Raising a need for a risk assessment of bromoform transferred from feed to food

By Dr. Rozita Spirovska Vaskoska (FoodLegal Scientist)

© Lawmedia Pty Ltd, June 2021

The risk of an adverse health effect from feed transferring a hazardous substance into the food chain is one of the lessons learned from the disastrous consequences for the UK beef industry that followed from the BSE outbreak. Thus, assuring safe food also means assuring safe feed for animals.

In recent years, Australian scientists have led international efforts to create animal feed supplements that have the effect of reducing methane emissions from cattle (both beef and dairy). Governments and corporations in Australia have invested heavily in the commercial application of this technology. Bromoform is the active substance in the formulation of the feed supplements sourced from seawater algae.

While the World Health Organization (WHO) has not done so, the U.S. Environmental Protection Agency (US EPA) has assessed bromoform as a probable human carcinogen based on evidence in animal studies.

Thus, two important questions arise from the expanded commercial use of feed supplements containing bromoform: 1) Is bromoform likely to end up in the food chain?; 2) Could there be a carcinogenic risk in humans through consumption of milk and meat if bromoform gets transferred from the supplemented feed to the milk or meat?

The importance of reducing methane emissions for the environment

The food chain is considered to contribute to an estimated 8% (UK) - 31 % (EU) of greenhouse emissions [1,2], with meat and dairy contributing half of these emissions to an overall estimate of 18 % [2]. Methods of calculation of calculation of emissions contributors vary, as do percentages calculated for different countries. It has been estimated that methane (CH4) and nitrous oxide (NO2) are the dominant emissions in the livestock industry in the UK, followed by carbon dioxide (CO2). Methane comes from enteric fermentation and manure management, while nitrous oxide comes from soils and manures [3].

Using seaweed feed supplements to reduce methane emissions

Several groups of scientists, including leading Australian researchers, found that there was scope for some seaweed-based feed additives to reduce methane production by the animal by interfering with the process of methanogenesis. In particular, these supplements are able to be derived from two types of seaweed being: Asparagopsis taxiformis and Asparagopsis armata. The benefit of adding these seaweed supplements to ruminant diet have been shown to include: the reduction of methane production reaching over 80 % in in vivo studies and 99% in in vitro studies [4]. Their methanogenesis reduction ability is due to the active compounds, the most important being bromoform. Bromoform is stored in gland cells of the seaweed. The mechanism of action of bromoform in methane reduction is reacting with reduced vitamin B12 and inhibition of the B12 dependent methyl- transferase step of methanogenesis [5].

Is bromoform likely to end up in the food chain?

To date, there are five studies that have looked at the transfer and retention of bromoform to milk and meat of cattle. Two of those studies did not detect bromoform in meat despite the high intake [4,6]. Two studies found similar levels in the milk of the control and the fed animals [7,8]. One study found bromoform transfer in the milk [9]. However, the levels were inconsistent: they found positive samples at 3 of the 18 tested time/level points and not in all cows [9].

Metabolic and toxicological studies for bromoform

Bromoform has been found in a case of an accidental human intoxication in the liver, kidney, brain, lungs and stomach/ intestines [10]. Animal studies have also shown its immediate presence in the blood and adipose tissue, but also showed bromoform has a quick metabolism, particularly in the liver [10]. Animal studies have shown excretion though the urine and lungs [10].

Bromoform belongs to a group of compounds known as halogens, which include bromoform and chloroform. Halogens have elements with large negative electron affinity that combine with other compounds to reach stability. The chemical similarity of bromoform to chloroform, which is a known carcinogen, has triggered scientific assessments of bromoform for its safety.

Animal studies of its safety have shown that bromoform can enlarge tumours in the large intestine and cause some developmental toxicity [10]. Results on genotoxicity of bromoform have been inconsistent [10].

Classification and guideline levels for bromoform globally and in Australia

Different evaluating bodies have approached classification of bromoform differently. Guideline levels have been established for bromoform or their chemical group (trihalomethanes) in Australia and globally in relation to drinking water.


The International Agency for Research on Cancer has placed bromoform in group 3, which means not classifiable as to its carcinogenicity to humans.

The World Health Organization (WHO) has set up a guideline value of 100 µg/L (0.1 mg/L) of bromoform as a disinfection by-product in drinking water [11].

The Tolerable Daily Intake (TDI) for bromoform has been set up at 17.9 µg/kg body weight and has been explained by the WHO as “based on the absence of histopathological lesions in the liver in a well-conducted and well documented 90-day study in rats, using an uncertainty factor of 1000 (100 for intraspecies and interspecies variation and 10 for possible carcinogenicity and short duration of exposure)”.


