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While fireworks can be visually appealing, the chemicals these explosives contain can negatively impact the environment on many levels. In the year 2016, 268 million pounds of fireworks were purchased in the United States alone. The trace metals and organic pollutants released by fireworks impact groundwater, air quality, and soil health. In a laboratory setting, lighting of blue, copper-containing fireworks led to an increase in formation of polychlorinated dibenzo-p-dioxins (PCDD), Polychlorinated dibenzofurans (PCDF) and hexachlorobenzene (HCB). Copper combines with the likes of oxygen to form copper oxide. This compound can then react with hydrogen chloride to form diatomic chlorine, which can chlorinate aromatic rings. The chlorinated aromatics are able to undergo condensation reactions mediated by copper cations to form PCDD and PCDF. These cyclic organic chemicals are classified as persistent organic pollutants due to their stability. Dioxins have very long half-lives, lingering below soil surfaces for greater than 10 years. This family of chemicals has been implicated in harming numerous marine ecosystems, specifically many species in the Great Lakes region.

Formation of diatomic chlorine:

Cu + ½ O2 ↔ CuO

CuO + 2 HCl ↔ Cu + H2O + Cl2

2 HCl + ½ O2 ↔ H2O + Cl2

Hexachlorobenzene (HCB) was once a common component of fireworks because it could be used as a chlorine donor, strengthening the color of the flame. The Stockholm Convention banned the use of HCB globally in 2001, owing to the fact that it has been classified as a persistent organic pollutant (POP). HCB is not easily degraded, with a half-life of 3-6 years in soil. China, one of the lead producers of fireworks worldwide, has regulations in place to monitor the contents of fireworks, specifically HCB content, though these policies have not been adhered to in past years. Certain fireworks imported from China in 2008 were banned from sale in Denmark because the EPA found HCB.

With the use of HCB in a firework, chlorines are given off as free radicals. HCB and several other chlorine compounds such as chlorides and perchlorates are used as chlorine donors for metals during combustion. Metal chlorides burn brighter and more efficiently, but they are hygroscopic and cannot be used by themselves in practical fireworks. This is why chlorine-donating compounds are used, as they produce free chlorine during thermal decomposition. They will react with metals to form metal chloride compounds, producing the desired color. Excess HCB that remains undecomposed, or decombinatory HCB products that re-form to produce more of this chemical remain in the atmosphere and can begin to bio-accumulate. HCB has been proven to confer adverse effects on aquatic organisms, and is a confirmed animal carcinogen.

The chemical characteristics of perchlorate anion are responsible for its persistence in surface and groundwater. Though perchlorate is a strong oxidizing agent, its redox reaction is not readily induced. The abstraction of the first oxygen of perchlorate to form chlorate is kinetically unfavorable due to the high activation energy of the transition state.

Perchlorate reduction potential (acidic conditions):

ClO4- + 8H+ + 8e- ↔ Cl- + 4H2O, E° = 1.287 VSulfur dioxide, a gaseous byproduct of sulfur combustion, is one of the chemicals polluting the air after the shooting of fireworks. In reacting with water molecules, sulfur dioxide is converted to sulphuric acid, producing what is referred to as acid rain. This accelerates weathering processes.

Upon lighting, fireworks contribute substantially to the levels of harmful particulates in the air supply. Particulate matter is usually comprised of alkali earth and alkaline metals, organic and elemental carbon, and secondary compounds like nitrate and other organic compound and ions. The World Health Organization deems safe PM2.5 (in a 24 hour period) to be 25 µg/m3. Due to atmospheric effects from the burning of fireworks in massive quantities during the 2017 Diwali festival, the Indian government banned the sale of fireworks for the festival in 2017. The use of fireworks, however, was authorized. A study conducted in Salkia, India in 2009 studied PM2.5 (μg/m3 ) concentrations before and after the Hindu light festival, Diwali. Potassium nitrate, one of the most common firework components, is commonly used as an oxidizer. It is combined with the likes of charcoal and sulfur in the air, producing solid particles which can be toxic if ingested.

6 KNO3 + C7H4O + 2 S → K2CO3 + K2SO4 + K2S + 4 CO + 2 CO + 2 H2O + 3 N2

A new class of environmentally friendly fireworks has been developed by researchers where perchlorate is replaced with nitrocellulose.