Calcium bromate

also: Bromic acid, calcium salt

A flour-bleaching and dough-strengthening agent, now banned in the UK and EU because of carcinogenicity concerns.

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E924bSynthetic

Calcium bromate

Bromate residues in baked goods are linked to kidney tumours in animal studies and are classed as possibly carcinogenic to humans by the IARC.

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What calcium bromate is, what it does and where you will see it

Why it’s worth knowing. Bromate residues in baked goods are linked to kidney tumours in animal studies and are classed as possibly carcinogenic to humans by the IARC. The additive is banned in the UK and EU and should not appear in any food sold here.

What is it?

Calcium bromate is the calcium salt of bromic acid. It is an inorganic oxidising compound that was used as a flour treatment agent, functioning in the same way as its close relative potassium bromate (E924a). Both salts release bromate ions in solution.

What does it do?

As an oxidising agent it strengthens gluten networks in bread dough, producing a more elastic structure that holds gas better during proving and gives a higher, lighter loaf. It was also used to bleach flour, making it appear whiter. The bromate is theoretically converted to non-reactive bromide during baking, but conversion is not complete in practice, leaving residual bromate in the finished product.

Where you will see it

Calcium bromate was historically used in commercial bread, flour, and other baked goods as a flour improver. It is not permitted in UK or EU food products. If you see any bromate listed on a label, that product should not legally be on sale in the UK.

What the science says

Animal studies: kidney tumours at multiple doses

Long-term feeding studies in rats and mice showed that potassium bromate caused tumours of the kidney (renal tubular cell carcinomas and mesotheliomas), the thyroid, and the peritoneum. Calcium bromate releases the same bromate ion and is expected to have the same biological activity. The IARC reviewed this body of evidence in 1999 and concluded that bromate is a complete carcinogen, acting as both a tumour initiator and a tumour promoter.

Potassium bromate caused renal tubular cell carcinomas and mesotheliomas in male rats in long-term drinking-water studies; calcium bromate releases the identical bromate ion and was grouped with it in the review.

1999AnimalIARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 73

The IARC classified bromate (including the calcium and potassium salts) as Group 2B: possibly carcinogenic to humans, based on sufficient evidence in animals and limited evidence in humans.

1999Regulatory reviewIARC Monographs Volume 73

Mechanism: oxidative DNA damage

Bromate ions generate reactive oxygen species inside cells. These damage DNA directly, particularly causing 8-hydroxydeoxyguanosine adducts in kidney cells, which is consistent with the pattern of tumours seen in animal studies. This mechanism operates independently of the route of exposure, meaning residues in baked bread are biologically relevant.

Bromate induces oxidative DNA damage via generation of reactive oxygen species, producing 8-OHdG adducts in renal tissue, a recognised marker of genotoxic carcinogen exposure.

1995Lab + animalUmemura et al., Japanese Journal of Cancer Research

Incomplete conversion during baking leaves residues

The original rationale for approving bromates as flour improvers was that they would be fully converted to inert bromide during baking. Studies showed this conversion is incomplete: detectable bromate residues remain in the crust and crumb of commercially baked products. This was a key factor in the EU's decision to withdraw the authorisation.

Surveys of baked bread found measurable bromate residues in finished products, contradicting the assumption of complete conversion during baking and establishing a route of human exposure.

1993RegulatoryUK Ministry of Agriculture, Fisheries and Food (MAFF) survey data cited in the EU Scientific Committee for Food opinion

Where it stands with the regulators

Not a permitted food additive in the UK or EU

Legal basis: UK FSA approved-additives list (assimilated from EU Regulation 1333/2008, Annex II). Calcium bromate does not appear in the list of authorised food additives. The EU withdrew authorisation for bromates as flour treatment agents in 1990 following Scientific Committee for Food opinions identifying carcinogenicity risk from residues.
Safe-intake limit (ADI): No ADI established; use not permitted
History: Bromates were used as flour improvers across Europe and North America from the mid-20th century. The UK prohibited bromate in flour from 1 April 1990; the EU-wide withdrawal of authorisation followed the same year, based on Scientific Committee for Food opinions identifying that bromate residues survived baking at measurable levels and posed a carcinogenicity risk. The IARC assigned bromate a Group 2B classification in 1999. In the USA, the FDA permits potassium bromate and calcium bromate in flour (at not more than 0.0075 parts per 100 parts flour). California lists potassium bromate on its Prop 65 register of chemicals known to cause cancer (listed as 'potassium bromate' and 'bromate'); calcium bromate is not separately named on the Prop 65 list, though the same bromate ion drives the concern. Most California bakers have switched to bromate-free processes to avoid mandatory Prop 65 warning labels. Canada banned potassium bromate in 1994. Calcium bromate shares the same regulatory fate as potassium bromate across all jurisdictions where bromates are prohibited.

Who should be careful

Everyone in the UK is already protected by the ban: calcium bromate should not be present in any food legally sold here. If you import food from countries where bromates remain permitted (primarily the USA), check the ingredients list for 'calcium bromate' or 'potassium bromate'.

The honest read

The science on bromate salts is unusually consistent. Animal studies across multiple species and dose levels repeatedly produced kidney and thyroid tumours. The mechanism, oxidative DNA damage producing 8-OHdG adducts, is well characterised and gives a plausible biological explanation. The IARC's Group 2B rating ('possibly carcinogenic to humans') reflects that direct human epidemiological data is limited, not that the animal evidence is weak. The EU's decision to ban bromates was driven by the straightforward finding that residues survived baking at measurable levels, meaning the original safety assumption, complete conversion to inert bromide, was wrong. The science has not moved toward rehabilitation: no re-evaluation has since found reason to re-permit them.

Common questions about calcium bromate

Is E924b banned in the UK?

Yes. Calcium bromate is not on the UK FSA list of approved food additives and is not permitted in any food sold in the UK. The same prohibition applies across the EU.

Why was calcium bromate banned?

Animal studies showed that bromate ions, which can survive incomplete baking, cause kidney tumours. The IARC classified bromate as Group 2B (possibly carcinogenic to humans) in 1999. The EU withdrew authorisation in 1990 after surveys found residues in finished bread products, disproving the original assumption that baking would convert all bromate to harmless bromide.

What foods contain E924b?

No foods legally sold in the UK or EU should contain calcium bromate. It was historically used in commercial bread and other baked goods as a flour improver and bleaching agent. It may still appear in some products imported from countries where bromates remain legal, such as the USA.

Is E924b vegan?

Calcium bromate is a synthetic inorganic salt with no animal-derived ingredients, so it would be vegan in origin. However, because it is banned in the UK and EU, the question of avoiding it for any reason is the same: check imported baked goods for 'calcium bromate' on the label.