Radioactivity concentrations and their radiological significance in sediments of the Tema Harbour (Greater Accra, Ghana)

Abstract

Studies on environmental radioactivity in tropical Africa are scarce. Therefore, a baseline study of natural (238 U, 210 Pb, 226 Ra, 232 Th, 228 Ra, 228 Th, 40 K) and anthropogenic (137 Cs) radionuclides was carried out on Tema Harbour (Greater Accra, Ghana) surface sediments and on their radiological significance. Grab surface sediment samples were collected from 21 stations within the Tema Harbour and their radioactivity concentrations measured by gamma spectrometry. The mean sediment radioactivity concentrations (Bq kg À1 dw) were 34 for 238 U, 210 for 210 Pb, 14 for 226 Ra, 30 for 232 Th, 29 for 228 Ra, 31 for 228 Th, 320 for 40 K, and 1.5 for 137 Cs. Large 238 U/ 226 Ra disequilibria were observed in the harbour sediments and a complex dynamics of several mixed sources of sediments within the Tema Harbour can be inferred from the spatial variations in the radioactivity concentrations. The estimated total absorbed dose rate in air (D), radium equivalent activity (Ra eq), external hazard index (H ex), annual gonadal dose equivalent (AGDE) and annual effective dose equivalent (AEDE) indicated no significant radiological risks from the sediment radioactivity concentrations. Application of the Environmental Risk from Ionising Contaminants Assessment and Management tool (ERICA) confirmed that the potential dose rates to biota from the sediment radioactivity concentrations are unlikely to pose appreciable ecological risks. The radioactivity levels are compared with levels reported in sediments from other coastal areas of the world.

Settling fluxes and sediment accumulation rates by the combined use of sediment traps and sediment cores in Tema Harbour (Ghana)

“…However, there is no direct riverine inflow in the Tema Harbour (Botwe et al, 2017b). The Tema Harbour layout and its operations have been described previously (Botwe et al, 2017a;Botwe et al, 2017b;Botwe et al, 2017c). Briefly, the Tema Harbour is a semi-enclosed coastal harbour situated in the Gulf of Guinea at Tema (Greater Accra, Ghana) with a water area of 1.7 km 2 (Fig.…”

“…The Main Harbour is concerned with shipping operations and has water depths ranging from 7.5 to 11.4 m (mean 8.5 m), a 240 m wide entrance and a breakwater of 4850 m length (Botwe et al, 2017b). The Fishing Harbour and the Canoe Basin are dedicated to the operations of semi-industrial, industrial and artisanal fishing vessels (Botwe et al, 2017c).…”

“…The average water temperature is around 23 °C with water salinity ranging from 30-35‰ (Botwe et al, 2017c). Tides in the study area are semi-diurnal with a tidal range of about 1.6 m. In the immediate coastal sea area, tidal currents range from b0.1 to 0.5 m•s −1 and wave heights range from 1 to 2 m (http://open_jicareport.jica.go.jp/pdf/11681632_ 03.pdf).…”

“…A portion of the Main Harbour (shown in Fig. 1) was dredged in March-April 2014, while the Canoe Basin was dredged in May 2013 (Botwe et al, 2017c). It is also worth noting that in 2013, the construction of a new wharf was started near the eastern margin of the dredged area, with the emplacement of the supporting concrete pillars.…”

Environmental radioactivity and trace metals in surficial sediments from estuarine systems in Ghana (Equatorial Africa), impacted by artisanal gold-mining

“…Other pollution indexes, such as the enrichment factor (EF) and the geo-accumulation index (I geo ) are based upon the comparison with suitable reference levels (Loring and Rantala, 1992). The radionuclide content in sediments can pose radiological hazards, and there are several established indexes for assessing the radiation dose to humans (e.g., Botwe et al, 2017) and to a series of reference organisms (Larsson, 2008).…”