Risk in Brief - Malachite Green in Foods

Malachite Green in Foods

Introduction

  1. 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

  1. MG is a synthetic dye used to colour different materials such as silk, wool, cotton and paper.
  2. MG has been used commonly worldwide in aquaculture as early as the 1930s and it 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.
  3. 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 reported to be detected in low levels in wild fish (including those fish that lived downstream from the effluents of treated sewage), which suggested that MG can exist as background contaminants in fish that have not been intentionally treated with MG.

Public Health Significance

  1. In some research studies in experimental animals, it was suggested that MG might cause thyroid gland follicular cell adenoma and carcinoma in rats while its main metabolite, LMG increased incident of liver cancer in mice treated with LMG in feed. However, there is yet inadequate evidence of carcinogenicity for MG or LMG in humans.
  2. The international food safety authority Joint FAO/WHO Expert Committee on Food Additives (JECFA) evaluated MG in 2009. JECFA considered that, due to its potential to cause cancer in experimental animals, it should not be used in food fish. Also, given the toxicological information available, abuse of MG in aquaculture may result in excessive exposure to MG by the consumers resulting in adverse health consequences.
  3. The International Agency for Research on Cancer (IARC) evaluated the carcinogenicity of MG and LMG in 2022. For MG, based on limited evidence for cancer in experimental animals and inadequate evidence regarding cancer in humans, it was evaluated as Group 3 (Not classifiable as to its carcinogenicity to humans). For LMG, based on sufficient evidence for cancer in experimental animals but inadequate evidence regarding cancer in humans, it was evaluated as Group 2B (Possibly carcinogenic to humans).

Regulation

  1. Codex has not established food safety standards for MG in food. However, Codex has established a recommended risk management measures on MG in 2014 stating 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."
  2. The US, the EU, 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. The EU has previously established a level of 2 μg/kg as a reference point for action for the sum of MG and LMG residues in food of animal origin and updated it to 0.5 μg/kg in 2019. This 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.
  3. 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

  1. Do not use MG on food fish from culture to retail levels. Operate all food fish-related businesses under good agriculture practices.
  2. 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

  1. Buy food fish from reputable sources. Do not patronise illegal hawkers selling food fish and their products.
  2. Maintain a balanced diet with a wide variety of food.

Risk Assessment Section
January 2024