Mercury levels in cormorants and petrels stable over past 50 years
Date: December 16, 2016
Source: McGill University
Researchers have discovered that levels of mercury in seabirds off the coast of British Columbia have remained relatively stable over the past 50 years. This might appear to be good news, but it is due to a decline in fish stocks near the surface which has forced seabirds to feed in areas where there are more bacteria (known as sulfate-reducing bacteria) which control the levels of mercury.
Although tiny, bacteria can be very important -- try to make yogurt or miso soup without them. Now, researchers at McGill University and Environment and Climate Change Canada have discovered that bacteria play an important role in determining the health of birds at the top of the food web. By using isotopic tracers called stable isotopes, researchers showed that seabirds feeding in areas rich in sulfate (a chemical that is an important food for sulfate-reducing bacteria that help break down organic matter) had high levels of mercury. Those same sulfate-rich areas were favoured by the sulfate-reducing bacteria which produce methylmercury, a toxic substance which is then taken in by the fish that eat them and eventually by the seabirds that feed on the fish.
The authors of a recent paper published in Environmental Science and Technology used seabird eggs collected along the Pacific coast of Canada over 47 years, and archived by Environment and Climate Change Canada in Ottawa. They documented a decline in mercury levels for several seabird species over 47 years. However, they traced that decline to a dietary switch from high-sulfate, mercury-rich fish to low-sulfate, mercury-poor fish. Thus, there was no overall change in mercury levels.
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