By Henry R. Hidell, III

Summary: Disinfection by-products (DBPs) in drinking water have arisen as a significant concern for public health. The issue is largely associated with chlorine use, but other DBPs include bromate formed in waters treated with ozone. While more U.S. municipalities have adopted ozone in recent years, water bottlers have employed its use in treatment processes for some time. Bottlers should review their method of ozone application as well as actual need for ozone in some instances.

The water industry, including bottled water and municipal suppliers, strives to provide high quality, risk-free drinking water to its consumers. It has a long history of seeking the best treatment methods and technologies to meet consumer demand for good-tasting, safe drinking water. With the exception of protecting its sources from contamination (by chemical spills, intentional waste disposal or application of agricultural pesticides and herbicides), the greatest effort by this industry to reduce health risks on an ongoing basis is associated with waterborne microbiological contaminants such as Cryptosporidium, Giardia, E. coli and viruses.

Common obstacles
Traditionally, municipalities have used chlorine in one form or another in combination with various methods of filtration as the most efficient and cost effective means to sanitize large volumes of water usually required in municipal systems. On the other hand, water bottlers have relied on microfiltration, ultraviolet (UV) irradiation and ozonation to sanitize their product. Distinct differences between the two market segments relate to water volumes each is required to treat. Many municipalities treat significant volumes of water measured in millions of gallons per day compared to the smaller volumes associated with bottlers whose daily consumption is measured in tens of thousands of gallons, which may be comparable to that of small community water systems.

Both industries face similar constraints in use of the best available technologies to provide their consumers with safe, high quality drinking water. During the last two decades, bottlers and municipalities have increasingly used ozone to provide sanitary water with excellent results. But chlorine has remained dominant in sanitizing municipal water because of familiarity of use, economics and the fact that ozone has a very limited residual presence. Also, except in the most modern distribution systems, ozone may cause piping deterioration. While more widely used than ever in the United States today, ozone in municipal supplies remains more common in Europe. Its effectiveness is the result of a high level of oxidation, causing a significant kill rate to most waterborne diseases. This may not eliminate the need for a residual chemical disinfectant but it significantly reduces it.

Potential health concerns
With bottlers, ozone has been the main method of sanitization since they can micromanage a finite, self-contained bottling system using ozone-resistant piping and filling equipment. In both industries, ozone and chlorine provide a residual disinfection quality to assure sanitary conditions throughout the municipal distribution system or in bottles. But each method of sanitization creates what are referred to as DBPs. These are components that occur when chlorine, ozone or other oxidizing/sanitizing agents react with various organic and inorganic components found in water. Although there has been significant ongoing research related to DPBs, there’s still little known about all the subsequent reactions that may occur in water.

The U.S. Environmental Protection Agency (USEPA), bottled water industry and municipal suppliers have identified the bromate ion as a potential health concern when using ozone as a disinfection agent. Although some municipal systems are affected by this, the bottling industry is more likely at risk and is presently seeking methods to reduce possible formation of bromate.

Conflicting findings
Bromate (Br03-) is formed when the naturally occurring bromide ion (Br-) encounters an oxidizing agent such as ozone (O3). As a result of contact, bromide is converted to bromate as a DBP. The health concerns about bromate formation in water treated with ozone surfaced in the mid-1980s as a result of some initial research completed by Japanese medical researchers1 looking at bromate as a common food and cosmetic additive. Potassium bromate (KBrO3) was the subject of the research. The Japanese studies conclusively determined that potassium bromate caused tumor formation in rats when injected or administered orally. These findings were published in proceedings of the International Workshop on Bromate and Water Treatment held in Paris in 1993, as well as professional journals. Earlier rodent research2 of the bromate ion related to potassium bromate used in bakery goods. This study indicated there was no evidence of carcinogenicity and no signs of toxicity effects in rats. The net result of the bakery study was that potassium bromate shouldn’t be considered a health problem.

Additional studies completed as late as 19983 showed tumor formation in rodents (mice and rats) when potassium bromate was injected or administered orally at concentrations of 20 parts per million (ppm)—1.5 milligrams per kilogram of the subject’s weight per day (mg/kg/day). This concentration is 1,000 times the proposed USEPA maximum contaminant level (MCL) of 10 micrograms per liter (µg/L)—or parts per billion (ppb)—for bromate, which has led to significant dissatisfaction within the water industry. Consequently, the USEPA’s Stage II Microbials/Disinfection By-Products Rule proposes to keep the bromate MCL at 10 ppb rather than lower it to 5 ppb. All parties have agreed additional research is necessary that will focus on threshold levels of exposure rather than the gross level of 20 ppm currently tested.

Cautious assumptions
Still, these studies have allowed regulators to cautiously assume potassium bromate consumption poses a potential but not yet quantified risk to human health. According to the USEPA, the mechanism of tumor induction by potassium bromate isn’t sufficiently understood to complete mechanistically based dose response modeling.

