Scientific Reports volume 12、記事番号: 4351 (2022) この記事を引用
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人工石材は、石工業界の労働者の間で珪肺症の症例が最近急増していることに関連した新しい建築材料です。 石工における潜伏期間の短い肺疾患の危険性を理解するために、制御された条件で人工石を乾式加工し、生成された吸入性粉塵を捕捉して物理的および化学的特性を分析することにより、リアルタイムの粉塵暴露シナリオをシミュレートしました。 比較のために天然の花崗岩と大理石も含めました。 加工石を切断すると、石英とクリストバライトの形で、吸入可能な結晶性シリカ含有量が 80% 以上の非常に細かい粒子 (< 1 µm) が高濃度で生成されました。 人工石には、重量比で 8 ～ 20% の樹脂と 1 ～ 8% の金属元素も含まれています。 比較すると、天然石には、呼吸に適した結晶質シリカがはるかに低く (4 ～ 30%)、金属含有量がはるかに高く (29 ～ 37%) ありました。 天然石の粉塵の放出も、人工石よりも表面積が小さく、表面電荷も低かった。 この研究では、人工石の種類内および人工石と天然石の間の物理的および化学的ばらつきが浮き彫りになりました。 この情報は最終的に、人造石の製造作業によってもたらされる特有の危険性を理解するのに役立ち、吸入可能な結晶質シリカへの曝露を低減することを目的とした特定の工学的管理手段の開発を導くのに役立ちます。
珪肺は、建設、冶金、石炭および金属採掘/採石などの産業で一般的に見られる職業性肺疾患です。 これは、石英、トリディマイト、またはクリストバライトの形で呼吸に適した結晶質シリカ (RCS) を吸入することによって引き起こされます1。 石英は、地球の地殻で最も豊富に存在する鉱物であり、特に石英を含む材料の機械的加工を伴う職業環境では、他の多形体よりも頻繁に遭遇します2。 クリストバライトへの職業上の曝露は、炉内での石英変換の結果としてセラミック産業や、クリストバライトを 85% 以上含むサンプルを処理する珪藻土産業でも発生する可能性があります 1,3。 コーサイトやスティショバイトなどの結晶質シリカの他の多形体にさらされることはまれです4。
人造石とも呼ばれる人工石は、キッチンやバスルームのカウンタートップ、床やファサードのタイルの製造に一般的に使用される新しい建築材料です。 その人気の理由は、耐久性、美しさ、多様性、そして手頃な価格です。 彼らの売上は衰える兆しがありません。 実際、米国の市場シェアは毎年 7.4% 増加すると推定されています5。 残念なことに、これらの新しい材料の人気の高まりは、業界の労働者の間で「加速性珪肺症」の出現に関連しています6。 悲しいことに、珪肺症の発症は、従来見られていたよりも短い曝露期間と短い潜伏期間の後に発生しました2。 スペインの研究では、2007 年から 2011117 の間に珪肺の症例が 61% 増加したと報告されており、これは短い期間内で重大な集団発生でした。 人工石粉への曝露の中央値は 11 年であり、珪肺症と診断された労働者の年齢中央値は 33 歳でした。 イスラエル、米国、オーストラリアでも同様に労働者の珪肺罹患率の増加が報告されています5、6、8。
人工石の労働者の健康に対する懸念は、人工石には通常 90% 以上の石英が含まれており、顔料とポリマー樹脂でマトリックスに結合されているという事実から生じています9。 比較すると、天然石は人工品に比べてシリカの含有量がはるかに少ないです。 大理石と花崗岩は、それぞれ 3% と 40% のシリカを含む 2 つの天然石です。 したがって、人工石の切断、穴あけ、研磨などの製造プロセスでは、大気中に石英を含む粉塵が高濃度になる可能性があります10。 興味深いことに、これらの機械プロセスは、粉塵への曝露を減らすために、水供給式の空気圧グラインダーやポリッシャーを使用して、湿潤条件下で実行されることが増えています。 それにもかかわらず、仕上げ作業は水分を抑制せずに手作業で行われることが多く、その結果、結晶質シリカにさらされる可能性が高くなります11。
80% crystalline silica, often as a combination of quartz and cristobalite. Two engineered stones had only quartz in their composition (> 90%), while the majority of the other samples contained between 42 and 88% quartz. In engineered stone samples with relatively low (< 25%) quartz, such as ES6 and ES12, cristobalite accounted for the rest of the mineralogical composition (Table 1). Cristobalite was present in several other samples, albeit in lower concentrations than ES6 or ES12. It was present in moderate levels (36 ± 4.1%) in ES2, ES3 and ES11 and in low levels (< 5%) in ES1 and ES4 (Table 1). Compared to crystalline silica minerals, albite and rutile were less commonly found in respirable engineered stone dust. When present, they were observed in very low amounts, typically < 5% (Table 1). The only exception was ES4 which had a varied mineralogical composition, including 13% rutile (Table 1). No muscovite was observed in engineered stones./p> white marble (11%) > white granite (3.6%). The natural stones comprised several other minerals for example, albite, a feldspar mineral commonly found in igneous rocks such as black granite. White marble contained predominantly calcite (66%) and dolomite (22%) and white granite contained mostly dolomite (91%)./p> 16%) (Table 1). Sample weight loss, as shown by a derivative thermogravimetric graph (DTG) (Supplementary Fig. S1), occurred in three stages: a small weight loss was observed while the sample was heated to up to ~ 300\(^\circ\)C, attributed to the desorption of water9; the second, and maximum, weight loss occurred at around 450\(^\circ\)C for all respirable engineered stone dust samples and was attributed to the loss of polymeric resin from the material. The third weight loss was observed at higher temperatures (~ 600\(^\circ\)C), but was considered minimal in comparison to the other two losses (Supplementary Fig. S1)./p> 90% of the dust particles had diameters in the size range of 190 nm to 825 nm (Fig. 1). The respirable dust emissions from cutting most engineered stones were similar in diameter, except for ES10 which had significantly finer dust, with particle diameter range of 142–295 nm (average 218 nm); in comparison, ES8 had the largest dust size with a particle diameter range of 459–1106 nm (average of 715 ± 91 nm) (Table 1, Fig. 1). Among all three natural stones, the black granite had a lower average particle size (503 nm) than the other two (534 and 675 nm respectively) (Table 1), but all three natural stones had particle size distributions comparable to those of engineered stones (Fig. 1)./p> 90%) content, such as ES8 (Table 1)./p> 2.50 ± 0.13 m2/g surface area, while the rest averaged 1.72 ± 0.11 m2/g in surface area. In comparison, the specific surface area of the natural