The Australian Drinking Water Guidelines establish a level of 250 µg/L (0.25 mg/L) for all trihalomethanes together and does not set up a specific guideline level for bromoform. The explanation is that these compounds are metabolized similarly in the human body [12]. The newest Australian guidelines (updated this year - 2021) mention the need to aim for a lower level of trihalomethanes, but also mention the valuable need of water disinfection by chlorine which prevents other safety risks [12].


By contrast to the WHO, the U.S. Environmental Protection Agency (US EPA) has categorized bromoform as a B2 Probable human carcinogen based on sufficient evidence of carcinogenicity in animals. The US EPA has set up the following guideline levels [14]:

  • Non cancer Reference Dose for Oral Exposure (RfD) 20 µg/kg- day (0.02 mg/kg- day) for hepatic lesions

In the USA, the Centre for Disease Control and Prevention (CDC) has stated that bromoform is not found in food [13].

However, whilst this might have been the case in the CDC study, this might no longer be the case if it has been shown that bromoform is able to be transferred to food through feed.

The importance of instigating regulatory assessment and monitoring immediately

In Australia there are two licensed producers of seaweed feed supplements for methane reduction, and the products are patented. Expansion in seaweed commercialization will accelerate a greater uptake by farmers seeking to improve sustainable cattle feeding practices. At the same time there are global initiatives in relation to ensuring the safety of seaweed products. In early 2021, a Safe Seaweed Coalition [14] was established at an international level to address consumer safety in relation to seaweed usage.

One of the recent studies that did not find any retention in meat nevertheless raised the need for close monitoring of the situation with the following statement: "Due diligence requires continued monitoring if inclusion periods are extended and the cumulative intake levels are increased which may be the case in some dairy systems“[6].

Clearly, if exposure to bromoform is likely to increase, it is important for Australian regulators to assess safety and to set regulatory levels regulatory levels for exposure in foods and that ongoing monitoring be mandatory.


1.      Gibbons, J.M., S.J. Ramsden, and A. Blake, Modelling uncertainty in greenhouse gas emissions from UK agriculture at the farm level. Agriculture, Ecosystems & Environment, 2006. 112(4): p. 347-355.

2.      Garnett, T., Livestock-related greenhouse gas emissions: impacts and options for policy makers. Environmental Science & Policy, 2009. 12(4): p. 491-503.

3.      Morgavi, D., et al., Microbial ecosystem and methanogenesis in ruminants. animal, 2010. 4(7): p. 1024-1036.

4.      Roque, B.M., et al., Red seaweed (Asparagopsis taxiformis) supplementation reduces enteric methane by over 80 percent in beef steers. Plos One, 2021. 16(3): p. e0247820.

5.      Honan, M., et al., Feed additives as a strategic approach to reduce enteric methane production in cattle: Modes of action, effectiveness and safety. Animal Production Science, 2021.

6.      Kinley, R.D., et al., Mitigating the carbon footprint and improving productivity of ruminant livestock agriculture using a red seaweed. Journal of Cleaner Production, 2020. 259: p. 120836.

7.      Roque, B.M., et al., Inclusion of Asparagopsis armata in lactating dairy cows’ diet reduces enteric methane emission by over 50 percent. Journal of Cleaner Production, 2019. 234: p. 132-138.

8.      Stefenoni, H., et al., Effects of the macroalga Asparagopsis taxiformis and oregano leaves on methane emission, rumen fermentation, and lactational performance of dairy cows. Journal of Dairy Science, 2021. 104(4): p. 4157-4173.

9.      Muizelaar, W., et al., Safety and transfer study: Transfer of bromoform present in asparagopsis taxiformis to milk and urine of lactating dairy cows. Foods, 2021. 10(3): p. 584.

10.   12.         RAIS. Formal toxicity summary for bromoform. 1995; Available from: https://rais.ornl.gov/tox/profiles/bromofrm.html.

11.   WHO, Guidelines for drinking-water quality. 2017.

12.   NHMRC. Australian Drinking Water Guidelines (2011)- Updated Marhc 2021. 2021; Available from: https://www.nhmrc.gov.au/about-us/publications/australian-drinking-water-guidelines#block-views-block-file-attachments-content-block-1.

13.   CDC, Public health statement for bromoform and dibromochloromethane. 2015.

14.   Coalition, S.S.; Available from: https://www.safeseaweedcoalition.org/.


This is general information rather than legal advice and is current as of 2 Dec 2021. We therefore recommend you seek legal advice for your particular circumstances if you want to rely on advice or information to be a basis for any commercial decision-making by you or your business.