Changes

Geologic materials that are characteristically rich in fluorine are organic clays and shales, carbonatites, phosphates, hydrothermal ores and silicic igneous rocks such as rhyolites, dacites and granites.<ref name=Setal2010 />

Geologic materials that are characteristically rich in fluorine are organic clays and shales, carbonatites, phosphates, hydrothermal ores and silicic igneous rocks such as rhyolites, dacites and granites.<ref name=Setal2010 />

Studies have shown that fluoride mineralization occurs in tectonically unstable areas such as zones of rifting and zones characterized by rise of fluoride from the lower [[crust]] or upper mantle. This explains why people living in the African Rift zones and volcanic areas have high concentration of fluoride in their natural water bodies. In the East African Rift, in particular, most of the lakes are contaminated by fluoride as a result of influx of fluoride from hot springs and volcanic gases.<ref name=Dvies /> The lake with the highest fluoride concentration occurs in this area−Lake Nakuru in the Kenyan Rift Valley. According to Davies,<ref name=Dvies /> the water of this lake has fluoride concentration in the order of 2800 mg/l. Other African countries with high fluoride concentration in groundwater include granitic areas in Ghana and parts of Malawi and Tanzania while sedimentary areas with high fluoride concentration are found in parts of North Africa and Senegal in West Africa.<ref name=Dvies /> Nigeria, Zimbabwe and Ethiopia had been hit by adverse health conditions triggered by nutritional fluoride imbalance.<ref name=Dvies />

Studies have shown that fluoride mineralization occurs in tectonically unstable areas such as zones of rifting and zones characterized by rise of fluoride from the lower [[crust]] or upper [[mantle]]. This explains why people living in the African Rift zones and volcanic areas have high concentration of fluoride in their natural water bodies. In the East African Rift, in particular, most of the lakes are contaminated by fluoride as a result of influx of fluoride from hot springs and volcanic gases.<ref name=Dvies /> The lake with the highest fluoride concentration occurs in this area−Lake Nakuru in the Kenyan Rift Valley. According to Davies,<ref name=Dvies /> the water of this lake has fluoride concentration in the order of 2800 mg/l. Other African countries with high fluoride concentration in groundwater include granitic areas in Ghana and parts of Malawi and Tanzania while sedimentary areas with high fluoride concentration are found in parts of North Africa and Senegal in West Africa.<ref name=Dvies /> Nigeria, Zimbabwe and Ethiopia had been hit by adverse health conditions triggered by nutritional fluoride imbalance.<ref name=Dvies />

===Health effects of Cadmium, Cd===

===Health effects of Cadmium, Cd===