What it is:

• An inorganic ion, bromate (Br03–) is a disinfection byproduct (DBP) that forms when the naturally occurring bromide ion (Br–, a form of the element bromine which, like chlorine, is a strong oxidant) reacts with ozone (O3):
  
  
  Br– + 03 → Br03–
  
  
• Tasteless, colorless, low volatility.
• In ozonation of water, the rate and extent of bromate formation depends upon the concentration of ozone used, the bromide ion concentration, pH and contact time. The reaction rate increases with increasing pH and levels off at about pH 8.8.

Occurence:

• Although the bromide ion is often found in natural waters and is harmless, bromate can form with ozonation of those waters. Bromate can also form under certain conditions of chlorine disinfection, especially in bright sunlight.
• Salts of bromate include sodium bromate (NaBr03) and potassium bromate (KBr03), both white crystalline substances that readily dissolve in water. Both are used in industrial processes.

Effects:

• Ingestion of very large amounts of bromate (as in poisoning, but unlikely with drinking water) causes nausea, diarrhea, vomiting and abdominal pain, as well as effects on the kidneys and nervous system, and hearing loss.
• Potential human carcinogen.

In the news:

• In August 2006, three separate bottled water recalls were issued in the northeastern United States due to elevated bromate levels.
• In June 2007 the city of Los Angeles drained 600 million gallons of water from the Elysian Park and Silver Lake reservoirs after excessive bromate levels were found in those waters.

Regulation:

• The US Environmental Protection Agency (EPA) has set the maximum contaminant level (MCL) for bromate in public water systems at 10 parts per billion (ppb).

Water treatment:

• Difficult to remove. Bromate is best controlled by limiting its formation. In bottled water production, precise control of the ozonation process is strongly recommended. Bromide concentration and ozone dose are good predictors of ozone formation.
• Lowering pH to less than 8, adding ammonia or controlling ozone reaction time and the ozone/dissolved organic carbon ratio have been recommended, although these methods can have disadvantages as well.