Breast feathers pulled from seabirds preserved in museum collections appear to document increases in mercury pollution over the span of more than a century, a new analysis has found.
This record matches up with the history of human emissions of this toxic element. Among the feathers, taken from black-footed albatross specimens, the average level of a particular form of mercury that accumulates in predators increased after 1940 and 1990. These times are benchmarks in the history of human mercury emissions.
In the 1940s, mercury pollution increased along with mineral mining and fossil fuel combustion. In recent decades, some countries have cut mercury pollution; however, in the 1990s industrializing Asian countries, particularly China, began emitting more and now dominate the sources of mercury pollution, according to the researchers, who published their results in the latest issue of the journal Proceedings of the National Academy of Sciences.
"Using these historic bird feathers, in a way, represents the memory of the ocean, and our findings serve as a window to the historic and current conditions of the Pacific, a critical fishery for human populations," said study co-author Michael Bank, a research associate in the Department of Environmental Health at Harvard School of Public Health.
A natural element, mercury's presence in the environment has been bolstered through manufacturing, burning coal and other human activities. In the oceans and other environments, microbes convert mercury into methylmercury, which accumulates in the tissues of the animals that consume it so that by the time it makes its way to the top of the food chain there's plenty of toxin buildup. Shellfish- and fish-eating animals at the top of the food chain, like seabirds and humans, are at risk for consuming harmful concentrations of the toxin, which can impair neurological development in human fetuses and young children.
The researchers found that the birds' mercury levels varied not only over time, but also with the individual albatross's position on the food chain — which influenced the amount of mercury that had accumulated in its food — and its body size, as measured by the length of a foot bone.
The black-footed albatross is an endangered seabird that eats fish eggs, squid, fish and crustaceans, and its range takes it throughout the northern half of the Pacific Ocean. The researchers looked at breast feathers from albatrosses collected between 1880 and 2002 and held at the Harvard University Museum of Comparative Zoology and the University of Washington Burke Museum of Natural History and Culture. They looked at a variety of chemical indicators in the feathers, including methylmercury and inorganic mercury, which, in the past, has been used by museum curators to preserve specimens. They found that while inorganic mercury declined over time, methylmercury increased.
The researchers infer that, based on work done on other birds, mercury poisoning may have begun to have harmful effects on the albatross populations beginning in the early 1980s. Over one-half of the more recent, post-1990s feathers contain methylmercury levels above this threshold, they write.
"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 researcher Anh-Thu Vo, who did her research while an undergraduate at Harvard and is currently a graduate student at the University of California, Berkeley.
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