What does it mean when a dye is premetalized with chromium or some other heavy metal? What are the risks of exposure from using a dye that is premetalized with chromium?

Name: Deanna
Message: I read in the archives the question about fiber reactive dyes and heavy metals, but wanted to ask about acid dyes and heavy metals, particularly the lanaset dyes, a few of whom, according to your table do contain heavy metals.  In particular Jet black contains chromium.  

I was wondering if you could explain what it means when a dye is premetalized with chromium or some other heavy metal and also talk about what the risk of exposure might be from using a dye that is premetalized with chromium.  I am primarily interested in dyeing wool. 

In premetallized acid dyes, such as many of the dyes in the Lanaset series, each metal atom, usually chromium, is complexed to either one or two molecules of the dye. The metal improves the fastness of the dye considerably. Dyeing with premetallized dyes is superior to mordant dyeing, in which the metal is applied to the wool as a separate reagent from the dye, because the dye is more predictable in color, and the process less harmful to the wool. Health and environmental hazards are also lower with premetallized dyes than with chromium mordants. Colors for premetallized dyes tend to be slightly brighter than those of mordant dyes, but less bright than those of non-metallized acid dyes. (Reference: Wool Dyeing, edited by David M. Lewis; published by the Society for Dyers and Colourists.)

As you know, chromium can be very hazardous when misused industrially. Overexposure and poisoning can result from breathing chromium fumes, such as from chromium-plating operations; less efficiently, ingestion and skin exposure can also result in chromium poisoning. Hexavalent chromium is much more easily absorbed than trivalent chromium and is considered more dangerous as a result. Hexavalent chromium has been classified as a human carcinogen, primarily due to a significant increase in lung cancer among those chronically exposed to high airborne levels, while trivalent chromium has not. Chromium used in dyeing is usually trivalent. However, trivalent chromium is not harmless in overdose, so it is wise to limit exposure for any form. Oddly, a form of trivalent chromium is also considered an essential part of human nutrition, in very low dosages; the requirement is between 50 and 200 micrograms per day.

Obviously, when working with Lanaset dyes, we should follow the usual good housekeeping procedures: no use of food preparation surfaces or equipment in dyeing; all food preparation surfaces must be covered; wear a properly fitting dustmask when working with  dye powders; wear gloves throughout use; keep dye powder containers closed except briefly when removing dye; no eating or smoking in the presence of dye powders or solutions.

It is useful to look at MSDS (Materials Safety Data Sheets) provided by dye suppliers. You should be able to obtain an MSDS for every potentially hazardous substance from the company from which you purchase it. PRO Chemical & Dye's MSDS for Lanaset Jet Black is not at all alarming, but it does indicate the appropriate precautions to be taken. Another MSDS page (at another site) indicates that Lanaset Black B dye powder contains 3.2% chromium, in the form of a Cr(III) organic-metal complex. Therefore, a dye painting solution of 1 teaspoon of Jet Black Lanaset dye that contains 2.5 grams of dye, dissolved in one cup (250 ml), contains 0.08 grams (which is equal to 80 milligrams or 80,000 micrograms) of chromium. After being diluted with 50 gallons of uncontaminated water, this dye concentration would meet the US EPA standard for chromium content of drinking water in the US, which is 100 micrograms per liter.  

All in all, I'd say you can go ahead and use as much Lanaset dye as you wish, without fear of hazard, as long as you do not breathe dye powder, eat or smoke around the dyes, get much skin exposure to the dye powder or solutions, or spill dye without cleaning it up properly. Just be careful to take the usual precautions.

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Posted: Friday - October 06, 2006 at 05:01 PM          

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