Thursday, May 10, 2007

What is asbestos?

Asbestos is usually thought of as a single mineral, or at least a family of minerals that is well defined and universally recognized. This is false. In fact, "asbestos" was a label created by the need to describe a group of six commercially available mineral fibers, namely actinolite, amosite, anthophyllite, chrysotile, crocidolite and tremolite (z) in litigation.

Figure B: Amosite Asbestos, The second most common type. Photo: New York State department of Environmental Conservation

The need for the catch-all “asbestos” became apparent when exposure to the fiber and its many products proved hazardous. Lawsuits by the first wave of injured workers led to the creation of an “approved list” of mineral specimens by the EPA, negotiated by the government, asbestos manufacturers, and lawyers representing the injured. It was and it remains an economic and political term, not a scientific one. (e)

Figure C: Tremolite Asbestos, Photo: New York State department of Environmental Conservation

As a result, the term asbestos doesn’t include all the possible fibrous mineral forms of impure magnesium silicate that behave like asbestos. Many of these could be considered just as carcinogenic, if not more so. Examples abound; there are Taconite mines in the United States, and while Taconite isn’t on the asbestos list, its carcinogenic track record certainly qualifies it as a health hazard.

Erionite is another fiber that is missing from the list and was recently identified as a particularly toxic asbestiform fiber. Erionite was found in the home building materials used in Turkish villages of Karain and Tuzkoy. It has been implicated in the deaths of hundreds of villagers over the years. (f) It is no longer disputed that Erionite causes mesothelioma and belongs on the registry of asbestos-like minerals. (ac) Deposits of Erionite have been found in San Bernardino County, California and it may well be found elsewhere in the world.

There are two basic forms of asbestos fibers: amphiboles, which are straight needle-like fibers, and serpentine asbestos, which consists of curled and more pliable fibers. Early studies seemed to indicate that only amphiboles caused cancer and there was a vigorous debate concerning conflicting studies as to whether Chrysotile asbestos was carcinogenic.
Recent research has proven that Chrysotile fibers do cause mesothelioma but but that Tremolite and Crocidolite are even more potent.

Figure D: Crocidolite Asbestos, Photo: New York State department of Environmental Conservation

The list of cancer-causing mineral fibers that should be classified as asbestos is still growing. Banning just those fibers known today as asbestos would resolve only a fraction of the problem. The continuing issue of exposure to asbestos-like materials and their health hazards is unlikely to go away in the foreseeable future.

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