Artificial stone countertops contain natural stone, quartz, resins, and Portland cement. The combination of these materials can contain more than 90% silica.1 In contrast, natural stone contains 50% or less silica.2 Artificial stone is desirable because it is lighter and thinner than natural stone, non-porous, and has strong mechanical resistance.3 Manufacturers also market the new material as stain and scratch proof, acid and fire resistant, environmentally friendly, and non-toxic while claiming these materials are indistinguishable from natural stone. Because of its desirable properties, artificial stone is a preferred choice in homes for kitchen or bathroom countertops and in retail and hospitality establishments. Cases of silicosis have recently been associated with the manufacture of artificial stone products, and a discussion of the industry practices leading to these occupational injuries is provided here.

What is silicosis?

Silicosis refers to a spectrum of pulmonary diseases caused by inhalation of free crystalline silica and is marked by scarring and thickening of the lung tissue which can progress to respiratory failure and death.4 Silica inhalation is the main cause of occupational respiratory disease worldwide,5 and differences in exposure can result in different forms of the pulmonary disease which include acute silicosis, accelerated silicosis, chronic silicosis, and progressive massive fibrosis.6 For example, high-intensity silica exposure is associated with acute and accelerated silicosis with acute silicosis developing within a few weeks to less than 5 years of high-intensity exposure7,8 and accelerated silicosis developing within 10 years of moderate – high levels of exposure.4 Chronic silicosis can develop following decades of exposure to silica dust and even progress after exposure has ceased.4

Silica, also known as silicon dioxide, exists as different forms with quartz being the most common form and a major component of granite (~30% free silica), slate (40% free silica), and sandstone (almost pure silica).9 Other forms of silica include tridymite, cristobalite, coesite, and stishovite.10-12 Although all these forms are biologically toxic, quartz is the predominant form involved in occupational exposures12 and pulmonary disease.9 The toxicity of silica results from the ability of silica surfaces to interact with water to form reactive silanol groups12 and to generate oxygen radicals.13-16 These reactive groups are capable of injuring target pulmonary cells which culminate in inflammation and fibrosis.17

Silica is found in more than 95% of rocks and present in many construction materials such as concrete, sand, mortar, and stone.18 Respirable silica (particles with diameters smaller than 10 microns) is created during the cutting, grinding, polishing, and crushing of these construction materials for the fabrication of consumer products.7 Historically, industries that generate respirable silica include mining, quarrying, sandblasting, masonry, stone cutting, foundry work, and ceramics4,19 Although the overall mortality to silicosis has decreased in the United States from 1969 to 2010 due to improved workplace protection and occupational health surveillance,20-22 up to 200,000 miners and 1.7 million non-mining workers in the United States still experience occupational exposures to inhaled silica, and new cases of silicosis are recognized worldwide every year.23-25

Silica exposure in the artificial stone industry

Consistent with this trend, hazardous silica exposures have increased22 with cases of silicosis being associated with the manufacture of artificial stone.26-34 Initial cases were reported in Spain in 2010 (26,35,36), followed by Israel in 2012,27 and then other countries including Italy,1,30 the United States,28,37 Australia,33,38 and Belgium.32 Studies of these outbreaks documented a prevalence of 25% among workers in Italy,1 54% in Spain,26 and 12% in Australia.38 Moreover, these cases progressed rapidly, suggesting that silicosis associated with artificial stone is more aggressive than classic silicosis,39 and occurs in young workers, with a median age of 29 years.40

Because of the widespread use of artificial stone, current efforts attempt to identify at risk workers and implement controls to limit silica exposure.41 Artificial stone is composed of finely crushed rock and synthetic resins with a high silica content (~90%),1,42 whereas natural stone contains 50% or less.2 Fabrication of artificial stone for use in countertops generates respiratory crystalline silica during cutting and grinding, and controlled studies show that aerosolized particles from cut or ground artificial stone have 3 times higher silica content compared to manipulated granite.43 These manipulations potentially expose workers to higher amounts of respirable silica compared to working with natural stone44 and pose a substantial risk for developing more severe forms of silicosis.26,28,33

Safety controls for the artificial stone industry

Although silicosis afflicts far fewer people in the United States than in the past,22 studies examining the sources of respirable silica during the fabrication of artificial stone suggest that standard control measures and use of personal protective equipment should be reevaluated.43,45 While wet cutting and use of respirators are effective when properly implemented, the amount of dust generated during grinding and polishing creates a layer of dust covering all surfaces, and these deposited particles are subject to resuspension.43 Studies have recommended that power tools for cutting, grinding, and polishing of artificial stone countertops include dust suppression.43,45,46 Furthermore, aggressive engineering controls should be implemented to keep dust levels at a minimum, avoid exposure during the manipulation process, and prevent dust resuspension.46 Additional controls would include floor drainage systems for cleaning, respiratory protection, and ventilation of confined spaces when cutting and grinding artificial stone.43

Conclusions

Collectively, silicosis associated with artificial stone fabrication progresses rapidly with patients developing respiratory failure. Silicosis is preventable if exposures to airborne silica can be controlled. Therefore, a need exists to identify at risk artificial stone fabrication workers in order to prevent the potential for excess exposure to silica dust and protect workers from increasing their risk for developing this pulmonary disease.

 

References

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