Characterization and classification of unregulated mineral fibers: The case of fibrous datolite from Rio Manubiola Valley, Parma, Italy

Abstract The widespread presence of mineral fibers necessitates their thorough identification, characterization, and assessment of potential health effects. This comprehensive approach is crucial for assessing and controlling exposure to hazardous fibers such as those in asbestos minerals. Within this framework, we present the first detailed investigation of fibrous datolite CaBSiO4(OH), a calcium boron hydroxide nesosilicate. Although this mineral commonly crystallizes in non-fibrous habits, a rare pearly-white fibrous deposit was identified within an ophicalcite from the Rio Manubiola Valley (Parma, Italy). While datolite is an industrial boron ore, its fibrous habit and potential human toxicity are currently unregulated. Therefore, alongside the crystal chemistry of the sample, this work includes an evaluation of its potential human toxicity and carcinogenicity by applying the Fiber Potential Toxicity Index (FPTI), a quantitative predictive model based on the physical-chemical and morphological parameters of a mineral fiber. Fibrous datolite is both chemically and structurally similar to its non-fibrous counterpart [space group P21/c, a = 4.83679(1) Å, b = 7.61346(2) Å, c = 9,63754(3) Å, β = 90.156°]. Regarding morphological parameters, the average length, width, and aspect ratio of individual datolite fibers are 9.80 μm (s.d. 5.39), 1.32 μm (s.d. 0.82), 9.53 (s.d. 6.05), respectively, classifying them respirable according to the World Health Organization (1997) fiber size criteria [length ≥5 μm, width ≤3 μm, and aspect ratio (length/width) ≥3:1]. Nevertheless, based on the FPTI model, fibrous datolite demonstrates one of the lowest potential toxicity/carcinogenicity scores, specifically 1.50(0.1), compared to all previously evaluated mineral fibers. This exceptionally low score is primarily attributed to its lack of biodurability and absence of iron or other metals in the crystal structure. Given its predicted null toxicological potential, fibrous datolite can be proposed as a potential negative standard for in vitro cell toxicity studies, aligning with the use of other non-toxic fibers like wollastonite.