A potentially dangerous element sometimes used in fireworks is mercury, which may serve as a chlorine donor. A chlorine donor is a compound that, when combined with a firework fuel, can produce or enrich certain colors. Mercury was also found in the blue sharks.
Color components are not the only potential problem. Lead dioxide, nitrate and chloride have all been used as oxidizers in fireworks. Oxidizers are compounds that produce oxygen to support the combustion of fuel. The new study found lead in the shark bodies.
Another recent study, published in the journal Food Chemistry, found very high levels of mercury in smoothhound sharks from South African waters.
Since these and numerous other papers that have identified such pollutants in sharks cannot pinpoint the exact source of the materials, fireworks have largely stayed under the radar of environmentalists conducting scientific research.
In May of this year, however, USGS scientists were able to directly link firework displays to an environmental contaminant called perchlorate.
Perchlorate is a compound used as an oxidizing agent in fireworks, and is also common in rocket fuels, explosives and even in certain nitrogen fertilizers. At high levels in drinking water, perchlorate can interfere with the function of the human thyroid gland.
Galen Hoogestraat, a USGS scientist, and his team found perchlorate at Mount Rushmore precisely where aerial fireworks displays took place from 1998–2009.
"The lack of alternative perchlorate sources in the area, such as a military site or agricultural land with applied fertilizers, and the presence of firework debris suggest that past fireworks are the perchlorate source," Hoogestraat said.
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Prior research has determined that perchlorate can accumulate in many fish species, so it is possible that some sharks may retain the compound too.
The above does not even take into account pollution resulting from the manufacturing, transportation and storage of fireworks, as well as noise pollution. Studies are ongoing regarding how the latter affects sharks, but it is hard to imagine how explosive firework displays and other loud and/or persistent noise resulting from human activities could not adversely affect them.
The noise, smoke and particulate matter resulting from fireworks can be harmful to humans as well, such that some environmentalists are asking that we declare our independence from firework pollution.
As an EarthTalk Q&A shares, "many environmental and public safety advocates would rather see the Fourth of July and other holidays and events celebrated without the use of pyrotechnics. Parades and block parties are some obvious alternatives. Meanwhile, laser light shows can wow a crowd without the negative environmental side effects associated with fireworks."