Bromoform (Tribromomethane)

Bromoform is one of four trihalomethanes monitored under the EPA's Stage 2 Disinfectants and Disinfection Byproducts Rule [1]. Like chloroform, it forms when chlorine used for water disinfection reacts with naturally occurring organic matter (humic and fulvic acids) in source water. The key difference is that bromoform formation is favored when the source water contains elevated bromide, which is common in coastal areas where seawater intrusion affects groundwater, and in areas with natural bromide-bearing geology [2]. Florida, California coastal communities, Hawaii, and parts of the Gulf Coast and mid-Atlantic have water supplies prone to elevated bromoform formation. Industrial production of bromoform for use as a solvent and flame retardant precursor also contributes to environmental contamination near production facilities [3].

Drinking chlorinated tap water from systems with elevated bromoform is the primary pathway for most affected communities [1]. Showering and bathing in such water is significant because bromoform, like other trihalomethanes, evaporates from hot water and is absorbed through skin. Indoor swimming pools with high bromide in source water can have elevated bromoform in pool air [2]. Seafood — particularly seaweed and kelp, which naturally accumulate bromine — contains small amounts of naturally occurring brominated compounds. Occupational exposure occurs in chemical manufacturing using bromoform as a synthesis solvent [3].

Bromoform is classified as a possible human carcinogen (IARC Group 2B) for colorectal, rectal, and bladder cancer based on animal studies and supporting epidemiological evidence [1]. It is generally considered more carcinogenic per unit dose than chloroform within the trihalomethane class. The liver is the primary target of acute toxicity — bromoform causes hepatocellular damage at high doses and is a CNS depressant. At environmental concentrations, the cancer risk is cumulative over decades of daily drinking water exposure [2]. The EPA regulates total trihalomethanes at 80 µg/L, but bromoform's higher per-unit carcinogenicity means communities with high bromoform fractions may be at elevated risk even when within the regulatory limit [3].

Residents of coastal Florida, Hawaii, and other areas with high natural bromide in source water or significant seawater intrusion into water supply aquifers face elevated bromoform in their drinking water [1]. People who drink high volumes of tap water daily have proportionally higher exposures. Indoor pool users in areas with bromide-rich water supply face pool air exposure [2].

Request your water utility's annual water quality report and check for total trihalomethane levels and, if available, the individual trihalomethane breakdown [1]. Install a granular activated carbon (GAC) or reverse osmosis filter on your drinking water — both effectively remove trihalomethanes including bromoform. Cold-water rinsing before entering a shower and a carbon shower filter can reduce bromoform absorption through skin and inhalation [2]. For coastal communities: advocate for your water utility to explore enhanced treatment to remove bromide from source water before chlorination, which dramatically reduces bromoform formation [3].