Bromate is a chemical substance that has become a focus of public health concern due to its potential presence in both processed foods and drinking water. The compound is not naturally occurring but rather arises through chemical reactions during manufacturing and water treatment processes. Understanding this chemical’s identity, its pathways, and its potential effects is necessary for appreciating regulatory efforts to minimize exposure.
The Chemical Identity of Bromate
Bromate refers to the bromate ion (\(\text{BrO}_3^-\)), a polyatomic oxoanion classified as a powerful inorganic oxidizing agent. It is often encountered as a salt, with potassium bromate (\(\text{KBrO}_3\)) being the most common commercial form. Bromate’s oxidizing property led to its use in various industrial applications, including its historical use as a flour additive.
When bromate acts as an oxidizer, it is chemically reduced to the stable and generally harmless bromide ion (\(\text{Br}^-\)). Health risks arise when this conversion process is incomplete, leaving residual bromate in the final product.
How Bromate Enters Food and Water Supplies
Bromate exposure occurs through processed foods where potassium bromate has been traditionally used as a dough conditioner in baking. Its oxidizing action strengthens the dough’s gluten structure, allowing for a better rise and improved texture. The intent is for oven heat to convert all bromate into harmless bromide during baking, but this conversion is not always complete.
The primary source of bromate in drinking water is its formation as an unintentional byproduct of disinfection. Water treatment facilities use ozone to disinfect source water. However, if the source water contains naturally occurring bromide ions, the ozone reacts with the bromide to create bromate. Factors like the concentration of bromide, the water’s pH, and the ozone dose influence the amount of bromate formed.
The Health Implications of Bromate Exposure
Bromate’s strong oxidizing nature can lead to oxidative damage to cellular components, including DNA. This genotoxic property is the basis for its classification by the International Agency for Research on Cancer (IARC) as a Group 2B substance, meaning it is “possibly carcinogenic to humans.” This classification relies on sufficient evidence of carcinogenicity observed in experimental animals, though evidence in humans is inadequate.
Studies in rodents identify the kidney as the major target organ for bromate toxicity, showing dose-dependent increases in renal tumors, including adenomas and carcinomas. Non-cancer effects like nephrotoxicity, which involves degenerative and necrotic changes in the kidney, are also consistently observed. Furthermore, long-term exposure in animal models has been linked to tumors in the thyroid and the lining of the abdominal cavity.
While acute, high-level exposure in humans can cause severe symptoms like nausea, vomiting, abdominal pain, and hearing loss, the main public health concern is chronic, low-level exposure. Long-term consumption of residual bromate is associated with the increased risk of cancer and organ damage observed in animal studies. The toxicity is attributed directly to the bromate ion, regardless of the salt it is paired with.
Controlling and Monitoring Bromate Levels
The recognition of bromate’s health risks has led to significant global variation in its regulation. Many regions, including the European Union, the United Kingdom, Canada, and Brazil, have completely banned the use of potassium bromate as a flour additive in food production. In other countries, such as the United States, its use is permitted but regulated under the assumption that it fully converts to bromide during baking.
For drinking water, the regulatory approach focuses on setting strict limits on the final concentration. The U.S. Environmental Protection Agency (EPA) has established a Maximum Contaminant Level (MCL) of 10 micrograms per liter (\(\mu\)g/L), or 10 parts per billion (ppb), for bromate in public drinking water systems. The World Health Organization (WHO) also recommends a limit of 10 \(\mu\)g/L, emphasizing that levels should be kept as low as reasonably achievable.
Water treatment facilities prioritize preventing bromate formation, as post-ozonation removal is complex. Mitigation techniques include:
- Lowering the pH of the water before ozonation.
- Adding chemicals like ammonia or hydrogen peroxide to interfere with the formation process.
- Optimizing the ozone dose and contact time.
Monitoring is mandatory for facilities using ozone to ensure that bromate levels remain below the established regulatory standard.