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1. Introduction
Crystalline silica, i.e., quartz, cristobalite and tridymite are abundant in rocks and minerals. Cristoballite and tridymite are particularly rare polymorphs in Finland, while approximately 12% of the Earth’s crust consists of quartz [1]. Substantial quantities of quartz can also be found in sand, sandstone, and granite, clay, shale, and slate [1]. Thus, products containing these minerals as main ingredients are usually rich in crystalline silica. Hence, occupational exposure to quartz is frequently an issue in many workplaces. In Finland, according to recent estimates, 50,000 workers from a total workforce of 2.7 million (1.8%) are exposed to quartz in significant quantities, some of which contract silicosis each year (the Register of Occupational Diseases in Finland, 2014).
Critical branches or tasks with respect to quartz exposure include mining activities, concrete industry, glass and porcelain industry, foundries, and building activities, such as stone masonry, facade renovation, sand blasting of buildings, tunneling, scrabbling, cutting, or drilling of stone and concrete [2,3]. In Finland, building activities are fairly intensive due to a continuous regional migration from rural areas to cities starting in the 1960s as well as from abroad to regional population clusters. Immigration to Finland has been increasingly frequent since joining the European Union (EU) in 1995. As building activities are presently on the rise, so are industries supporting building activities, including foundries, as well as the production of cement and concrete slabs, plates, tiles, and asphalt [4]. In addition, new mines and plants that enrich metals and minerals have opened in Finland over recent decades, and the production of metal ores and metal concentrates have increased approximately ten-fold from 2006 to 2016 [5]. With this in mind, it is not surprising that while quartz exposure has declined after the signing of the European treaty on “The Agreement on Workers Health Protection through the Good Handling and Use of Crystalline Silica and Products Containing it”, i.e., NEPSI agreement, the number of workers exposed to quartz has remained stable [6,7].
The health risks of crystalline silica come from breathing respirable dust (particle diameter < 10 µm, median diameter = 4.25 µm [8,9]. The dust penetrates the alveolar region of the lungs and may cause silicosis-usually a nodular pulmonary fibrosis-as well as lung cancer [3,10,11,12,13]. Respirable quartz particles cause...