Research Summaries > Processes Domain |
HalePost-deposition metal bioavailability in northern forests is not well understood, thus is an unknown in predicting the fate of trace metals added as a result of human activity. Understanding trace metal fate and using that knowledge to predict the concentrations of metals in soils and vegetation, as well as losses of metals from soils, are essential for ecological risk assessment. The aim of this project is to better understand the bioavailability of metals in soils after deposition to the ecosystem, and how this changes with biological and geological processes. Specifically, this project examines:
Chemical speciation of the metals in the soil-plant continuum is critical to understanding the potential for binding versus leaching, and chemical speciation of free metal is being investigated as a basis for predicting metal bioavailability and bioaccumulation. The solid phase of soils is omnipresent and is an important supplier of trace elements. Given that the activities of free metal in solutions are exceedingly small relative to total soil metal contents, a better understanding of the processes controlling and buffering soil solution free metal activities are critical. Diffusive gradients in thin films (DGT) is a recent tool that combines a chelating resin and a diffusive gel and allows a quantification of metal supply rates from the solid phase. It is a promising tool to enable better predictions of bioavailability through improving our understanding of the role of metal buffering in trace metal supply to vegetation. Initial work at the Univ. de Montréal indicates that this technique is especially useful in defining the immediately available pool (probably metal already in solution as free ions) and the ability of the soil to re-supply this pool from complexed metal (in solution or on soil particles). ‘Vegetation’ can be a sink for metals during both growth and decomposition, and the relative sizes of these roles is dependent on plant species, metal, concentrations of the metal in soils and air, and stage of life. Studies of coniferous foliage decomposition have demonstrated that the concentration of Cu, Zn, Pb and Ni increased in needle litter, in Finland, at a site very close to a smelter (McEnroe and Helmisaari, 2001). Studies of decomposition in the field at Sudbury and Rouyn-Noranda have revealed that deciduous and coniferous foliage and fine roots can be net accumulators of some metals during decomposition, varying with location (D. Johnson, PhD 2002). It is unknown whether there is no metal loss from decomposing vegetation, with some gain from atmosphere and/or soil, or whether there is vigorous exchange, with a net gain. Laboratory studies of decomposition, under controlled hydration and temperature, would clarify this, and other, questions. The application of DGT to characterizing the speciation of metal flux to and from decomposing vegetation has the potential to answer these questions. Ultimately, these data will contribute to ecological risk assessment of metal emitting activities (smelting of base metals, as well as other industrial or transport activities involving these metals; incineration of a wide range of wastes also results in the production of metal containing aerosols) on forest health and productivity. Return to 2003 Domain Research Projects
Hare (top of page)The aim of our MITE-RN research is to develop and test in the field theoretically-based models that relate metal concentrations in animals to those in their surroundings. To develop such models we need to understand the chemical and biological processes involved in metal uptake by organisms. To understand the exposure of burrowing animals to metal in the sediment compartment versus that in the overlying water-column compartment, we are investigating the manner in which invertebrates construct and irrigate their burrows as well as the impact of sedimentary metals on this behaviour. We are also measuring the relative importance of food and water as metal uptake routes for animals. Because competition between H+ and Cd2+ ions can have a major impact on Cd bioaccumulation, we are determining at what trophic level in the food chain leading to the biomonitor Chaoborus this competition occurs. Such information will help us to develop mechanistic models that will allow us to use organisms as biomonitors to estimate metal concentrations in a biologically meaningful way. Return to 2003 Domain Research Projects
