As-Cd-Cu-Hg-Pb-Zn

The geochemical maps for smelter-related metals in humus show that concentrations are related primarily to distance from the stack at Flin Flon. Estimating the degree of soil contamination resulting from the smelting activity, however, requires an understanding of natural, or "background", concentrations. Levels of metals in uncontaminated soils primarily reflect the nature of the local rock modified to varying degrees by geochemical processes such as leaching or precipitation. "Background" concentrations may also include a very small indistinguishable anthropogenic fallout component from long-range atmospheric transport.

In this study, median concentrations for each element were determined for samples collected near Snow Lake, an area where smelter contamination was not recognized in humus samples. The Snow Lake area is geologically similar to Flin Flon, but removed (>100 km) from the effects of the smelter. Median values were also determined using sample sites located beyond a radius of 0, 50 and 75 km from the smelter. These calculations indicate that, for the smelter metals, median values decrease significantly between samples collected beyond 0 and 50 km, and vary slightly between samples collected beyond 50, 75 and 100 km from the smelter. A breakdown of samples collected beyond 50 km from the smelter by the major bedrock units shows that the variation in median values is largely due to the bedrock type. For example, humus samples have generally higher Cu and Zn concentrations at sites collected over volcanic rocks naturally enriched in those metals. Therefore, by eliminating the most highly contaminated samples (<50 km from smelter), the median value for each element provides a good approximation of regional background concentrations.

Table 1
Median of element concentrations in humus (<0.425 mm) as a function of distance from the smelter.

^a Eliminates slightly to extremely contaminated samples (appr. 50% tile)

^b Eliminates very slightly to extremely contaminated samples, and some background sample