While the need for fortified foods and water (mineral water) is gaining considerable importance, trace element contamination is ever-increasing in the environment at the same time. This book discusses the importance of fortified foods and water, and the overall significance of trace elements in human health (i.e. metal ions role in life). It first addresses the fundamentals of mineral nutrition in plants and animals (including humans); then the geochemistry, bioavailability, uptake, and enzymology of trace elements; further chapters are devoted to environmental contamination and health implications. Finally, case studies are discussed to tie in other elements and topics. Fe, Ca, Zn, As, Se, Mn, and Cu. as essential elements, and Cd, Pb, and Hg, as toxic elements are addressed, since the combined reaction of a toxic and essential element can be harmful, if not fatal.   The possible role of metal speciation and anions (chloride, sulphate, nitrate, and carbonate) will also be covered, as well as the effect of "toxic" metals on the homeostasis of essential metals.   In summary, the book addresses the double-edged sword of trace elements, emphasizing that in the proper quantities, they produce health benefits, but in lesser or greater quantities, they can be harmful and even deadly.