The second most common element on Earth can slowly scar a worker's lungs
Silicon and oxygen make up about three quarters of the Earth's crust, so silica is everywhere: in granite, sandstone, sand and mortar. Cutting, drilling or blasting those materials throws up dust fine enough to lodge where lungs exchange gases, beyond the reach of mucus or coughing. There it triggers scarring that has no cure.
Silicosis is a form of pneumoconiosis, an occupational lung disease caused by breathing crystalline silica particles smaller than 10 micrometres. Once the dust settles in the alveoli, immune cells called macrophages swallow it and release inflammatory signals such as tumour necrosis factor and interleukin-1. Those signals prompt fibroblasts to lay down collagen around each particle, building nodules with a distinctive onion-skin layering. The response appears to run through a molecular sensor known as the NLRP3 inflammasome.
Not all silica behaves the same. Crystalline silica comes in seven forms depending on the temperature at which it formed, chiefly quartz, cristobalite and tridymite; quartz is the world's second most common mineral after feldspar. Amorphous silica, such as diatomaceous earth, is less toxic but not harmless, and heating can convert it into crystalline forms. Finely ground silica flour, used in polishes, paints and cosmetic fillers, has been linked to every type of the disease.
Timing depends on the dose. The chronic form, the most common, follows ten or more years of low-level exposure and may surface 10 to 30 years after it began, often visible on an X-ray before any symptoms. Heavier exposure produces accelerated disease within 5 to 10 years, and very intense exposure can cause acute silicosis within weeks to five years. Small nodules can merge into masses of a centimetre or more, called progressive massive fibrosis. Because the X-ray picture can resemble tuberculosis or pneumonia, misdiagnosis happens, and a recent analysis argued that X-rays miss enough cases that the burden among miners is underestimated.
The damage spreads beyond scarring. People with silicosis have about three times the usual rate of tuberculosis, perhaps because silica impairs the macrophages that kill the bacteria. In 1996 the International Agency for Research on Cancer classed crystalline silica as carcinogenic to humans, with lung cancer risk two to four times higher in those with silicosis. The disease is largely preventable: removing exposure comes first, then dust control with water-fed tools and ventilation, with respirators as the last line of defence.
Source: Silicosis
