Study focuses on impact of arsenic in Yellowknife
Northern News Services
Yellowknife (May 02/01) - The environmental legacy of gold mining permeates the soil and rock of the Yellowknife area.
During a half century of operation, the two gold mines flanking Yellowknife emitted thousands of tonnes of arsenic trioxide. The highly toxic dust settled on rock and soil around the mines. Plumes from gold roaster stacks overlapped the city.
| Arsenic content Samples taken in Yellowknife in 1999-00:
|
Currently, two studies are under way. Kingston's Royal Military College of Canada (RMC) is analyzing samples from Yellowknife gardens to measure how much arsenic is absorbed by plants and how readily arsenic in plants and animals is absorbed by the human body.
The Yellowknife Soil Arsenic Remediation Committee (YSARC), composed of government, health, environmental and industry representatives, has contracted a consultant to do a human health risk assessment.
YSARC will use that assessment and RMC studies to develop guidelines that will be used in cleaning up the mine sites. It will set arsenic content levels for industrial, recreational and residential lands by September.
YSARC will host a meeting May 15 to update the public on its work over the last year.
Air to land
Because of the geochemical composition of the rock mined at Giant and Con, the mechanical and chemical alchemy required to produce gold bars included cooking the crushed ore at 485 C.
Fumes that came from the roaster carried tiny particles of arsenic trioxide and sulphur dioxide.
"These materials, if emitted into the environment, present a potential health hazard," reported the 1977 Canadian Public Health Association Task Force on Arsenic.
Arsenic flowed continuously from the Giant roaster stack into the environment -- in smaller amounts over the years when different scrubbing technology was introduced -- for 50 years. Con shut down its roaster in 1970 after 29 years of operation.
The harmful effect of sulphur dioxide, an acidic gas, is evident in the almost vegetation-free stretch of Ingraham trail that passes through the gouged landscape of Giant mine.
The dispersion of arsenic trioxide particles followed the same pattern, settling thickest near the roaster stacks.
Soil samples taken last year from the base of the Giant Mine roaster stack contained 87,000 parts per million of arsenic.
The arsenic content of Canadian soils typically ranges from 4-14 ppm. One of the RMC reports suggests the levels of 50-56 found in Dettah are natural to this area. The 1977 report noted background levels in soil 80 kilometres from Yellowknife were 25 ppm.
Arsenic: not all bad
Due to be released in June, the latest RMC study will attempt to identify the type of arsenic in soil samples taken in the area.
"Total arsenic doesn't really tell you anything," said Ken Reimer, the RMC professor overseeing the research.
It is not a generalization to say arsenic is found everywhere. It's the 12th most common element in the human body, and is present in the earth's crust and seawater. Most shellfish contain high levels of arsenic.
Humans are generally unaffected by naturally occurring arsenic. Two aspirin-sized tablets of its man-made cousin, arsenic trioxide, would be fatal.
There is no direct way to distinguish the two in soils.
"You can't per se, pick up the soil and say, 'Oh, I see arsenic trioxide here," said Reimer. It is possible to distinguish different types of arsenic in plants and animals.
Analysis of soil relies on an analysis of the mineral composition of the rock of the area. Once a 'fingerprint' is developed, the presence of arsenic trioxide can be determined by comparing how closely samples conform to the fingerprint.
Plant studies
The June study will also reveal how much arsenic plants draw from the soil and how much of the arsenic in plants is absorbed by the body when they are eaten.
Reimer would not reveal the results of the plant studies -- he wants those who provided the plant samples to get the information first -- but did say, "I would eat the garden vegetables."
That backs up the 1977 report, which found garden plants absorb little arsenic trioxide.
Reimer and members of the study team will present the results of the latest study at a public meeting in Yellowknife next month.
