Spatio-temporal study of water quality variables in the Rio de Ondas Hydrographic Basin, west of Bahia, Brazil using multivariate analysis.

Water bodies are containers that receive a large load of water quality variables through the release of domestic, industrial, and agricultural effluents. With this focus, this work aimed to conduct a temporal-spatial variability study in the Rio de Ondas Hydrographic Basin through multivariate statistical analysis. For this, seventeen collection sites were established in four stations along the Rio de Ondas and its tributaries between 2017 and 2018. Ionic chromatography with suppressed conductivity was used for ions determination, while ICP-OES determined metals' total concentrations. The land use and occupation assessment between 1985 and 2021 was using data from MapBiomas were used and the descriptive and multivariate analysis of the data using version free of the Statistica software. The results showed that, in 30 years, there was a growth of 569% of agricultural activities in the watershed area, with significant suppression of native vegetation, favoring the transport of contaminants to rivers. Ca2+, PO42-, Al, Cu, and Zn concentrations showed a statistically significant difference between the seasons, with higher medians in the rainy season. Rainy season influenced the formation of three groups in the PCA, consisting of electrical conductivity, salinity, TDS, and PO42- (group 1); temperature, Fe, SO42-, and Cl- (group 2); and Ca2+, Mg2+, Na+, and HCO3- (group 3). The strong correlation between parameters of each group indicates anthropic influence on the watershed's water quality. However, levels are within the potability standard.

Trace metal dynamics in an industrialized Brazilian river: A combined application of Zn isotopes, geochemical partitioning, and multivariate statistics.

The Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (δ66/64ZnJMC ≈ + 0.30‰) and anthropogenic (δ66/64ZnJMC ≈ + 0.15‰) end members. The lighter δ66/64ZnJMC values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds.

Adapted Sequential Extraction Protocol to Study Mercury Speciation in Gold Mining Tailings: Implications for Environmental Contamination in the Amazon.

Artisanal small-scale gold mining (ASGM), an increasingly prevalent activity in South America, generates mercury-contaminated tailings that are often disposed of in the environment, leading to the introduction of mercury into ecosystems and the food web, where it bioaccumulates. Therefore, studying the geochemical processes involved in the desorption and dissolution of mercury in these tailings is essential for critical risk evaluations in the short and long term. For this purpose, sequential extraction procedures (SEPs) can be useful because they help to identify the phases to which Hg is associated, although they also have limitations such as a lack of selectivity and specificity. In this work, we propose a modified four-step SEP: exchangeable mercury (F1), oxidizable mercury (F2), mercury bound to Fe oxides (F3), and strongly bound mercury (F4). To test this adapted sequential extraction method, we evaluated the Hg contamination in mercury-contaminated tailings of the Amazon basin. The results revealed a total mercury concentration of 103 ± 16 mg·kg-1 in the tailings, with a significant portion in F1 (28% of the total), where Hg was bioavailable. The large Hg concentration in F3 (36%) suggested that Fe oxides likely contribute to mercury retention. Together, the SEP results emphasize the urgent need for improved surveillance of gold mining activities and responsible tailings management practices to mitigate environmental contamination and safeguard the health of the Amazon ecosystem.

Metal record of copper-based antifouling paints in sediment core following marina construction and operation.

Marinas are central hubs of global maritime leisure and transport, yet their operations can deteriorate the environmental quality of sediments. In response, this study investigated the metal contamination history associated with antifouling paint uses in a sediment core collected from Bracuhy marina (Southeast Brazil). Analysis target major and trace elements (Cu, Zn, Pb, Cd and Sn), rare earth elements (REEs), and Pb isotopes. The modification in Pb isotopic ratios and REEs pattern unequivocally revealed sediment provenance disruption following the marina construction. Metal distribution in the sediment core demonstrates that concentrations of Cu and Zn increased by up to 15 and 5 times, respectively, compared to the local background. This severe Cu and Zn contamination coincides with the onset of marina operations and can be attributed to the use of antifouling paints.

Exploring a new approach for assessing the fate and behavior of the tailings released by the Brumadinho dam collapse (Minas Gerais, Brazil).

In 2019, the Brumadinho dam rupture released a massive amount of iron ore mining tailings into the Paraopeba River. Up to now, it remains a public health issue for the local and downstream populations. The present study aims to assess the behavior and fate of metal contamination following the disaster. Using new sampling strategies and up-to-date geochemistry tools, we show that the dissolved metal concentrations (< 0.22 µm cutoff filtration) remained low in the Paraopeba River. Although the tailings present high metal concentrations (Fe, Mn, Cd, and As), the high local background contents of metals and other previous anthropogenic contamination hamper tracing the sediment source based only on the geochemical signature. The Pb isotopic composition coupled with the metals enrichment factor of sediments and Suspended Particulate Matter (SPM) constitutes accurate proxies that trace the fate and dispersion of tailing particles downstream of the dam collapse. This approach shows that 1) The influence of the released tailing was restricted to the Paraopeba River and the Retiro Baixo reservoir, located upstream of the São Francisco River; 2) The tailings' contribution to particulate load ranged from 17 % to 88 % in the Paraopeba River; 3) Other regional anthropogenic activities also contribute to water and sediment contamination of the Paraopeba river.

