This session will focus on medical hazards which arise directly from radiological and chemical effects resulting from exposure to geological materials. Radiologically, radon is a significant naturally occurring health hazard. Radon-222 is the second leading cause of lung cancer after tobacco smoking and is also an accelerating factor in smoking-related lung cancer risk. There are other natural radioactive hazards such as radium (radon is a radium daughter) and uranium, thorium and daughters, various compounds of these formerly used in luminous paints, and cosmic radiation. Geochemically, the focus is the recognition and explanation of phenomena occurring between geological materials and typical interfaces of the human body. This aspect of the session welcomes presentation of research that discusses the application of geochemical principles, methods and instrumentation to the study of human health. Especially welcome are contributions that focus on the unique relation between geochemistry and the diagnosis, treatment, inception and/or progression of disease. Both radiological and chemical hazards can occur together and detection of one can indicate presence of the other: indeed, radon gas might serve as an indicator of otherwise difficult to identify abandoned mine wastes and workings and their associated geochemical hazards. This session will present a broad range of papers including methodological, technological and interpretative aspects, as well as case-study material.