1. There are recent concerns over the
presence of the potential carcinogenic chemical malachite
green (MG) in eels, processed eel products and freshwater
fish. 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. Malachite green (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 is considered
by many in the food industry as an effective antifungal
agent. It has been used for the treatment of parasitic,
fungal and protozoan diseases in fish.
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.
Public Health
Significance
1. International food safety authorities
such as the Joint FAO/WHO Expert Committee on Food Additives
(JECFA) and the International Agency for Research on
Cancer (IARC) have not evaluated the safety of MG.
2. In some research studies in experimental
animals, MG was found to be toxic to the liver, cause
anaemia and abnormalities in the thyroid, and affect
the foetal development of the experimental animals.
3. Animal studies also found that MG
may cause liver tumours in mice. However, there is yet
no evidence of carcinogenicity for MG in humans.
4. As for genotoxicity (ability to cause
damage to genes), there are conflicting evidences in
the international scientific community on whether MG
and LMG cause gene mutation or damage to the gene.
5. 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.
6. However, in light of the recent findings
on the levels of MG found in freshwater fish available
locally, exposure to such levels of MG is unlikely to
cause significant adverse health consequences to the
consumers. It has been estimated, using international
standard risk assessment methods inferred to humans
based on results of animal studies, that significant
adverse health effects due to MG are not expected even
when a person consumes up to 290 kg of freshwater fish
each day. For eels, which were found to contain relatively
higher levels of MG, significant adverse health effects
due to MG are not expected when a person consumes up
to 7 kg of eels a day.
Regulation
1. Codex has not established food safety
standards for MG in food.
2. The US, the EU (including the UK),
Canada, Japan, Thailand, Singapore and the Mainland
do not permit the use of MG as a veterinary drug on
food animals, aquaculture or fish for human consumption.
3. In Hong Kong, MG has been included
in the Harmful Substances in Food Regulations 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. In the light of the available scientific
information and levels of MG detected in freshwater
fish and eels recently, risk of significant adverse
health effects of MG due to consumption of freshwater
fish or eels is considered remote.
2. Buy food fish from reputable sources.
Do not patronise illegal hawkers selling food fish and
their products.
3. Maintain a balanced diet with a variety
of food.
