By Linda Felaco
The dangers of prolonged mercury exposure are well known. They include impaired memory and language and motor skills and reduced attention span. Exposure to mercury used to treat felt hats caused hatters to appear confused or disturbed, hence the expression “mad as a hatter,” which inspired Lewis Carroll to create the character of the Mad Hatter in Alice’s Adventures in Wonderland. When animals ingest mercury, it is not easily excreted and tends to concentrate in fat tissue, which is why pregnant women are advised to limit their consumption of fatty fish. In addition to ingesting it from eating seafood, here in Charlestown we’re exposed to mercury via air pollution from trash incinerators due west and upwind from us along the Connecticut coast, as well as from coal-fired power plants.
Now atmospheric scientists have found another way that we’re exposed to mercury: Mercury vapor travels in coastal fog.
Scientists had presumed that atmospheric mercury deposited on surfaces via either raindrops or a process called “dry deposition,” in which vaporized atoms stick to or chemically react with an exposed surface. Now, atmospheric chemists at the University of California, Santa Cruz, conducting field experiments in and around Monterey Bay have found that concentrations of mercury in fog droplets were up to five times the highest concentration ever seen in rainwater, they reported in Geophysical Research Letters in February. These concentrations were far in excess of what anyone would have predicted. The researchers estimated that between 61% and 99% of the monomethyl mercury—which is readily absorbed by the human body—deposited in coastal ecosystems around Monterey Bay over the course of a year comes from fog and concluded that similar concentrations would be expected to be found in other coastal areas, including Charlestown.
Another way coastal residents are exposed to mercury is when winds stir up waters from the sea floor, where microbes living in the sediment consume mercury-tainted organic matter and generate a compound called dimethyl mercury. This compound evaporates when the contaminated waters reach the surface and ends up being split into several components, including monomethyl mercury, by chemical reactions driven by sunlight. Researchers aren’t sure whether those reactions take place in the atmosphere or within fog droplets, but either way, the monomethyl mercury ends up in the droplets, which winds can then carry to the coast.
Could mercury poisoning explain some of the bizarre antics of our Town Council, such as Deputy Dan Slattery’s witch-hunts and confusion over the meaning of legal documents? Without taking blood samples, we can’t know for sure. But it does make me glad I live farther inland where I don’t have as much exposure to coastal fog.