bromate

A space-filling model of the bromate anion

The bromate anion, BrO−3, 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).

Bromates are formed many different ways in municipal drinking water. The most common is the reaction of ozone and bromide:

Br⁻ + O₃ → BrO−3

Electrochemical processes, such as electrolysis of brine without a membrane operating to form hypochlorite, will also produce bromate when bromide ion is present in the brine solution.

Photoactivation (sunlight exposure) will encourage chlorine dioxide or (see below) liquid or gaseous chlorine to generate bromate in bromide-containing water.

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

Br₂ + 2 OH⁻ → Br⁻ + BrO⁻ + H₂O

3 BrO⁻ → BrO−3 + 2 Br⁻

Human health issues

Bromate in drinking water is undesirable because it is a suspected human 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 enclosed atmospheric tank contact systems, lowering the water pH to between 5.9 - 6.3, and limiting the doses of ozone.

Reservoir pollution

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 water containing 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 formed bromate. The decontamination took 4 months and resulted in the discharge of over 600 million US gallons (2.3×10^⁶ m³) of contaminated water.^[4]

On June 9, 2008 the LADWP began covering the surface of the 10-acre (4 ha), 58-million-US-gallon (0.22×10^⁶ m³) open Ivanhoe reservoir with black, plastic balls to block the sunlight which causes the naturally present bromide to react with the chlorine used in treatment. It will require 30 million of the 40 cent balls to cover the Ivanhoe and Elysian reserviors.^[5]

References