Bromate
From Wikipedia, the free encyclopedia
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−
[edit] 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.
[edit] 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 (2.3×106 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 (0.22×106 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]
[edit] References
- ^ "Potassium Bromate (Group 2B)". International Agency for Research on Cancer: Summaries and Evaluations. Canadian Centre for Occupational Health and Safety. http://www.inchem.org/documents/iarc/vol73/73-17.html. Retrieved on 2008-03-09.
- ^ Kurokawa, Yuji (July 1990). "Toxicity and carcinogenicity of potassium bromate—a new renal carcinogen". Environmental Health Perspectives 87: 309–35. doi:. PMID 2269236.
- ^ "Coke recalls controversial water". BBC News. 2004-03-19. http://news.bbc.co.uk/1/hi/business/3550063.stm. Retrieved on 2008-03-09.
- ^ "DWP To Drain 2 Reservoirs After Potentially Harmful Chemical Found". KNBC News. 2007-12-14. http://www.knbc.com/news/14858647/detail.html. Retrieved on 2008-03-09.
- ^ "DWP drops 400,000 balls onto Ivanhoe Reservoir". http://www.latimes.com/news/local/la-me-balls10-2008jun10,0,5878575.story.
