State-of-the-science assessment of non-asbestos amphibole exposure: Is there a cancer risk?

Abstract

The distinction between amphibole asbestos fibers and non-asbestos amphibole particles has important implications for assessing potential cancer risks associated with exposure to amphibole asbestos or amphibole-containing products. Exposure to amphibole asbestos fibers can pose a cancer risk due to its ability to reside for long periods of time in the deep lung (i.e., biopersistence). In contrast, non-asbestos amphibole particles are usually cleared rapidly from the lung and do not pose similar respiratory risks even at high doses. Most regulatory and public health agencies, as well as scientific bodies, agree that non-asbestos amphiboles possess reduced biological (e.g., carcinogenic) activity. Although non-asbestos amphibole minerals have been excluded historically from Federal regulations, non-asbestos structures may be counted as asbestos fibers on the basis of dimensional criteria specified in analytical protocols. Given the potential to mischaracterize a non-asbestos structure as a "true" asbestos fiber, our objective was to assess whether exposure to non-asbestos amphiboles that may meet the dimensional criteria for counting as a fiber pose a cancer risk similar to amphibole asbestos. We reviewed analytical methods as well as the mineralogical, epidemiological, and toxicological literature for non-asbestos amphiboles. No evidence of demonstrable cancer effects from exposure to non-asbestos amphiboles that may be counted as fibers, under certain assessment protocols, was found. Data gaps (industrial hygiene data for amphibole-exposed cohorts), inconsistencies (analytical laboratory methods/protocols used to count fibers), and sources of potential bias from misclassification of exposure were identified.

Modeling mesothelioma risk factors from amphibole fiber dimensionality: mineralogical and epidemiological perspective

“…In addition, upper limits of percentage total EMP of EMPA and EMPB from 11 amphibole cleavage fragment populations described by Wylie () are included in Table , including data for cleavage fragment populations of grunerite (with small amounts of actinolite) collected on air monitoring filters by the Mine Safety and Health Administration (USA) in 1975 from the Homestake Gold Mine, South Dakota (Wylie et al, ). Mesothelioma excess risk has not been reported from exposure of miners and millers to amphibole cleavage fragments (reviews by: Addison & McConnell, ; Gamble & Gibbs, ; Williams, Dull, Adams, Rose, & Van Orden, ). Particles with widths ≤0.25 μm were only found in one cleavage fragment sample.…”

Comparative Risks of Cancer from Drywall Finishing Based on Stochastic Modeling of Cumulative Exposures to Respirable Dusts and Chrysotile Asbestos Fibers

“…Published historical data on amphibole mineral contaminants in joint compound, however, do not provide sufficient information to conclude that the minerals were amphibole asbestiform fibers and not elongate tremolite cleavage fragments . Until the characteristics of the mineral being studied are clearly determined, there will be confusion as to the biological effect of asbestos and nonasbestos amphibole minerals . Exposure monitoring in the 1970s reported peak asbestos fiber concentrations (as total fibers) in excess of the then Threshold Limit Value (TLV) of 5 fibers longer than 5 μm per cc (5 f/cc) during the mixing of dry‐mix joint compound with water, sanding of joint compound, and clean‐up activities …”

“…(7) Until the characteristics of the mineral being studied are clearly determined, there will be confusion as to the biological effect of asbestos and nonasbestos amphibole minerals. (8) Exposure monitoring in the 1970s reported peak asbestos fiber concentrations (as total fibers) in excess of the then Threshold Limit Value (TLV) of 5 fibers longer than 5 μm per cc (5 f/cc) during the mixing of dry-mix joint compound with water, (9) sanding of joint compound, and clean-up activities. (1,6,10) Mesothelioma and excess lung cancer deaths have been reported among drywall construction workers based on death certificates listing drywall construction as usual occupation.…”

Asbestiform and non-asbestiform morphologies in a talc and vermiculite mine from the province of Córdoba (Argentina): a case study

“…Considering that these sectors are in contact with the talc-chlorite zone, materials rich in prismatic amphiboles could be incorporated during grinding and potentially generate cleavage fragments (non-asbestiform according to Gunter et al 2007) with dimensions within of the range of respirable particles. Although their hazardousness has been discussed (Mossman 2008;Williams et al 2013), it is a topic that should be addressed for this type of mine.…”