Concern for Chromium (Cr) and Chrome(VI) use in Leather,Textiles (wool, cashmere and angora),Plastics item, Metals items.

Description:
Chromium (Cr) is a hard metal which can exist in 3 forms or valencies ~ Chrome (0), Chrome (III) / trivalent chromium and Chrome (VI) / hexavalent chromium.

Metallic Chromium ~ does not occur naturally but is extracted from natural chromite ore. It is used to harden steel and provide corrosion resistance in alloys.

Chrome (0) ~ the metallic, non-hazardous form/valency of chromium.

Chrome (III) / Trivalent Chromium ~ a non-hazardous form/valency of chromium. The predominant valency of chromium which occurs in nature in compounds in rocks, soil, plants and volcanic emissions. It also occurs naturally in foodstuffs and is one of the essential nutrients needed by the body. Chromium (III) sulphate is used to tan leather and is non-hazardous. It is a greeny blue colour and gives rise to the name ‘wet blue’ in the tanning stage.

Chrome (VI) / Hexavalent Chromium ~ a hazardous form/valency of chromium which rarely occurs in nature but is formed when trivalent chromium is oxidised. This usually occurs in the presence of oxygen combined with other factors, such as extremes in pH and temperature and can occur in poorly tanned leathers. The salts of chrome (VI) are orange in colour and a slight orange colour can sometimes be detected in metal coatings containing hexavalent chromium. Chrome (VI) is a carcinogen, skin irritant and is hazardous in the environment.

Chemically
The chemical element chromium has got the symbol Cr and the atomic number 24. It is a hard silvery-metallic and polish metal, which is resistant to corrosion and tarnishing. Chromium exhibits a wide range of possible oxidation stages, with the states +2, +3 and +6 are the most common. The oxidation state +3 of chromium is the most stable one. The reason for this is its half-filled d3-subshell.

Where it may be found/Possible application:
Leather ~ Chrome (VI) mainly found in poorly tanned leathers. Occurs in the ‘after-chroming’ process due to poor selection of chrome powder and inappropriate processing conditions which lead to the oxidation and conversion of Cr(III) into Cr(VI). This can happen during shipping and storage and can be dependent on a number of conditions such as heat and pH and if leathers are excessively neutralised prior to dyeing. Strong alkalines such as ammonia should be avoided when processing leather and the application of bleaching (oxidising agents) for pale coloured leathers could also cause chrome (VI) formation.
Textiles (wool, cashmere and angora) ~ rarely found in textiles but can be found in some wool products dyed with 2-stage after-chrome dyes where chromates are applied after dying to improve colourfastness.
Pigments and dyes ~ chromium found chrome mordant dyeing, after chromed dyes and some pre-metallised / metal complex dyes.
N.B. Pre-metallised or metal complex dyes containing Chromium are not hazardous during wear as the chromium is fixed within the dyestuff. Pre-metallised / metal complex dyes in waste water effluent are hazardous to the environment and should be treated correctly before be water is discharged into water ways.
Plastics ~ in colourants.
Metals ~ chromium used in stainless steel, alloys and plating used for trims and household products etc. Added to cutlery to increase its strength and polish.

-In form of metalized dyestuffs.
-In form of oxidants for dying with sulfide dye and / or vat dye.
-In chromium tanning for leather products (Cr-VI).

Reason for concern/Effects:
Humans ~ Chrome (VI) highly toxic, carcinogenic, skin irritant. Can cause a wide range of effects ranging from cancer to rashes and skin ulcers, dizziness and vomiting. Chrome (0 & III) ~ no concern as not hazardous.
Environment ~ Chrome (VI) bioaccumulative, highly toxic and carcinogenic to micro organisms and aquatic species. Chrome (0 & III) ~ no concern as not hazardous.

Hexavalent chromium (Cr-VI) is highly toxic and can easily penetrate skin. Its compounds have been established to be carcinogenic and skin irritating.

Exposure:
Humans ~ Chrome(VI) from products in direct and prolonged contact with the skin or from ingestion if a product is sucked or swallowed. Chrome(VI) used in production of chrome plated objects can be especially hazardous to workers.
Environment ~ Chrome(VI) via water from effluent and waste water discharged from production plants.

Alternatives:
Leather ~ Chrome tanned leathers can still be used but have to be processed correctly to ensure low levels of Chrome (VI) on the finished product and in waste water effluent. Alternatively vegetable tanned leather can be used but there is a price premium and colourfastness properties are sometimes harder to achieve.
Akdehyde (wet white) and Novel tannages (Epoxytan) are two other alternatives.

Chrome tanned leather will not pass BS EN71 part 3 (aka toxicity testing) so in these cases, vegetable tanned leathers should be used.

After chromed wool dyes ~ alternative dyes are available such as reactive dyes.

Comments:
Leather ~ due to Cr(III) being readily converted into Cr(VI) during storage and transit regular testing should be carried out on high risk products after prolonged storage or transit.

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1 Response

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