Resources: Bromide in Surface Water

What is bromide and where do you find it naturally in surface waters?
Bromine (Br2) is a chemical element (atomic number 35) belonging to the highly reactive halogen group, which also includes fluorine, chlorine, and iodine. Halogens are oxidizing agents that form anions by accepting an electron (their outer electron shell is one electron short of being full). Bromide (Br-) is the anion of the element Bromine. Since elemental bromide is highly reactive, it does not occur freely in nature, but instead exists as salts (e.g. NaBr, AgBr) or acids (e.g. HBr, HOBr; WHO 2018). Bromide naturally occurs in the earth’s crust, seawater, salt lakes, and underwater brines (VanBriesen 2014). Fossil fuels, such as coal, also contain varying concentrations of bromide (Kolker et al. 2006). The highest natural concentrations of bromide are found in seawater (66-68 mg/L), shale geologic formations (24 mg/kg), and coastal groundwater (2.3 mg/L) and soils (850 mg/kg). In the United States, inland groundwaters, fresh surface waters, and drinking water sources do not typically have naturally high bromide values (0.014-0.2 mg/L; VanBriesen 2014).
What are the risks associated with bromide in source water?
Bromide in itself is not a risk to human or ecosystem health when present in source water (WHO 2009). However, during drinking water decontamination, bromide reacts with natural organic matter (NOM) and chemical disinfectants present in source water to create brominated disinfection byproducts (DBPs), which may pose a significant threat to human health (Richardson et al. 2007). During the drinking water treatment process, chemical disinfectants are used to remove pathogenic microbes and nuisance metals. Hundreds of species of DBPs can be produced at various stages of the drinking water disinfection process depending on source water characteristics, disinfectant type, engineering practices, water distribution network characteristics, and climate (Krasner 2009). Since the 1970’s when DBPs were first discovered in finished drinking water (Rook 1974), many toxicological and epidemiological studies have examined the relationship between DBP exposure and potential human health consequences (Charrois and Hrudey 2012). Elevated bromide in source water is particularly concerning because brominated DBPs have been shown to be more carcinogenic and cytotoxic than their chlorinated analogs (Richardson et al. 2007, Pan et al. 2014, Ersan et al. 2019). Importantly, even a relatively low increase in source water bromide concentration can shift the species and quantity of DBPs produced during drinking water disinfection to a greater number of brominated DBPs (Singer and Reckhow 2011, Mctigue et al. 2014) escalating the risk of adverse human health effects (Richardson et al. 2007, Ersan et al. 2019). Recently, Regli et al. (2015) estimated an increased risk of bladder cancer associated with elevated source water bromide at concentrations equivalent those frequently associated with anthropogenic contamination.
What are anthropogenic drivers of increasing bromide concentrations?
Historical bromide uses include early photograph development (silver bromide) and sedatives in human medicine (potassium bromide) during the 18th and 19th centuries (Soltermann et al. 2016). The first significant anthropogenic releases of bromide into the environment occurred in the 1920s-1990s when brominated compounds were added to gasoline to prevent lead deposition in the engine (Thomas et al. 1997). Engine combustion of the added bromine released methyl bromide gas (also called bromomethane) into the environment. The use of methyl bromide as an agricultural fungicide also represented a significant anthropogenic release of bromide until its use was largely phased out by the 2000s (Taylor 1994). Finally, bromide has been released as a waste product of potassium (potash) mining activities and found to elevate surface water bromide concentrations in several European countries, particularly the River Rhine (Flury and Papritz 1993) and the Llobregat River (Ventura and Rivera 1985). Salt mining still a major industry in various parts of the world and continues to create water quality issues when brines pollute source waters (Valero and Arbós 2010). Current anthropogenic sources of bromide include energy extraction and utilization, coal-fired power plants, water treatment, flame retardants, pre-planting and post-harvest biocides, agricultural herbicides, municipal waste incinerators, landfill leachate, road deicers, and pharmaceuticals (Vainikka and Hupa 2012, Mctigue et al. 2014, VanBriesen 2014, Winid 2015).
Why is it important to understand what is driving increasing bromide concentrations?
Elevated levels of bromide in source water leads to a higher production of brominated DBPs following drinking water disinfection (Cowman and Singer 1996). Brominated DBPs are more carcinogenic than their chlorinated analogs, meaning that there are greater human health risks associated with drinking, food preparation, and bathing with chemically-disinfected water (Richardson et al. 2007, Yang et al. 2014). Also, greater source water bromide levels can lead to increased formation of unregulated DBP classes, including halonitromethanes, haloamides, haloacetronitriles (Krasner et al. 2006, Pressman et al. 2010), which may be more harmful than regulated DBPs (Richardson et al. 2007). Source water bromide concentration is one of the most important DBP formation factors and elevated bromide can lead to as much as a two-fold increase in both regulated and unregulated DBPs (Hua et al. 2006, Sfynia 2017). Short-term exposure to high levels of DBPs has been weakly associated with restricted fetal growth (small for gestational age; Grellier et al. 2010), while long-term exposure to DBPs is consistently associated with an increased risk of urinary bladder cancer (Villanueva et al. 2003, 2004, Costet et al. 2011). Identifying drivers of increasing bromide concentrations in source water is essential because once bromide levels are elevated, there are no practical methods to remove the anion prior to disinfection (Rivera-Utrilla et al. 2019). Further, there are no practical methods available to reduce the number of brominated DPBs in finished water following drinking water treatment (Rivera-Utrilla et al. 2019). The best method to control bromide levels in source water and prevent the formation of brominated DBPs in finished drinking water is to regularly monitor bromide levels and if elevated levels are detected, then identify and stop anthropogenic inputs of bromide.
This information was prepared by faculty and students from the University of Georgia as part of a research program funded by the SFY2017 Regional Water Plan Seed Grant, “Bromide Concentrations in Surface Drinking Water Sources for Butts County” funded through the Georgia Environmental Protection Division.
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Ersan, M. S., C. Liu, G. Amy, and T. Karanfil. 2019. The interplay between natural organic matter and bromide on bromine substitution. Science of the Total Environment 646:1172–1181.
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This information was prepared by faculty and students from the University of Georgia as part of a research program funded by the SFY2017 Regional Water Plan Seed Grant, “Bromide Concentrations in Surface Drinking Water Sources for Butts County” funded through the Georgia Environmental Protection Division.