stones (range of 0.439 – 0.878 m2/g) was lower than the engineered stones (Supplementary Information Table S1)./p> 6% by weight elemental content (Fig. 3a)./p> 1% wt.) elements, it was observed that the following elements were in trace amounts in engineered stones: Cu, P, S, Ni, Co, Cr, Sn, Zr and Cl (Fig. 3a). Elements Fe, Ca, Mg, and K were predominantly in minor distributions. Certain elements such as Ca, Mg, Na and Ti had a range of concentrations from minor to major elemental fields./p> 80% by weight crystalline silica and 8–20% resin21. Further characterisation of the RCS was undertaken on the basis that the crystalline structure of the minerals may exert an influence on their toxicity22. In our study, 9 out of 12 engineered stone respirable dust samples had a combination of quartz and cristobalite structures, although quartz was still the dominant structure, forming > 55% of the total mineralogy. Cristobalite was the second most common mineral, while albite and rutile were detected in smaller amounts. Quartz and cristobalite differ from one another in their mineralogy, surface characteristics and natural association with other elements23. Early studies comparing the dose response of quartz and cristobalite on pulmonary function in rats showed that both structures were similarly detrimental to the lungs, although cristobalite elicited a slightly faster response than quartz24. However, subsequent animal experiments and epidemiological studies discounted these findings, by showing no evidence for differences in the inflammatory and fibrogenic potentials of quartz and cristobalite23. Horwell et al.4 even showed that cristobalite-rich volcanic ash was less toxic than expected and posed less of a respiratory health hazard than quartz. They attributed this finding to the relative open structure of cristobalite compared to quartz, which allows the substitution of cations such as aluminium (Al3+) and sodium (Na+) in the Si tetrahedral, hence affecting cristobalite toxicity1,4. Taken together, these studies show insufficient evidence that either mineral is more toxic than the other. Nonetheless, the high concentration of crystalline silica in the respirable dust from engineered stones may be cause for concern as quartz and cristobalite are the only crystalline silica minerals recognised as Group 1 carcinogens—“carcinogenic to humans”—by the International Agency for Research on Cancer25./p> 85% quartz) had a bimodal distribution, with one mode in the same range as in this study (~ 500 nm), whereas the other was in the ultrafine particle (UFP) range, commonly defined as particles < 100 nm29. Although visually observed, UFPs were not measured in the present study, likely due to the limitations of the air sampling or particle size analysis techniques. We are currently exploring some real-time measurement of UFP using direct reading instrumentation for more precise dust exposure assessment during engineered stone fabrication tasks./p> 0.7) and particle imaging by SEM, the dust particles in our study were, in fact, heterogenous in shape, size and structure. Apart from particle size and morphology, the surface properties of quartz have been reported to also play an important role in cytotoxicity, suggesting that the specific surface area of engineered stones may be a useful parameter for characterisation and differentiation between engineered and natural stones26,31,32./p> 1%) quantities in the samples studied, possibly originating from the pigments and resins37,38. Although generally considered non-toxic, Ti (titanium dioxide, TiO2) has been shown to be an aetiological agent for lung inflammation, especially in the ultrafine fraction39,40. The possible role of metals in the toxicity of silica has been elicited before. For example, Clouter et al.41 (and references therein) suggested that the toxicity of quartz involves Fe. While the presence of Fe and Al has been considered for the potential reason for the differing zeta potentials of black granite and other natural stones, this could not explain the greater negative zeta potential of engineered stone compared to the black granite, since the concentration of Fe and Al is much lower in engineered stone. Several other elements not found in the natural stone samples were detected in the engineered stone ones, but only in trace quantities. Therefore, while we cannot exclude any role of metal ions in silica toxicity, it is unlikely that any such effect is mediated though the pathway linked with the generation of zeta potential./p>
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