An estimated 8.5 million Ethiopians, 12 percent of the country’s population, are at risk from fluoride, a chemical substance which can become toxic when consumed in high concentration, the private Daily Monitor English- language newspaper reported Saturday.

A high concentration of the substance in water used for domestic consumption becomes toxic and spoils the natural color and texture of human teeth, the report said, quoting Berhanu Gizaw, a geological survey expert.

Studies indicate the volcanic rocks of East Africa are found to be richer in fluoride than analogous rocks in other parts of the world.

The expert noted the acidic rocks such as pumice deposits are likely to be sources for anomalous amounts of fluoride and sodium in the surface and ground water of the East African Rift Valley in Ethiopia.

Other than the acid volcanic nature of rocks, on the other hand, the current understanding of high fluoride concentrations in the ground waters of the rift are believed to be enhanced due to the high CO2 pressure, hydrothermal heating, and low calcium and low salinity fluids while high fluoride, salinity and alkalinity in closed-basin lakes result from evaporative concentration, according to the expert.

He explained that fluoride has various other impacts on health depending on the amount of concentration in the water supply.

The expert noted that if the amount of concentration is between the range of 1.5 and 3.5Mg/L, a kind of enamel hyperplasia, known as dental flourosis, will occur when taken during the period of enamel maturing.

He said the result was a destruction of the ameloblasts and the production of abnormal mottled enamel.

As to the possible remedies, the expert said proper water management in potentially affected areas will significantly reduce the risk.