« June 2006 Table of Contents
Seafood FAQ: Don’t let malachite green put you in the red
The banned substance is showing up in Asian eel and basa
By Steven Hedlund
June 01, 2006
First it was chloramphenicol. Then it was nitrofurans. Now
it's malachite green, a chemical dye whose name derives from
its iridescent green color, similar to the mineral
Trace amounts of malachite green, a banned substance, are
showing up in farmed seafood products. Since late last year,
the Food and Drug Administration has busted at least four Asian
companies for exporting malachite-green-tainted eel and basa to
the United States.
So far, the emergence of malachite green has received more
press in Canada, where imported eel and locally raised salmon
have tested positive for the substance in recent months. But
the issue is beginning to garner some media interest in the
United States, as the FDA has stepped up inspection of seafood
suspected of containing malachite green.
Not much is known about the substance among importers,
distributors, retailers and restaurateurs, let alone the media
and consumers. Now is an ideal time to learn about malachite
green, before the issue draws more media attention.
Q. What is malachite green?
Malachite green, a triphenylmethane dye, can be used as a
fungicide to treat fungal, bacterial and parasitic infections
in fish and fish eggs.
The substance can also be used to color paper, cotton, wool,
silk, jute and leather. As a result, malachite green can be
found in the effluent of pulp-and-paper mills.
Q. Are there laws governing its use?
The United States, Canada, European Union, Japan and Chile
are among the countries that prohibit the use of malachite
green in food production.
The FDA has a zero-tolerance policy for malachite green and
its metabolite, leucomalachite green, meaning no food
containing any detectable level of the substances can be sold
in the United States.
The FDA tests for malachite green at a sensitivity level of
1 part per billion.
Health Canada in April began testing at a level of 1 ppb on
an interim basis. The European Union and Japan test at levels
of 2 ppb and 5 ppb, respectively.
Q. What are the potential
adverse health effects of
The National Toxicology Program, part of the U.S. Department
of Health and Human Services, published a study in 2005 that
found malachite green didn't cause cancer in female mice but
may cause tumors to form in the liver and thyroid and mammary
glands of female rats.
Canada's Food Safety Network says malachite green poses "no
immediate risk" to human health and notes that it's "very
unlikely" humans will get sick from eating fish containing
trace amounts of malachite green. Health Canada in April
advised the public that "the probability of serious adverse
health consequences associated with daily consumption of fish
containing trace amounts of malachite green and leucomalachite
green is remote."
All three organizations agree that additional research is
necessary to better determine whether malachite green is
harmful to human health.
Q. Which seafood items are tested for malachite green?
Catfish is the first seafood item the FDA tested for
malachite green. In fiscal 2005, 160 samples of catfish were
examined, and no residues of malachite green were detected.
In fiscal 2006, the FDA began testing primarily basa, salmon
and eel, in addition to catfish, for malachite green and plans
to inspect a total of 285 samples. Samples are obtained from
cold-storage warehouses, where importers hold product.
As of late May, four Asian companies were listed on the
FDA's Import Alert for shipping malachite-green-tainted seafood
to the United States. Three are Chinese eel exporters, the
other a Vietnamese basa exporter. Two occurred late last year,
the others in April.
The shipments were detained, and the companies are barred
from exporting the products to the United States until they've
been tested and found free of malachite green.
"Cheap, effective and readily available," malachite green is
used in aquaculture in many Asian countries, where the
substance is either legal or the ban on it isn't adequately
enforced, says an FDA official.
The Canadian Food Inspection Agency detected trace amounts
of malachite green (the highest was 0.3 ppb) in samples of
salmon from two British Columbia farms in 2005.
Wild salmon has also tested positive for malachite green in
the past, leading scientists to theorize that the fish were
contaminated by paper-and-pulp mill effluent. The CFIA and
Department of Fisheries and Oceans inspected 99 samples of wild
salmon in 2005, but none contained malachite green.
In March, a Quebec importer voluntarily recalled a Taiwanese
brand of grilled eel after trace amounts of malachite green,
leucomalachite green and nitrofurans were found in samples of
Q. Is demand for testing
on the rise?
SDLq Yes," says Ronald Patton, president of Grobest USA, a
Taiwan-based firm that operates dozens of fish-feed mills and
processing facilities throughout Asia and conducts tests for
"More and more seafood buyers are requesting malachite-green
tests before shipment," Patton
reports. "The problem [in
accommodating the requests] is the extremely high cost of the
Currently, there are two methods used to test seafood for
malachite green: HPLC (high performance liquid chromatography)
and LC/MS/MS (liquid chromatography/mass spectrometry/ mass
Both methods "involve high-
sensitivity equipment, delicate
extraction processes and skilled equipment operation," says
"In short, [you] prepare a test solution from a sample,
prepare standard solutions of malachite green and inject those
solutions into HPLC or LC/MS/MS, then calculate the
malachite-green content," he explains.
Both test methods can detect less than 1 ppb of malachite
green. HPLC takes at least six hours to complete, LC/MS/MS, at