This book is dedicated to the occurrence and behaviour of PHEs in the different compartments of the environment, with special reference to soil. Current studies of PHEs in ecosystems have indicated that many industrial areas near urban agglomerates, abandoned or active mines, major road systems and ultimately also agricultural land act as sources and at the same time sinks, of PHEs and large amounts of metals are recycled or dispersed in the environment, posing severe concerns to human health. Thanks to the collaboration of numerous colleagues, the book outlines the state of art in PHEs research in several countries and is enforced with case studies and enriched with new data, not published elsewhere. The book will provide to Stakeholders (both Scientists Professionals and Public Administrators) and also to non-specialists a lot of data on the concentrations of metals in soils and the environment and the critical levels so far established, in the perspective to improve the environmental quality and the human safety.