Separation and Characterization of Respirable Amphibole Fibers from Libby, Montana

Abstract

The vermiculite mine in Libby, Montana, was in operation for over 70 yr and was contaminated with asbestos-like amphibole fibers. The mining, processing, and shipping of this vermiculite led to significant fiber inhalation exposure throughout the community, and residents of Libby have developed numerous pulmonary diseases such as lung cancer and mesothelioma. The present study describes the separation of Libby 6-mix into respirable and nonrespirable size fractions by means of aqueous elutriation. The elutriator, designed to separate fibers with aerodynamic diameters smaller than 2.5 μm (respirable) from larger fibers, used an upward flow rate of 3.4 × 10 −4 cm s −1 . The resultant respirable fraction constituted only 13% of the raw Libby 6-mix mass, and less than 2% of the fibers in the elutriated fraction had aerodynamic diameters exceeding 2.5 μm. Surface area of the elutriated fibers was 5.3 m −2 g −1 , compared to 0.53 m −2 g −1 for the raw fibers. There were no detectable differences in chemical composition between the larger and smaller fibers. Such harvesting of respirable fractions will allow toxicological studies to be conducted within a controlled laboratory setting, utilizing fiber sizes that may more accurately simulate historical exposure of Libby residents' lungs. Importantly, this work describes a method that allows the use of material enriched in more uniform respirable material than raw Libby 6-mix, making comparisons with other known fiber preparations more valid on a mass basis.Vermiculite historically extracted from Zonolite Mountain near Libby, Montana, was contaminated with a toxic form of naturally occurring fibrous and asbestiform amphibole, occurring in veins throughout the deposit (Pardee & Larsen, 1929). As a result of nearly 70 yr of mining and processing activities, the Libby area was contaminated with a complex mixture of dust including these amphibole fibers, and many of the homes within Libby are (Wright et al., 2002). High concentrations (>100 million fibers/cm 2 ) of these amphibole fibers have even been found in the bark of Libby trees (Ward et al., 2006). Asbestos exposures have led to considerable health problems in the community, including reduced pulmonary function, elevated autoimmune responses, and increased mortality from lung cancer, malignant mesothelioma, and fibrosis (McDonald et al., 2004;Pfau et al., 2005;Whitehouse, 2004).The form of asbestos in Libby's contaminated vermiculite has been characterized as belonging to the amphibole (double-chain silicate) mineral group, including both regulated (tremolite) and unregulated (primarily winchite and richterite) fibers (Meeker et al., 2003). These various fibers within Libby amphibole asbestos differ in their relative proportions of cations (Mg, Ca, Fe, Na, K). On the basis of their diverse chemical composition, Libby amphibole fibers are distinct from the more typical and well-characterized and -studied amphibole fibers. According to Meeker et al. (2003), most of the Libby particles display characteristics that...

Pulmonary Inflammatory and Fibrotic Responses in Fischer 344 Rats After Intratracheal Instillation Exposure to Libby Amphibole

“…Water elutriation was utilized to obtain Libby amphibole and amosite within the target respirable range for rodent species (PM 2.5 ; Webber et al 2008). This technique separates amphibole particles with aerodynamic diameters smaller than 2.5 µm from larger fibers according to a sedimentation settling velocity based upon the particle density and radius.…”

“…This technique separates amphibole particles with aerodynamic diameters smaller than 2.5 µm from larger fibers according to a sedimentation settling velocity based upon the particle density and radius. Briefly, the raw sample (i.e., LA or amosite) was sonicated (by cup-horn sonication) in deionized water for a total of 3 min (20-s bursts followed by 20-s rest intervals) and placed into the elutriation system (illustrated in Webber et al 2008). This system consisted of a glass separatory funnel (500 ml; where the sample is placed), piston pump (Cole-Parmer Instrument Co., Vernon Hills, IL), and Tygon tubing (SaintGobain Performance Plastics Co., Valley Forge, PA).…”

The role of iron in Libby amphibole-induced acute lung injury and inflammation

“…The sample was size fractionated by water elutriation as described previously (Webber et al, 2008) in order to isolate a rat respirable fraction (PM 2.5 ) using a settling velocity of 3.4 × 10 −4 cm s −1 . Transmission electron microscopy showed 97.8% (135/138) of elutriated fibers with aspect ratios ≥5, consistent with the composition of fibers obtained from the PM 2.5 elutriated fraction of the 2000 collection (Meeker et al, 2003;Webber et al, 2008;Lowers & Bern, 2009).…”

Vascular and Thrombogenic Effects of Pulmonary Exposure to Libby Amphibole

“…The sample was further size fractionated by water elutriation as described previously (Webber et al 2008) in order to isolate a rat respirable fraction (PM 2.5 ) using a settling velocity of 3.4 × 10 −4 cm/s. Transmission Electron Microscopy showed 97.8% (135/138) of elutriated fibers had aspect ratios ≥5.…”