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Seafood FAQ: Don’t let malachite green put you in the red

The banned substance is showing up in Asian eel and basa

Highly sensitive, expensive lab equipment is required
    to conduct HPLC (high-performance liquid chromatography)
    testing, one of two tests for malachite green. - Photo courtesy of the Grobest Group
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 malachite.

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 malachite green?

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 the product.


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 malachite green.

"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 testing equipment."

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 spectrometry).

Both methods "involve high-
sensitivity equipment, delicate 
ex­traction processes and skilled equipment operation," says Patton.

"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 least 
a day.


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