High levels of mercury found in mountain lions linked to coastal fog
Coastal fog, bioaccumulation and biomagnification contributes to mercury levels that approach toxic thresholds in pumas
a naturally occurring element, is released into the environment through
a variety of natural processes and human activities, including mining
and coal-fired power plants. In its elemental form, mercury is a global pollutant, that as an atmospheric pollutant can travel around the world.
atmospheric mercury rains down on oceans, it is converted by anaerobic
bacteria in deep waters to methylmercury, the most toxic form of
mercury. Upwelling brings some methylmercury to the surface, where it is
released back into the atmosphere and carried by fog. At high
concentrations, methylmercury can cause neurological damage, including
memory loss and reduced motor coordination, and it can decrease the
viability of offspring.
The new study: Marine fog brings more than cooler temperatures to coastal areas.
Researchers at UC Santa Cruz have discovered elevated levels of mercury
in mountain lions, the latest indication that the neurotoxin is being
carried in fog, deposited on the land, and making its way up the food
Concentrations of mercury in pumas in the Santa Cruz
Mountains were three times higher than lions who live outside the fog
zone. Similarly, mercury levels in lichen and deer were significantly
higher inside the fog belt than beyond it.
Photo: Mountain lion lounging in a cottonwood tree (Credit: Justin Shoemaker)
At least one lion studied had mercury levels known to be toxic to
species like mink and otters, and two others had "sublethal" levels that
reduce fertility and reproductive success.
found in pumas are approaching toxic thresholds that could jeopardize
reproduction and even survival, according to the researchers, whose
findings appear in an article that is available free online.
by Peter Weiss-Penzias, an environmental toxicologist who has pioneered
the study of pollutants in coastal fog, the study is the first to trace
the atmospheric source of super-toxic methylmercury in the terrestrial
food web up to a top predator.
"Lichen don’t have any roots so
the presence of elevated methylmercury in lichen must come from the
atmosphere," said Weiss-Penzias. "Mercury becomes increasingly
concentrated in organisms higher up the food chain."
mercury levels in fog present no health risk to humans, the risk to
terrestrial mammals may be significant. With each step up the food
chain, from lichen to deer to mountain lions, mercury concentrations can
increase by at least 1,000 times, said Weiss-Penzias.
study included fur and whisker samples from 94 coastal mountain lions
and 18 noncoastal lions. Mercury concentrations in the coastal samples
averaged about 1,500 parts per billion (ppb), compared to nearly 500 ppb
in the noncoastal group. At least one lion studied had mercury levels
known to be toxic to species like mink and otters, and two others had
"sublethal" levels that reduce fertility and reproductive success.
concentrations of mercury present an additional potential threat to a
top predator that is already coping with habitat loss and other risks
posed by humans, said senior author Chris Wilmers, a professor of
environmental studies and the director of the Puma Project.
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 Wilmers. "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."
The source of fog-borne mercury
"Fog is a stabilizing medium for
methylmercury," said Weiss-Penzias. "Fog drifts inland and rains down in
microdroplets, collecting on vegetation and dripping to the ground,
where the slow process of bioaccumulation begins."
Top predators, an international treaty, and a foggy bike ride
is present in coastal areas that border oceans, environmental
"hotspots" that are also home to high concentrations of humans.
Weiss-Penzias is eager to investigate mercury levels in coastal Chile,
where the top predator is a lizard, while Wilmers is curious about
mercury levels in coyotes, bobcats, and birds in coastal areas.
need to protect the top predators in the environment," said
Weiss-Penzias. "They're key-stone species. They perform ecosystem
services. When you change one thing, it has cascading effects through
As an example of cascade effects, Wilmers cited
the removal of wolves from many states in the eastern United States,
which resulted in more coyotes, who preyed on foxes that had
historically kept the rodent population in check. The loss of foxes
ultimately made way for more rodents, which help transmit Lyme disease,
said Wilmers, who added, "Locally, potentially, mountain lions keep deer
and small predators in check, which could reduce Lyme disease."
global effort to protect humans and the environment from mercury
includes the Minamata Convention on Mercury, an international treaty
that was adopted in 2013. Named after a Japanese city that endured a
dire incident of mercury poisoning, the treaty is broad in scope,
encompassing the entire life cycle of mercury.
for the future of that treaty to understand all the different ways that
mercury impacts the environment," said Weiss-Penzias.
atmospheric chemist, Weiss-Penzias said he first became curious about
fog-borne pollutants about a decade ago while riding his bike to work.
"I was riding through this absolute fogstorm, with water dripping off my
glasses, and I just wondered, 'What's in this stuff?'" he recalled.
Hypothesizing that mercury might de-gas out of the ocean and end up in
fog, he collected samples and sent them to a lab.
"The lab called me, saying they'd have to re-run the tests, because they didn't believe the numbers," said Weiss-Penzias.
This article has been republished from the following materials. Note: material may have been edited for length and content.
The original publication:
Peter S. Weiss-Penzias, Michael S. Bank,
Deana L. Clifford, Alicia Torregrosa, Belle Zheng, Wendy Lin &
Christopher C. Wilmers, Marine
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