Do fireworks cause pollution at the cottage? That is, are they bad for the lake water?—Melvin Bradley, via email
Yes. Yes, they are. Most research on the water quality impact of fireworks has focussed on perchlorate, an oxidizer that, in combination with the firework’s fuel source, creates the heat and gas necessary for an explosion. Perchlorates are the focus because they’re a significant component of fireworks, says Richard Wilkin, a geochemist with the Environmental Protection Agency. Fireworks contain all kinds of other stuff, says Wilkin, but “there’s no observable buildup of these metals in water.”
Perchlorates aren’t great: evidence suggests that they interfere with thyroid hormone production in fish and humans. That said, almost all research on perchlorate contamination of freshwater lakes post-fireworks shows the same pattern: a spike in perchlorates, followed by a decrease to pre-fireworks levels. In one study of Canadian surface waters in the Great Lakes basin, perchlorate was found in Hamilton Harbour four days after a Canada Day fireworks display, but was undetectable at the same site a week later.
“The ecosystem is getting some contamination,” says Wilkin. “But the typical trend is for the concentration to come down. Generally, we haven’t seen spiking such that the levels of perchlorates become sustained.” This is thanks to “natural attenuation,” i.e., the ability of the lake to, on its own, reduce the contaminants that we put into it. (Natural “perchlorate-reducing organisms”—bacteria in lake sediment—can lower the levels by using the compounds for respiration.)
The impact of perchlorate on a particular lake will depend on a lot of factors: the size of the lake and its depth; the frequency of fireworks displays and the amount of fireworks per display; even the temperature and the health and state of the lake at the time.
Will two or three holiday fireworks displays per year destroy your lake? Probably not. What about fireworks every weekend? What would cause “some contamination” to turn into “a lot of contamination”? Wilkin suspects that if the concentration of perchlorates became too high, it would be detrimental to even the organisms in the lake that use perchlorates. But “I am not aware of any research on what that ‘too high’ concentration is,” he says.
Does it matter? Everyone knows that the most acceptable level of contamination—from fireworks, septic systems, microplastics, blue-green algae, boat engines—is no contamination at all.
This question was originally published in the Winter 2019 issue of Cottage Life magazine.
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