Washington: Feathers collected from rare Pacific seabirds over the past 120 years have shown an increase in a type of toxic mercury that likely comes from human pollution, US researchers said on Monday.
Scientists at Harvard University took samples from feathers belonging to the endangered black-footed albatross from two US museum collections, said the study in the Proceedings of the National Academy of Sciences.
The feathers, which dated from 1880 to 2002, showed "increasing levels of methylmercury that were generally consistent with historical global and recent regional increases in anthropogenic mercury emissions," the study said.
Methylmercury is a neurotoxin that can cause central nervous system damage and comes from burning fossil fuels.
Rising levels of mercury in fish and seafood are believed to pose dangers to human health, and pregnant women and young children are particularly urged to limit the amount of some types of fish in their diets.
"Using these historic bird feathers, in a way, represents the memory of the ocean," said study co-author Michael Bank, a research associate in the Department of Environmental Health at Harvard School of Public Health.
"Our findings serve as a window to the historic and current conditions of the Pacific, a critical fishery for human populations," Bank said.
The highest concentrations in feathers were linked to exposure by the birds in the post-1990 timeframe, which coincided with a recent spike in pollution from Asian carbon emissions in the Pacific region, the study said.
Mercury pollution from Asia went from about 700 tons annually in 1990 to 1,290 tons in 2005, the study said, noting that China became the largest emitter of such pollutants in 2005 with 635 tons.
Pre-1940 levels of mercury in bird feathers were the lowest in the study.
The black-footed albatross is listed as endangered by the International Union for Conservation of Nature, which estimates about 129,000 of them are living in the northern Pacific, mainly near Hawaii and Japan.
The birds feed primarily on fish, fish eggs, squid and crustaceans.
The high levels of mercury in their feathers could indicate a link between their high-mercury diets and their decreasing numbers, said the study.
"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," said lead author Anh-Thu Vo, a graduate student at the University of California, Berkeley.
Banks added that "mercury pollution and its subsequent chemical reactions in the environment may be important factors in species population declines."