Spying asbestos

Science News,  Feb 23, 2008  by Janet Raloff

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Contractors and building inspectors may soon find themselves dyeing to see asbestos.

Owing to the mineral's strength, limited chemical reactivity, and insulating properties, manufacturers have added traces of asbestos over the years to a host of building materials, including those made from concrete. But identifying which materials host the carcinogenic mineral is crucial for detection and cleanup. Doing so has proven problematic because the fibers are both microscopic and colorless.

[ILLUSTRATION OMITTED]

Unless you tint them. And that's just what Japanese researchers have done to chrysotile--the most commonly used form of asbestos.

They identified a red dye and an indigo-hued dye that bind to magnesium, a component of asbestos. Each dye can impart visible color even when the fibers account for no more than 0.1 percent of the mass of a piece of concrete--the minimum asbestos content triggering regulatory action in Japan and some other nations.

Because the coloring agents also bind to the calcium in cement, concrete must first be treated with a chemical to tie up its calcium. But in such pretreated concretes, dyes tint only the asbestos--and the intensity of color increases quantitatively with growing fiber content. Yoshihiko Oke of Tohoku University in Miyagi, Japan, and his colleagues describe the technique in an upcoming issue of Environmental Science & Technology.

"We can easily do the test onsite"--and in minutes, Oke says.

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