Sorption of Inorganic Mercury on Soils from Ankobra Basin in the South - Western Part of Ghana

Understanding the adsorption of mercury on soil from aqueous solution is necessary for tracing the fate of mercury in the environment. This study was undertaken to predict the fate of mercury emitted from artisanal gold mining activities within the Ankobra basin. Total mercury (THg) concentrations were determined in soils close to River Ankobra and its major tributaries in the south-western part of Ghana by Cold Vapour Atomic Absorption Spectrophotometry. THg content of the soils ranged from 0.051 μgg to 0.366 μgg with an average of 0.15 μgg which was below the level (200 μgg) set by US EPA. THg correlated positively (r = 0.57) with the organic matter content of the soil. Sorption of Hg (II) onto the soils had an L type isotherm and the distribution coefficient (Kd) ranged from 41.4 μgg -1 to 182.2 μgg. The Freundlich model showed a better fit followed by Langmuir model and linear. The superiority of Freundlich model to the other models could be attributed to the heterogeneous surface energies and exponential distribution of active sites which are characteristics of such soils. All the soils had adsorption intensity (n) lower than one, indicating the soils could be good sorbent for Hg (II). This suggests that Hg fate and availability in soil for runoff and leaching could be low for soils with such characteristics. INTRODUCTION Human activities such as mining and associated smelting, burning of fossil fuels, and industrial uses of mercury (Hg) in paints, batteries, medicine, and dentistry have been increasing the global reservoir of atmospheric mercury since the beginning of the industrialized period (Fitzgerald et al., 1998). This Hg is widely distributed via atmospheric processes, and deposition from the atmosphere into terrestrial and aquatic systems even in remote areas has led to the recognition of Hg as a global pollutant (Jackson, 1997; Fitzgerald et al., 1998). Point sources are important in delivering Hg to aquatic systems, but atmospheric Hg deposition, either directly to the aquatic system or indirectly via deposition to terrestrial watersheds and its subsequent transport, is also © 2013 Kwame Nkrumah University of Science and Technology (KNUST) Journal of Science and Technology, Vol. 33, No. 3 (2013), pp1-15 1