A comprehensive and critical assessment of selenium levels in both natural and man-made materials and systems is presented in this publication. The book begins with a treatment of the chemistry and analytical chemistry of the element and an important discussion of the status and reliability of analytical data together with the approach to be followed in extracting, managing and presenting the information. An in-depth treatment of selenium is arranged according to groupings of the different materials and systems. Each chapter discusses the occurrence of selenium in and distribution among components of the specified system. Additionally, easy reference compilations of concentration data based on critical assessment of the selenium literature are provided, along with a comprehensive listing of the pertinent literature. The book concludes with chapters on the biogeochemistry of selenium in natural systems. Throughout, consideration is given to both total selenium and its compounds.