The Aleutian Islands, though far away from the world's industrial centers, are no sanctuary from mercury contamination. Newly published research adds ducks on Unalaska Island to a list of Aleutian animals showing elevated levels of mercury in their bodies.
The study, published in the journal Marine Pollution Bulletin, found that harlequin ducks in Unalaska, the biggest Aleutian community, have been picking up mercury from the blue mussels they eat.
Harlequin ducks from Kodiak, also part of the study, had detectable mercury in their blood as well, but at much lower levels than that in the Unalaska ducks, the study found. Mercury levels in the Unalaska ducks' blood averaged 0.31 parts per million and were nearly eight times as high as those in the Kodiak ducks.
The study was conducted by the Maine-based Biodiversity Research Institute, U.S. Geological Survey, U.S. Fish and Wildlife Service and other organizations.
The study analyzed samples of blood taken from live harlequin ducks from 2005 to 2008. Those measurements showed mercury recently consumed by the birds, in contrast to levels measured in feathers, which show past exposure to mercury.
The direct source of the Unalaska and Kodiak ducks' mercury appears to be the local blue mussels they eat — and the mussels themselves were found to have mercury, in patterns similar to those found in the ducks, the study said.
Blue mussels get their food through a filtering process. As they consume plankton and other tiny floating bits of food and other material, they pick up environmental mercury, the study's lead author said. "They are great local environmental indicators in that sense — they are stationary and accumulate locally available environmental toxins," Lucas Savoy, waterfowl program director at the Biodiversity Research Institute, said in an email.
Within the two islands, Unalaska and Kodiak, mercury levels varied somewhat depending on site. All 115 ducks sampled had measurable levels of mercury in their bodies, the study found.
The harlequin duck study adds to a body of evidence about mercury in the Aleutians, where fish, birds and mammals have been found to have elevated levels of the contaminant. Mercury is also toxic to humans.
Among fish, three-spined stickleback in the island of Agattu in the farthest western reaches of the Aleutian chain were found with relatively high mercury levels, according to a study by scientists from the University of Alaska and the USGS. That study, published in 2014 in the journal PLOS ONE, found mean mercury levels in the fish to be .55 parts per million, above the 0.3 parts per million guideline for human consumption used by the Environmental Protection Agency.
A 2007 study of several wild food sources used by Aleutian residents found mercury in fish, birds and eggs. Nine of 15 fish species evaluated had samples with mercury levels over EPA's 0.3 parts per million standard, and 95 percent of pigeon guillemot muscle sampled had mercury at levels above that guideline, according to the study, by scientists from several organizations, including the Aleutian Pribilof Island Association.
The source of environmental mercury in the Aleutians is yet unknown, Savoy said. They could be natural, like volcanic eruptions, or they could be industrial, he said. There are some strong suspicions that mercury pollution from Asia is being carried in the atmosphere and in the ocean to the Aleutians, he said. If so, Kodiak Island seems much less exposed to such sources, the harlequin duck study would indicate.
It is unclear whether there should be any worries about the mercury levels found in the Unalaska harlequin ducks, Savoy said.
"There certainly appears to be a healthy population of harlequins in the Aleutians, so it is difficult to say if levels are high enough to be a concern to harlequins or other near-shore marine birds sharing the same resources," he said by email. Harlequin ducks can live up to 20 years in the wild, so they could potentially accumulate harmful levels of mercury over their relatively long lifetimes, he said.