Evaluation of concentration of mineral ions in water after defluoridation with bone char

Abstract

Fluoride is an essential mineral that is present in trace amounts in the human tissue but is concentrated in bones and in teeth where it forms part of the bone and teeth crystalline structure. Ingestion of levels of fluoride greater than 1.5 mg/L during the period of tooth formation causes dental fluorosis while individuals depending on water supplies with fluoride levels greater than 3-6 mg/L or ingesting more than 10-20 mg of fluoride daily are likely to develop skeletal fluorosis after lO—2O years of exposure. Several defluoridation agents have been employed to remove fluoride from water. Bone char is the most widely used defluoridating agent in developing countries Kenya being one of them. Bone char is obtained by heating bones in a kiln at temperatures of 40()—500°C in a controlled flow of air. The chaired bones are packed in specially constructed defluoridating buckets. Apparently, due to the enormity of the fluoride problem, little attention seems to have been given to the effect the defluoridation agent may have on other essential mineral ions in water. Fluoride is believed to be removed from water by either the process of ion exchange with the hydroxyl ion of the bone hydroxyapatite or by adsorption. The metals which have long accumulated in the bone during the process of growth and metabolism could leach into water, or those in water could be captured just like fluoride during defluoridation. This study sought to find out whether when bone char is used as a defluoridating agent affects the concentration of some essential mineral ions in drinking water. Columns simulating defluoridation buckets were packed with bone char and water samples to be defluoridated collected after a resident time of 30 minutes. The water samples collected were analysed for changes in K+, Na+, Mg2+, Fey, Ca2+, Cl’, C032’, HCO3’, SO42’ and PO43" concentrations. Flame photometric method was used to determine the concentrations of KT and Na+ while Mg“, Fe2+ and Ca2+ were analysed using an Atomic Absorption spectrophotometer. The concentrations of chlorides, carbonates and bicarbonates were determined titrimetrically while that of phosphates was done colorimetrically. The concentration of Ki, Nal, Cl‘, C0321 HCO3‘, Ca2+ and Fe” decreased on defluoridation. The concentration of Mgr’, SO42’ and PO43’ increased on defluoridation but not above the WHO recommended levels. The pH also increased and in some cases above the WHO recommended range. However, defluoridation was not found to affect the quality of drinking water.