Research Activities

MITHE-SN Theme Research Priorities

The research comprising the three themes¹ of the proposed network (Aquatic Ecosystems, Soils and Plants, and Foods and Ingested Particles) is presented separately in the following sections, but in reality, they represent a cascade of effects along food webs, from the lowest trophic levels to the highest consumers.

For example, the research which will be carried out in the Aquatic theme will focus on protecting the health of freshwater ecosystems, as their continued productivity is critical to both recreational use of water, its direct consumption, and as a source of food. Both domestically and internationally, Canada defines itself through its relationship to fresh waters, perhaps more than any other country in the world. Thus, stewardship of this prized resource is central to Canada's global environmental role.

The research carried out in the Soils theme will address the transfer of metals to vegetation, not so much from the perspective of phytotoxicity, but rather considering plants as vectors of metal transfer to humans through dietary intake. The Soils research will touch on such nationally important issues as Cd in Western Canadian grains and oilseeds, as well as the fate of metals applied to soils through the application of residues from industrial and municipal processes.

The research carried out in the Ingesteds theme will focus on the potential for Canadians to be exposed to metals through diet and inhalation, i.e. food and ingested particles (e.g., soil, house-dust, paint particles). As most Canadians are not occupationally exposed to metals, ingestion constitutes the exposure route of greatest importance. Understanding the relative roles of soils, dust and food in this exposure is a very important aspect of risk assessment. Without this information the most effective risk management options cannot be recommended.

For each of the themes, the same three questions drive the research projects:

• distinguishing the magnitudes and roles of natural background and anthropogenic metal inputs in biotic exposure to metals;
• estimating the bioavailable fraction of metals in the exposure media, thus better quantifying the true exposure concentrations; and
• determining the factors that influence bioavailability of metals in media, so that predictive models can be developed for use in the development of site-specific metals criteria.

Research to address these three questions will vary according to the media and endpoints of importance to each theme, and the specific hypotheses to be tested. As well, the specific metals to be studied in each project will be similarly tailored to the project; however, metals and metalloids of prime interest include: Cd, Cu, Pb, Ni, Tl, U, Zn, As and Se. The answers to the three questions will significantly advance entry and exposure characterizations, as well as enable prediction of exposure, based on site-specific characteristics. Question one will be addressed by both Soils and Ingesteds; questions two and three will be addressed under all three themes.

1. Note that for brevity, the Aquatic Ecosystems theme is referred to as Aquatic, the Soils and Plants theme is referred to as Soil, and the Food and Ingested Particles is referred to as Ingesteds.