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.