Mercury and arsenic pollution in soil and biological samples around the mining town of Obuasi, Ghana

Samples of soils, plantain (Musa paradisiaca), water fern (Ceratopteris cornuta), elephant grass (Pennisetum purpureum), cassava (Manihot esculenta) and mud fish (Heterobranchus bidorsalis) were collected from Obuasi and its environs, which is the most active gold mining town in Ghana. The distribution of mercury and arsenic in these samples from fourteen sampling sites was determined. The annual average surficial soil concentrations of As and Hg from 14 sampling sites have the mean and SD of 12.92 +/- 17.48 (range = 2.11-48.87 mg kg(-1) d.w.) and 0.93 +/- 0.58 (range = 0.29 - 2.52 mg kg(-1) d.w.), respectively. The annual average concentrations of As and Hg from plant and grass samples show the mean and SD of 9.05 +/- 17.50 (range = 0.49 - 78.71 mg kg(-1) d.w.) and 1.85 +/- 2.04 (range = 0.12 - 9.68 mg kg(-1) d.w.), respectively. Plant/soil concentration ratios of As and Hg showed elevated values for the grass samples, especially from sites within 4 km of the Pompora Treatment Plant. The high bioaccumulation ratios of fern reflected both soil and air sources of pollution. The results substantiated a mercury and arsenic concentration gradient in the area, thereby indicating that the local environment is contaminated by mining activities.