In this study, we analysed the impact of heavy metals and plant rhizodeposition on the structure of indigenous microbial communities in rhizosphere and bulk soil that had been exposed to heavy metals for more than 150 years. Samples of the rhizosphere of Silene vulgaris and non-rhizosphere soils 250 and 450 m from the source of emission that had different metal concentrations were collected for analyses. The results showed that soils were collected 250 m from the smelter had a higher number of Cd-resistant CFU compared with the samples that were collected from 450 m, but no significant differences were observed in the number of total and oligotrophic CFU or the equivalent cell numbers between rhizosphere and non-rhizosphere soils that were taken 250 and 450 m from the emitter. Unweighted pair group method with arithmetic mean (UPGMA) cluster analysis of the denaturing gradient gel electrophoresis (DGGE) profiles, as well as a cluster analysis that was generated on the phospholipid fatty acid (PLFA) profiles, showed that the bacterial community structure of rhizosphere soils depended more on the plant than on the distance and metal concentrations. The sequencing of the 16S rDNA fragments that were excised from the DGGE gel revealed representatives of the phyla Bacteroidetes, Acidobacteria, Gemmatimonadetes, Actinobacteria and Betaproteobacteria in the analysed soil with a predominance of the first three groups. The obtained results demonstrated that the presence of S. vulgaris did not affect the number of CFUs, except for those of Cd-resistant bacteria. However, the presence of S. vulgaris altered the soil bacterial community structure, regardless of the sampling site, which supported the thesis that plants have a higher impact on soil microbial community than metal contamination.

The time-dependent uptake of metal ions (Al, Cr, Fe, Zn, Sr, and Ba) by cyanobacterium Arthrospira platensis from the complex industrial effluents of an engineering company (electroplating units of the Tactical Missiles Corporation, Dubna, Russia) was investigated. The preference of spirulina biomass for metal ions was observed as follows: Ba >Fe > Sr > Al > Zn > Cr. According to neutron activation analysis data, the degree of metal retention increased rapidly in the first 5–15 min of the reaction but remained the same or slightly decreased after this period. The efficiency of metal removal varied from 37% for chromium to 100% for barium. The thermodynamic analysis of wastewater chemical composition was performed in order to determine the speciation of heavy metals. Ion exchange, precipitation, and metal ion interaction with functional groups of the cyanobacteria cell wall were defined as the main mechanisms of metal ion removal.

Nano zero valent iron (nZVI) is an excellent adsorbent/reductant with wide applicability in remediation of persistent contaminants in soil, water and groundwater aquifers. There are concerns about its environmental fate, agglomeration, toxicity and stability in the air. Several modification methods have applied chistosan, green tea, carboxyl methyl cellulose and other coating substances to ensure production of nZVI with excellent air stability and effectiveness. The synthesis of a novel green nZVI (gNZVI) with Harpephyllum caffrum leaf extracts was successfully executed in the current study. Production of gNZVI involved the simultaneous addition of an optimum amount of the NaBH₄ and H. caffrum extract to FeCl₃ in an inert environment (Nitrogen). The solution was stirred for 30 min, washed with dilute ethanol (50%) and freeze dried. This procedure offered the best option for the synthesis of gNZVI in terms of nontoxic and inexpensive choice of stabiliser/reductant. Systematic characterisations using TGA, TEM, SEM, XRD, FT-IR and XPS confirmed the synthesis of crystalline, stable, reactive, well-dispersed and predominantly 50 nm diameter sized gNZVI compared to the conventionally synthesised nZVI which is 65 nm. The activity testing using Orange II sodium salt (OR2) confirmed the effectiveness of the synthesised gNZVI as an excellent Fenton catalyst with 65% degradation of 20 ppm OR2 dye in 1 h reaction time.

