J. Phys. IV France 107 (2003) 107
DOI: 10.1051/jp4:20030255

Mercury and arsenic in the gold mining regions of the Ankobra River basin in Ghana

W. Bannerman^{1, 2}, M. Potin-Gautier¹, D. Amoureux¹, S. Tellier¹, A. Rambaud³, M. Babut⁴, A. Adimado² and C. Beinhoff<sup>5

1</sup>  Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, UMR 5034, Université de Pau et des Pays de l'Adour, avenue de l'Université, 64000 Pau, France
²  Chemistry Department, K. N. University of Science & Technology, Kumasi, Ghana
³  Université de Montpellier 1, Département Sciences de l'Environnement & Santé Publique, 15 avenue Ch. Flahault, 34060 Montpellier cedex 1, France
⁴  Cemagref, Freshwater Biology Research Unit, CP. 220, 69336 Lyon cedex 9, France
⁵  United Nations Industrial Development Organisation (UNIDO), Vienna International Centre, P.O. Box 300, 1400 Vienna, Austria

Abstract
The river Ankobra flows through the principal gold mining centres in Western Ghana, draining a total area of 8272 km ² to join the Atlantic ocean. Mercury is used by thousands of small-scale miners in the region to amalgamate gold. Ores mined in some deep shafts and surface mines are arsenopyrites and the region is marked by the presence of heaps of arsenic - rich mine tailings from both past and recent activities. This study was conducted to assess the impact of mining activities on the distribution and speciation of arsenic and mercury in the aquatic environment of the Ankobra River. In all, water (filtered and non-filtered) and bed sediments were collected from various locations within the watershed. Principal parameters investigated include total mercury, arsenic (III), arsenic (V), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). Seasonal and spatial variations of these parameters were investigated. Quality control systems were adopted at both the environmental and analytical stages of the study. ln general, areas close to the mining centres are the most pollilited. As (V)/As (III) ratios in water are reversed after the first 100-km of the river length with the onset of industrial influence downstream.

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