The World Health Organization has determined a provisional guideline value for the presence of bromate in water at 25 mg/L. But the USEPA is being extremely conservative in its position relative to establishing an MCL for bromate (at 10 µg/L) in the face of scientific evidence. The interspecies extrapolation or risk from rat to human sensitivity is unknown and any suggestion of a specific magnitude of risk is totally speculative at best. In fact, at this moment, there’s no indication bromate is a human carcinogen except through rat extrapolation. A carcinogen in rats isn’t necessarily ipso facto a carcinogen in humans. And bromate research of human carcinogenicity to date relates only to food-based bromate not the form of bromate common in water, sodium bromate (NaBrO3).

Effects on the industry
What does this mean for the water treatment industry? Overall, municipal water systems and bottlers should examine ozone application as a sanitizing agent. This will impact the European water utilities to a much greater extent than in the United States. However, water bottlers generally face a more complex problem. Almost all bottlers in the United States use ozone at some point in their water treatment train for sanitizing containers and product.

Bromide’s occurrence in water doesn’t necessarily indicate the final product will exceed the proposed USEPA guideline of 10 mg/L for bromate. The efficiency of conversion from bromide to bromate is reported to be influenced by a great number of variables such as ozone concentration, bromide concentration, pH, ammonia if present, presence of hydroxyl radicals and alkalinity, to name a few.4 However, if source water contains a level of 7 mg/L of bromide and a 100 percent conversion efficiency to bromate occurs, the resulting level of bromate in the water would slightly exceed the proposed MCL of 10 mg/L. This efficient level of conversion isn’t likely given all the factors that influence it.

It’s necessary for bottlers and municipalities to analyze their source water for the presence of bromide. The microbiological quality of the water should be assessed to determine if there’s any seasonal variation in the presence of waterborne pathogens as well. If the water has experienced little or no microbiological contamination, then it may be possible to significantly reduce the use of ozone and rely more on microfiltration and UV irradiation for treatment of the water itself. However, if a bottler or municipality experiences microbiological contamination of a type and level that would put the product at risk, it may be necessary to consider using another water source less prone to microbial contamination. Use of advanced water treatment technologies such as reverse osmosis, deionization or distillation may be required to address proper sanitation of the product. With application of these advanced technologies, there would be no chance of bromate conversion since the bromide would be removed from the source water.

The issue of DBPs remains one of significant concern for the water treatment industry. The specific issue of bromate requires additional research to allow regulators to identify actual risk to product quality and human health. All companies and municipalities that employ ozone should assess probable conversion of bromide to bromate in their treatment procedures by assessing bromide levels in their source waters. It may be determined that, in most cases, bromate poses a very low-risk threshold to most bottlers and municipalities.

In summary, both industry segments will have to recognize:

  • That there’s no direct evidence potassium bromate represents a risk to human health,
  • That ozonation remains the most effective means to sanitize water for municipalities and bottlers,
  • That municipalities and bottlers should monitor bromide levels possibly present in their waters, and
  • That ozone’s effectiveness is a result not only of concentration but contact time and, therefore, municipalities and bottlers should carefully monitor ozone injection to assure the lowest concentrations possible for effective sanitation.

All interested parties should monitor new USEPA regulations related to bromate—as well as, for bottled water producers in particular, how the U.S. Food and Drug Administration responds to them—to assure science supporting any recommendations is sound and relates specifically to human health.


  1. Kurokawa, et al., “Toxicity and carcinogenicity of potassium bromate—a new renal carcinogen,” Environmental Health Perspectives, 87: 309-335, 1986.
  2. Fisher, et al., “Long-term toxicity carcinogenicity studies of the bread improver potassium bromate 1:studies in rats,” Food & Cosmetic Toxicology, 17: 33-39, 1978.
  3. De Angelo, et al., “Carcinogenicity of potassium bromate administered in the drinking water to male B6C3F1, mice and F344/N rats,” Toxicologic Pathology, 26 (5) 587-594.
  4. Minear, R.A., and G.L. Amy, eds., Disinfection By-Products in water Treatment: The Chemistry of Their Formation and Control, CRC Press Inc., Boca Raton, Fla., 1996.

About the author
Henry R. Hidell III, president of Hidell-Eyster International, is an internationally recognized expert in applied water and beverage as well as environmental remediation technologies. He’s active with the International Bottled Water Association and serves as U.S. Administrator of the Association Internationale de la Distribution, Bruxelles. He holds a bachelor’s degree in geology from West Chester University and a master’s degree in land use planning from Southern Illinois University. Hidell can be reached at (781) 749-8040, (781) 749-2304 (fax) or email:

FYI: More on Bromate
For additional reading on this topic, see the following articles:

  • Grubbs, T.R., “Government Regulations, Part 2 of 2: An Update on the USEPA’s
    Microbial and Disinfection By-Product Rules,” WC&P, January 2000.
  • Davis, G.B., “Ozone and Bottled Water: New Developments on Allowable Bromate Levels in Drinking Water,” WC&P, February 1999.
  • Rice, R.G., and P.K. Overbeck, “Ozone and the Safe Drinking Water Act: Parts II & III,” WC&P, November and December 1998.

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