Chakrabarti (top of page)We will apply the WHAM/VI equilibrium speciation model to predict the speciation of the MITE-RN core metals (Cu, Cd, Zn, Pb, Ni) in some metal-impacted lakes and soil pore waters in the Rouyn-Noranda area of northwestern Quebec, and in some soil pore waters and through-fall precipitation samples from the Sudbury area. We will compare the WHAM/VI predictions with our experimental observations of metal speciation. We will apply the metal speciation techniques that we have developed for determination of metal speciation in fresh waters from lakes, soil pore waters and through-fall precipitation. This will be done by applying several electroanalytical and spectroscopic techniques that we have developed in our research laboratories which have been tested and found to provide metal speciation information that is independent of the metal speciation techniques used to obtain the results. These metal speciation techniques will provide quantitative measures of metal Speciation Parameters (Dissociation Rate Coefficient, Diffusion Coefficient, and Stability Constant of metal complexes) and are based on the analytical timescale of measurement. Hence, they are independent of the analytical techniques used to measure them and are related to fundamental properties of metal complexes in the freshwater systems. This study will provide information on the speciation of the core metals, Cu, Cd, Zn, Pb, and Ni, in lakes, and soils in the Rouyn-Noranda and Sudbury areas. Return to 2003 Domain Research Projects
Courchesne (top of page)Understanding the processes that regulate the movement of trace metals through soils, their uptake by plants and their subsequent transport towards waters bodies is vital to insure the sustained development of terrestrial and aquatic ecosystems. The mobility of solutes in soils is generally considered to be controlled by interactions with reactive sites present at the surface of soil materials such as organic matter, metallic oxides, clay minerals and soil microorganisms. Traditionally, the bulk fraction of the soil matrix is used to characterize the reactivity of a given soil and its potential interaction with solutes. However, the soil is an extremely heterogeneous environment and to focus our attention exclusively on the bulk soil might be misleading when trying to gain new knowledge on the biogeochemistry of trace metals and on the risk associated with exposure to metals. Because of the influence of plant activity on soils, the rhizosphere appears as a key component of the heterogeneity of soil materials. Due to its proximity to the site of elemental uptake by plants, the rhizosphere is a critical component of plant:soil systems. Clearly, several lines of evidence suggest that the extent of the functional role of the rhizosphere on the biogeochemical cycling of elements is much larger than the volume fraction it occupies in the field. In this context, an approach that integrates the soil rhizosphere is needed to gain new insights into the processes that control the storage, cycling and bioavailability of trace metals in terrestrial ecosystems. Return to 2003 Domain Research Projects
Dillon (top of page)The objective of this project is to measure the amount of various metals stored in all of the major compartments in the Plastic Lake catchment, including both the aquatic and terrestrial components, to measure the fluxes between the compartments, and to determine the factors that control the magnitude of these fluxes. These data will be used for development and testing of fate and transport models. We will also attempt to partition the sources of some of the metals between anthropogenic and natural components. Return to 2003 Domain Research Projects
Diamond (top of page)Fate models are useful for linking chemical discharge rates with resultant concentrations. This linkage can be used to establish reasonable discharge limits or can be used with risk analysis and assessment to estimate the potential for the predicted concentration to result in adverse health effects. We have developed a general model that estimates the concentrations, rates of movement and distribution of interconverting metal species in aquatic systems. The model, TRANSPEC, couples TRANsport and SPECiation/ complexation models. This research will further evaluate the model by application to estimate metal fate in Kelley Lake, Sudbury, which has elevated concentrations of Ni and Cu due to past and continuing loadings from mining and mineral processing activities. This lake has been well studied in terms of metal distribution and factors affecting this distribution. We also aim to use TRANSPEC to evaluate the relative mobility of these and other metals (Cd, Co, Pb and Zn) using Kelley Lake as a test system. This aspect of the research will contribute to the assessment of the hazard posed by metals. Return to 2003 Domain Research Projects
Wang (top of page)Metal speciation is the key to understanding the geochemical processes (e.g., cycling and mobility) and biological effects of metals in the aquatic environment. The overwhelming role of reduced sulfur species (RSS) in determining the speciation of class B metals (e.g., Cd, Cu, Hg, Pb and Zn) in anoxic natural waters is increasingly being recognized, as more reliable stability constants for RSS-metal complexes are being determined. Recently, the possibility has been raised that metal-sulfide clusters that are resistant to oxidation could also play an important role in controlling the speciation of class B metals in oxygenated waters. Given the important consequences that the widespread occurrence of these clusters would have for determining metal speciation, we are determining their presence in surface waters of Shield lakes and evaluating their importance in controlling the speciation of metals. |