Graduate student's study finds correlation in rising mercury levels in birds and atmosphere

Photo: Graduate student Anh-Thu Vo examines a seabird specimen.
Allyse Bacharach/Staff
Graduate student Anh-Thu Vo examines a seabird specimen.

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Sarah Burns talks about a study regarding an endangered species of seabird.

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An increase in methylmercury levels in one of the Pacific Ocean's endangered species of seabird was found to coincide with rising levels of human-generated mercury emissions, according to a study by a UC Berkeley graduate student published Monday in the online edition of Proceedings of the National Academy of Sciences.

The research - led by Anh-Thu Vo as a part of her senior thesis project when she studied at Harvard University as an undergraduate - analyzed a collection of black-footed albatross feathers housed by the Harvard Museum of Comparative Zoology and the University of Washington's Burke Museum of Natural History and Culture. The feathers ranged in origin from 1880 to 2002 and were examined for their content of methylmercury - a specific form of mercury Vo said the birds consumed with their food.

"From the literature, we knew that the (mercury) levels in these birds were among the highest in sea birds along the Pacific," Vo said. "Given that it is an endangered species, we were concerned that it might be contributing to or undermining the potential for this endangered species to have positive population growth."

According to Vo, past research has shown a link between dietary mercury exposure in the birds and reproductive problems, including decreased egg-laying and decreased territorial fidelity. Because the mother can transfer mercury to her eggs, high levels of mercury can also lead to problems with the eggs themselves, including a decreased level of hatching success and an increased level of mortality in the developing bird embryo.

The study states that changes in methylmercury levels over time were consistent with "historical global recent regional increases in anthropogenic emissions."

Vo said the anthropogenic emissions - those created by humans - are caused in part by the combustion of fossil fuels, mining and waste disposal.

Michael Bank, one of the co-authors of the study and a research associate at Harvard, said recent anthropogenic mercury emission rates have seen particular growth out of Asia and especially in China, adding that economic growth is often coupled with an increase in pollutants.

According to Vo, though the study does provide evidence for a correlation between historical mercury emission levels and the levels found in the albatross feathers, it does not necessarily provide evidence for a link between the human-caused levels and the feather levels.

"If that is the case that anthropogenic emissions significantly explain these increases in the feather levels over time, I think it would be a good idea to reduce these emissions, because mercury has no benefit to animals," Vo said.

Vo said that while the Pacific Ocean is "an important fishery for human populations," she would be cautious to extend the findings of the research to human populations but added that mercury levels can affect people who "disproportionately incorporate" these food sources into their diets.

The study was largely possible because of the extensive historical museum collections, Vo said.

"The original collectors a century ago could not have envisioned how their specimens would be used," said Carla Cicero, staff curator of birds at the UC Berkeley Museum of Vertebrate Zoology, in an email. "The same is true today as new techniques become available for studying questions that are relevant to both science and conservation."

Contact Sarah Burns at [email protected]

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