Study Links Coastal Fog with High Levels of Mercury in Mountain Lions

Scientists have identified a possible link between toxic levels of mercury in mountain lions and coastal fog.
John Loeffler

Scientists have discovered a possible link between high levels of mercury in mountain lions and marine fog, indicating that the toxic metal is being deposited on land and then making its way up the food chain.

Toxic levels of mercury in mountain lions possibly linked to marine fog

Scientists at the University of California Santa Cruz have identified elevated levels of mercury in mountain lions, a new indicator that the toxic metal is being carried ashore through normal marine fog.


The higher concentration of mercury found in pumas that live in the Santa Cruz Mountains was three times the levels found in mountain lions that live outside the "fog zone" for the region. Scientists have also found elevated levels of mercury in the lichen and deer population that also live inside the fog zone.

Publishing their findings in the journal Nature, the researchers believe that the contaminants are transmitted from the sea to land through the coastal fog that makes the region famous — think San Francisco's Golden Gate Bridge blanketed in fluffy white fog in the early morning hours — which then deposits these contaminates on land. After it is deposited, it then makes its way up the food chain.

"Lichen don't have any roots so the presence of elevated methylmercury in lichen must come from the atmosphere," said Peter Weiss-Penzias, an environmental toxicologist who led the research. "Mercury becomes increasingly concentrated in organisms higher up the food chain."

While not a threat to human health, the mercury transmitted through coastal fog might present an elevated risk to coastal animal life, as the concentration of mercury from lichen to deer to mountain lion can multiply by nearly a thousand times.

The study examines the fur and whisker samples from 94 coastal mountain lions and 18 non-coastal lions. mercury concentrations found in coastal lions averaged 1,500 parts per billion (ppb) compared to 500 ppb for non-coastal lions. At least one lions had levels of mercury known to be toxic to smaller species like mink and otters, while two others had levels that were considered below lethal but which still interfered with fertility and reproduction.

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"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," said Chris Wilmers, a professor of environmental studies and the director of the Puma Project, a joint collaboration between UC Santa Cruz and the state of California. "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."

Mercury is a natural metal most commonly released into the environment through various natural and human-induced industrial processes, such as mining and coal-fired power generation.

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

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