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Typically potassium perchlorate is used to speed up the fuel-burning process that drives those Roman candles and fireworks. As the fireworks displays burn they should consume most of the perchlorate. However there are times the reaction snuffs out before all the fuel is consumed, which will leave behind some of the chemical. Excess perchlorate can at times also be added to pyrotechnics.
The problem can be that what isn't consumed can inhibit the working of the thyroid gland. According to
an article in Chemical & Engineering News perchlorate has also been identified as a potential human health hazard. John A. Conkling, is a pyrotechnics expert and adjunct professor of chemistry at Washington College, in Chestertown, Md. According to studies it suggests that it inhibits the thyroid's ability to take up iodine from the bloodstream and can reduce the production of thyroid hormone. But because the anion is highly water soluble, it readily slips into groundwater. Conkling said,
"The major effort in most areas of environmentally friendly pyrotechnics research is to find perchlorate replacement materials."
The article mentions a study in 2007 by the U.S. Environmental Protection Agency where they measured perchlorate levels in a small lake in Oklahoma where an annual Fourth of July fireworks show is held. Within 14 hours of the display, perchlorate levels in the water were 1,000 times higher than they were naturally.
Chemists are trying to revise the fireworks displays by using compounds with a high nitrogen content to supply the energy that drives the burning reaction. Getting all that energy from breaking nitrogen bonds means that less perchlorate is needed to make those beautiful displays in the sky.
With less perchlorate it means less smoke, which will also mean fewer coloring agents, which usually consist of heavy metals like strontium, barium and copper, which are needed to dazzle those who like to celebrate their Fourth by watching some fireworks displays.
Another compound that is in the new fireworks, nitrocellulose, doesn't need perchlorate to light up the night.
Darren Naud of DMD Systems told Chemical & Engineering News
, "Nitrocellulose is probably one of the best low-smoke ingredient. It burns with little smoke, and there's no fallout or residual combustion by-products that are nasty. There's just [carbon dioxide], water and nitrogen."
According to Live Science some of the greener pyrotechnics have already been in use in fireworks displays held outdoors and indoors during concerts.
Happy Fourth of July to all that celebrate the day.
