Immobilization of Fluoride in Soils through Soil Properties - A Review

Fluoride (F) is one of the elements that are important in dental and skeletal formation in human beings. If present at optimal levels, it plays a very important role of preventing dental carries. However, its excessive uptake causes dental fluorosis and under extreme cases it causes skeletal fluorosis. F finds its route to human beings mainly through drinking water. However, substantial quantities of F can be taken by human beings through ingestion of food substances that contain elevated quantities of F. For example, tea can accumulate as high as 2965 mg kg-1 in their leaves. Therefore F in agricultural soils can be a source of F contamination. Despite the fact that F in crops can be a significant cause of fluorosis, studies on F dynamics in soils and its eventual uptake by crops has received little attention. Therefore this review article presents information on soil properties that enhance or deter F solubility in soils and its eventual bioavailability and the concomitant effects to crop plants. Soil physico-chemical conditions that affect the distribution of different F species and consequently its bioavailability and the uptake by plants have been discussed where pH is the most crucial factor. Cations like Ca and Mg in soils precipitate F thereby rendering it immobile. F in soils can be immobilized by organic amendments. Literature further shows that F is less mobile in heavy textured soils than in light textured soils. Therefore, this article reviews soil properties that can be manipulated so as to attain F immobilisation in soils and deter its uptake. The review has highlighted research gaps on F dynamics, mobilization/immobilization in soils. It is expected that this review will open a call for further research on the identified gaps.