This means the body has a very hard time getting rid of it. Little by little, mercury accumulates in someone exposed to it over time. Eventually the buildup reaches dangerous levels. Mercury, like other metals, occurs naturally in rocks. When a rock containing mercury dissolves or breaks up, mercury is released into water, air, or soil.
Bacteria take in tiny particles of mercury, combining it with methane to produce methyl mercury.
This is the most toxic form of mercury, and it can damage brain cells. When the feathers stop growing, they stop taking in mercury. By analyzing loon feathers, scientists can determine how much mercury a loon was exposed to during the time it molted into its feathers. The mercury stays in the feathers as long as the feathers exist. All natural systems have tiny amounts of mercury.