Arsenic pollution in the Yellowknife Area from gold smelter activities

Gold has been mined on a large scale at Yellowknife located in the sub-arctic North West Territories of Canada since 1938. The gold is associated with arsenopyrite ores, with necessitates the oxidation of the arsenic and sulphur by roasting at two Yellowknife smelters. Other metals are also present in the ore, notably antimony. As₂O₃ and SO₂ are emitted into the atmosphere. Large quantities of arsenic were liberated in the past and despite improvements in emission control, significant emission still occur. In order to assess the amount and extent of arsenic contamination in the local environment and the potential exposures and sources to man, soil samples and samples of the native vegetation were collected in and around the town of Yellowknife and the two smelters. Arsenic and antimony analyses were done by instrumental neutron activation analysis using the SLOWPOKE facility at University of toronto. Air-dried plant samples were bombarded at a neutron flux of 1·10¹²n cm²s and soil samples at 2.5·10¹¹n cm²s for 6 minute periods. The¹²²Sb and⁷⁶As-ray emissions at 559 keV were analysed after decay periods of 24–48 hours and compared with standard solutions and NBS standards. Zinc, copper, lead and cadmium analyses were done by atomic absorption spectrophotometry. Arsenic was found to be accumulated in the soils in the vicinity of the two smelters to levels of several thousand ppm. Concentrations greater than 500 ppm occurred in the soil of Yellowknife townsite, and greater than 50 ppm occurred at all sites sampled within 15 km of the town. Antimony levels were about 10% of arsenic and were highly correlated with arsenic. Zinc occurred to 500 ppm around the smelters. Compared with background levels, the foliage of several native species showed substantial arsenic accumulation, up to several hundred ppm in birch. Only 5–25% of this arsenic could be removed by careful washing. Evidence suggests the arsenic is taken up from the soil creating an ongoing arsenic contamination problem. Soil arsenic levels are also sufficiently high to inhibit root growth in soils over a very extensive area.