Great Lakes Article:

Study warns of Great Lakes fish mercury levels
Canadian Press
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 warns.

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 Toxicology Centre.

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 range.

Some had consumption levels that required counselling on exposure reduction strategies, according to the studies' findings, published in the August edition of Environmental Research.

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.