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The bromate
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 of contaminated water.
On June 9, 2008 the LADWP began covering the surface of the , 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. 3 million of the 40 cent balls are required to cover the Ivanhoe and Elysian reservoirs.
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
, BrO, is a bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
-based oxoanion. A bromate is a chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
that contains this ion. Examples of bromates include sodium bromate, (), and potassium bromate
Potassium bromate (KBrO3), is a bromate of potassium and takes the form of white crystals or powder. It is a strong oxidizing agent.
It is a toxic and carcinogenic compound.
Preparation
Potassium bromate is produced when bromine is passed throu ...
, ().
Bromates are formed many different ways in municipal drinking water. The most common is the reaction of ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...
and bromide:
: Br + → BrO
Electrochemical processes, such as electrolysis of brine without a membrane operating to form hypochlorite
In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ...
, will also produce bromate when bromide ion is present in the brine solution.
Photoactivation
A photoswitch is a type of molecule that can change its structural geometry and chemical properties upon irradiation with electromagnetic radiation. Although often used interchangeably with the term molecular machine, a switch does not perform work ...
(sunlight exposure) will encourage liquid or gaseous bromine to generate bromate in bromide-containing water.
In laboratories bromates can be synthesized by dissolving in a concentrated solution of potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
(KOH). The following reactions will take place (via the intermediate creation of hypobromite):
: + 2 OH− → Br + BrO +
:3 BrO → BrO + 2 Br
Human health issues
Bromate in drinking water is undesirable because it is a suspected humancarcinogen
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...
. Its presence in Coca-Cola's Dasani
Dasani () is an American brand of bottled water created by the Coca-Cola Company, launched in 1999. It is one of many brands of Coca-Cola bottled water sold around the world. The product is filtered and bottled.
Marketing
United States
Coca- ...
bottled water forced a recall of that product in the UK.
Bromate formation during ozonation
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.Reservoir pollution
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 of contaminated water.
On June 9, 2008 the LADWP began covering the surface of the , 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. 3 million of the 40 cent balls are required to cover the Ivanhoe and Elysian reservoirs.
Natural occurrence
Currently no bromate-bearing minerals (i.e., the ones with bromate ion being an essential constituent) are known.See also
Other bromine anions:References
{{Bromates Carcinogens