Impacts Domain Executive Summary 2000

Research Priorities > Impacts Domain

Executive Summary, 2000

Research Team

U. Borgmann (Environment Canada, NWRI; co-domain leader), P.G.C. Campbell (Université du Québec, INRS-Eau; co-domain leader), L.H.M. Chan (Macdonald College, McGill University), D.G. Dixon (University of Waterloo), L. Grapentine (EC-NWRI), A. Hontela (Université du Québec à Montréal, UQAM), J.B. Rasmussen (McGill University), D.G. McDonald (McMaster University), A.M. Scheuhammer (Environment Canada, CWS), C.M. Wood (McMaster University)

Summary

The ongoing research activities in the Impacts domain specifically target the freshwater environment. The aquatic environment, and in particular aquatic sediments, represents a very important sink for metals that are introduced into the surficial environment, whether they be from natural or anthropogenic sources. Additionally, aquatic organisms are inherently vulnerable to metal pollution, dissolved metals being recognized as more "bioavailable" than those associated with the solid phase. Research in the Impacts domain is designed to strengthen the links between metal speciation / partitioning in the exposure media ® metal accumulation by exposed organisms (tissue / body metal concentrations in indigenous organisms) ® metal speciation within the exposed organism (notions of metal essentiality, metal detoxification) ® metal-induced effects at the organism and population levels. The research includes both laboratory studies under controlled conditions and field work along existing metal gradients, e.g., downwind and downstream from past/current metal smelters. Clear linkages exist among the projects in the Impacts domain at the conceptual level, e.g.: influence of metal speciation on metal bioavailability; importance of food and / or sediments as a vector for metal uptake; elucidation of metal detoxification mechanisms; detection of subclinical metal-induced effects in indigenous aquatic organisms and their predators.

The following research questions are addressed in the Impacts program:

How is metal speciation in the exposure medium related to metal-induced effects at the cellular and individual levels?
Under conditions of chronic exposure, how does food ration (quality; quantity) affect metal toxicity at the organism level?
How is metal speciation within the organism related to metal-induced effects?
Can metal body concentrations in exposed organisms provide a better insight into metal-induced effects at the organism and population levels of organization than obtainable from environmental concentrations?

Role in Risk Assessment for Metals in the Environment

Research in the <Impacts> domain, together with that in the <Sources> and <Processes> domains, has been designed to advance our understanding of risks to environmental health posed by metals in the environment. Attempts to define the impacts of metals on aquatic ecosystems have traditionally involved laboratory experiments under defined conditions (toxicity tests) and, to a lesser extent, field observations on impacted indigenous populations (abundance; condition; growth; reproduction). 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 <Impacts> domain we are currently exploring this approach with aquatic biota, including benthic invertebrates, indigenous fish and waterfowl. The ongoing research will provide data on metal-induced effects relevant to the effects characterization step in Ecological Risk Assessment.

Scientific Background (from 1999 summary)

Aquatic organisms can take up metals, both essential and non-essential, from water and/or food. For both modes of uptake, the total metal concentration [M]_T (i.e., in the water column or in the diet) is an unreliable indicator of how much metal will be taken up by the organism. To predict metal bioaccumulation one must consider the speciation of the metal, some metal forms being more "bioavailable" than others [2].

The concept of metal speciation and its relevance to metal bioavailability do not stop at the biological surface, however. Once within the organism the metal can be directed to different tissues, to different compartments (vacuoles, granules, concretions, cytosol, ...), within each of these compartments the metal will tend to partition among different ligands [3]. Intuitively one would expect the intracellular bioavailability of a metal, i.e. its effects (deleterious or otherwise) on the host organism after absorption, to vary as a function of its tissue distribution and its intracellular partitioning within a given tissue. The corollary is that relations between metal body burdens in aquatic organisms and metal-induced effects at the organism, population and community levels are likely to be improved if the metal body burdens are expressed not as total metal ... but rather in terms of the metal=s partitioning within particular target tissues.

The long-term objectives of the project are thus (i) to demonstrate a mechanistic link between the intracellular speciation of metals and the manifestation of deleterious effects at the organism and population levels, and (ii) to provide rationale/validated measurement endpoints for the ecological risk assessment of metals.

Practical Background (from 1999 summary)

Over the time frame 1998-2004 we propose to test relations between metal body burdens in aquatic organisms and metal-induced effects at the organism, population and community levels at three levels: with aquatic invertebrates (Dixon and Borgmann), with indigenous fish (Campbell, Hontela, Rasmussen) and with waterfowl (Chan and Scheuhammer). Various funding options are being explored for the period 1999-2004 (e.g., applications to NSERC for University-Industry funding in the <Research Network> or <Cooperative Research and Development> areas). However, since we could not realistically expect to receive levered funding until 1999 at the earliest (i.e., well after the 1998-99 field season), we designed the 1998-99 research program on the basis of a budget of $75,000.

Overall Goals (from 1999 summary)

An overriding goal for the current funding exercise was to maintain and foster interactions among those MITE researchers who are involved in research on the impacts of metals in the environment. The 1998-99 time-frame was thus seen as a transition year, during which these contacts were maintained even while we worked on obtaining complementary funding from NSERC and other sources. Each sub-project was designed to test certain key hypotheses and to yield short-term results that will help us to refine the experimental approached for the subsequent field work.