Dissolved fluoride in the Lower Ganges-Brahmaputra-Meghna River system in the Bengal Basin, Bangladesh

The dissolved fluoride (F-) in the Lower Ganges-Brahmaputra-Meghna (GBM) ri ver system, Bengal basin, Bangladesh, was studied during 1991-1993 to deter mine its distribution and source in the basin, and its annual flux to the B ay of Bengal. The concentration of dissolved F- varied between 2 and 11 mu mol l(-1) with statistically significant variations both spatially and temp orally in the basin. Such variations are attributable to the geology of the individual subbasins (Ganges, Brahmaputra and Meghna), dilution by rainwat er during monsoon and groundwater contribution to the river systems during dry season. Correlation coefficients among F- and major cations and anions suggest diverse inorganic processes responsible for regulating the concentr ation of F- in these river systems. However, fluorite seems to be one of th e major sources of dissolved F-. The concentration of F- in the Lower GEM r iver system is low compared to the rivers draining Deccan Plateau and arid regions of the subcontinent, for example, Yamuna and its tributaries. Howev er, it is within the range of most of the other Peninsular and Himalayan ri vers. The GEM system contributes about 115 x 10(3) tonnes year(-1) of disso lved F- into the Bay of Bengal, and thus accounts for about 3% of the globa l F- flux to the oceans annually.