Malachite Green in Foods
- There are concerns over the presence of the potential carcinogenic chemical malachite green (MG) in various freshwater fish and their products. This brief gives an account of this substance and the risk to public health in light of available scientific information and the recent food surveillance findings.
- Malachite green (MG) is a synthetic dye used to colour different materials such as silk, wool, cotton and paper.
- MG has been used commonly worldwide in aquaculture as early as the 1930s and is considered by many in the fish farming industry as an effective antifungal and antiprotozoal agent. It has been used for the treatment of parasitic, fungal and protozoan diseases in fish and applied as a topical antiseptic.
- When fish is treated with MG, this substance will be absorbed and metabolised in tissues of fish. It has been reported that one of its major metabolites, namely, leucomalachite green (LMG), would persist in fish tissues for a long period of time. It was also more recently reported to be detected in low levels in wild fish (including those fish that lives downstream from the effluents of treated sewage), which suggest MG can exist as background contaminants in fish that are not intentionally treated with MG.
Public Health Significance
- The international food safety authority Joint FAO/WHO Expert Committee on Food Additives (JECFA) had evaluated MG in 2009. The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of MG.
- In some research studies in experimental animals, MG was found to be toxic to the liver, and abnormalities in the thyroid, and affect the foetal development of the experimental animals.
- Animal studies also suggest that MG may cause thyroid gland follicular cell adenoma and carcinoma in rats and liver cancer in mice. However, there is yet no evidence of carcinogenicity for MG in humans.
- As for genotoxicity (ability to cause damage to genes), there are some evidences that a genotoxic mechanism may be possible in certain high dose LMG animal experiments.
- Due to its ability to cause cancer in experimental animals, it is not appropriate to use MG in food fish. Given the toxicological information available, extensive abuse of MG in aquaculture may result in excessive exposure to MG by the consumers resulting in adverse health consequences.
- As MG and LMG are possibly both genotoxic and carcinogenic, the margin of exposure approach has been used by JECFA for risk assessment, based on the pivotal effect of induction of hepatocellular adenomas or carcinomas in female mice treated with LMG. The MOE values can be used to compare the level of concerns among different exposure levels.
- Codex has not established food safety standards for MG in food. However, Codex has established a recommended risk management measures on MG in 201stating that "In view of the JECFA conclusions on the available scientific information, there is no safe level of residues of malachite green or its metabolites in food that represents an acceptable risk to consumers. For this reason, competent authorities should prevent residues of malachite green in food. This can be accomplished by not using malachite green in food producing animals."
- The US, the EU (including the UK), Canada, and the Mainland do not permit the use of MG as a veterinary drug on food animals, aquaculture or fish for human consumption. At the same time, the EU has also established a level of 2 μg/kg for MG and LMG residues in aquatic products, which acts as an action limit for internationally traded food consignments in EU, below which food consignments with MG and LMG levels will not be rejected.
- In Hong Kong, MG has been included in the Harmful Substances in Food Regulations since 2005 to prohibit the presence of MG in all food sold in Hong Kong. This legislative amendment makes it an offence to import or sell for human consumption any food containing MG. Offenders will be prosecuted and upon conviction will be liable to a fine of $50,000 and to imprisonment for 6 months.
Advice to the Trade
- Do not use MG on food fish from culture to retail levels. Operate all food fish-related businesses under good agriculture practices.
- Buy fish from reputable suppliers or importers. Avoid buying fish from dubious sources. In case of doubt, ask for and check documents and certificates accompanying the consignment to ensure the supply is MG free.
Advice to Consumers
- Buy food fish from reputable sources. Do not patronise illegal hawkers selling food fish and their products.
- Maintain a balanced diet with a wide variety of food.
Risk Assessment Section