Coalinga Chrysotile: A Short Fibre, Amphibole Free, Chrysotile: Part V - Lack of Amphibole Asbestos Contamination

Abstract

Exposure to asbestos in the indoor built environment has been a concern for many years. The most common exposures in that setting are to short ultra-thin, naturally defibrillated form of fibrous asbestiform chrysotile and possibly trace amounts of short, non-asbestiform amphibole. Coalinga chrysotile is a short fibre mineral that was mined from a large ore body in California. It has been investigated in considerable detail since, although it is widely believed to be amphibole free, evidence for this has not hitherto been summarised. Analytical results from investigations that directly searched for amphiboles and geological studies from which the presence or absence of amphibole can be inferred, have indicated that Coalinga chrysotile is free of amphibole asbestos. Indeed, numerous investigations, performed over almost half a century, using a variety of techniques including the most sensitive methods, and studying many thousands of samples have failed to find any amphibole asbestos in Coalinga chrysotile. Only very rarely have non-asbestiform, “non-friable” amphibole (so-called cleavage fragment) minerals been found in the New Idria serpentine body but away from the ore zone. A large body of animal and human evidence indicates such cleavage fragments lack biological potential.

Health risk of chrysotile revisited

“…Ilgren (2004) summarized these results stating that “Only very rarely have non-asbestiform ‘non-friable’ amphibole (so-called cleavage fragment) minerals been found in the New Idria serpentine body but away from the ore zone”.…”

Review: The Fiber Width of Coalinga Chrysotile: Reduced Respirability due to its Thick Nature in an Aerosol and its ``Ultra-Thin'' Nature in Aqueous Solution (In Vivo)

“…Bernstein et al [19] found clusters [2,12]. 28 Indoor Built Environ 2008;17:27- 41 Ilgren in air samples taken from their animal exposure chambers and the King City Mill. They said these were dramatically different from Canadian fibers [20] and ''composed of multiple fibrils of shorter length''.…”

“…''A series of electron micrographs of defibrillated Canadian Grade 7R and defibrillated New Idria flake were prepared and the external diameters of a statistical sampling of the fibrils appearing on each photographic plate were measured using an optical microscope with a filar eyepiece. Histograms of the distribution of fibril diameters determined in this way are shown in ( Figure 5; also [28]). The Canadian specimen had a larger average diameter and a greater variation in diameter than the New Idria material.…”

“…Many workers have demonstrated that the surface areas for Coalinga and Stragiari chrysotile fiber (both formed geologically in a similar manner [28]) are ''higher than those reported for any natural chrysotile'' [13,27]. High surface areas would be expected with the lack of inter-and intra-fibrillar matrix (see ''Clean surfaces'' in the following paper [37], illustrated in Figure 2) and extremely narrow width (above) (also see [27]).…”

Coalinga Chrysotile under the Microscope

“…This muddies the waters somewhat. One problem is that some amphibole minerals are found in close association with chrysotile, although this is not the case with the chrysotile in question [3]. Also, the fibrous amphiboles and chrysotile were, in the past, lumped together for commercial reasons and all given the name ''asbestos''.…”