The collective stupidity of people never fails me... Looking at the list of feared substance that occur in Hong Kong, I can only say, good luck, my friend. Below lists a handful of substance that has been publicized in Hong Kong for being added to food (legally or illegally) and are of utmost hazard to your health:
(1) Malachite green
(2) Melamine
(3) DEHP (Bis(2-ethylhexyl) phthalate and other similar plasticizer)
(4) Cochinea colouring
This is the first installment of a four-article series on the public reaction to chemical substances identified in food.
Malachite green
Malachite green is an aniline dye which is commonly used in production of green articles made of e.g. silk, leather or even toilet paper. Another use of it is in eradicating protozoan disease, notably Ichthyophthirius multifiliis which is better known as white spot disease (白點病), a prevalent parasite of freshwater fish.
Malachite green has been implied in causing cancer, change in genetic material, abnormal babies as well as toxicity to lung[2]. Together with its metabolite in fish, leukomalachite green, these produces an increase of liver DNA adduct in rats (a measurement of genotoxicity), in a dose-related manner in concentrations above 91ppm[3]. There is also an increase in lung adenoma (a benign tumor) in the tested rats.
There is, however, in this 2-year tumorigenesis study, no increase in the occurence of liver tumor.
According to the press release by CFS, HKSAR[4], the samples concerned contained 16ppm and 0.0025ppm respectively (by LC-MS/MS among other methods[5,6]), well below the concentration that has been observed to cause significant genotoxicity.
In fact, most of the samples acquired in Hong Kong afterwards contained up to 5ppb (part per billion) only - which is, higher than the EU directive (<2ppb) but lower than the Japanese directive (<10ppb).
The ban is correct
I for one am surprised that samples would contain as much as 16ppm, far above the possibility of contamination, and this points much more to (illegal) usage of malachite green in that particular case. The ban means that future products would be tested for it with sensitive assays and the fisheries will have an incentive NOT to use malachite green in their fish-farming practice.
But the reactions are stupid
The dose makes the poison - Paracelsus
The trouble though, with these incident is that most of those who wrote about these had little idea that toxicity is related to the dose - even something as innocent as pure water or pure oxygen could be a poison if given in large enough a dose and/or long enough a time period, but even cyanide could be nontoxic if given in small enough a dose.
What people says about these malachite green-tainted eels?
"致癌鰻魚驚世大發現"[7] - Written by a chemistry teacher.
What's the deal? The dosage isn't even remotely near the carcinogenic levels. To make it worse, he further wrote "孔雀石綠經已被証實為可以致癌的物質" - when has it been classified to be a known carcinogen? The WHO publishes a list of known carcinogen - one can check here. There are some borderline evidence of carcinogenesis - e.g. a significant increase in "pooled liver adenoma and carcinoma"[8]. Yes, one can say that it is a potential carcinogen (with all the indirect evidence) but proven to be carcinogenic?
And then the worst in the article: "右圖為被過量孔雀石綠浸過的甲魚，魚身已被染成綠色" - what's remaining in the malachite green tainted fish is mostly leukomalachite green which had longer half-life (of 10 days) than malachite green - which is not coloured at all. To add to it, the observed amount (even the wow-factor 16ppm detected) will unlikely add any colour to the specimen.
Please, for god's sake - learn before you teach.
[1] Do you really expect a source on this? It's April Fool's day!
[2] Srivastava S, Sinha R, Roy D. Toxicological effects of malachite green. Aquat Toxico. 2004 Feb 25; 66(3): 319-29.
[3] Culp SJ, Beland FA, Heflich RH et al. Mutagenicity and carcinogenicity in relation to DNA adduct formation in rats fed leucomalachite green. Mutat Res. 2002 Sep 30;506-507:55-63.
[4] http://www.cfs.gov.hk/english/press/2006_10_06_1_e.html
[5] Tang HPO, Choi JYY, Analysis of Malachite Green in Fish Samples. Downloaded from: http://www.govtlab.gov.hk/g/texchange/malachite_a.pdf,
[6] Tang HPO, Choi JYY, Analysis of Malachite Green in Fish. Downloade from: http://www.govtlab.gov.hk/g/texchange/malachite_b.pdf
[7] http://www.plkchc.edu.hk/CustomPage/59/chemsir/dailylife/eel_malachite_green_toxic.htm
[8] Culp SJ, Mellick PW, Trotter RW et al. Carcinogenicity of malachite green chloride and leucomalachite green in B6C3F1 mice and F344 rats. Food Chem. Toxicol., 44 (2006), pp. 1204–1212.
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