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.

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.

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.