Research Summaries > Impacts Domain |
Campbell (top of page)Attempts to define the impacts of metals on aquatic ecosystems have usually involved laboratory experiments under defined conditions (toxicity tests) and, to a lesser extent, field observations on impacted indigenous populations. Traditional ecological risk assessment (ERA) approaches have largely relied on the former approach, comparing a laboratory-derived "predicted no effect concentration" (PNEC) with the "predicted environmental concentration" (PEC). PNEC values have been derived from single species laboratory toxicity tests, the results of which are used to develop a distribution of species sensitivities to a particular metal; it is then assumed that this distribution (derived from laboratory test species) represents the distribution of species sensitivities in a generic and diverse aquatic community. This laboratory-based approach is predicated on the assumption that metals are affecting the target species of interest directly, either via waterborne or diet-borne metal exposure. It is also possible that metal effects on a consumer organism may be indirect, i.e., they may be mediated via the wood web. Such food-web mediated effects are not accounted for in the aquatic toxicity testing approach. In recognition of the shortcomings of the laboratory approach, a limited number of workers have ventured into the field to collect indigenous aquatic organisms from metal-contaminated waters, and to compare these organisms with specimens from reference environments. Comparisons have been made at the physiological, population and community levels, and differences attributed to the presence of metals in the contaminated systems. However, almost without exception these studies have concentrated on the biological differences among sites and have neglected to define the metal exposure regime to which the indigenous organisms have been exposed. To link these two approaches, one needs a common measure of metal exposure in laboratory and field settings. The determination of metal concentrations or burdens in tissues (or whole organisms) has been suggested as a means of achieving this linkage. In the present project we are exploring this approach with indigenous fish, having expanded the concept of metal "body burden" to take into account the speciation of the metal within the organism, i.e., the organism's ability to detoxify the metal. The project has been designed to look for metal-induced effects on a biosentinel species, yellow perch (Perca flavescens), in lakes located along an existing metal gradient, downwind and downstream from past/current metal smelters. We are seeking evidence both for direct physiological effects, as defined above, and for food-web mediated bioenergetic effects. In the case of direct effects, a key hypothesis to be tested is that there exists a mechanistic link between the intracellular speciation of the metals and the manifestation of deleterious effects at the organism (physiology, endocrine and metabolic status, growth, reproductive status) and population (abundance, production, reproductive fitness) levels. Specifically, we are investigating the following linkages: chronic metal exposure metallothionein induction perturbed intracellular metal partitioning endocrine / physiological impairment diminished growth efficiency reduced survival, altered population age structure and population dynamics. In the case of food-web mediated effects, we are focusing on the following sequence: chronic metal exposure reduced food abundance of certain dietary components increased energetic costs of feeding reduced growth efficiency and ultimately stunting, i.e., we are looking for evidence of "energetic bottlenecks" imposed by the absence of key prey components that are necessary for normal diet shifts and growth to occur. Different life stages of yellow perch (Perca flavescens) have been chosen as trial biosentinel organisms. In Years 1 and 2 the main study area was centred around Rouyn-Noranda, in Northwestern Quebec; in Year 3 we initiated exploratory studies on lakes in the Sudbury area; in Year 4 we pursued this comparison of contamination, physiological and growth indices in the two areas. Year 5 will be the wrap-up year, involving extensive comparisons and collaboration with Projects C2 and C3. Return to 2003 Domain Research Projects
Couture (top of page)Work conducted by Project C5 will take place in two distinct phases: (i) metals depuration study, and (ii) Rouyn-Noranda fish sampling. During the metals depuration study, we will examine the rates and extent of tissue metal depuration and recovery of metabolic capacities, condition and growth in wild YP collected from metal-contaminated environments, compared to fish from reference sites. To this end, we will capture fish from 3 lakes in a metal gradient in the Sudbury area and maintain them in captivity at the Laurentian University facility in clean water and with a clean invertebrate diet ad libidum. Regular periodic sampling of captive reference and metals-adapted wild YP over the recovery period will allow us to determine tissue metal depuration rates as they relate to recovery of metabolic capacities and metallothionein concentrations in key tissues (e.g., liver, kidney, muscle). Data collected in 2003 will be added to the information collected this year in a smaller scale pilot experiment in which fish from one