Soils: their implications to human health.

This paper reviews how the health of humans is affected by the world's soils, an association that to date has been under appreciated and under reported. Soils significantly influence a variety of functions (e.g. as a plant growth medium; its importance on the cycling of water; as a foundation for buildings) that sustains the human population. Through ingestion (either deliberate or involuntary), inhalation and dermal absorption, the mineral, chemical and biological components of soils can either be directly beneficial or detrimental to human health. Specific examples include: geohelminth infection and the supply of mineral nutrients and potentially harmful elements (PHEs) via soil ingestion; cancers caused by the inhalation of fibrous minerals or Rn gas derived from the radioactive decay of U and Th in soil minerals; and tetanus, hookworm disease and podoconiosis caused by skin contact and dermal absorption of appropriate soil constituents. Human health can also be influenced in more indirect ways as soils interact with the atmosphere, biosphere and hydrosphere. Examples include: the volatilisation of persistent organic pollutants (POPs) from soils and their subsequent global redistribution that has health implications to the Aboriginal people of the Arctic; the frequent detrimental chemical and biological quality of drinking and recreational waters that are influenced by processes of soil erosion, surface runoff, interflow and leaching; and the transfer of mineral nutrients and PHEs from soils into the plants and animals that constitute the human food chain. The scale and magnitude of soil/health interactions are variable, but at times a considerable number of people can be affected as demonstrated by the extent of hookworm infection or the number of people at risk because they live in an I-deficient environment. Nevertheless, it can often be difficult to establish definite links between soils and human health. This, together with the emergence of new risks, knowledge, or discoveries, means that there is considerable scope for research in the future. Such investigations should involve a multidisciplinary approach that both acquires knowledge and ensures its dissemination to people in an understandable way. This requires an infrastructure and finance that governments need to be responsive to.