Many an early morning photograph has captured an eerily beautiful vista: the Golden Gate Bridge ensconced in dense fog. Aside from being the bane of ship captains everywhere, fog has typically been known as harmless – until now. Researchers say the amount of fog along California’s coast is increasing, and with it, so are the levels of the mercury it contains. A form of mercury called monomethylmercury has been found in surprising amounts in the fog, and, although it doesn’t pose a direct threat to human health, it could create long-lasting problems for the food chain.

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In high enough concentrations, monomethylmercury is extremely dangerous for people, as it’s been linked to severe health conditions like kidney failure, birth defects, and neurological impairment. Although the coastal fog contains higher than expected amounts of this form of mercury, it’s still well below the level necessary to immediately harm residents. The public health concerns come into play lower in the food chain, as many small mercury-contaminated animals are consumed by predators. Those carnivores end up with much higher concentrations of mercury in their systems. This is similar to the food chain contamination that prompts people to limit seafood intake out of concern for mercury poisoning.

Related: Ocean mercury levels have tripled since the Industrial Revolution

Levels of monomethylmercury have been rising for decades, as has the incidence of fog, according to Clive Dorman of San Diego State University. Dorman analyzed records of ships in the coastal areas in northern California and Oregon and found the number of foggy days went up 7.4 percent between 1960 and 2007. That increase reflects a similar trend to other high-fog regions of the world.

Animals that humans consume aren’t in immediate danger, according to the researchers, but further studies will continue to track the fog’s mercury and its effects. Right now, humans aren’t likely to suffer any ill effects due to contaminated foods, unless they choose to dine on spiders which have been found to exceed the FDA’s accepted limit for mercury.

Via Popular Science

Images via Bharathram Pattabhiraman/Flickr and National Park Service