Mercury and other Elements in the Pra River Basin, Ghana

Abstract

Total mercury (THg) concentrations in sediment cores (0-10 cm depth), soil profiles (0-6 cm), camivorous/herbivorous fish tissues, and “Black” samples were determined using Cold Vapour Atomic Absorption Spectroscopy (CVAAS). The samples were obtained from twenty-one, twenty, seven, and four sites respectively in the Pra River Basin. K0-Instrumental Neutron Activation Analysis (k0-INAA) method was used to validate HNO3/HF/HCI digestion in the determination of THg in the geological samples, and thirty-four elements in soil (0-1 cm) samples. Precision and accuracy for all reference materials were good. Hydrofloric (HF) acid combination was best digestion procedure for THg determination in all geological samples from the basin. The least (2.20-3.23 mg/kg) and highest (103-770 mg/kg) THg in the soil from twenty sites were recorded at Twenedurase and Dunkwa-on-Offin sites respectively. Also, the least (0.01- 0.02 mg/kg) and highest (0.23-20.8 mg/kg) THg in sediments from twenty-one sites were recorded at Kwahu Praso and Beposo sites respectively. The highest THg (1,673 mg/kg) in “Black” samples was recorded at Dunkwa-on-Offin 1. All carnivorous fish muscle from Nkontinso site had THg (0.376-0.983 pg/g) above 0.3 pg/g and THg (0.014-0.262 pg/g) in herbivorous fish muscles were below 0.3 pg/g. The elements, As, Hf, Se, Zr, U, Sb, W and Au in the soil were found to bind THg. Monazite-Ce was found in the 0-1 cm soil from Kibi site. HF acid digestion was the best procedure for THg determination in the geological samples in the river basin. All soils had THg above background levels of 0.07 mg/kg. Dunkwa-on-Offin site is THg “hotspot” in the basin and carnivorous fish from Nkontinso site are not safe for consumption.