Behavior of metallurgical zinc contamination in coastal environments: A survey of Zn from electroplating wastes and partitioning in sediments.

The contamination of coastal environments by metallurgical wastes involves multiple biogeochemical processes; accordingly, understanding metal behavior and risk evaluation of contaminated areas, such as Sepetiba Bay (Rio de Janeiro, Brazil), remains challenging. This study coupled Zn isotopic analyses with sequential extractions (BCR) to investigate the mechanisms of Zn transfer between legacy electroplating waste and the main environments in Sepetiba Bay. This metallurgical waste showed a light bulk isotopic signature (δ66/64ZnbulkJMC = +0.30 ±â€¯0.01‰, 2 s, n = 3) that was not distinct from the lithogenic geochemical baseline, but was different from signature of mangrove sediment considered as anthropogenic end member (δ66/64ZnJMC = +0.86 ±â€¯0.15‰) in a previous isotopic study in this area. Zn isotopic compositions of sediment samples (ranging from +0.20 to +0.98‰) throughout the bay fit a mixing model involving multiple sources, consistent with previous studies. In the metallurgic zone, the exchangeable/carbonate fraction (ZnF1) exhibited high Zn concentrations (ZnF1 = 9840 µg g-1) and a heavy isotopic composition (δ66/64ZnF1JMC = +1.10 ±â€¯0.01‰). This finding showed that, in some cases, the bulk isotopic signature of waste is not the most relevant criterion for evaluating trace metal dispersion in the environment. Indeed, based on the BCR, it was observed that part of the anthropogenic metallurgical Zn was redistributed from the exchangeable/carbonate fraction in the waste to the surrounding mangrove sediment. Then, this contaminated sediment with heavy δ66/64Zn values was exported to other coastal environments. In Sepetiba Bay, contaminated sediments revealed a large concentration of ZnF1 fraction (up to 400 µg g-1) with a heavy Zn isotopic signature. This signature also matched the Zn isotopic signature of oysters in Sepetiba Bay reported by other studies; hence, measurement of the isotopic exchangeable/carbonate fraction has important implications for tracing the transfer of anthropogenic Zn to biota.

Evaluation of Total Mercury in Sediments of the Descoberto River Environmental Protection Area-Brazil.

To evaluate the total mercury accumulation (THg) in the Descoberto river basin environmental protection area (DREPA), nine sediment and water samples were collected from the Descoberto reservoir (lentic environment), and 23 in its tributaries (lotic environment), which are located in a densely urbanized area within the Descoberto river watershed, Brazil. The following physicochemical parameters of water were determined: dissolved oxygen (DO); hydrogen potential (pH); total dissolved solids (TDS); nitrate (NO3-); chloride (Cl-); temperature (T); sulfate (SO42-), and in sediment, the concentration of total mercury (THg) and volatile material (VM) was determined. THg concentrations in sediments showed a significant difference (p = 0.002) between tributaries (0.03 µg g-1 ± 0.02) and reservoir (0.08 µg g-1 ± 0.04), indicating accumulation in the lentic environment. Most of the results evaluated for ecotoxicological risks presented values below the concentration, at which adverse effects would rarely be observed, ERL (effects range low). However, in relation to the enrichment factor (EF), applied to identify the anthropogenic contribution, the results indicate that most of the samples are moderately polluted through atmospheric deposition due to vehicular traffic and agriculture. These results show that the likelihood of methylation in the lentic environment is higher than in the lotic environment.

Influence of hydrodynamic conditions on the degradation of 1-butyl-3-methylimidazolium chloride solutions on boron-doped diamond anodes.

This study assessed the influence of hydrodynamic conditions on the degradation process of 1-butyl-3-methylimidazolium chloride (BMImCl) solution on a boron-doped diamond anode in a filter-type electrochemical reactor configuration. The results show that this parameter did not significantly affect this process when operating in the laminar regime. However, in the transition regime (Re ≥ 2000), higher flow rates resulted in a faster removal of BMImCl and total organic carbon, making the process more efficient. Following BMImCl degradation, nitrates were generated at the cathode, then reduced at the cathode to ammonium; combination with free chloride produced at the anode led to the transformation of chloride into combined chlorine forms instead of more toxic oxianions such as chlorate and perchlorate. Thus, the flow rate can be a key parameter for defining operating conditions in which the target BMImCl is more effectively degraded with reduced generation of undesirable secondary products.