Sodium bromide may be one of the most widely relied-upon algae treatments in the pool industry. For many service professionals, it is not just another tool — it is the tool.
As Scott Hamilton of United Chemical put it, technicians often tell him, “It’s the only stuff that works.”
But in recent years, that tool has come under increasing regulatory scrutiny.
In 2023, as part of its ongoing pesticide registration review process, the U.S. Environmental Protection Agency moved to restrict the use of sodium bromide in outdoor pools, citing concerns that it can contribute to the formation of bromate — a disinfection byproduct linked to cancer.
As part of that process, updated labeling requirements were mandated, limiting how and where these products can be used, particularly in applications exposed to sunlight.
Today, product labels for sodium bromide-based algicides state that they are not for use in outdoor pools — exactly where most service professionals want to use them.
The result is a practical contradiction: a product widely viewed as effective has been restricted in the very conditions where it is most often needed.
Into this conflict steps Scott Hamilton, a longtime industry figure and the CEO of United Chemical, a manufacturer of sodium bromidebased products, including Yellow Treat. He comes from a family with deep roots in pool chemistry — his father, Jock Hamilton, developed the Hamilton Index and founded United Chemical — and both father and son spent decades working with water chemistry in the field.
His company also funded the recent field study examining bromate formation in outdoor pools — a fact disclosed in the report and one that will inevitably raise questions about independence and bias.
Hamilton does not dismiss those concerns. But he also does not back away from the product. He has said, in essence, that if sodium bromide were shown to pose a meaningful health risk, he would remove it from the market. He has also framed the study in broader ethical terms, stating that the goal was to avoid repeating the kind of industry behavior seen in the past — “don’t be like the cigarette companies.”
That tension — between industry interest and stated transparency — sits at the center of the conflict.
The study itself, as outlined in Part 1, published in the April 1 issue of Service Industry News, confirms that bromate can and does form in outdoor pools under certain conditions — but suggests that formation may be more limited, and more dependent on dosing practices, than was earlier assumed.
Now, the question is not whether the study is correct, but whether it is complete enough to support — or challenge — current regulatory decisions.
Laboratory research has long shown that bromide can be converted to bromate under controlled conditions. The unresolved question is whether those same reactions occur — and to what extent — in real pools, where chemistry is more complex.
This study attempts to answer that by moving into field conditions.
But an important variable was left out.
Cyanuric acid — present in most outdoor pools — was not included in the United Chemical study.
That omission is not minor. Cyanuric acid is increasingly understood to play a central role in how chlorine behaves in real water.
CYA binds with chlorine and reduces its immediate oxidative strength. In practical terms, it buffers the concentration of highly reactive hypochlorous acid and slows chlorinedriven reactions. Because bromate formation depends on the stepwise oxidation of bromide, reducing chlorine’s effective reactivity would be expected to slow that pathway.
That does not mean bromate would not form in the presence of CYA. But it does mean that both the rate and total yield are likely to differ — potentially significantly — from what was observed in the United Chemical study.
For that reason, the results are best understood as representing an essentially worst-case scenario that may still not fully reflect typical outdoor pool conditions.
United Chemical has acknowledged that gap. In a company statement, Hamilton said, “We expect the EPA will soon provide us with additional testing parameters to fulfill their requirements,” and added that future work will examine “exactly how CYA influences and suppresses bromate formation” as well as the long-term accumulation of bromate over time.
That points to another limitation: duration.
The United Chemical study tracked bromate formation over a period of days. What it does not yet address is how bromate behaves over weeks or months.
In practice, bromate is relatively stable once formed. It does not readily break down under normal pool conditions. Long-term behavior is therefore likely governed less by chemical decay and more by system dynamics — whether additional bromate continues to form; whether levels plateau as reactive pathways are exhausted; or whether concentrations decline through dilution mechanisms such as splash-out, backwashing, or partial draining.
Whether bromate accumulates, stabilizes, or gradually declines over a full season remains an open question.
At the same time, the study identifies a different driver of bromate formation than the one emphasized in regulatory discussions. While the EPA has focused in part on sunlight and UV exposure, the field data point instead to chlorine dosing — particularly repeated high-dose applications — as the dominant factor. That distinction matters.
If bromate formation is primarily driven by UV exposure, then restricting outdoor use becomes a logical regulatory response. If, instead, formation is driven largely by how chlorine is applied, then the issue shifts from the product itself to how it is used in practice.
In practical terms, that includes how much chlorine is added at one time; how often high-dose treatments are repeated; and whether those treatments are applied in water that already contains bromide from prior use. Those variables can differ widely from pool to pool — and from technician to technician.
The reality may be that both mechanisms — UV exposure and chlorine dose — play a role. But their relative importance remains unresolved.
That uncertainty extends to risk. The study’s modeling places estimated lifetime cancer risk within the EPA’s accepted range. On paper, that suggests the exposure level is considered tolerable under current regulatory frameworks.
But “acceptable” does not mean insignificant.
A modeled risk of approximately 1 in 21,800 falls within the EPA’s accepted range of 1 in 1,000,000 to 1 in 10,000 — but toward its upper end.
