Tree rings can reliably track mercury pollution in the atmosphere.
Researchers studied a Yukon gold mining town that operated from 1905 to 1966.
If you mercury to river gravel, it binds to gold, separating it from sediment. Heat the deposit. Mercury separates and you get gold. During heating, some mercury diffuses into the atmosphere, and trees absorb it.
By examining cores taken from trees growing in the area, researchers got yearly accounts of atmospheric mercury levels.
Levels spiked when gold mining operations started expanding, and reduced to natural levels when the site closed.
Mercury levels have recently begun to go up in the Yukon, Northwest Territories, and Alaska.
There are international treaties to reduce mercury pollution, but many countries continue the practice.
By expanding their study sites and using tree rings as an archive to study past changes in mercury levels, researchers can understand present increases and potentially prevent future ones.
Original article:
Using tree rings, U of T researchers measure history of mercury contamination in Yukon
Original study:
The tree-ring mercury record of Klondike gold mining at Bear Creek, central Yukon