BioEd Online

Feathers from museum collections have helped scientists to prove that mercury levels have risen in Albatrosses during the past century.

To trace toxin levels over time, the researchers measured the amount of methylmercury in breast feathers plucked from specimens of the endangered black-footed albatross (Phoebastria nigripes) collected between 1880 and 2002, from sites spanning the northern Pacific Ocean. The results are published today in the Proceedings of the National Academy of Sciences¹.

Methylmercury is the organic form of the heavy metal that builds up in tissues, and it is stably incorporated into feathers. Human activities, such as the burning of fossil fuels, introduce mercury to ecosystems, where it can taint the food sources of many species, including humans.

Anh-Thu Vo, who designed the study while an undergraduate at Harvard University in Cambridge, Massachusetts, says that growing up near the Gulf of Mexico spurred an early interest in the toxic effects of environmental pollutants.

"I'd always heard warnings about mercury bioaccumulation in fish, but I really wanted to focus on seabirds because they are among the top predators in the marine food web," says Vo, now a graduate student at the University of California, Berkeley.

Apex predators such as the albatross are especially vulnerable to mercury biomagnification, whereby the toxin becomes more concentrated as it travels up through the food chain.

Going up

Vo and her collaborators found that methylmercury levels roughly doubled over the 120-year study period, with an increasing number of feathers from later years showing levels near the upper limit of the sublethal threshold for the common loon². It is not known whether that same level adversely affects the albatross.

Collin Eagles-Smith, an ecologist for the US Geological Survey in Corvallis, Oregon, who studies mercury bioaccumulation, says that the study "finally provides some strong evidence for a phenomenon that had been widely speculated but never supported with data".

But he says the lack of information on the physical effects of mercury in the albatross is a concern. "We need to try and understand whether or not these birds actually experience a deleterious effect," he says. "Sensitivity to mercury can vary dramatically among seabird species."

Study author Michael Bank, an ecotoxicologist at Harvard School of Public Health in Boston, Massachusetts, agrees. "This is an important data set, although it is difficult to make strong inferences about the toxicological effects in this species," he says. "However, the methylmercury concentrations are high enough that they likely warrant concern, especially since mercury has no benefit for animal life."

Tenuous link

Daniel Jaffe, an atmospheric chemist at the University of Washington in Bothell cautions against drawing conclusions about global emission rates or sources from the study. "They really focused on a large-scale change," Jaffe says, pointing to small sample sizes from broadly distributed collection sites. "We certainly know the emission pattern for mercury has changed dramatically over the last century, but there are still things we don't understand."

Vo agrees that interpretive caution is necessary, explaining that increasing methylmercury in the albatross only loosely corresponds to estimates of increased anthropogenic mercury output. Still, using preserved specimens is valuable for understanding historical trends in exposure levels, Vo adds. "These analyses can be expanded to different species, different time frames, different regions, different contaminants," she says.