Dear Byron,
Not likely to get malachite green (MG) contamination from nature at those levels (>2ppb). If this banned fungicide (not approved to be used on food producing animals) is not being added through the primary production of the tilapia (used to treat ectoparasites such as gill flukes, ich and trichodina as well as bacteria and fungal infections) and shrimp, it is most likely to come from the balanced feed (similar to the problems with crystal violet - another banned triphenylmethane dye) and/or environmental contamination..
Malachite green and its major metabolite, leuco-malachite green (LMG) has been reported to have mutagenic and carcinogenic effects on humans. When malachite green is used in aquatic animals, it will be metabolized to leuco-malachite green. The non-polar LMG has been found to retain in catfish muscle for a longer period of them, 10 days for LMG compared to 2.8 in MG. It has been determined that the half lives of the retention of malachite green and leuco-malachite green in catfish muscle is 2.8 days. Therefore, laboratory analyses must determine both MG and LMG and report results as the sum of both.
Possible sources of contamination:
* Paper or Textile production facilities: MG is used as an industrial dye in some manufacturing applications, including pulp and paper and textiles. Discharges from such operations could contaminate rivers, streams and other water bodies.
* Balanced feed: chicken meal/bone, fish meal and/or rice/soybean contaminated with triphenylmethane dyes
* Rice/corn/soybean crops - if nearby, or alternating crops with tilapia ponds could be a source of contamination
* Sterile Gloves - check the gloves used at the processing plants. Some brands will have triphenylmethane dyes' powder.
Hope this helps.
Regards,
Sergio Sanchez
-----Original Message-----
From: owner-seafood@ucdavis.edu [ mailto:owner-seafood@ucdavis.edu]On
Behalf Of Byron Gurdián García
Sent: Thursday, October 11, 2007 9:18 AM
To: seafood@ucdavis.edu
Subject: Malachite green
Dear Sefood Commnunity:
I want to know about natural sources of malachite green, if they exist.
The point is that some samples taken from St. Peter fish ponds and aquacultured shrimp have 2 ppb of malachite green, this levels reached the MRL for this residue.
I also took samples in the river, before the ponds and after the ponds, but haven't gotten the results.
On the other hand apparently agrochemicals used in different crops such as rice have in their formulation malachite green.
I hope your prompt support
Byron
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