SOURCE: UC Santa Cruz

DATE: November 26, 2019

SNIP: 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 chain.

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.

Mercury levels 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.

Although 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.

The 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.

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

As 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.