Abstract
PurposeTrace metals accumulate in the food web and can pose high risks to human health and aquatic biota. We investigated seasonal and spatial variations of Cu, Zn, Pb, Co, and Ni mobility in surface sediments (0–5 cm) and their potential toxicity.Materials and methodsThe sampling was carried out in three embayments of the Ebrie Lagoon (Côte d’Ivoire) during the rainy and dry seasons. The sequential and kinetic extraction methods were used to assess Cu, Zn, Pb, Co, and Ni mobility and their potential toxicity. Analysis of variance (ANOVA) was performed to ascertain spatial and seasonal differences.Results and discussionThe results showed that contrarily to Co, distribution patterns of Zn and Cu in the sediment fractions showed no spatial and seasonal variability. On the other hand, Pb and Ni distribution patterns varied highly across the bays but not seasonally. Nevertheless, repeated measurements over a long period of time should be carried out to better understand the seasonal variability of metal distribution in sediment phases. Cu, Pb, Co, and Ni were abundant in residual fraction (56.93–71.66%) in the bays. On the contrary, a very high portion of Zn (up to 70%) could be remobilized. Cu, Pb, Co, and Ni formed mainly inert complexes in sediments, while Zn formed labile complexes. Zn could pose high risk to biota, Co and Ni a medium risk, and Cu and Pb a low risk.ConclusionsA combination of both sequential and kinetic methods revealed that both Zn and Pb formed labile complexes in the exchangeable and iron/manganese oxide fractions. Sequential extraction showed high Pb concentrations in the iron/manganese oxides. Thus, Zn and Pb may be highly available, which confirmed fish Pb concentrations exceeding WHO safe limits found by previous studies. Therefore, potential mobility of metals could be better assessed by the exchangeable and iron/manganese oxide fractions obtained by sequential extraction methods.
Highlights
Potential mobility of metals could be better assessed by the exchangeable and iron/manganese oxide fractions obtained by sequential extraction methods
The mobility and potential risk of Zn, Cu, Pb, Co, and Ni were assessed in the Ebrie Lagoon using kinetic and sequential extraction methods from February 2012 to May 2012
Comparing kinetic and sequential extraction results, we found that high concentrations of Zn and Pb in the exchangeable and in the iron/manganese phase in the Ebrie Lagoon sediments could result in significant bioaccumulation of these elements
Summary
Sediments are an important sink for trace metals (Kouassi et al 2015; Mahu et al 2015; Zhang et al 2016). They are considered as appropriate indicators of metal pollution in aquatic systems. Metals can be released from sediment through many processes, such as sediment resuspension and release, diffusion and advection from sediments, and biotransfer through organisms Metals form both residual complexes and non-residual complexes in sediment systems. While the former are inert, nonresidual complexes show gradual levels of mobility in the water column depending on their thermodynamic stability.
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