High arsenic levels found in some Yellowknife lakes

Decades of pollutants from a nearby gold mine have raised the arsenic levels of some Yellowknife lakes above the recommended limit for drinking water.

According to research by Mike Palmer, an environmental monitoring specialist, some of the lakes around the Giant Mine gold mine contain arsenic concentrations that can be unsafe for drinking water.

The concentrations ranged from 6.5 billion parts per billion to 1,800 parts per billion—a shocking amount considering the recommended limit for drinking water is 10 parts per billion.

Researchers have been monitoring arsenic levels in 100 lakes within 30-kilometers of the mine, which opened in 1948. When the mine closed in 2004, it had produced 20,000-tonnes of arsenic trioxide dust—the lethal byproduct of extracting gold—in its 50 years of operations. That poisonous dust then settles into the snow and flows into nearby rivers and lakes each spring as the snow melts.

Palmer found that larger lakes that connect to even bigger lakes had lower levels, but smaller, organic lakes were more greatly affected. The Long Lake, which also encompasses the popular vacation spot Fred Henne Park, was at 39.7 parts per billion, which is almost four times the recommended amount.

And although the numbers seem daunting on paper, Palmer says further analysis is required to fully understand the situation.

“One of the questions against and one of the important things to recognize is that the bioavailability and toxicity of arsenic really depends on its speciation,” Palmer told the CBC.

Basically, this means that although the readings suggest high arsenic levels, not all types of arsenic have the same toxicity level.

For instance, the highly soluble arsenic dust that was pumped from the gold mine’s roaster stack and into the air and the nearby lakes is much more toxic than the arsenic found in the rock throughout the city.

Palmer’s future research will focus on speciation and understanding what types of arsenic are present in Yellowknife lakes.