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Why chromium causes dermatitis

CEMENT PRODUCERS have warned that their prices will rise late next year as new European health and safety regulations begin to bite.

As NCEI went to press the Internal Market Council of Ministers was expected to approve a directive which would severely limit the soluble chromium content of all European cements.

The move is designed to cut the incidence of cement-induced eczema and dermatitis among concrete workers.

But most cements will be unable to meet the new limits without using special additives.

This will push up production costs.

'A vast increase in demand for the additive is inevitable, ' said British Cement Association (BCA) head of external affairs Martin Casey.

'This means higher production costs, not to mention the capital cost of installing the equipment to add the additive.'

The new equipment will be needed to reduce the content of soluble chromium in cement.

Denmark has been working to the new soluble chromium levels of no more than two parts per million for 20 years.

All German-bagged cement now contains an admixture if the natural soluble chromium level of the cement is above 2ppm.

Casey said the BCA's position was that the most cost effective way to cut the risk of 'chrome dermatitis' was to strictly enforce personal protective equipment regulations.

'Another problem is that there is no test available that can measure soluble chromium content in all types of cement, ' he said.

'A new test is urgently being developed in Europe, but it's unlikely to be ready until at least two years after the new Chromium's atomic structure allows it to exist in two forms, trivalent chromium - Cr III - and hexavalent chromium - Cr VI . Each can combine with either three or six compatible atoms of other elements to form a range of compounds.

Significantly, Cr VI dissolves more readily in water.

All Portland-type cements are made from raw materials that contain minute traces of Cr III . This is converted to Cr VI in cement kilns, at temperatures higher than 1,400infinityC or more.

Freshly mixed concrete is a highly alkaline material, thanks to the calcium hydroxide released by the hydrating cement. As a result it can sensitise unprotected skin.

Then the Cr VI in wet cement can easily pass through the skin and penetrate cell walls, where the body's chemistry converts it to Cr III . In this form the chromium easily bonds to proteins, triggering an allergic reaction.

Most cement producers are expected to add 0.35% by weight of ferrous sulphate to the cement clinker during the final grinding process to control Cr VI content.

In the wet cement this reduces the Cr VI to Cr III , which then precipitates out as insoluble chromium hydroxide.

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