10,326
edits
Changes
Jump to navigation
Jump to search
Line 170:
Line 170: + + − + − − [[File:UNN_Medical_Geology_Fig_7.png|thumb|400px|{{figure number|7}}]]
→Toxicity effects of excess fluoride
===Toxicity effects of excess fluoride===
===Toxicity effects of excess fluoride===
[[File:UNN_Medical_Geology_Fig_7.png|thumb|400px|{{figure number|7}}(A) Rickets (skeletal fluorosis) in a three year old child; (B) Dental fluorosis (Selinus et al, 2010).]]
With an electronegative value of 4.0, fluorine is the most reactive element on earth. It has very low dissociation energy. This means that it has the tendency to accept electrons from other elements, and has the greatest ease to form strong bonds. The fluoride ion has an ionic radius of 1.33 Ȧ and an ionic charge of -1; this is similar to that of the hydroxyl ion which has ionic charge of -1 and ionic radius of 1.32 Ȧ (Schamschula and Barmes, 1981).
With an electronegative value of 4.0, fluorine is the most reactive element on earth. It has very low dissociation energy. This means that it has the tendency to accept electrons from other elements, and has the greatest ease to form strong bonds. The fluoride ion has an ionic radius of 1.33 Ȧ and an ionic charge of -1; this is similar to that of the hydroxyl ion which has ionic charge of -1 and ionic radius of 1.32 Ȧ (Schamschula and Barmes, 1981).
Fluoride (F-), the ionic form of fluorine, can stimulate bone formation and it also has been demonstrated to reduce dental caries at doses of at least 0.7 mg/l in drinking water (Selinus et al, 2013). Concentration in the excess of this figure leads to adverse health effects called fluorosis (Table 4). Dental fluorosis occurs when the fluoride ions continually substitute for hydroxyl ions in the apatite [Ca10 (PO4)6(OH, F, Cl, Br)2] crystals of the enamel. The enamel loses its glittering appearance as chalky white patches develop; this is called mottled enamel (Schamschula and Barmes, 1981). Dental fluorosis proceeds to change the colour of the teeth from chalky white to yellow, brown or black. Finally, the yellow, brown or black patches become dissolved (Fig. 7).
Fluoride (F-), the ionic form of fluorine, can stimulate bone formation and it also has been demonstrated to reduce dental caries at doses of at least 0.7 mg/l in drinking water (Selinus et al, 2013). Concentration in the excess of this figure leads to adverse health effects called fluorosis (Table 4). Dental fluorosis occurs when the fluoride ions continually substitute for hydroxyl ions in the apatite [Ca10 (PO4)6(OH, F, Cl, Br)2] crystals of the enamel. The enamel loses its glittering appearance as chalky white patches develop; this is called mottled enamel (Schamschula and Barmes, 1981). Dental fluorosis proceeds to change the colour of the teeth from chalky white to yellow, brown or black. Finally, the yellow, brown or black patches become dissolved ([[:File:UNN_Medical_Geology_Fig_7.png|Fig. 7]]).
[[TABLE 4]]
[[TABLE 4]]
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 (Selinus et al, 2010).
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 (Selinus et al, 2010).