Understanding seasonal variations in As and Pb river fluxes and their regulatory mechanisms through monitoring data

The Doce River Basin (DRB) suffers with the adverse impacts of mining activities, due to its high level of urbanization and numerous industrial operations. In this study, we present novel insights into contaminant flow dynamics, seasonal variations, and the primary factors driving concentration levels within the region. We conducted an extensive analysis using a database sourced from the literature, which contained data on the contamination of arsenic (As) and lead (Pb) in the Doce River. Our primary aim was to investigate the patterns of As and Pb flow throughout the entire basin, their response to seasonal fluctuations, and the key parameters influencing their concentration levels. The results showed significant seasonal fluctuations in As and Pb fluxes, peaking during the rainy season. The 2015 Fundão dam breach in the DRB led to notable changes, elevating elemental concentrations, particularly As and Pb, which were subsequently transported to the Atlantic Ocean. These increased concentrations were primarily associated with iron and manganese oxides, hydroxides, and sulfates, rather than precipitation, as evidenced by regressions with low R2 values for both As (R2 = 0.07) and Pb (R2 < 0.001), concerning precipitation. The PCA analysis further supports the connection between these elements and the oxides and hydroxides of Fe and Mn. The approach employed in this study has proven to be highly effective in comprehending biogeochemical phenomena by leveraging data from the literature and could be a model for optimizing resources by capitalizing on existing information to provide valuable insights for drainage basin management, particularly during crises.

Trace element bioaccumulation in the hepatic tissue of juvenile green turtles (Chelonia mydas) stranded along the Campos and Espírito Santo basins, southeastern Brazil

This study analyzed the concentrations of 15 (Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, V, Zn) toxicologically important trace elements in the livers of 110 green turtles stranded in two areas of the Brazilian coast. These areas are essential for the refuge, feeding, and reproduction of the species, and the information obtained is intended to support the development of conservation strategies. Higher concentrations were observed in the Região dos Lagos, RJ in almost all elements, except for Al, Mo, Pb, and V. This location showed statistically higher differences in the concentrations of Cd (4.66 ± 2.33 μg.g-1), Fe (846.62 ± 583.06 μg.g-1), and Zn (27.17 ± 10.90 μg.g-1). The differences in trace element concentration patterns between the two study areas are likely influenced by multiple factors, including the bioavailability of trace elements, oceanic upwelling events, anthropogenic activities, habitat characteristics, and organism-specific metabolic processes.

Seasonal variation, contribution and dynamics of trace elements in the drainage basin and estuary of the Serinhaém river, BA

In the present study a mass balance calculation was used to quantify trace elements (Al, Ba, Cd, Cr, Cu, Fe, Mn, Pb, Ti, V and Zn) fluxes exported from the Serinhaém River estuary to the Atlantic Ocean. The studied elements exportation in the particulate fraction showed higher fluxes in the first sampling campaign and a high export rate to the Atlantic Ocean during this period. The physical-chemical parameters showed the highest values in sampling campaign 1. These variations are probably the cause of the different trace elements behavior in fluvial and estuarine areas, where removal and addition processes between particulate and dissolved phases took place, affecting distribution coefficient and fluxes to the Atlantic Ocean. EPA ecosystems present values in accordance with Brazilian legislation for pristine areas, however, monitoring programs must be carried out in the region, to avoid future environmental problems.

Mercury levels in an environmentally protected estuarine area in Northeast Brazil: partitioning in the water column and transport to the ocean

In this study, total Hg concentrations (HgT) were determined in the suspended particulate matter (SPM) and the dissolved fraction of the water column to evaluate their behavior through a gradient of physical-chemical parameters in a continuum between rivers and the Serinhaém River estuary of the Pratigi Environmental Protection Area, a pristine environment without point sources of Hg contamination, located in Northeast Brazil. Twelve points were sampled, forming a river-estuary transect, and two samplings were carried out (April and September 2019). Significant spatial and temporal effects were detected only for particulate HgT and not for dissolved HgT. Considering both samplings, the mean HgT concentrations in SPM were 1112 ± 824 and 44 ± 33 ng·g^-1 in the river and estuary, respectively. Also, HgT concentrations in the dissolved fraction (1.61 ± 0.61 ng·L^-1) were below the limits established by environmental agencies (CONAMA = 2 μg∙L^-1 and USEPA = 1.4 μg·L^-1). Salinity and SPM concentrations were important predictors of HgT in the water column (R² = 0.81, p < 0.0001; R² = 0.56, p < 0.0001, respectively). Mercury transport to the ocean through SPM was 2 kg∙year^-1, 4000 times greater than the dissolved fraction.

Doce River Estuary: Geochemical Changes Following the Largest Tailing Spill in South America

Accidents involving economic activities of great impact, such as mining, have caused massive environmental damage. In November 2015, the dam of Fundão, located in the city of Mariana, MG, broke and released 5 × 10⁷ m³ of tailings in the nearby ecosystems, including the Doce River. The physicochemical changes that occurred in the Doce River estuary were analyzed, as well as the trace metal concentrations, both 1 day before and 1 month after the disaster. The analyses of the collected samples (water and sediment) showed changes to the physicochemistry regarding dissolved oxygen, SPM, and temperature (p = 0.008, 0.001, 0.036, respectively). It also detected metals (Fe and Al) in the dissolved fraction beyond the limits recommended by the Brazilian legislation. There was an increase in the total concentrations of Fe and Cd in the sediment after the rupture of the dam and a change in mobile metals (Al, Cd, Cr, Cu, Fe, Ni, Pb, and Zn), with higher concentrations of mobile metals being found closer to the ocean (p = 0.06356). After the rupture of the dam, there was a change in the granulometric fraction of the sediment, which became composed mainly of silt and clay. All of the results showed a change on the Doce River estuary, caused by the arrival of the tailings, which can result in future harmful effects with the release of metals present in the sediment and adsorbed to the particles. The changes to the sediment, such as changes in the granulometric fraction, can have negative consequences for the benthic community.