1 The importance of particular metals in the human diet has been realized within the Dast few decades, and the idea that geology might be related to health has been recognized for a number of elements such as iodine, zinc and selenium. For example, soils with low iodine contents produce crops, and animals deficient in iodine. A lack of iodine in the human diet leads to some serious diseases. 2 The ultimate source of metals within the human body is rocks, which weather into soil, gaining or losing some of their chemical constituents. The crops we eat selectively remove from the soil the elements that they require for growth. The water we drink contains trace elements leached from rock and soil. Thus the geology and geochemistry of the environments have effects on the chemistry and health of plants, animals and people. 3 So far there is no data to suggest that people living on metal - rich soils experience a pot