Search

This study investigated the distribution and fractionation of metals (Mn, Ni, Pb, Cr, Cu, Zn, As, Cd, Hg and Sn) in surface sediments of Tema Harbour (Greater Accra, Ghana) as well as its ecological implications. Significant differences in sediment concentrations of Mn, Ni, Cr, Cu, Zn, As and Sn were observed across the Tema Harbour. Geochemical indices indicate that Cd, Hg, Pb, Cu, Zn, As and Sn in the Tema Harbour sediments derived mainly from anthropogenic sources, while Mn, Ni and Cr were mainly of lithogenic origin. Metal fractionation revealed a predominance of Al, Mn, Ni, Pb, Cr, Cu, As and Sn in the residual phase. In contrast, Cd and Hg were mainly present in the exchangeable phase, while Zn was mainly associated with the reducible phase. Based on the metal fractionation in the Tema Harbour sediments, the potential risks of metal bioavailability were high for Cd and Hg, low-medium for Mn, Ni, Zn, As and Sn and low for Pb, Cr and Cu. A screening-level ecotoxicological assessment revealed high potential toxicity of Hg and moderate potential toxicities of Pb, Cu, Zn, As and Cd in the Tema Harbour sediments. The potential influence of the buffer intensity, silt-clay, total organic carbon and carbonate content on the metal distribution in the Tema Harbour sediments was also inferred from their correlations. Comparison with previous studies did not reveal a progressive increase in metal contamination at the Tema Harbour since the year 2000. [ABSTRACT FROM AUTHOR]

We present results of a preliminary geochemical assessment of Cd, Pb, V, As, Ni, Cu, Zn, Mg, Al, K, Ca, and Fe in marine sediments from the Eastern Equatorial Atlantic, off the Coast of Ghana. Samples were taken along 4 regions G1, G2, G3 and G4 at approximately 25 m, 100 m, and 250 m, 500 m and 1000 m depths. Elemental compositions were assessed through the estimation of Al-normalized enrichment factors and geochemical accumulation indices, and the concentrations determined to produce any potential toxic effects to biota. Significant enrichment of the bottom sediments with Cd, Ni and As were observed at some locations with sediments showing signs of heavy pollution with As at region G4. Apart from Ni, V and As which were beyond threshold effects levels at most regions, all other metals were below probable effect levels. Both natural and anthropogenic processes controlled trace metal accumulation and distribution in the Ghanaian coastal environment. [ABSTRACT FROM AUTHOR]

The original version of this article unfortunately contained a mistake in the article title. [ABSTRACT FROM AUTHOR]

Total sediment concentrations of Cd, Cu, Pb, Zn, As, and Hg obtained from the Ankobra, Sakumo II, and Volta estuaries in Ghana were used to generate contaminant probability density distributions and species sensitivity distributions in AQUARISK. Results of the tier 1 assessment showed Cu, Cd, Zn, and Pb were not of concern in the Ankobra as their measured values and the 99th percentile of the fitted distributions were lower than the SQG low-trigger values. Mercury (Hg) and As were however, identified to be of concern in this estuary. In the Sakumo II estuary, Cu, Cd, Pb, and Hg have been identified to be of concern because their concentrations are higher than the SQG low-trigger values. Hg has been identified as the only metal of concern in the Volta estuary. The total proportion of species likely to be affected by the combined concentration of Cd, Cu, and Zn measured from Ankobra, Sakumo II, and Volta were 14%, 16%, and 12%, respectively, according to the Bur III distributional analysis of the ecotoxicology data. The measured median sediment concentrations of As and Hg in the Ankobra estuary greatly exceeded the median sediment concentration targets to achieve a 5% or less exceedence of the SQG low value. Similarly, in the Sakumo II estuary, the measured median sediment concentrations of Cu, Pb, and Hg greatly exceeded the median sediment concentration targets to achieve a 5% or less exceedence of the SQG low. For the Volta estuary however, other metals except Hg fall below the target values. [ABSTRACT FROM AUTHOR]

This study aimed at assessing trace element concentrations in two representative estuaries of Ghana (Pra and Ankobra) affected by gold-mining, relative to the levels of the unaffected Volta estuary. Surficial sediments ( n  = 16–17) were sampled at each estuary and analysed by ICP-MS for 25 elements after pseudo-total digestion. The enrichment and geoaccumulation indexes revealed a moderate to significant contamination of As, Ag and Cu in the Pra and Ankobra estuaries. Spatial maps of concentrations revealed non-localized sources. High As concentrations were attributable to runoff transport and sedimentation of gold mining-tailing particles, as suggested by results from granulometric distributions, correlation and PCA analysis. The probabilities of surpassing the probable effects level (PEL) were 77% for As, 50% for Cr and 27% for Ni in Ankobra; these values were of 13%, 23% and 10% for the Pra. Results reveal potential future implications on ecosystems and human health in these both estuaries as result of the gold-mining activity. [ABSTRACT FROM AUTHOR]

Theoretical and experimental studies have shown that activity concentrations of fallout radionuclides (such as 137Cs and excess 210Pb) decrease with particles size in aqueous suspensions. This paper is aimed at reviewing the theoretical fundamentals for granulometric speciation of radionuclides, and at exploring its practical use in the analytical context of gamma spectrometry for the radiometric dating of recent sediments, with view to: i) improving the detection of 137Cs (since its use as independent chronostratigraphic mark is challenging in the southern hemisphere because its low fallout rate), ii) supporting refined CIC models and normalization techniques in 210Pb-based radiogeochronologies. The work uses surface sediments sampled from the Tinto Estuary (SW Spain), affected by mining and phosphate-fertilizer industries, and from the Ankobra Estuary (Ghana), affected by intensive artisanal gold-mining. Granulometric classes have been separated by a sieving column with decreasing mesh sizes and the obtained cumulative percentage of mass mathematically described by a Rosin-Rammler particle-size distribution. The target radionuclides for gamma spectrometry were 210Pb, 226Ra and137Cs, complemented with 40K, 234Th and 228Ra. Results revealed that, far from ideal experiments, under actual environmental conditions the increase in activity concentrations with decreasing particle sizes is too moderate, and in general they are affected by larger counting uncertainties due to the small available amount of mass. Indeed, there was no correlation between grain-size and 137Cs concentrations (p = 0.25), and similarly for excess 210Pb (p = 0.53). No effect of the organic matter content was observed in 137Cs (p = 0.58) and excess 210Pb (p = 0.85) concentrations. Present results pose some concerns to the general use of granulometric speciation in the context of gamma spectrometry for supporting the radiometric dating of recent sediments. A detailed discussion on the use of normalization methods is also presented. • Radionuclide uptake in aqueous suspensions is proportional to particles surface. • Measuring 137Cs and 210Pb in physically separated grain-size class in sediment core. • Target: improving detection of 137Cs in southern hemisphere and 210Pb normalization. • Results reveal weak particle-size effects under actual environmental conditions. [ABSTRACT FROM AUTHOR]