That estimate is based on a modeled bromate concentration of roughly 0.47 ppm in pool water and standard exposure assumptions. It does not assume that swimmers are drinking pool water as a primary source, but instead accounts for incidental ingestion — small amounts swallowed during swimming — along with dermal contact over time.
Among those pathways, ingestion is considered the dominant contributor to bromate exposure, while dermal absorption is negligible.
For comparison, the EPA’s drinking water standard for bromate is 10 parts per billion (ppb), reflecting daily lifetime consumption — a far more continuous exposure scenario than recreational swimming.
That difference highlights the core issue: exposure context matters.
Hamilton argues, however, that the disagreement may go deeper than exposure assumptions alone.
He points to toxicological research suggesting that bromate’s harmful effects are not simply proportional to dose (a linear model), but depend on whether the body’s natural defenses are overwhelmed (a threshold model). In this view, bromate causes damage by generating oxidative stress inside cells — producing reactive oxygen species that can damage DNA — but only once antioxidant defenses are depleted.
At lower exposure levels, those defenses may neutralize bromate before significant damage occurs. Some studies also suggest that bromate can be reduced to bromide in the acidic environment of the stomach, further limiting how much reaches target tissues.
If that interpretation is correct, it would mean that below a certain threshold, bromate exposure may produce little to no measurable effect — a fundamentally different conclusion than the EPA’s linear model, which assumes that any exposure carries some degree of risk.
That position is not currently reflected in EPA risk assessments, which continue to apply a conservative linear model for bromate.
This is not a minor technical disagreement. It is a fundamental difference in how risk is defined.
And it helps explain why the same data can lead to different conclusions.
For some regulators, a modeled risk near the upper end of the acceptable range may still justify restriction. For others, particularly if a threshold mechanism is supported, that same exposure level may be considered negligible.
This is where science gives way to judgment.
And that judgment has real-world consequences.
For service professionals, sodium bromide remains an effective solution for difficult algae problems — particularly in cases where other treatments fall short. At the same time, the conditions identified in the study as increasing bromate formation — repeated shocking; high chlorine levels; and unknown treatment history — are part of everyday field work.
That creates a situation where risk is not just a function of chemistry, but of use.
Handled conservatively, bromate formation may remain limited. Handled aggressively — or unknowingly, in a pool with existing bromide — it may not.
What the study ultimately defines is not a single, fixed level of risk, but a range of possible outcomes — and that uncertainty is central to the regulatory response.
Whether sodium bromide is ultimately viewed as a manageable tool or an unnecessary risk will depend not just on what the science shows, but on how much uncertainty regulators are willing to accept.
And it is a question that will likely be answered not by a single study, but by how science, policy, and practice ultimately converge.
Notes:
1. Sai et al. (1994) – A possible role for oxidative stress in potassium bromate (KBrO3) carcinogenesis. (Carcinogenesis, 15: 8-12): This is a foundational study. The researchers demonstrated that bromate induces lipid peroxidation and generates 8-hydroxydeoxyguanosine (8OHdG), a primary marker of oxidative stress, specifically in the renal proximal tubules (the target site for bromate tumors).
2. Umemura et al. (1995) – Role of oxidative stress in potassium bromate-induced carcinogenesis. (Cancer Letters, 94: 213-218): This study further confirmed that a single, large intragastric dose of bromate causes severe oxidative damage. More importantly, it established a dose-response relationship showing that lower doses do not trigger this same cascade, hinting at a biological threshold.
3. Ballmaier and Epe (2006) – Oxidative DNA damage induced by potassium bromate under cell-free conditions and in mammalian cells. (Mutagenesis, 21: 29-33): This study demonstrated that bromate's ability to damage DNA is entirely dependent on its interaction with cellular reductants, specifically glutathione (GSH). This supports the argument that as long as the cell has an adequate supply of GSH (at low exposure levels), the bromate is neutralized and no damage occurs.
4. Umemura and Kurokawa (2006) – Etiology of bromate-induced cancer and possible modes of action— studies in Japan. (Toxicology, 221: 154-157): A vital synthesis of decades of Japanese research. The authors concluded that oxidative stress and cytotoxic responses (cell death) in the kidney are the direct drivers of cell proliferation and tumor formation. They explicitly suggested that no-effect levels (thresholds) for carcinogenicity lie between 15 and 30 ppm in the drinking water of test subjects, below which the body effectively repairs itself.
5. Wolf et al. (1998) / DeAngelo et al. (1998): While these were the primary rat bioassays the EPA used to establish their original linear risk assessment, modern toxicologists frequently re-analyze the doseresponse data from these exact studies. The data tables show that at the lowest tested doses, the incidence of tumors was not statistically significant from the control groups, which actively supports a non-linear, practical threshold curve.
6. Keith et al. (2006) – Kinetics of Bromate Reduction by Hydrogen Sulfide in Buffer and Human Gastric Juice. (Chemosphere, 64: 15151522): This highly influential study investigated whether bromate could be decomposed in the human stomach before reaching target organs. The researchers concluded that in the acidic environment of the stomach, up to 99% of the bromate ion is rapidly reduced to harmless bromide. This provides a massive, built-in physiological threshold that protects humans from trace amounts of bromate in drinking or swimming pool water.
