Study warns of Great Lakes fish mercury
Published August 3rd, 2004
TORONTO — Canadians who routinely eat fish from the Great
Lakes should pay close attention to fish advisories in
order to avoid high blood mercury levels, a new study
Anyone eating 100 fish meals or more each year should
be careful about the type and source of the fish they
are consuming, especially if they are of reproductive
age, say researchers at the University of Toronto's department
of public health sciences, Health Canada and the Quebec
The research was divided into two studies -- one measuring
mercury levels in anglers who fished from designated contaminated
areas in Mississauga and Cornwall, Ont.; the other examining
mercury levels in sport-fish eaters from Hamilton, Ont.,
Toronto, Windsor, Ont., Niagara, Ont., and Detroit.
All 86 sport-fish consumers had detectable blood mercury
levels, including two with levels above the accepted normal
Some had consumption levels that required counselling
on exposure reduction strategies, according to the studies'
findings, published in the August edition of Environmental
Among the anglers examined in the study, 87 per cent
had detectable blood mercury levels -- but they were within
Health Canada's acceptable range. According to the study,
about 176 of the 232 anglers who participated in the study
ate their catch.
Mercury, which can be found in a number of foods due
to environmental factors, can affect human reproductive
functions and may be toxic to a fetus, says Donald Cole,
the lead researcher of the report and a professor at the
university's department of public health sciences.
"We're exposed to mercury through a whole variety
of sources," he says.
"It comes out of incineration process, coal-burning
processes, etc. So it's in the environment. It's widespread,
and so it probably gets into a number of our foods."
The study also found that Asian Canadians who ate sports
fish exhibited the highest blood mercury levels, mostly
due to their higher overall fish consumption. Mercury
levels among European Canadians and anglers who consumed
sports fish were about one-third as high.
Cole says the study illustrates the dilemma of balancing
the risks and benefits of eating fish, citing the food's
Omega-3 fatty acids, which offer cardiovascular protection.
Avoiding Great Lakes fish doesn't resolve the issue,
he says. Some ocean fish found in grocery stores are also
known to accumulate mercury.
The Ontario Ministry of the Environment has a guide to
eating sports fish, he adds.
"The bigger the fish you get, the more likely it
is to have accumulated mercury," he says.
"But it also varies a lot with topography. If you're
in a lake with hard rocks and quite acid, then you're
more likely to have more mercury in the fish."
The most common fish consumed in the study included bass,
yellow perch and walleye.
Walleye has historically had more mercury than other
types of fish in the Great Lakes, Cole says. But fish
that eat other fish -- such as large trout and salmon
-- are more likely to accumulate mercury.