Abstract:

Beginning in the 1800's, mining, smelting, and logging activities have influenced soils and continue to play a role in the cycling of metals mobilized by human activities in the soils. In the last several years the regional distribution of metals in the soil profile for the Sudbury Region has become of great concern because of smelter sourced metal inputs. In 2001, the Sudbury Regional Soils Project (SRSP) released information regarding soil metal concentrations in the soil profile for the areas affected by smelter inputs.<br/>The purpose of this study was to determine the influence of smelter inputs on the selenium behaviour and potential bioavailability in the soil. Seven sites within the Greater Sudbury area were selected for sampling with reference to data presented in the SRSP. Six of these sites were within the smelter impacted zone and one reference site was chosen outside the immediate impact area. Samples were incubated over 50 days to simulate saturation conditions and the supernatant was analysed at 20 time intervals for eighteen elements, including selenium. <br/>Within this study the metal concentrations obtained within close proximity to smelter sources were much greater than those determined further from the sources. The range in selenium concentrations within the sites were from 0.02 ([mu]g/g) in the reference site to 10 ([mu]g/g) at the closest proximity to the smelters. All metal concentrations within the smelter impact zone were significantly greater than at the reference site. The behaviour of selenium was then modeled using two computer programs: CHEAQS (Chemical Equilibria in Aqueous Solution), and Visual Basic 6.0. The solid and solution phases were measured and modeled to determine the speciation behaviour and potential bioavailability under these conditions. <br/>After a maximum saturation time of 50 days the predicted species of occurrence for selenium was HSeO3- at the impacted sites and the reference site. Similar soil types and physical and chemical characteristics were found at the impacted and reference sites. These physical and chemical characteristics of the soil play a dominant role in controlling the release of selenium into the soil environment. All sites exhibited mildly reducing conditions and a slight increase in pH from mildly acidic to mildly alkaline. In this study, the predicted behaviour of Se under saturated conditions did not differ within the sites. The behaviour was controlled dominantly by initial Se concentration, soil pH and the redox potential of the soil. Important metal interactions were also highlighted in this study, notably the correlation between the release of selenium and iron into the soil solution. <br/>Although smelter input has increased the concentrations of trace elements within the smelter impact zone, these elevatedconcentrations have a tendency to remain in the LFH horizon of the soil profile. The metal release from water saturation is not enough to affect a significant downward movement of mobile and potentially bioavailable metals through the soil profile with respect to the saturation timeline of this study.