Metal fractionation in sediments as a tool for assessing the availability of trace metals: The case of Apipucos Reservoir

The worldwide concern about trace metal pollution has been increasing in recent years due to the increase in anthropogenic trace metal inputs to the various ecosystems. The quantification of the chemical species of metals in sediments is essential for estimating the bioavailability of the metals in the environment. The objective of this study was to characterize the present level of metal pollution in the Apipucos Reservoir, Brazil, and determine its degree of toxicity to plants and animals. For this purpose, sediment cores were collected and its metal content (Zn, Pb, Cd, Co, Mn, Fe, Cu) was analyzed by atomic absorption spectrometry after sequential extraction. The results showed that there is more Fe and Mn than other metals (Fe>Mn>Pb>Zn>Cu). Besides, the concentrations of Fe and Mn are very high in the exchangeable and available phases, which are mobile and available fractions in sediments. The results also indicate that Fe, Mn and Cu could be mobilized under oxidizing conditions. Lead was found mainly in the reducible phase whereas Zn was found on available and reducible phases. Cobalt and Cadmium, although included in the set of metals analyzed, were not found in the sampled sediments. Sediment dating showed that the first sedimentary layers are about 30 years old. - Highlights: ► The ranking of the concentrations of metals in sediments: Fe>Mn>Pb>Zn>Cu. ► Cu is relatively immobile, present on the oxidizable phase. ► Fe and Mn are in the exchangeable phase, being highly mobile and available. ► Pb and Zn were found on the reducible phase, being available for animals and plants. ► Sediment dating demonstrated that recent sediment ages are about 30 years old