Sudan dyes are widely used as coloring agents in various solvents, waxes, and polishes. However, the dyes are environmental contaminants and Sudan I is a weak carcinogen, and its removal from wastewater remains challenging. Here, we developed a new strategy for Sudan dye degradation for use in the non-alkaline conditions typically found in wastewater. By combing glucose oxidase (GOD) and horseradish peroxidase (HRP), we avoided the hydrogen peroxide-induced HRP damage and inactivation. Moreover, the GOD-HRP-coupled degradation of Sudan dyes were enhanced by the addition of different kinds of phenols. Systematic investigations were carried out to determine the optimal process parameters (i.e., phenol concentration, pH value, temperature, and enzyme dose) for degrading Sudan I with GOD and HRP. Also, this strategy could be applied to degradation of Sudan II and Sudan III. We were also able to co-express GOD and HRP in a prokaryotic-like polycistronic expression system in Pichia pastoris, based on the internal ribosome entry sites (IRES). Therefore, this fermented liquid containing GOD and HRP might be used in the future to degrade pollutants in weakly acidic conditions.

Spatially variable areas, or hotspots, of elevated mercury (Hg) concentrations in soil, water, and wildlife occur throughout the Everglades wetland ecosystem. This study investigates the stoichiometric controls of Hg relative to soil, water, and biotic components. Surface water, porewater, soil, periphyton, and Gambusia spp. (mosquitofish) were collected from hotspots and non-spot stations and analyzed for various parameters, including total mercury (THg), organic carbon (OC), total carbon (TC), total phosphorus (TP), and total nitrogen (TN) between late 2010 and early 2013. Soil nutrient ratios were significantly different between hotspot and non-hotspot stations, indicating a difference in trophic status and position along the decay continuum or differences in limiting nutrients. Overall, soil total Hg concentrations were negatively correlated with soil TC/TN, while soil TC/TP and soil TN/TP molar ratios and soil THg were negatively correlated at hotspot stations. Meanwhile, mosquitofish THg was negatively correlated with soil TC/TN molar ratio and positively correlated with soil TC/TP and TN/TP molar ratios, suggesting trophic truncation. Soil, surface water, and porewater THg, TC, and OC interactions resulted in significant differences between hotspot and non-hotspot stations and between molar ratios of C, N, and P. Periphyton-surface water THg/OC homeostasis and soil nutrient ratios significantly explained mosquitofish THg concentrations, further indicating a trophic influence on mosquitofish THg and potential hotspot dynamics. Several factors and processes including bottom-up trophic interaction and vegetation influence on Hg accumulation dynamics and food-chain length explain the development and persistence of Hg hotspot formation within the Everglades system.

Biodegradable polymer poly(3-hydroxybutyrate) (P3HB) has been used as a matrix to construct slow-release formulations of the fungicide tebuconazole (TEB). P3HB/TEB systems constructed as films and pellets have been studied using differential scanning calorimetry, X-ray structure analysis, and Fourier transform infrared spectroscopy. TEB release from the experimental formulations has been studied in aqueous and soil laboratory systems. In the soil with known composition of microbial community, polymer was degraded, and TEB release after 35 days reached 60 and 36 % from films and pellets, respectively. That was 1.23 and 1.8 times more than the amount released to the water after 60 days in a sterile aqueous system. Incubation of P3HB/TEB films and pellets in the soil stimulated development of P3HB-degrading microorganisms of the genera Pseudomonas, Stenotrophomonas, Variovorax, and Streptomyces. Experiments with phytopathogenic fungi F. moniliforme and F. solani showed that the experimental P3HB/TEB formulations had antifungal activity comparable with that of free TEB.

