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Science fiction speculates as to what it would be like if, instead of the carbon atomic backbone that characterizes biology on earth, long chains of elemental silicon were the starting point for the chemistry of life. What this might mean in practice is best epitomized by Star Trek’s Dr. McCoy, who, faced with treating such a silicon-based off-world life form, protests that he is a doctor, not a stonemason. A recent mass outbreak of lung injury at a supermarket, tied to a stain-proofing spray, underscores that for those of us who evolved on this planet, long chains of silicon don’t work out so well.
The outbreak occurred when a silicon polymer was sprayed on a tile floor as a stain-protective agent. The fundamental characteristic of a polymer is a long chain of repeated molecules connected end-to-end. For silica-containing polymers, alternating the silica with atoms of oxygen makes a particular type of polymer called siloxane. Each silicon atom can make up to four molecular bonds, just like carbon (in fact, that key similarity spurs speculation about silicon-based rather than carbon-based life). Because there is room for four bonds, besides the two oxygens flanking each silicon atom, up to two other side arms can be also be attached. It turns out the adding side arms containing carbon, creating a hybrid of organic carbon and inorganic silicon, makes a really nifty “alkylsiloxane” polymer with special surface and lubricating properties.
The manufacturers of a product called Stain Repellent Super decided that alkylsiloxane would do just the trick in the repelling department. Unfortunately, when two workers applied the product with a pressure gun, they generated a fine mist of the chemical. Even more unfortunately, this meant exposure was not limited to the empty ground floor where they were operating – the chemical drifted up one floor to the supermarket above. In the end, 39 persons, mostly bystander customers inhaled the alkylsiloxane. Within six hours all were having symptoms. The most serious effect was lung damage – in 18, symptoms serious enough to require medical evacuation to a hospital that could treat them. Later, when the product was tested on laboratory mice, it did pretty much the same thing as it did to humans. The researchers studying the phenomenon posited that the same chemical properties that give alkylsiloxane its coating ability also helps it disrupt the native fluid that lines the lung’s air sacs. That fluid, under normal conditions, keeps the lungs open and functioning.
This toxic outbreak, which was only recently detailed in the medical journal Clinical Toxicology (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4086232/), occurred in Greenland (27 of the victims were Inuit and the rest were Danish Caucasians). But that should not be a consolation to the rest of us. Aerosol coating spray injuries from consumer and commercial products have been a worldwide phenomenon. The new incident is important, though, because it proves that siloxanes also can cause what was already firmly linked to another family of chemical treatment sprays based on fluorine-containing polymers. Such fluoropolymers, too, may very well be good for water production and bad for air sacs. Illness from members of the fluorpolymer family has been reported (and continues to occur) since the early 1990s, including involvement of the CDC (http://www.cdc.gov/mmwr/preview/mmwrhtml/00022198.htm).
For both alkylsiloxane and fluorocarbon aerosol lung damage, symptoms start within several hours after using such a spray product. The syndrome can be life-threatening in severe cases. Exposures can occur in industrial settings but more often, it is consumers who become ill from over-the-counter products. Moreover, the exposure can be relatively brief and even take place outdoors. Typically, when multiple people are similarly exposed, many, if not most, become ill. This is not an allergy. Waterproofing leather and fabric sprays have dominated these reports, but the Greenland outbreak was not the first to involve a floor stain protector. Other products have included rust-proofing spray, grout sealer, and even a ski wax. Most medical reports of these cases leave out the product name, perhaps out of fear of legal action. The Greenland account was almost all the more exotic for naming the Stain Repellent Super name. Most of the outbreaks, even the ones that have received a fair amount of attention, end up with the “voluntary” recall of a specific product.
Then a decent interval passes, until the next new culprit arrives.
