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, (NaBrO
3), and potassium bromate, (KBrO
Photoactivation (sunlight exposure) will encourage liquid or gaseous bromine to generate bromate in bromide-containing water.
In laboratories bromates can be synthesized by dissolving Br
2 in a concentrated solution of potassium hydroxide (KOH). The following reactions will take place (via the intermediate creation of hypobromite):
Although few by-products are formed by ozonation, ozone reacts with bromide ions in water to produce bromate. Bromide can be found in sufficient concentrations in fresh water to produce (after ozonation) more than 10 ppb of bromate—the maximum contaminant level established by the USEPA. Proposals to reduce bromate formation include: lowering the water pH below 6.0, limiting the doses of ozone, using an alternate water source with a lower bromide concentration, pretreatment with ammonia and addition of small concentrations of chloramines prior to ozonation.
On December 14, 2007, the Los Angeles Department of Water and Power (LADWP) announced that it would drain Silver Lake Reservoir and Elysian Reservoir due to bromate contamination. At the Silver Lake and Elysian reservoirs a combination of bromide from well water, chlorine, and sunlight had formed bromate. The decontamination took 4 months, discharging over 600 million US gallons (2.3×106 m3) of contaminated water.
On June 9, 2008 the LADWP began covering the surface of the 10-acre (4 ha), 58-million-US-gallon (0.22×106 m3) open Ivanhoe Reservoir with black, plastic shade balls to block the sunlight which causes the naturally present bromide to react with the chlorine used in treatment. 30 million of the 40 cent balls ($12 million) are required to cover the Ivanhoe and Elysian reservoirs.
Currently no bromate-bearing minerals (i.e., the ones with bromate ion being an essential constituent) are known.