Textbook in PDF format This book discusses linkages between the natural and disturbed chemical composition of the earth's surface and ecological and human health. It reviews the environmental geochemical cycles of natural elements and persistent toxic substances (PTS) in the environment, highlighting the degradation of soil and water resources due to human activities such as extraction and usage of minerals. There is an attempt to provide evidence concerning the health effects of consuming contaminated food, due to frequent consumption of mercury-laden fish. Lastly, sources, fates, and ecological effects of various PTS are presented, including microplastics and associated chemicals