The Fate of Asbestiform Minerals Across a Development Sequence in Serpentinitic Landscapes.

Naturally occurring asbestos poses a potential danger to human health and can be found in serpentinized ultramafic parent materials and soils, which appear throughout California.  This makes researching naturally occurring asbestos in soil an important issue from a regulatory standpoint as well as for land use and management. The objective of this study was to examine the weathering patterns of naturally occurring asbestos minerals in soil horizons across a developmental sequence in serpentinitic landscapes.  The two groups of soil profiles reflect a weathering gradient with the soil temperature and moisture ranging from thermic and xeric bordering on aridic in the weakly developed soils, to thermic and xeric in the moderately to well developed soils.  In this project we examined fiber abundance and location in the soil profiles using the pipette method for particle size analysis, x-ray diffraction (XRD) patterns, and polarized light microscopy (PLM).  We identified the presence of chrysotile in the weakly and moderately to well developed sites in all horizons from the XRD patterns as well as PLM.  In the weakly developed soil, the percentage of total chrysotile, chrysotile fibers and chrysotile bundles to the other point counted primary minerals increased with depth.  The moderately to well developed soils displayed similar trends with the total chrysotile and chrysotile bundles increasing with depth, however the chrysotile fibers decreased with depth.  The moderately to well developed soils also contained lower quantities of chrysotile present throughout the profiles.  These depth trends suggest that the weathering pathway of chrysotile initiates as bundles liberated from parent material, then likely break down into fibers through the physical weathering processes, such as in the upper horizons of the moderately weathered soils.