Brucite, a natural raw material used worldwide, can be contaminated by asbestos

Brucite is a hydroxide mineral [Mg(OH)₂] with a hexagonal structure (space group P3m1) consisting of sheets of Mg-centered octahedra. Brucite is a raw material of commercial importance used for several applications, such as flame retardant and smoke suppression product for insulating materials and coatings, inorganic additive in ceramic inks, pigments and cements, for CO₂ sequestration and as MgO source. Brucite is a widespread mineral frequently found in marble as a product of alteration of periclase, or as an accessory mineral in metamorphic limestones and dolomite schists, but more commonly brucite crystalizes during the serpentinization of ultramafic rocks. Given the possible concomitant occurrence of naturally occurring asbestos (NOA) in serpentinites, the presence of brucite in these rocks should arise concern. The most common asbestos type in serpentinites is chrysotile, which is classified by the International Agency for Research on Cancer (IARC) as a human carcinogen. North America, North Europe and China are the largest producers and exporters of this raw material, but no particular precautions are taken as it is considered a safe product. To date, the occurrence of chrysotile in commercial brucite had never been reported. Our study demonstrates that this view must be reconsidered. Through multi-analytic protocol based on morphometric, chemical and mineralogical analyses, we highlighted the evidence of respirable regulated chrysotile (serpentine asbestos) fibers in a commercial brucite currently traded worldwide. The presence of a serpentine phase was evidenced by chemical analyses, X-ray powder diffraction and thermogravimetric-thermodifferential analyses while the occurrence of breathable regulated fibers was confirmed by morphometric observations through scanning electron microscopy. Especially, fibers with length >5 µm, width <3 µm, length/width ratio >3, in a concentration of 169 mg/kg (0.02 wt%) were found. In the light of these findings, we think that brucite-exposed workers should be aware of the potential hazard associated with the use of raw brucite. Therefore, we suggest that an asbestos-free certification should be imposed to the brucite mining companies and distributors, through the implementation of a multidisciplinary protocol or at least by electron microscopy, to rule out the occurrence of asbestos. Similar future studies may affect ‘doubtful’ raw materials commonly marketed, such as diopside, olivine and magnesite.