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Because Life Is a Never-Ending Disaster Movie, San Francisco's Fog May Be Tainted with Toxic Mercury

Fog is way safer than tuna sushi, but it still needs to be studied, says a UC Santa Cruz researcher.


Just as the dungeness crab ban partially lifted and we thought the world was safe again, here comes the news that fog is slowly poisoning us. Recent research by oceanographers and environmental toxicologists has found that marine fog is pulling in mercury from the ocean and depositing it on the coast, in a pattern of currents just now becoming clear to scientists. “The fog works like a mop, mopping up the toxins from the oceans and then wringing them out over the watershed,” explains Kenneth Coale, an oceanographer at the Moss Landing Marine Laboratories. The researchers discovered that fog’s concentrations of monomethyl mercury, a neurotoxin, are about 20 times that of rain, making San Francisco’s daily snuggle with Karl feel, well, dirtier than usual. 

So what exactly does this mean? Should we all run inside at 4 p.m.? Hold our breath in the Sunset? It’s not quite like that, explains UC Santa Cruz associate researcher Peter Weiss-Penzias, who worked on the fog study in question. “The levels floating around in the air or in fog droplets are very low, and we wouldn’t consider it a health risk at all,” he says. They’re far below the dietary threshold for humans, which is 0.3 parts per million. That is, if a food’s mercury concentration is above 0.3 parts per million, “you’re recommended not to eat it,” he says. “What we’re measuring in fog water is in the parts per trillion range. So it’s 1 million times more dilute.”

The risk, infinitesimal as it is, lies in the fact that mercury bioaccumulates, or builds up, in living things. So it’s true that San Francisco's blanket is adding, ever so slightly, to the toxins we consume every time we scarf down tuna sashimi. And the researchers have seen bioaccumulation in action in our coastal flora and fauna. The Chronicle notes that wolf spiders found along the coast during foggy periods had levels of the monomethyl mercury above 3 parts per million. (So, you know, don’t eat those.) 

But Karl’s miasmic charms—unlike the precious rain we haven’t bothered to nickname—are the very things that make him potentially more noxious. Fog is made up of droplets that are very small and very numerous, which adds up to a lot of surface area and allows it to efficiently absorb soluble gases, says Weiss-Penzias. So there could be other stuff in it besides mercury: We just don’t know. Unlike rainwater, which we know is clean, “there’s been no reserach on fog,” says Weiss-Penzias. “We don’t know what else is in the fog.” 

So, uh, Karl, this is a bit awkward considering we’ve been together this long. But would you consider getting tested? Cool? Yeah, we know… miss you too. XOXO.


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