Wednesday, January 13, 2016

The many names of silicosis

Silicon, a metalloid situated just beneath carbon in the periodic table, is the second most abundant element in the Earth's crust after oxygen. These two elements join together in all sorts of interesting ways to form silicate minerals, which collectively comprise the vast majority of the Earth's rocks and minerals. One of the major forms of silicate is silicon dioxide (silica), usually occurring as quartz crystals. Silica is found all over the world, being a component of sedimentary (e.g. sandstone), igneous (e.g. granite), and metamorphic (e.g. slate) rocks. Sand is often composed of broken up silica-containing rocks.

Working with silica can result in the generation of particles capable of sticking around in the air for a while as a dust if they are stirred up. If these particles are small enough, they can be inhaled deep into a person's lungs and cause an inflammatory response. Essentially, white blood cells known as macrophages consume the tiny silica particles and proceed to freak the heck out. As part of this freak out, they tell other cells called fibroblasts to pump out collagen. Over time, this can lead to the formation of nodules of relatively inflexible fibrous tissue, producing a condition known as silicosis where it is progressively more difficult to breathe. People with silicosis are more susceptible to catching tuberculosis and other infectious lung diseases, and are also more likely to develop lung cancer. It's a crappy, preventable illness.

The glowing flecks are silica crystals stuck in the lung tissue of a person with silicosis (Source)

Due to the ubiquity of silica in the Earth's crust and our long-standing interest in extracting rocks from the ground and using these rocks to do or make things, people have been coming down with silicosis for thousands of years. It was known to the ancient Greeks, with Pliny (1st century AD) mentioning the use of respirators constructed from pig bladders as protection against toxic dusts.

A particularly brutal outbreak of silicosis occurred among workers tasked with constructing the Hawk’s Nest Tunnel in West Virginia in the 1920s. The rock through which the tunnel was made was full of silica, and workers weren't given masks or other protection against dust exposure. Nearly a third of the estimated 2,500 people who spent time in the tunnels died from an acute (brief and severe) form of silicosis, and most of the remaining workers eventually ended up with the disease.

What the lungs of mice exposed to silica look like compared to unexposed controls (Source)

Being an ancient illness, silicosis has acquired many names: chalicosis, dust consumption, flint disease, ganister disease, grave-digger's disease, grinders' asthma, grinders' consumption, grit consumption, knife grinder's phthisis, masons' disease, miner's asthma, miner's phthisis, potters' rot, schistosis, sewer disease, and slate workers disease.

Taking a look at the origins of these names:
  • Chalicosis and flint disease refer to silicosis caused by inhaling particles of flint, a type of rock made up of tiny quartz crystals. Flint has a long history of being used to make tools, ceramics, and building stones. Axes and arrowheads were crafted way back in the Stone Age by striking pieces of flint with other rocks to break off bits and thereby shape the flint into tools.
  • Consumption and phthisis are other words for tuberculosis, but can also be used in a more general way to refer to any long-lasting and progressive lung disease. Due to the similar effects tuberculosis and silicosis have on lung tissue (e.g. the formation of nodules), silicosis has sometimes been called pseudo-tuberculosis.
  • Ganister is a dense type of sandstone ground up to make crucibles and silica bricks used to line furnaces.
  • Several of the names for silicosis include the word grinder, as people employed in this occupation historically used grindstones made of sandstone to sharpen knives and other metal tools.
  • Silicosis came to be known as grave-digger's disease and sewer disease because it occurred among people who dug graves or excavated sewer tunnels in regions containing lots of sandstone (e.g. Sydney, Australia).
  • Masons who cut grindstones and millstones from silica-containing rocks were also prone to silicosis. Carl Linnaeus, an 18th century scientist and physician (perhaps best known for his work in the fields of taxonomy and ecology), reported that grindstone cutters usually died of lung disease prior to turning 30.
  • Miners who excavate silica-containing rocks can develop silicosis. This includes gold miners, since this metal sometimes occurs with quartz.
  • Potters' rot is silicosis associated with the manufacture of pottery objects. This typically involves mixing up silica, clay, and previously broken pottery, and pouring the result into moulds for firing. Silica dust can become airborne during the casting process as well as when broken pieces are crushed for reuse.
  • Schistosis refers to silicosis caused by inhaling slate dust. Slate, which contains silica, is mostly used to make roof and floor tiles, and workers who cut these tiles may be exposed to dust.

A couple of other silica-containing materials capable of causing silicosis are sand (used for such activities as sandblasting, metal casting, and glass manufacture), scouring powders made from pulverized sand, concrete (when cut, drilled, or jackhammered), and diatomaceous earth.


Corn JK. 1980. Historical aspects of industrial hygiene — II. Silicosis. American Industrial Hygiene Association Journal 41(2):125-133.

Donaldson K, Seaton A. 2012. A short history of the toxicology of inhaled particles. Particle and Fibre Toxicology 9:13. [Full text]

Holt PF. 1956. Silicosis and related diseases. Science Progress 44(175):435-448. [First page]

Quaintance PA. 1934. Silicosis: A study of 106 pottery workers. American Journal of Public Health and the Nations Health 24(12):1244-1251. [Full text]

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