Bromate

  The bromate anion, BrO₃^-, is a bromine-based oxoanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, (NaBrO₃), and potassium bromate, (KBrO₃).

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Bromates are formed when ozone and bromide ion react according to the following abbreviated reaction:

Br^- + O₃ → BrO₃^-

Bromate is also formed in electrochemical processes, such as formation of hypochlorite ion used in municipal water processes, when bromide ion is present. Additionally bromate ion is produced when chlorine dioxide is used in water, the bromide ion is present, and the water is exposed to sunlight.

This reaction occurs in water systems where bromide is dissolved in water and ozone is used to disinfect the water, especially under high pressures. This reaction is undesirable because bromate is a suspected carcinogen^[1][2]. The presence of it in Coca Cola's Dasani forced a recall of that product in the UK.^[3] Proposals to reduce bromate formation include switching to atmospheric tank contact systems, lowering the water pH to between 5.9 - 6.3, and limiting the doses of ozone.

In laboratories bromates can be synthesized by dissolving Br₂ in a concentrated solution of potassium hydroxide (KOH). The following reactions will take place:

Br₂ + 2 OH^- → Br^- + BrO^- + H₂O

3 BrO^- → BrO₃^- + 2 Br^-

Silver Lake and Elysian Reservoir Incident

On December 14, 2007, it was announced by the Los Angeles Department of Water and Power (LADWP) that the Silver Lake and Elysian reservoirs were going to be drained due to bromate contamination. Bromate usually forms when bromide is purified using ozone, a method used at filtration plants. In the case of the Silver Lake and Elysian reservoirs, however, a combination of bromide from well water, chlorine and sunlight mixed to form bromate. The decontamination is expected to take 3 to 4 months and will result in the discharge of over 600 million gallons of contaminated water. [[1]]

References

1. ^ International Agency for Research on Cancer--Summaries and Evaluations: Potassium Bromate (Group 2B)
2. ^ Toxicity and carcinogenicity of potassium bromate--a new renal carcinogen, Environmental Health Perspectives, July 1990, volume 87, pages 309-335
3. ^ Coke recalls controversial water, BBC News, 19 March, 2004.