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Toxic mercury concentrations found in California's coastal fog — and the area's mountain lions

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Fog along the coast of the Santa Cruz Mountains in California contains significant levels of toxic mercury — and it's already hurting wildlife in the area. 

The findings come from a recent study published in the journal Nature, and conducted by environmental toxicologist Peter Weiss-Penzias and a team of researchers at University of California, Santa Cruz. Most significantly, the team observed that mercury concentrations in mountain lions (also known as pumas, cougars, and panthers) in the fog area was three times higher than that of mountain lions outside the fog area. 

To conduct the study, the researchers ran tests on fur and whisker samples from 94 coastal mountain lions and 18 mountain lions who live outside of the fog zone. The team had previously collected the samples for a previous study, and they had been preserved for possible future studies. Interestingly, they found that the coastal mountain lions had an average mercury concentration of about 1,500 parts per billion (ppb), compared to the noncoastal mountain lions' mercury concentration of 500 ppb, as explained in a press release on ScienceDaily

The researchers were able to trace the mercury concentrations in mountain lions back to fog by looking to the food chain. They also observed increased mercury levels in deer (who lions eat) and lichen (a plant that deer eat) in the fog zone.

"Lichen don't have any roots so the presence of elevated methylmercury in lichen must come from the atmosphere," Weiss-Penzias said, according to ScienceDaily. "Mercury becomes increasingly concentrated in organisms higher up the food chain."

But why is there increased mercury in the atmosphere (and the fog) in the first place? As explained by the New Hampshire Department of Environmental Services, there are three primary ways mercury enters the environment: from natural processes like volcanoes, forest fires, and soils; from natural processes that reintroduce mercury into the environment, like ocean water evaporation; and from the burning of fossil fuels or mining, which accounts for 42 percent of anthropogenic (human-caused) mercury emissions, according to the EPA.

"Mercury is a global pollutant," Weiss-Penzias explained. "What's emitted in China can affect the United States just as much as what's emitted in the United States."

Luckily these mercury concentrations in the fog do not present any health risk to humans — however, they do to animals. The study observed alarmingly high levels of mercury in several mountain lions, two of whom had "sublethal" mercury levels known to reduce fertility and reproductive abilities, according to ScienceDaily.

Chris Wilmers, a professor of environmental studies, the director of the Puma Project, and a co-author on the study, noted that the risks of increasing mercury concentrations in mountain lions could put the local coastal population at risk, since the mountain lions are already feeling the effects of the climate crisis, such as habitat loss.

"These mercury levels might compound the impacts of trying to make it in an environment like the Santa Cruz Mountains, where there is already so much human influence, but we don't really know," Wilmers told ScienceDaily. "Levels will be higher 100 years from now, when the Earth's mercury budget is higher because of all the coal we're pumping into the atmosphere."

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