Dangerous levels of mysterious toxin showing up in Año Nuevo seals
Along the shores of Año Nuevo State Park, blue and green waves crash upon the sand.
David Burns, a docent for the past five years, has endless anecdotes about the mighty elephant seals that arrive here twice a year, once to breed and once to molt. He and other docents even tell the story of a local creature nicknamed T.S. Elephant Seal, who had a large permanent scar from a toilet seat that had wrung itself around his neck. The tale comes with a warning.
“Basically, stop screwing up the environment,” he says, as the sun begins to set, casting shadows along fields of tall grass.
In the distance, a lone elephant seal lets out a bark, as if in agreement.
But this vibrant ecosystem may be facing even greater dangers than household trash. Under the pristine-looking waters of Año Nuevo, a potential threat looms. It isn’t a Great White Shark or some mythical sea monster, but rather an elemental compound.
The threat is methylmercury, and a growing body of evidence shows it is in extraordinarily high concentrations in the elephant seal population. While experts say humans aren’t at risk, they aren’t sure what the toxin, which can cause neurological damage to mammals, is doing to the ecosystem in and around the state park, which is just north of the Santa Cruz-San Mateo County border.
UCSC Biology Professor Russell Flegal and two recent UCSC students co-authored a report on the topic, which ran in a September issue of the Proceedings of the National Academy of Sciences of the United States of America. In tests, the researchers found high methylmercury levels in the fur of elephant seals. They also tested water levels around California and found that Año Nuevo’s waters had alarmingly high levels of the neurotoxin, eight times higher on average than the rest of the state—leading them to believe this is connected to elephant seals. The levels spiked to 17 times higher during molting season.
This wasn’t entirely new information. Previous studies have found high concentrations of mercury, which can stop brain growth in fetuses, in seal blood and tissue samples, and in 1981 Flegal discovered that mussels in Año Nuevo have higher concentrations than those in other areas.
Methylmercury is easily absorbed by marine life through two ways—direct dumping of waste, often from mercury mines, and atmospheric pollution. According to the Environmental Protection Agency, it can take centuries for the concentration levels to breakdown, meaning high levels will only continue to grow.
The EPA estimates that coal burning is the number one source of mercury pollution in the atmosphere. The element is then released back into the ocean and land as precipitation. It isn’t clear where exactly the sources might be. For over 100 years, there was a mercury mine in the Santa Cruz Mountains. Now a Santa Clara County Park, the Almaden Quicksilver Mines, which closed in 1971, were 25 miles from Año Nuevo. But Sarah Peterson, a biologist with the United States Geologic Survey who has studied sea lions, doesn’t think there is any connection between the two.
For the recent study, Flegal worked with Jenn Cossaboon, who graduated from UCSC in 2012, and Priya Gangulia, who got her doctorate from UCSC in 2013.
Cossaboon’s team looked at the compound’s total concentration in each site and compared the inorganic, or nontoxic, concentrations to organic ones—mercury in its toxic, methylated form. For the seven comparison sites, they deduced that about two percent had methylated, which is typical for contamination near highway runoff. During the breeding season at Año, that number rose to four percent methylated. However, during the molting season, the biologists found an extraordinary 43 percent of the total mercury was methylated.
“Not only are they very large animals,” says Cossaboon, now a graduate student at San Diego State University, “but they also have a ‘catastrophic molt,’ so they’re shedding their whole top layer of fur in a matter of four to six weeks.
The group estimates that each individual seal sheds about half a pound of methylmercury each year.
These findings made waves around the country, and one of the study’s more surprising aspects was its response from journalists. A Google news search on mercury and elephant seals reveals a host of science blogs blaming the elephant seals specifically for the mercury levels—as if the species itself were wreaking havoc on the marine ecosystem. “I think the media picked it up that way for the headlines,” Cossaboon says with a chuckle.
Of course, the elephant seals are only shedding higher levels of mercury because they are ingesting higher levels of it, and the dangerous levels of mercury can be traced back to human activity.
Methylmercury is a biomagnifier, meaning the higher up the food chain it goes, the more concentrated it becomes. Pinnipeds, like elephant seals and sea lions, are particularly susceptible.
For example, a fish that feeds on plants with high levels of methylmercury will absorb a lifetime of the compound, which stays in that fish’s system. When an elephant seal feasts on a school of polluted fish, methylmercury accumulates within it. When it molts, the toxin is released back into the already polluted water to be re-absorbed by the ecosystem and start the cycle again, only this time at higher concentrations.
The previous UCSC study into elephant seals found the blood and tissue of elephant seals contains the highest concentration of mercury ever reported for a predatory animal.
Author Sarah Peterson, tells GT the level “was much higher than we were initially anticipating.”
Elephant seals were chosen for both studies because they are the only pinniped species in the northeastern Pacific Ocean that feed almost entirely on fish and squid from the mesopelagic zone, a deep water layer extending from 650 to 3,300 feet. Studies have shown anaerobic bacteria—microorganisms that can live in extremely low or no oxygen—physically change, or “methylate,” the chemical makeup of inorganic mercury into methylmercury. How and why that happens is still unknown.
“This is an important finding, because we are just now learning about some of the nuances of how mercury moves around the environment,” says biologist and Año Nuevo director Patrick Robinson. “We usually think of the deep Pacific Ocean as a pristine place, but even this remote area is touched by human activity.”
In fact, Peterson’s work and similar studies from her colleagues have shown that levels of methylmercury in deep-ocean-feeding elephant seals is comparable to that found in the tissue levels of harbor seals foraging in San Francisco Bay.
While there are “no observable side effects” of mercury poisoning in the elephant seals, Peterson is quick to point out this doesn’t necessarily mean there aren’t any. She compares it to our years of limited knowledge about the adverse effects of smoking tobacco, saying we just don’t have the information on the seals yet.
“It’s challenging to detect effects if you can’t actually see them,” Peterson stresses. “You can’t see if anything is happening below the surface. We don’t know if there’s any effect of the contaminant on these animals that’s happening on a cellular or neurological level. We have no idea.”
POOL SHED Research shows that when elephant seals molt, they release contaminants like methylmercury, a pollutant often rooted in mercury mining. PHOTO: DAN COSTA, UCSC