Scientists say the level of mercury has increased nearly 50 times in the feathers of an Arctic bird species over the past 130 years.
Canadian biologists have analyzed museum feather samples of the ivory gull over that period.
In a study published March 18, they say the species has been exposed to mercury for decades, from scavenging on the carcasses of mammals.
The team says it could have implications for the bird's ability to reproduce and raise chicks.
Mercury levels are going up in other Arctic birds, fish, and mammals, mainly due to atmospheric pollution caused by coal burning.
The ivory gull breeds in Canada, Greenland, the Norwegian island of Svalbard, and islands off northern Russia.
The species is endangered in Canada. Elsewhere, it is classified as near-threatened by the International Union for Conservation of Nature.