Emissions of nitrous oxide (N₂O) from wetland ecosystems are globally significant and have recently received increased attention. However, relatively few direct studies of these emissions in response to water depth-related changes in sediment ecosystems have been conducted, despite the likely role they play as hotspots of N₂O production. We investigated depth-related differential responses of the dissolved inorganic nitrogen distribution in Phragmites australis (Cav.) Trin. ex Steud. rhizosphere versus non-rhizosphere sediments to determine if they accelerated N₂O emissions and the release of inorganic nitrogen. Changes in static water depth and P. australis growth both had the potential to disrupt the distribution of porewater dissolved NH₄⁺, NO₃⁻, and NO₂⁻ in profiles, and NO₃⁻ had strong surface aggregation tendency and decreased significantly with depth. Conversely, the highest NO₂⁻ contents were observed in deep water and the lowest in shallow water in the P. australis rhizosphere. When compared with NO₃⁻, NH₄⁺, and NO₂⁻, fluxes from the rhizosphere were more sensitive to the effects of water depth, and both fluxes increased significantly at a depth of more than 1 m. Similarly, N₂O emissions were obviously accelerated with increasing depth, although those from the rhizosphere were more readily controlled by P. australis. Pearson’s correlation analysis showed that water depth was significantly related to N₂O emission and NO₂⁻ fluxes, and N₂O emissions were also strongly dependent on NO₂⁻ fluxes (r = 0.491, p < 0.05). The results presented herein provide new insights into inorganic nitrogen biogeochemical cycles in freshwater sediment ecosystems.

In recent years, high concentrations of hexavalent chromium, Cr(VI), have been observed in the groundwater system of the Asopos River Basin, raising public concern regarding the quality of drinking and irrigation water. The work described herein focuses on the development of a groundwater flow and Cr(VI) transport model using hydrologic, geologic, and water quality data collected from various sources. An important dataset for this goal comprised an extensive time series of Cr(VI) concentrations at various locations that provided an indication of areas of high concentration and also served as model calibration locations. Two main sources of Cr(VI) contamination were considered in the area: anthropogenic contamination originating from Cr-rich industrial wastes buried or injected into the aquifer and geogenic contamination from the leaching process of ophiolitic rocks. The aquifer’s response under climatic change scenario A2 was also investigated for the next two decades. Under this scenario, it is expected that rainfall, and thus infiltration, will decrease by 7.7 % during the winter and 15 % during the summer periods. The results for two sub-scenarios (linear and variable precipitation reduction) that were implemented based on A2 show that the impact on the study aquifer is moderate, resulting in a mean level decrease less than 1 m in both cases. The drier climatic conditions resulted in higher Cr(VI) concentrations, especially around the industrial areas.

Using ZnO nanoparticles, comparisons between sorption and sono-sorption efficiencies, equilibrium and kinetics in Direct Red 23 have been researched under the various experimental conditions. Pseudo-second-order model was practiced for the experimental data. The mechanism of the dye uptake was clarified based on the analyses of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Brunauer-Emmett-Teller (BET) surface area and total pore volume of the nanoparticles were obtained. The highest Direct Red 23 (DR23) removal efficiencies by sorption and sono-sorption processes were determined as 78.6 and 96.8 %, respectively. Experimental data have been evaluated according to Langmuir, Freundlich and Dubinin-Radushkevich. The mean energies of sorption and sono-sorption processes were calculated to be 16.22 and 25.41 kJ/mol, respectively. Arrhenius equation was used to calculate the activation energies. ΔH° and ΔG° values indicated that sorption and sono-sorption processes were endothermic processes. But, negative free energy values of ΔG° indicated that sorption and sono-sorption processes were favoured at high temperatures.

Brazil is an important country within the global mineral industry. The main reserves of phosphate rock in Brazil are contained in the states of Goiás and Minas Gerais, at the Catalão and Tapira cities, respectively. Atmospheric inputs due to the mining of phosphate rock may have various effects on human health in areas near these types of mines. Thus, this work evaluated the influence of phosphate mining on the chemical composition and annual atmospheric deposition in Catalão (GO) and Tapira (MG), Brazil. The pH of rainwater was 6.90 in Catalão and 6.80 in Tapira. The ionic concentrations (in μeq/L) at both study sites decreased in the following order: Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ for cations and HCO₃ ⁻ > NO₃ ⁻ > SO₄ ²⁻ > PO₄ ³⁻ > F⁻ > Cl⁻ for anions. High Ca²⁺ content indicates that Ca²⁺ contributes to the neutralisation of the rainwater pH in both of the areas studied. The annual atmospheric deposition of NO₃ ⁻ and SO₄ ²⁻ can be attributed to the use of diesel-powered trucks in and around mining areas. Soil dust derived is responsible for the annual atmospheric deposition of Na⁺ and K⁺. Phosphate mining activities are the main source of the annual atmospheric deposition of PO₄ ³⁻ and F⁻.

