fireworks such as lead could have on the body. Nevertheless, Gordon said they could create respiratory issues. “People could have, especially susceptible people like asthmatics, increased episodes,” Gordon said.

Kristin Van Hook, chair of the American Academy of Pediatrics section on pediatric pulmonology and sleep medicine, told CNN that the particles can also have a negative effect on children’s respiratory systems. She suggested that children avoid standing in the vicinity where the firework smoke is blowing.

“Allow the adults to be the ones to set off the fireworks and stay upwind from it so that the smoke is blowing in the breeze,” Van Hook said. She recommended limiting the amount of time children are exposed to firework fumes and watch carefully for any signs of trouble breathing.

Looking ahead, Gordon said that he would like to conduct experiments using humans at a fireworks show to see the real-time effects of the particles on the body, but that in the past he has faced challenges. Specifically, the changing wind direction makes it hard to know where to stand, Gordon said.

Gordon recommended families to be aware of the dangers fireworks smoke post to children and suggested everyone stay downwind while around fireworks. He also asked for more safety regulations from the fireworks industry. “I propose that … they make sure they are importing safer fireworks and that that’s what the consumers use,” Gordon said.

The study was published in the journal Particle and Fiber Toxicology.