Biogeochemical Monitoring in Medical Geology
How can we determine the distribution of metals and other elements in our environment? The Geological Survey of Sweden started an innovative monitoring of metals in a monitoring/mapping program in 1980. Before 1980, traditional inorganic stream sediments were used, a method still employed all over the world, but not really suitable for medical work. A new method is used, whereby metal concentrations are determined in organic material consisting of aquatic mosses and roots of aquatic higher plants. These are barrier-free with respect to trace metal uptake and reflect the metal concentrations in stream water (Brundin 1972, 1988, Kabata-Pendias,1992, Selinus 1989). Aerial parts of many plant species do not generally respond to increasing metal concentrations in the growth medium because of physiological barriers between roots and above-ground parts of plants. These barriers protect them from uptake of toxic levels of metals into the vital reproductive organs. The roots and mosses, however, respond closely to chemical variations in background levels related to different bedrock types in addition to effects of pollution. The biogeochemical samples provide information on the time-related bioavailable metal contents in aquatic plants and in the environment. One great advantage of using biogeochemical samples instead of water samples is also that the biogeochemical samples provide integrated information of the metal contents in the water for a period of some years. Water samples suffer from seasonal and annual variations depending on, for example, precipitation. The mapping program now covers about 65% of the land area of Sweden (40,000 sample sites, one sample every 6 km²), where about 80% of the population of Sweden is living. This means that there is now available an extensive analytical data base for use in environmental and medical research (Freden 1994). One example of the use of biogeochemical monitoring concerns high cadmium contents in Sweden. In noncontaminated, noncultivated soils, Cd concentration is largely governed by the amount of Cd in the parent material (Thornton 1986). If the substrate concentration is higher than in background concentrations, Cd is readily taken up by roots and is distributed throughout the plants.