Scientists studying mercury levels have identified wetlands in central Nova Scotia as one of five known "hotspots" of the neurotoxic metal in eastern North America, according to revised research to be published in January.

The team of U.S. and Canadian researchers looked at mercury levels in yellow perch and common loons for traces of the potent neurotoxin and found five regions where those concentrations exceeded those established for wildlife and human health.

A lay study released two years ago identified the area around Kejimkujik National Park in Nova Scotia and the LaMauricie region in Quebec as mercury hotspots, but a more rigorous approach to the data collection has downgraded the Quebec region as "an area of concern" or "potential hotspot" due to incomplete data.

Nine areas of concern also identified

Also newly identified as a potential hotspot is the Lepreau region in southern New Brunswick.

The new findings, to be published in the January 2007 issue of the scientific journal BioScience, identify five mercury "hotspots" and nine "areas of concern" in eastern North America.

Mercury is a highly potent toxin that persists in the environment, builds up in the food chain and can cause neurological damage to humans, who are exposed mainly through eating fish.

High acidity of lakes cited

While the other four established hotspots, located in New England and New York, are nearer industrial centres, the area identified in central Nova Scotia has become a hotspot because of the high acidity of its lakes, said David Evers, the lead researcher of the study.

"Some habitats are naturally sensitive to mercury. Low ph lakes typically have more of the bacteria which converts mercury into an organic part of the food web," Evers, the head of the BioDiversity Research Institute in Maine, told CBC News Online.

"The lakes could have a naturally low pH because it lacks the limestone or bedrock to create a more neutral pH, or it could have its pH lowered from sulphur or acid rain. It really creates a double-whammy because those places affected by acid rain are also more sensitive to mercury," he said.

Though mercury is not directly harmful at ambient levels, it can be concentrated and chemically modified in aquatic food chains, resulting in dangerous levels of methylmercury in some species.

Wetlands more susceptible

Regions can get mercury from both local and regional sources, said Evers, but whether that mercury stays in the system depends on the region's makeup. Wetlands, for example, are far more susceptible to mercury accumulation than dry grasslands.

Evers recommends emission reductions as the simplest way to reduce mercury content. The group's analysis of 1999 reductions near the Merrimack River watershed in New England found mercury levels for the loon subsequently fell from 4 parts per million to 1.5 in just three years.

For fish-eating birds two to three ppm is seen as an approximate mercury threshold, Evers said.

The loons in the area near Kejimkujik in Nova Scotia averaged levels of 5.5 ppm, plus or minus 1.4 over the years studied. The problem was also widespread: 93 per cent of loons in the region had mercury concentrations at high levels of concern.

Role of emissions questioned

Cutting local emissions might not have the same effect on the Nova Scotia region as it did in New England because Kejimkujik and the surrounding area are more influenced by regional and global sources of mercury, Evers said.

Coal-fired power plants are seen as the largest industrial source of mercury emissions in Canada.

Provincial and territorial environment ministers agreed in October of 2006 to voluntary standards to cut mercury emissions from coal-fired plants by 60 per cent in less than four years.

The study looked at only a sampling of regions in northeastern North America and is not comprehensive for Canada, Evers said.