Geochemistry and health and medical geology into the 21st century

Since ancient times man has known of the effects of environmental factors on health but it is only in the last 100 years or so that these links have been understood scientifically. Geochemistry in its strictest sense is the study of rock chemistry and at first it may seem there is little connection with human health. However, rocks are a major source of the 92 naturally occurring chemical elements found on Earth. Approximately 25 of these are known to be essential to plant and animal life in trace amounts, including Ca, Mg, Fe, Co, Cu, Zn, P, N, S, Se, I and Mo. On the other hand, an over-abundance of these elements can cause toxicity problems. Some elements such as As, Cd, Pb, Hg and Al have no/limited biological function and are generally toxic to humans. Rocks break down to form the soils on which we grow our crops and raise animals and the water that we drink travels through rocks as part of the hydrological cycle.