What is malachite green, the illegal additive in aquaculture?
Live fish pulled from shelves
Around November 23, 2016, observant consumers noticed that many supermarkets had no live fish for sale. Regarding this unusual phenomenon, the relevant authorities declined to be interviewed, and the supermarkets were also vague. Before any credible official information was released, all kinds of speculation circulated, such as suspicions that water quality pollution had occurred in Beijing, or rumors that water body pollution had contaminated freshwater fish.
On November 23, 2016, the official Weibo account of the Beijing Municipal Food and Drug Administration, "Capital Food and Drug", posted a message attempting to dispel consumers' doubts. The message stated that in 2016 Beijing sampled and tested a total of 1,034 aquatic products citywide, with a pass rate of 96.62%; from 2015 to November 2016, the city sampled and tested a total of 2,661 aquatic products, with an overall pass rate of 95.94%. According to information from the Beijing Food and Drug Administration, aquatic product sampling took place every month and every quarter, covering Beijing's major aquatic product markets, shopping malls and supermarkets, and catering enterprises, and the overall sampling results were good.
"It is true that most supermarkets have stopped selling live fish, but the specific reason is unknown; it is the merchants' own independent business behavior," said a staff member of the Beijing Food and Drug Administration. This staff member acknowledged that supermarkets had pulled live fish from shelves, also admitted not knowing the reason, and offered a habitual explanation: independent business behavior. However, if many merchants all adopted this kind of "independent behavior", then it was a public crisis.
On November 24, 2016, Caixin interviewed an "authoritative source" at the State Food and Drug Administration, who gave an "authoritative conclusion": "On November 17, the State Food and Drug Administration issued a notice for special inspections of aquatic products in ten cities, one part of which was sampling and testing for veterinary drug residues. After that, the Second Food Supervision Department (responsible for distribution) prepared to conduct sampling inspections in the Beijing market, and the news leaked out, causing all aquatic products on the market to be withdrawn from sale." This authoritative source also explained: "This shows, first, that confidentiality work was done poorly. Second, that hidden rules exist in the market, and operators felt guilty, so they pulled products from shelves first and asked questions later."
It was later learned that the Beijing Food and Drug Administration planned to implement the "Special Rectification Plan for Excessive Antibiotics, Banned Compounds and Veterinary Drug Residues in Livestock, Poultry and Aquatic Products" issued by five departments including the Food Safety Office of the State Council. On the basis of sampling and testing key varieties such as turbot, snakehead and mandarin fish (the three fish) and monitoring malachite green and nitrofurans (the two drugs), it also further expanded the scope of sampling in light of the characteristics of sales in the Beijing market, conducting comprehensive sampling and routine monitoring of multiple varieties of marine fish and freshwater fish on the market. Unfortunately, this news leaked, and to avoid testing, supermarkets simply carried out a "voluntary withdrawal" of live fish - I won't sell fish, so why inspect me?
What is malachite green?
So what exactly is malachite green, the substance whose presence in the live fish sold by supermarkets they had no confidence about? Malachite green is a synthetic organic compound belonging to the triphenylmethane class of green dyes. It is both a dye and a drug that kills fungi, bacteria and parasites, and long-term use in excessive amounts can cause cancer. Although it is called malachite green, it does not actually contain malachite; the two merely have similar colors. Malachite and malachite green are two completely different substances.
After malachite green enters the body of aquatic animals, it rapidly metabolizes into fat-soluble leucomalachite green. Malachite green has potential carcinogenic, teratogenic and mutagenic effects, and its use in aquaculture has not been approved by the U.S. Food and Drug Administration (FDA); according to the provisions of EU Act 2002/675/EC, the total residue limit of malachite green and leucomalachite green in food of animal origin is 2 ppb; Japan explicitly stipulates that malachite green residues must not be detected in imported aquatic products; in China, the agricultural industry standard "NY5071-2002 Guidelines for the Use of Fish Drugs in Pollution-Free Food" also lists malachite green as a banned drug. Unfortunately, because there is no cheap and effective substitute, the use of malachite green in aquaculture has been repeatedly prohibited yet continues.
Malachite green rapidly metabolizes into leucomalachite green in the body of aquatic animals, and the toxicity of leucomalachite green even exceeds that of malachite green, so the total amount of malachite green and leucomalachite green is usually used as the limit indicator for malachite green residues in food of animal origin. Physicochemical detection methods for malachite green include: thin-layer chromatography, spectrophotometry, high-pressure liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, and so on; by comparison, immunological detection methods are more commonly used.