A granular hydrogel of chitosan-g-poly(vinylimidazole-co-2-acrylamido-2-methyl propane sulfonic acid) was successfully synthesized by one-step free radical polymerization based on the grafting backbone of chitosan and the monomers of vinylimidazole and 2-acrylamido-2-methyl propane sulfonic acid. The resulting hydrogel could be used as the adsorbent for the efficient and selective removal of Hg²⁺ ions from the aqueous solution. The adsorption results could be well described by the pseudo-second-order kinetic mode and the Langmuir isotherm model with a maximum adsorption capacity of 363.55 mg/g for Hg²⁺. Furthermore, the as-prepared granular hydrogel exhibited an excellent cycling stability for the adsorption of Hg²⁺ after multiple repeated adsorption-desorption process. It suggested that the obtained granular hydrogel has potential application for Hg²⁺ removal and recovery from wastewater. Graphical Abstract A kind of granular hydrogel with excellent selectivity adsorption of Hg2+ ions was successfully synthesized by grafting polymerization of VIM and AMPS onto the CTS backbone via a facile free radical polymerization.

In this study, a novel water-insoluble zinc–Schiff base complex, Zn(II)-N-salicylaldehyde-2-hydroxyanil (abbreviated as Zn-salen), was synthesized and used as a heterogeneous photocatalyst for the activation of molecular oxygen to degrade organic pollutants in aqueous solution under visible light irradiation (λ ≥ 420 nm). The catalyst was characterized by FT-IR, UV–vis spectroscopy, NMR, and MS analysis. Zn-salen displays a selective adsorption and degradation of electropositive organics, such as rhodamine B (RhB), methylene blue (MB), and o-phenylenediamine (OPD). After using cetyl trimethyl ammonium bromide (CTAB) to change sulforhodamine B (SRB) into RhB-like electropositive molecule, the degradation of SRB increased up to 96 % after 4 h of irradiation, indicating that the selectivity arises from the charge interaction between the catalyst and substrates. Zeta potential of Zn-salen also reveals that the catalyst surface is negatively charged in neutral solution, suggesting that the catalyst is selective towards positively charged substrates due to an electrostatic force of attraction. The photocatalyst was active within a wide pH range (pH 3–11) and chemically stable and can be reused over 10 times. In addition, ¹O₂ and O₂·⁻ were involved in photocatalytic degradation but O₂·⁻ appears to be the primary reactive oxygen species.

Using an indoor microcosm assay, we analyzed the biodegradation of total petroleum hydrocarbons (TPHs) by autochthonous bacterial populations in mining soil in the presence of a surfactant (Tween 80). The kinetic behavior of TPH biodegradation involved fast and slow stages. Initially, heterotrophic and hydrocarbonoclastic bacteria increased in abundance by an order of magnitude, but both groups decreased to close to their initial population sizes by the end of experiment. The most efficient final biodegradation (61.5 %) was achieved using soil with 0.5 % added surfactant. Polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) were used to analyze changes in the bacterial community structure. During the fast biodegradation phase, bacterial species richness as indicated by DGGE profiles was reduced after long periods of TPH biodegradation with exposure to Tween 80. The distribution of families was modified, but no particular pattern could be identified. The main bacterial genera were Acinetobacter, Pedomicrobium, Halomonas, Rhizobium, Cryobacterium, Pseudomonas, Lysobacter, Thermomonas, and Stenotrophomonas. Acinetobacter exhibited the highest species richness and was the most abundant and persistent genus, followed by Pedomicrobium and Rhizobium. Decreasing TPH biodegradation can be attributed to a reduction in the microbial population and the disappearance of most of the initial bacterial genera. The correlation between TPH biodegradation and microbial population dynamics helps explain long bioremediation times and can facilitate actions for increasing bioremediation efficiency.