Life responds to, and is controlled, by a complex world of chemical elements and compounds. To manage environmental risk, we must understand what elements are harmful to life, where they occur, and how likely they are to affect us. An important and unique role for geoscience is to define the natural controls on geochemical background, and to estimate environmental reactivity. An outstanding challenge for geoscience is to identify the minerals that contain the trace elements of potential environmental concern. This is important since the chemical and physical propeties of the host minerals play a key role in the behavoir of elements of potential environmental concern.

The potential for elements to affect biological process depends both on their chemical form and their concentration at the earth's surface. Elements, including metals like copper, lead, zinc, and mercury (Cu, Pb, Zn, Hg), and metalloids like arsenic (As), can be either helpful or harmful to life, and are commonly both. The elements copper and selenium, for example, are essential for life at low concentration and can be harmful at high concentration. In the youthful soils of Canada the natural sources of trace metals are rock-forming minerals comprising soil parent materials. What elements are present, how they are released through weathering and biological process, at what rate, and in what form, all depend on their mineral host. Consequently, mineralogy is a key to estimating element reactivity and environmental risk management.

In Canada, geochemical maps reflect bedrock composition and geological process, principally glacial, that affect the origin and composition of surficial deposits. Their direct use for environmental risk assessment is not simple. Sample mineralogy and element bioavailability depend on numerous factors, including the geological origins of the media sampled, the mineral host species, and sampling and analytical protocols. For trace elements identified on Environment Canada's Priority Substances List (PSL), natural background concentrations can exceed risk threshold levels over large areas 1000's of ha extent. The question for MITE is: what do geochemical maps mean for environmental risk management?

Activity

Geochemical modeling will expand our knowledge of soil mineralogy by developing new approaches for mineralogical analyses. These will help define mineralogical controls on geochemical background variation, and the apportionment of trace elements among minerals and sample media.