This study aimed to estimate in laboratory the temporal production of methylmercury during the filling of reservoirs of hydropower plants and to correlate it to the ecosystem of different locations in northern Brazil: Jirau hydropower plant in the Madeira River in the state of Rondônia (white waters—under construction), Cana Brava hydropower plant in the Tocantins River in the state of Goiás (clear waters—completed), and the Negro River in the Amazon (black waters—comparative). After collecting water, soil, and sediment samples in the regions mentioned, a microcosm was created to reproduce the conditions close to those found in nature. Water/soil/Hg⁰/Hg²⁺ and water/sediment/Hg⁰/Hg²⁺ were added to glass recipients. Next, methylmercury concentration was monitored by atomic fluorescence spectrometry, total organic carbon by TOC 5000A, and physical and chemical parameters such as pH, redox potential, and dissolved oxygen, for 25 days. The results obtained allow concluding that organic matter plays an important role, providing excess methyl groups to react with inorganic Hg and form organic Hg. The Negro River, which has higher contents of organic matter in its soil, water, and sediment, presented higher potential of mercury methylation in both experiments performed, followed by rivers Madeira and Tocantins.

The reduced natural water sources on the one hand and the large amount of wastewater produced by the textile industry on the other hand lead to the requirement of an effective reuse of textile wastewater. In this study, the treatment of textile wastewater by the reverse osmosis membrane system and membrane capacitive deionization (MCDI) system has been investigated to improve the quality and the recovery rate of the effluent for reclamation. The maximum chemical oxygen demand (COD) removal efficiency obtained at 10 bar was 96.3% for BW30 reverse osmosis membrane. Diversified operating conditions, including working voltage and flow rate, were investigated systematically in the MCDI system which is an effective water purification technology. According to the obtained experimental results, the COD removal efficiency was thoroughly increased by rising the working voltage (from 0.2 to 1.2 V) and the flow rate (from 5 to 17.5 ml/min). The flow rate and the working voltage at which the COD from textile wastewater removal ratio was the highest were 10 ml/min and 1.2 V, respectively. A life cycle approach has also been implemented for the comparison of environmental impact assessment of the two desalination systems. In this study, a life cycle approach has been implemented for the comparison of environmental friendly impact assessment of the two desalination systems. It is concluded that MCDI system is much more environmental friendlier with 5641 times less values for damage assessment categories, on average.

During phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals, the phytoremediation plants are often stressed by pollutants, which would reduce the efficiency of phytoremediation. The addition of organic acids from root exudates could alleviate the stress. In this study, three organic acids (citric acid, succinic acid, glutaric acid) were added to investigate the effects of organic acids on the stress response of Scirpus triqueter L. at two pyrene–lead concentrations. The activities of reactive oxygen species, malondialdehyde, plasma membrane H⁺-ATPase, and vacuolar H⁺-ATPase and PPase activity, as well as the activities of antioxidant enzymes (SOD, POD, and CAT) in Scirpus triqueter L. were determined. The addition of organic acids could effectively reduce the activities of reactive oxygen species, malondialdehyde, plasma membrane H⁺-ATPase, and vacuolar H⁺-ATPase and PPase activities. Under higher pollution, the damage of plant plasma membrane is more serious, but the addition of citric acid can alleviate this situation and even more effective than the relief under low pollution. The effect of citric acid was more significant than that of succinic acid and glutaric acid. These results demonstrated that organic acids could attenuate the stress of pyrene and lead to Scirpus triqueter L.