contaminated and one reference lake were examined. In the second phase of this project, YP will be collected from five lakes forming a metal contamination gradient near Rouyn-Noranda, PQ. This sampling effort will parallel the YP sampling effort we conducted in 2002 in Sudbury-area lakes. In brief, we will sample approximately 120 YP from each of 5 Rouyn-Noranda-area lakes in late spring (from June 1st) and in late summer (from August 1st). Sampling will be done in collaboration with Project C3 who will be conducting field work in the region during those periods. The same parameters collected in Sudbury during the 2002 effort will be measured in 2003 in Rouyn-Noranda fish, including size, age, condition, tissue and dietary metal concentrations, and tissue metabolic capacities (anaerobic and aerobic capacities, determined using a suite of enzyme assays). Effects examined will include direct toxic effects as assessed by indicators of metabolic performance and oxidative damage, and their relationships to tissue metal concentrations and dietary metal uptake. Condition and metabolic performance in YP will also be related to indirect effects of food web disturbances investigated by Project C3 in the same lakes. YP surveys will also include assessment of longevity. Gut contents, as a surrogate for YP diet, will be analyzed in terms of quantity (as a proportion of gut and fish weights) and quality (including ionic (Ca, Na) and metal (Cd, Cu, Ni and Zn) composition). These data will be used to identify relationships between environmental contamination—including diet—and tissue metal concentrations, aerobic and anaerobic capacities, growth, and condition. This field-based research is strongly linked to current MITE-RN aquatic effects research conducted by Projects C2 and C3. By field validating laboratory-derived models through our collaboration with Project C2, and by providing comparative data for Sudbury and Rouyn-Noranda, this project will improve the ERA relevance of MITE-RN research activities. Ultimately, data from this study will strengthen the current ERA paradigm and improve environmental regulations that attempt to protect wild fish in metal-contaminated systems. Return to 2003 Domain Research Projects
DixonAll Canadian water quality guidelines for metals are based on single metals, despite the fact that aquatic organisms are invariably exposed to mixtures of metals. The approach most often used for environmental risk assessment at specific sites suspected of metal contamination is to assess the metals present individually. A unified approach that addresses the interactions of metals, for both uptake and impact, is one of the most pressing needs in metal toxicology. This research examines the interactions of waterborne and sediment-derived metal mixtures with the aquatic invertebrate Hyalella azteca, with an aim to develop relationships between water chemistry, toxicity and tissue residues. Development of relationships between sediment, waterborne and tissue metal concentrations should allow a solid estimate of bioavailability. Overall the work will allow metal speciation and uptake (pharmacokinetic) models to be linked for more meaningful and defensible metals risk assessment. There are few studies which address the issue of dietary uptake of metals in Hyalella azteca. This research will examine the relationship between food, waterborne and tissue concentrations of metals in Hyalella azteca. This may assist in forming more complete pharmacokinetic models. Return to 2003 Domain Research Projects
Wood (top of page)Laboratory-based studies are being employed to understand and model the chronic impacts of Cd, Zn, and Cu on the health of fish in the wild, exposed to these metals via the water, via the diet, and via both routes. Particular emphasis is placed on the modifying effects of acclimation water chemistry (hardness, pH, metal levels etc.), on the influence of diet quantity and quality (particularly ionic content), on lab-to-field validation of the results, and on endpoints useful for Biotic Ligand Modeling (e.g. tissue specific bioaccumulation, subcellular partitioning, physiological indicators of toxicity). In this context, we are first extending the current acute BLMs for waterborne Cu, Cd and Zn to the yellow perch (YP, Perca flavescens), a species endemic to the metal-impacted lakes of Rouyn-Noranda, Sudbury, and other sensitive areas on the Canadian Shield. The goal here is to bring our level of knowledge on the YP up to that on the rainbow trout (RBT, Oncorhynchus mykiss), the model species on which most patho-physiological and BLM development work has been performed to date. We are also examining the influence of acclimation and exposure history on the BLM characteristics, a key step in the development of chronic BLMs. Simultaneously, we are experimentally analyzing the complex interactions of dietary quantity and quality (Ca, Na, energy content) on the responses of RBT to chronic metal exposures, in both the water and the diet. This issue is of great relevance in understanding trophic and bioenergetic responses in the field, as well as in the development of gastrointestinal BLMs, but has not been considered in previous studies. The results will contribute to both environmental regulatory strategies and market protection for metals, and strengthen our global and regional risk assessment framework for metals in the environment. |