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Republished with permission from Watersheds Canada. Blog by: Nathaniel Sneyd-Dewar, Riparian Habitat Restoration Intern Fireworks have long been a spectacular sight for people worldwide, but outside of the sounds and visuals, the effects of dispersed particles are less considered. While once reserved for national holidays and other major occasions, fireworks have become increasingly affordable, available, and used by families and friends in increasingly diverse locations. This shift presents a change from large shows in urban centres to firework displays in more rural locations like parks, cottages, and campsites. With more rural areas exposed to fireworks, more sensitive environments will see increased negative impacts on wildlife and vegetation, as well as an increase in wildfire risk. If you are considering a fireworks show or are aware of one in your area, there are important precautions you can take to make your property and surrounding area more resilient to wildfires. Chemistry & Concern The blast charge inside a firework ignites the spherical stars (black gunpowder) made from metals, salts, and adhesives (Hoogestraat & Rowe, 2016). The amount of energy released depends on the included elements. Bright colour flashes are produced based on the choice of metal. For example, lithium and strontium create reds, copper for purples and blues, barium for greens, titanium gives silver-white, aluminum appears yellow-white, and iron produces a gold effect (Hoogestraat & Rower, 2016). Heavy metals like lead and chromium are known for their clear danger to human and environmental health and are thus banned from fireworks in many countries (Hickey, et al, 2020). When a firework explodes, it releases microscopic particulate matter in both solid and liquid form. This is inhalable and falls to land and water where it is a concern for human, animal, and environmental health. In addition to particulate matter, there are harmful gases released, like sulphur oxide, nitric oxide, and carbon monoxide. There are over 53 chemicals in fireworks in the form of fuels, oxidizers, and binding agents to produce coloration and sound effects (Furin, et al., 2015). Over 15 years, Environmental Protection Agency (EPA) air sampling showed significantly higher levels of strontium, barium, and copper the day or two after major holidays, demonstrating the clear health impact of fireworks (Hickey, et al, 2020).  Beyond the heavy metals, toxic gases, and other polluting elements of fireworks are perchlorates (ClO4-). Perchlorate is a component in fireworks, rocket fuels, and some explosives, and despite being present in some geological formations, primarily are found moving through the environment due to human-made sources (Hoogestraat & Rowe, 2016). Perchlorate salts are found in many water supplies, especially near areas of rocket fuel use and creation, and to a lesser degree fireworks-related activity (Hoogestraat & Rowe, 2016). Perchlorate increases the spread of firework displays (explosion height, flash and light effect, etc.), transforming into chlorate and chlorine upon explosion, where the free chlorine combines with the present metals to produce the expansive colours (Mohan, 2019). While the components of fireworks often fall to land and enter the soil, there is a reasonable chance of it reaching water bodies through the soil as most of the metals and perchlorate have a strong resistance to breaking down into ecologically manageable forms (Furin, et al., 2015). Fireworks production also creates perchlorates, as often found in groundwater, tap water, surface water, and bottled water in areas with high fireworks production (Mohan, 2019). Perchlorate is of concern as it interferes with thyroid function by inhibiting the thyroid glands' uptake of iodide and overall hormone production, something that is critical for human functioning (Mohan, 2019). Water Implications At Mount Rushmore National Memorial in South Dakota, USA, water samples from surface and groundwater from several locations with proximity to, downstream of, and from drinking water wells around the site for Fourth of July fireworks were collected (Hoogestraat & Rowe, 2016). Collected samples near Mount Rushmore were approximately one magnitude higher than the park boundary reference points for both perchlorate and 22 of the 25 sampled metal types (Hoogestraat & Rowe, 2016). With multiple reference points for groundwater, surface water, and aquifers, there was a clear correlation to proximity with the firework site, with the highest levels in nearby soil (Hoogestraat & Rower, 2016). A primary point of concern was the perchlorate levels of the drainage basin that feeds drinking water wells, which were above the EPA Drinking Water Health Advisory levels of 15 µg/L with a range of 0.2-38 µg/L in groundwater, 2.2-54 µg/L in surface water and even significant levels in drinking water wells with 0.61-19 µg/L (Hoogestraat & Rower, 2016). Groundwater testing in Long Island, New York showed tens of µg/L perchlorate within 100m of fireworks sites and is of particular concern with slower dispersal compared to open water bodies and as a drinking water source (Mohan, 2019). Another example is Canada Day fireworks in Hamilton Harbour, Ontario which remained at maximum perchlorate levels for the following four days and became undetectable a week later (Wilkin, et al, 2007). Similar studies on perchlorate degradation in water showed 20-80 days for undetectable levels and as long as 90 days in one example (Wilkin, et al, 2007). The negative impacts extend well beyond humans and can have a drastic influence on animal health, behaviour, and habitat.  Wildlife Impacts While the Mount Rushmore study presents contamination levels of concern in waterways from large firework displays, the relative scale of fireworks to water body size needs consideration as a small-scale show has the potential for pronounced impacts on water quality and wildlife habitat. Noise and light are the most often considered distress effects on animals, a fact well-known by pet owners (Bateman et al., 2023). The consequences to wildlife are likely under-realized as impacts on young offspring increase with a stress hormone response and influence the behaviour and location of birds, mammals, and other animals (Bateman et al., 2023). Perchlorate is also very water-soluble but has a kinetically stable ion which is not reactive and is resistant to adsorption in solution, resulting in plant uptake (Furin et al., 2015). These factors make it a concern for aquatic organisms exposed through their food sources in the water they inhabit (Bateman et al., 2023). Perchlorate can negatively alter thyroid function in fish at concentrations as low as 100 µg/L and over exposure times of 30 days (Wilkin et al., 2007). Fish in contaminated areas can accumulate several thousand parts per billion (ppb) of perchlorate in their head and hundreds of ppb in their fillets (Wilkin et al., 2007). A gap remains between tracking the other sources of perchlorate and determining the long-term impact on water from fireworks. Thankfully, there are new options for replacing fireworks with drone shows (Bateman, et al., 2023), or the perchlorates with nitrogen-rich salts to reduce polluting effects (Mohan, 2019). While there is still cause for concern with the noise and light effects (Bateman, et al., 2023), and a lack of research on firework impacts to water, there are clear changes we can make to improve the situation for humans, animals, and the freshwater we all depend on (Mohan, 2019).  References
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