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.