Review: Coalinga Chrysotile: Dissolution, Concentration, Regulation and General Relevance

Abstract

Coalinga chrysotile's lack of biological activity in animals and humans is due to its amphibole-free nature, short fiber length, and enhanced width, all of which contribute to a greatly reduced bio-persistence. Compared to most other chrysotile types, it has greater solubility and enhanced dissolution, especially the very small percentage of long, thin respirable fibers that reach the alveolar portions of the lung. In consequence, the mineral poses no health threat. The ultra-structural features underlying the susceptibility to dissolution include spiral structures, permanent ledges, an absence of inter- and intra-fibrillar matrix, extremely narrow fibrillar width giving very high surface areas and surface reactivity potentials, and a relatively high number of fibrillar `ends'. Any fibers released from products made from Coalinga type material; including friction products, ceiling tiles, acoustic tiles, shingles, piping and other cement products as well as fireproofing materials, through manipulation will, on aerosolization, show re-aggregation and other properties of the parent fiber. Fiber analysis of any chrysotile containing material has always been problematic because of the fundamental structure of the fibers. Research has shown the need for indirect preparation methods of Coalinga type chrysotiles for risk assessment purposes. Direct preparation methods do not give correct answers and therefore cannot reflect biological potential. Fiber counts made by phase contrast microscopy, for example, will include large numbers of long pseudo-fibers and give results that are very misleading. The true biological nature of short and long Coalinga type chrysotiles can only be predicted using the results of indirect analysis.