Changes

Elements are released from rocks through weathering− the process by which rocks are broken down into smaller components.

Elements are released from rocks through weathering− the process by which rocks are broken down into smaller components.

Physical weathering is the process by which rocks are broken down into smaller chunks without altering its mineral content. It occurs through temperature changes and by the action of the wind. Temperature variation leads to the development of flakes on the rocks whose removal exposes subsequent layers to further heating and cooling and, then, to chemical weathering. Physical disintegration of rocks is also caused by the action of burrowing animals and plant roots. Freezing of water in crevices of rocks is another force that disintegrates rocks making them prone to chemical weathering.<ref name=Setal2010>Selinus, O., R. B. Finkelman, and J. Centeno, (Eds), 2010. Medical Geology – A Regional Synthesis. Springer, Germany, 392p.</ref>

Physical weathering is the process by which rocks are broken down into smaller chunks without altering its mineral content. It occurs through temperature changes and by the action of the wind. Temperature variation leads to the development of flakes on the rocks whose removal exposes subsequent layers to further heating and cooling and, then, to chemical weathering. Physical disintegration of rocks is also caused by the action of burrowing animals and plant roots. Freezing of water in crevices of rocks is another force that disintegrates rocks making them prone to chemical weathering.<ref name=Setal2010>Selinus, O., R. B. Finkelman, and J. Centeno, eds., 2010, Medical geology—A regional synthesis: Berlin, Springer, 392 p.</ref>

Chemical weathering describes the process that alters the chemistry of minerals. It can proceed through hydration, hydrolysis, oxidation, reduction and dissolution. Chemical weathering is fuelled by water and weak soil acids.<ref name=Setal2013 />

Chemical weathering describes the process that alters the chemistry of minerals. It can proceed through hydration, hydrolysis, oxidation, reduction and dissolution. Chemical weathering is fuelled by water and weak soil acids.<ref name=Setal2013 />

In addition to these, there are processes that make the various elements available to plants: sorption and desorption. According to Selinus et al,<ref name=Setal2013 /> sorption is the retention of metal ions on the surfaces of soil particles through mutual attraction between oppositely charged particles. Desorption refers to the release of these metal ions for plant use as a result of alterations in pH and redox conditions. By consuming plants and animals raised on such soils, man comes in contact with the elements originally in the rocks.

In addition to these, there are processes that make the various elements available to plants: sorption and desorption. According to Selinus et al.,<ref name=Setal2013 /> sorption is the retention of metal ions on the surfaces of soil particles through mutual attraction between oppositely charged particles. Desorption refers to the release of these metal ions for plant use as a result of alterations in pH and redox conditions. By consuming plants and animals raised on such soils, man comes in contact with the elements originally in the rocks.

Another pathway through which humans come in contact with the earth’s elements is by water intake whether from man-made wells, rivers, streams or lakes.<ref name=Skinner /> These emanate from groundwater which might have leached both toxic and non-toxic elements from rocks through which it flowed.

Another pathway through which humans come in contact with the earth’s elements is by water intake whether from man-made wells, rivers, streams or lakes.<ref name=Skinner /> These emanate from groundwater which might have leached both toxic and non-toxic elements from rocks through which it flowed.

Inhalation of volcanic gases and dust from deserts, un-tarred roads, mines and volcanic emanations form another important pathway of exposure to dangerous elements. Volcanism is the principal process that brings elements to the surface from deep within the earth. The volcanic eruption of Mount Pinatubo is a splendid example of the dramatic effects of geology. During just two days in June ,1991, Mount Pinatubo, Philippines ejected 10 billion metric tonnes of magma and 20 million tonnes of SO2 for over 15,000 meters high into the atmosphere; the resulting aerosols influenced global climate for three years. This single event introduced an estimated 800,000 tonnes of zinc, 600,000 tonnes of copper, 550,000 tonnes of chromium, 100,000 tonnes of lead, 1000 tonnes of cadmium, 10,000 tonnes of arsenic, 800 tonnes of mercury, and 30,000 tonnes of nickel to the surface environment (Garrett, 2000).

Inhalation of volcanic gases and dust from deserts, un-tarred roads, mines and volcanic emanations form another important pathway of exposure to dangerous elements. Volcanism is the principal process that brings elements to the surface from deep within the earth. The volcanic eruption of Mount Pinatubo is a splendid example of the dramatic effects of geology. During just two days in June 1991, Mount Pinatubo, Philippines, ejected 10 billion metric tonnes of magma and 20 million tonnes of SO2 for over 15,000 meters high into the atmosphere; the resulting aerosols influenced global climate for three years. This single event introduced an estimated 800,000 tonnes of zinc, 600,000 tonnes of copper, 550,000 tonnes of chromium, 100,000 tonnes of lead, 1000 tonnes of cadmium, 10,000 tonnes of arsenic, 800 tonnes of mercury, and 30,000 tonnes of nickel to the surface environment (Garrett, 2000).

==Health issues arising from selected elements and geological materials and processes==

==Health issues arising from selected elements and geological materials and processes==