Geochemistry of trace metals in surface sediments from the continental slope of the states of Sergipe and Alagoas, Northeastern Brazil

Geochemical analyses were used to determine the origin and identify the main factors that lead to the metal trace distribution on the surface sediments from the continental slope of Sergipe in Brazil. Sediment samples were collected during the dry and rainy periods, from 36 sampling points distributed at water depths from 400 to 3000 m. In general, no effect of seasonality was observed on the metal concentrations and no significant differences were observed between the depth ranges. The correlation analysis indicated the continental origin as the most predominant, followed by authigenic deposition. Anthropogenic enrichment was not noted, nor was the possibility of adverse aquatic biota effects. The results made it possible to understand the contribution of rivers in the transport and transfer of particulate matter to the coastal region, in addition to providing new information on the content of trace metals in tropical Atlantic sediments.

Analyses of colloidal, truly dissolved, and DGT-labile metal species and phosphorus in mining area surrounded by tailing dams using self-organising maps

The knowledge of size-distribution and lability of metals and nutrients in freshwater systems is important for estimation of the ecological effects of mining. However, it is still limited in several mining areas such as the Quadrilátero Ferrífero (Brazil) which was severely polluted by the collapse of the Fundão tailings dam in November 2015. In this study, results of an investigation from 2014 using a neural network named self-organising map (SO-Map) into the conditions of selected trace metals that are of particular importance to mining areas (Cr, Cu, Co, Mn, Ni, Pb, Zn) are presented. Additionally, P was considered by its high importance as a nutrient and sites later affected by the dam burst were also included by chance. Water samples were collected at six sites in dry and rainy seasons and filtered and ultrafiltered for determination of total dissolved (<0.45 μm) and truly dissolved (<1 kDa) fractions. Diffusive gradients in thin films (DGT) devices were deployed in situ for determination of the DGT-labile fraction. All data were analysed using SO-Map and Spearman's rank correlation. Phosphorus in the Carmo River occurred mainly in the truly dissolved and DGT-labile fractions. The higher amounts of this element in the river water (up to 263 μg L^-1 of total P) might be related to untreated sewage discharge. Moreover, the concentrations of other trace metals (Mn, Cu, Co, Ni, Zn) were high, even under the "natural" conditions (before the dam failure) due to natural and anthropogenic factors such as local lithology and mining.

Characterization of dissolved organic matter in an urbanized estuary located in Northeastern Brazil

The Sal River estuary, which is located in the state of Sergipe, Northeastern Brazil, stands out as an urban estuary, anthropogenically impacted by untreated and treated wastewater discharge. Synchronous fluorescence spectroscopy and measurement of dissolved organic carbon (DOC) were used for characterization of dissolved organic matter (DOM) in the estuarine water. Dissolved organic carbon concentrations ranged from 7.5 to 19.0 mg L^-1 and, in general, the highest values were recorded during dry season. For both seasons (dry and rainy), DOC presented an inverse linear relationship with salinity, which indicates a conservative dilution of organic matter coming into the estuary. During rainy season, anthropogenic organic constituents and humic substances from land-based sources predominated in DOM composition, carried by river flow. Whereas during the dry season, it has been observed a significant increase of products generated by microbial degradation of anthropogenic organic matter. The relationships between fluorescence intensity and salinity suggest a conservative behavior during rainy season and a non-conservative behavior during dry season, with addition of fluorescent organic matter into the intermediate zone of the estuary. Photodegradation by action of sunlight caused a decrease in fluorescence intensity of humic and tryptophan-like constituents and the release of photoproducts, resulting in an increase in fluorescence intensity of protein-like constituents.