June 2007, the FDA blocked the importation of several varieties of seafood due to continued malachite green contamination. Malachite green has been banned in the United States since 1983 in food-related applications. The substance is also banned in the United Kingdom. It is prohibited from the use in food in Macao. Animals metabolize malachite green to its leuco form. Being lipophillic (the leuco form has a log P of 5.70), the metabolite is retained in catfish muscle longer (HL = 10 days) than is the parent molecule (HL = 2.8 days). Toxicity The (oral, mouse) is 80 mg/kg. Rats fed malachite green experience "a dose-related increase in liver DNA adducts" along with lung adenomas. Leucomalachite green causes an "increase in the number and severity of changes". As leucomalachite green is the primary metabolite of malachite green and is retained in fish muscle much longer, most human dietary intake of malachite green from eating fish would be in the leuco form. During the experiment, rats were fed up to 543 ppm of leucomalachite green, an extreme amount compared to the average 5 ppb discovered in fish. After a period of two years, an increase in lung adenomas in male rats was discovered but no incidences of liver tumors. Therefore, it could be concluded that malachite green caused carcinogenic symptoms, but a direct link between malachite green and liver tumor was not established. Detection Although malachite green has almost no fluorescence in aqueous solution (quantum yield 7.9x10−5), several research groups have developed technologies to detect malachite green. For example, Zhao et al., demonstrated the use of malachite green aptamer in microcantilever based sensors to detect low concentration of malachite green. References Further reading Schoettger, 1970; Smith and Heath, 1979; Gluth and Hanke, 1983. Bills et al. (1977) External links U.S. National Institutes of Health U.S. Food and Drug Administration U.K. Department of Health Malachite green - endospore staining technique (video) Triarylmethane dyes Staining dyes PH indicators Antimicrobials Aromatic amines Fish medicine Dimethylamino compounds