Cadmium and mercury are non-biodegradable toxic metals that may cause many detrimental effects to the thyroid gland and blood. Vitamin C has been found to be a significant chain-breaking antioxidant and enzyme co-factor against metal toxicity and thus make them less available for animals. The current study was performed to find the effect of individual metals (cadmium and mercury), their co-administration, and the ameliorative effects of vitamin C on some of the parameters that indicate oxidative stress and thyroid dysfunction. Cadmium chloride (1.5 mg/kg), mercuric chloride (1.2 mg/kg), and vitamin C (150 mg/kg of body weight) were orally administered to eight treatment groups of the rabbits (1. control; 2. Vit C; 3. CdCl₂; 4. HgCl₂; 5. Vit C + CdCl₂; 6. Vit C + HgCl₂; 7. CdCl₂ + HgCl₂, and 8. Vit C + CdCl₂ + HgCl₂). After the biometric measurements of all experimental rabbits, biochemical parameters viz. triidothyronine (T₃), thyroxine (T₄), thyroid-stimulating hormone (TSH), and triglycerides were measured using commercially available kits. The results exhibited significant decline (p < 0.05) in mean hemoglobin, corpuscular hemoglobin, packed cell volume, T₃ (0.4 ± 0.0 ng/ml), and T₄ (26.3 ± 1.6 ng/ml) concentration. While, TSH (0.23 ± 0.01 nmol/l) and triglyceride (4.42 ± 0.18 nmol/l) were significantly (p < 0.05) increased but chemo-treatment with Vit C reduces the effects of Cd, Hg, and their co-administration but not regained the values similar to those of controls. This indicates that Vit C had a shielding effect on the possible metal toxicity. The Cd and Hg also found to accumulate in vital organs when measured by atomic absorption spectrophotometer. The metal concentration trend was observed as follows: kidney > liver > heart > lungs. It was concluded that Cd and Hg are toxic and tended to bioaccumulate in different organs and their toxic action can be subdued by vitamin C in biological systems.

To effectively combat global warming, an enormous reduction in CO₂ emissions is required. Cameroon, which is currently the largest emitter of CO₂ in the CEMAC subregion, has committed to reducing its greenhouse gas emissions by 32% by 2035. However, previous studies in Cameroon have only addressed the relationship between economic growth, energy consumption, and CO₂ emissions without estimating all causal relationships at the same time. Moreover, no study has yet decomposed this country’s CO₂ emissions to date. To fill these research gaps and further assess the determinants of these CO₂ emissions, an extended Kaya identity and the Logarithm Mean Divisia Index (LMDI I) have been applied in this paper to identify, quantify, and explain the main drivers of Cameroon’s CO₂ emissions from 2007 to 2014. Seven effects were measured and the main findings show that carbon intensity and the emission factor increased by 0.57% and 107.50% respectively. Regarding contributions to the increase of CO₂ emissions, the population effect was the most positive followed by the activity effect, whereas the energy intensity, the substitution of fossil fuels and the penetration of renewable energies have contributed to reduce the CO₂ emission. To enable Cameroon to not only achieve the goals of its vision but also develop a low-carbon economy, this paper provides some proposed avenues that should be considered by policymakers.

In this study, the cellulose nanocrystals (CNC) obtained by acid hydrolysis of microcrystalline cellulose (MCC) are customized by suspension to obtain a spherical CNC hydrogel. The N-(2-aminoethyl) (3-amino-propyl) methyldimethoxyansile (AEAPMDS) preparation was grafted to spherical CNC hydrogel using a water phase heat treatment. Finally, aerogel samples were obtained by tert-butanol replacement and freeze-drying. The test results confirmed that the aminosilane was grafted on CNC. Electron micrographs and N₂ sorption isotherms showed that the pores of the aerogel were partially blocked due to the introduction of AEAPMDS, and the specific surface area was decreased. Due to the presence of chemisorption, the amount of CO₂ adsorbed at a pressure of 3 bar by the modified aerogel (2.63 mmol/g) was greatly improved compared with the unmodified aerogel (0.26 mmol/g), and the adsorption results were fit well by the Langmuir model. Thus, our experiments provided the opportunity to develop a new CO₂ absorbent material.

The present study aims to assess the impact of a gold mine located in the southeastern part of Burkina Faso on local soil quality. This information is needed in order to determine any health hazards and potential remediation strategies as the mining site is expected to be turned over to the local community after the closure of the mine. For the purpose, total minor and trace elements analysis as well as a sequential extraction were performed and results were interpreted using different methodologies: enrichment factor (EF), geoaccumulation index (Igeo) computed using two separate background samples, and comparison to selected national standard. The soil analysis revealed a moderate to significant soil EF and Igeo with hotspots located closer to the ore processing plant and on the east side of the site, with a maximum arsenic concentration of 286.55 ± 12.50 mg/kg. Sequential extraction revealed, however, that less than 2% of the arsenic is found in the exchangeable part. Cobalt and zinc are more distributed in the different fractions than arsenic. Geogenic and anthropogenic contributions were revealed by the study. Graphical Abstract .

