Assessment of the potential health hazard of fibrous glaucophane

Abstract

<p>The widespread concern on the environmental hazards and public health issues related to exposure to respirable dusts from naturally occurring asbestos (NOA) in principle should also apply to deposits of mineral fibres other than the currently regulated six asbestos minerals. Recent studies highlight that glaucophane can assume a fibrous habit resembling the regulated amphibole asbestos minerals. Glaucophane, sometimes occurring in a fibrous habit, is a major mineral component of blueschist rocks of the Franciscan Complex, USA. Recently, fibrous blueschist occurrences within the Franciscan Complex were being excavated in California for construction purposes (<em>e.g.</em>, the Calaveras Dam Replacement Project) and concern existed that the dust generated by the excavation activities might potentially expose workers and the general public to health risks. For this reason, fibrous glaucophane (Gla) was considered to represent a potential health hazard as NOA by the dam owner, the San Francisco Public Utilities Commission, though an evaluation of the potential health hazard of this mineral fibre was not mandatory per local state and federal regulations. To fill this gap, the potential toxicity/pathogenicity of Gla from the Franciscan Complex has been assessed using the fibre potential toxicity model (FPTI) model and specific <em>in vitro</em> toxicity tests. FPTI is an analytical tool to predict the toxicity/pathogenicity of minerals fibers, based on physical/chemical and morphological parameters that induce biochemical mechanisms responsible for <em>in vivo</em> adverse effects. This model delivers an FPTI index aimed at ranking the toxicity and pathogenicity of a mineral fibre. Compared to asbestos minerals, the FPTI of Gla is considerably higher than that of chrysotile, comparable to that of tremolite and lower than that of crocidolite. Biological responses of cultured human lung cells (THP-1 and Met-5A) following 24 and 48h of exposure to different doses of Gla (25, 50 and 100 µg/mL), have been determined by Alamar Blue viability, Extra-cellular lactate dehydrogenase (LDH) and Comet assays. Generation of reactive oxygen species (ROS) has been evaluated performing the luminescent ROS-Glo™ assay. Crocidolite UICC asbestos (100 µg/mL) was also tested for comparison. Results of in vitro tests showed that Gla may induce a decrease in cell viability and an increase in LDH release in tested cell cultures in a concentration dependent mode. Overall, the rank of the investigated fibres in increasing order of cytotoxicity is: Gla (25 μg/mL) < Gla (50 μg/mL) < crocidolite (50 μg/mL) < Gla (100 μg/mL). For both the cells lines, Gla was able to induce DNA damage. Moreover, it was found that Gla can induce the formation of ROS. The chemical-structural features and biological reactivity of Gla confirm that this mineral fibre is a toxic agent. Although Gla induced lower toxic effects compared to the carcinogenic crocidolite, the inhalation of its fibres may be hypothetically responsible for the development of lung diseases. For a conclusive understanding of the mechanisms of the cellular/tissues responses to fibrous glaucophane, <em>in vivo</em> animal tests should be performed and compared to our outcome to stimulate a critical evaluation and a classification by the International Agency for Research on Cancer (IARC).</p>