The study shows that the observed increase in methylmercury levels, most likely from human-generated emissions, can be observed and tracked over broad time periods in organisms that live in the Pacific Ocean.

The study, which was published in PNAS, has important implications for both environmental and public health, say the authors.

"The Pacific in particular warrants high conservation concern as more threatened seabird species inhabit this region than any other ocean," says lead author Anh-Thu Vo, who did her research while an undergraduate at Harvard and is currently a graduate student at the University of California, Berkeley. "Given both the high levels of methylmercury that we measured in our most recent samples and regional levels of emissions, mercury bioaccumulation and toxicity may undermine reproductive effort in this species and other long-lived, endangered seabirds."

The researchers collected feathers from black-footed albatross specimens in the Harvard University Museum of Comparative Zoology and the University of Washington Burke Museum of Natural History and Culture and analysed methylmercury in samples from 1880 to 2002. They found increasing levels of methylmercury that were generally consistent with historical global and recent regional increases in anthropogenic mercury emissions.

"Methylmercury has no benefit to animal life and we are starting to find high levels in endangered and sensitive species across marine, freshwater, and terrestrial ecosystems, indicating that mercury pollution and its subsequent chemical reactions in the environment may be important factors in species population declines," says study co-author Michael Bank of Harvard School of Public Health (HSPH).

Consumption of mercury-tainted fish from the Pacific Ocean is an important source of human exposure to methylmercury in the US and may lead to adverse neurodevelopment effects in children, claims Bank.