Water encountering biomass can affect the change in its chemical composition and properties through the leaching process. In the leaching process, leachates are formed, and their composition depends on the type of biomass and the time of exposure to the solvent (water). The aim of the study was to analyze the influence of time of contact of water with biomass on changing the chemical composition of the leachates formed during long-term (counted in days) leaching of pine bark (Pinus sylvestris). Long-term leaching contributes to a loss of organic and inorganic compounds, and in this study, an intensive extraction of biomass components was noted from the first day of leaching. Along with the extension of the leaching time, values for electrical conductivity, concentration of mineral fraction (ashes), concentration of volatile matter, and concentration of total organic carbon significantly increased in the leachates. However, no linear relationship between the extension of the leaching time and the increase in the concentration of chlorides, sulfates, nitrogen, phosphorus, and other elements in the leachates was observed. This study will allow to better understand the impact of vegetation communities on the aquatic and terrestrial ecosystems, as well as help to provide adequate conditions of storage of biomass for technological purposes. Graphical Abstract

Fecal indicator bacteria (FIB) inhabiting stream sediments have become a concern with regard to recreational and irrigation water quality. Sediments contain higher concentrations of E. coli and other FIB than the overlying water column. The objective of this work was to evaluate the effect of temperature oscillations on the populations of both E. coli and enterococci in sediments and the water column. The study was conducted in a microcosm system with flow-through chambers representing a small stream with two different sediment textures. Bovine manure was freshly collected and mixed with both clayey and sandy sediment. Temperatures within the chambers oscillated from 17° to 28 °C which is representative of a diurnal summer temperature range for Maryland; the control chambers were kept at 22 °C. The effect of temperature oscillations differed depending on the sediment texture. Bacterial populations in the sandy sediment immediately increased before net die-off began. Conversely, in the chambers with the clayey sediments, there was no immediate increase in concentrations in the oscillation chambers as compared to the controls. There were significantly higher populations of both E. coli and enterococci within the oscillation sandy texture chambers compared to the control constant temperature chambers; that was not the case in the clayey sediment chambers. The die-off rates in the sandy sediments were greater than those in the clayey sediments; in the latter, bacteria populations remained almost constant throughout the experiment. Temperature oscillations should be simulated in experiments designed to estimate and compare inactivation rates for fecal indicator bacteria in sediments for future inferences on microbial water quality.

Arsenic (As) is a well-known highly toxic and carcinogenic element. A combination of electrodialytic remediation (EDR) after soil washing with flocculant addition targeting remediation of a soil polluted with As from wood preservation industry is the focus of this paper. The fine fraction (< 0.063 mm) from the washed soil after dry sieving was also considered. The EDR experiments were carried out in a 2-compartment cell applying 0.01 mA/cm² during 14, 7 and 3 days. The suspended soil slurry was placed in cathode compartment separated by anion exchange membrane (AEM) of the anolyte where the pH was kept at 10. The soil was highly polluted with As, and the EDR was able to remove between 50 and 80% corresponding to 400–478 mg As/kg of soil. The major part of the As was removed within the first 3 days (63%), and approx. 10% more of As was released doubling the time of the experiment: 72% in 7 days and 80% in 14 days. The pre-treated soil showed higher As initial concentration, but did not show a clear advantage in terms of removal rate as the original soil (not washed or sieved) showed 80% of As removal comparing with 61% and 50% for washed and fine fraction, respectively (although the absolute removed concentration was similar). The sequential extraction results confirmed that As was bound into more mobile fractions in original soil, and the higher removal was mainly due to its larger exchangeable and reducible fractions compared to the oxidizable and residual fraction in pre-treated soil.