Radioecological assessment and radiometric dating of sediment cores from dynamic sedimentary systems of Pra and Volta estuaries (Ghana) along the Equatorial Atlantic

摘要

The Volta and Pra estuaries (Ghana, West Africa) are dynamical sedimentary systems whose natural equilibrium is being affected by anthropogenic activities. This paper reports depth-distributions of Pb-210, Ra-226, Th-234, K-40, Ra-228 and Cs-137 for two sediment cores from these estuaries. Bulk densities were not steady-state and well correlated with K-40 (p < 0.00005). Unsupported Pb-210 profiles were incomplete, non-monotonic and showed large fluctuations. The assumptions involved in the common Pb-210-based dating models were not meet in these dynamical scenarios, and the use of Cs-137 as a time-marker is difficult in Equatorial and South-Hemisphere countries due to its low fallout rates. Chronologies have been solved with the new Pb-210-based TERESA model, which operates with varying but statistically correlated fluxes and sediment accumulation rates (SAR). The core from the Volta reflects the conditions prevailing after the construction of the Akosombo Dam, with a mean SAR of 1.05 +/- 0.03 g cm(-2).y(-1), while a higher value of 2.73 +/- 0.06 g cm(-2).y(-1) was found in the Pra, affected by intense gold mining activities along its course. Radiological and radioecological assessments have been conducted by applying the UNSCEAR protocols and the ERICA model, respectively. The measured radionuclide concentrations do not pose any significant risk for the environment and human health. (C) 2017 Elsevier Ltd. All rights reserved.