WASHINGTON, United States (AFP)—An “unforgettable” tribute to America, or a health hazard that will terrorise animals and pollute the environment?

That’s the question as Washington prepares to break the record for the world’s largest fireworks display on the United States’ 250th birthday on Saturday.

The Trump administration’s “Freedom250” project has hired Pennsylvania-based Pyrotecnico to launch more than 850,000 fireworks shells across 10 sites around the Lincoln Memorial and Potomac River, starting at 10:30 pm and lasting 40 minutes.

That is around 40,000 more than the current Guinness World Record, set in Bocaue, Philippines in 2016, and roughly 50 times more than Washington’s usual annual show.

“Freedom250” has billed it as the “unforgettable” capstone for a day of performances, flyovers and acrobatics displays at the National Mall, claiming it will bring hundreds of thousands of visitors and calling it a generational event.

They haven’t however disclosed the bill for the affair and did not respond to a request seeking the sum.

– ‘Frightening’ numbers –

“Fireworks are a tried-and-true American tradition,” Jodi Dague, Pyrotecnico’s director of marketing, told AFP. “They bring back childhood memories and allow families to create new ones. It’s a reason to gather and celebrate.”

Not everyone is convinced.

“First let me say, I like fireworks — I think they’re fun,” Russell Dickerson, a professor of atmospheric chemistry at the University of Maryland told AFP, but said the number in question was “frightening.”

“In my professional opinion, it’s probably ill-advised to try to set off 850,000 fireworks… on a hot, stagnant, already polluted day. I’m not going down to the Mall and I certainly would not bring my grandchildren there.”

The biggest concern is fine particulate matter, he explained — particles 2.5 micrometers or smaller that can penetrate deep into the lungs, enter the bloodstream and even cross the blood-brain barrier.

The EPA’s 24-hour standard caps exposure at 35 micrograms per cubic meter. After a fireworks show, “it dissipates substantially in a few hours, but in those few hours, people are going to be exposed to huge amounts,” Dickerson said, adding that the smoke could cut visibility to a few hundred yards.

Making matters worse is a heat wave gripping the East Coast, with firework smoke and pollution liable to last longer without rain to clear it, and hot weather itself increasing background levels of pollution as the power grid strains under increased demand for cooling and as vehicles emit more.

“The amount of pollution that we produce is apocalyptic during this one particular day,” Glory Dolphin Hammes, CEO of IQAir’s North American division, told AFP.

Data compiled by the Swiss-based company from public and private sources showed that hourly PM2.5 in Washington peaked at 11 pm on July Fourth, last year at 133 micrograms per cubic meter. The Air Quality Index peaked at 208, levels more commonly associated with South Asian cities.

Epidemiologically, PM2.5 spikes are linked to a rise in emergency room visits, Hammes said, with longer-term impacts on heart and lung health from chronic exposure. Beyond particulate matter, fireworks contain trace metals that produce their bright colors, and burning them releases harmful volatile organic compounds.

– Sounds of freedom –

Fireworks are also traumatising for pets, particularly dogs, which tremble and even bolt from their homes in fear.

Adrian Aceves, a physician living in downtown Washington, said he’d be staying in with his five-year-old mutt Rosy, “trying to distract her with treats and toys, and I will medicate her.”

Then there’s wildlife: a recent European study found Arctic migratory geese flew away from their sleeping sites in response to New Year’s Eve fireworks and never returned.

And a 2016 US government study found perchlorate, an oxidising agent used in fireworks, had made its way into groundwater and surface water around Mount Rushmore National Memorial, which holds annual July 4 shows.

But Erica Walker, an assistant professor of epidemiology at Brown University School of Public Health, said the harms of fireworks need to be weighed against the joy they bring, drawing a distinction between ongoing sources of noise and pollution and those confined to a single day.

“As an American who has ancestors here who descended from slavery, Independence Day for me is incredibly relevant,” she said. “I think for me those are the sounds of independence… it’s also the sound of freedom, without trying to sound all corny.”