The goal of this study is to introduce an adaptation of the Eulerian-Lagrangian localized adjoint method (ELLAM) for the simulation of mass transport in fractured porous media, and to evaluate the performance of ELLAM in such a case. The fractures are represented explicitly using the discrete fracture model. The velocity field was calculated using the mixed hybrid finite element method. A sound ELLAM implementation is developed to address numerical artifacts (spurious oscillations and numerical dispersion) arising from the presence of fractures. The efficiency of the developed ELLAM implementation was further improved by taking advantage of the parallel computing on shared memory architecture for the tasks related to particles tracking and linear system resolving. The performance of ELLAM was tested by comparing its results with the Eulerian discontinuous Galerkin method based on several benchmark problems dealing with different fracture configurations. The results highlight the robustness and accuracy of ELLAM, as it allows the use of large time steps, and overcomes the Courant-Friedrichs-Lewy (CFL) restriction. The outcome also shows that ELLAM is more efficient when fracture density is increased.

In this study, the Load ESTimator (LOADEST) and eight-parameter regression models were evaluated to estimate instantaneous pollutant loads under various criteria and optimization methods. As shown in the results, LOADEST, commonly used in interpolating pollutant loads, could not necessarily provide the best results with the automatically selected regression model. The various regression models in LOADEST need to be considered to find the best solution based on the characteristics of watersheds. The recently developed eight-parameter model integrated with a genetic algorithm (GA) and the gradient descent method (GDM) was also compared with LOADEST, indicating that the eight-parameter model performed better than LOADEST; however, depending on whether the eight-parameter model was used for calibration or validation, its performance varied. The eight-parameter model with GDM could reproduce the nitrogen loads properly outside the calibration period (validation). Furthermore, the accuracy and precision of model estimations were evaluated using various criteria (e.g., R², gradient, and constant of a linear regression line). The results showed higher precisions with the R² values close to 1.0 in LOADEST and better accuracy with the constants (in linear regression line) close to 0.0 in the eight-parameter model with GDM. Hence, on the basis of these findings, we recommend that users need to evaluate the regression models under various criteria and calibration methods to ensure more accurate and precise results for nitrogen load estimations.

Microcystins (MCs) are endotoxins produced by cyanobacteria in freshwaters globally. With known potential for human health risks, rapid and effective treatment methods are needed for MCs. Previous studies have shown photocatalysis can achieve rapid half-lives with UV lamps and slurries of TiO₂. In this experiment, rates and extents of solar photocatalysis of MCs were measured using bench-scale reactors with fixed films of TiO₂ for solutions with a range of cellular:aqueous MC ratios. Since cellular MCs can be removed physically, photocatalysis rates were measured following sand filtration to discern the extent of MC removal post-filtration. Since UV energy drives photocatalysis using TiO₂, rates of removal were calculated as a function of cumulative UV insolation and time. For water containing < 10% aqueous MC, filtration removed 90% of total MC, and the subsequent photocatalysis half-life was 0.37 MJ/m² (or 111 min). For water with ~ 50% aqueous MCs, filtration removed 52% of the total MCs, and the average half-life for photocatalysis was 0.38 MJ/m² (or 138 min). For the > 90% aqueous MC treatment, filtration removed 0% MCs, and the photocatalysis half-life for MCs was 0.37 MJ/m² (or 135 min). Previous studies have used clarified waters; however, results from this study are likely representative of scenarios with waters containing confounding water characteristics and use of solar light for UV, as anticipated in developing countries with less advanced water treatment methods. Photocatalysis is a rapid and effective process for decreasing concentrations of MCs and could be useful for mitigating risks from MC exposures in drinking water.

Regional serious contamination of polychlorinated biphenyls (PCBs) is threatening the local residents and ecosystem. PCBs are often very stable, but the extractable portion which is mainly responsible for their risk in sediment might be decreasing due to biodegradation and formation of non-extractable residues. In the present study, the natural reduction of extractable PCBs in regional contaminated sediments during a period of 5 years was investigated. Besides, influences of sediment organic matter on the reduction of extractable PCBs and the toxicity were studied by incubating sediments spiked with PCBs and humic acid for 5 years. The loss percentage of extractable PCBs reached 40.3%, 46.9%, 63.5%, and 70.1%, respectively in sediments at site B, C, D, and E of Nanguan River during 5 years. The sediment organic matter content was significantly correlated with the loss percentage of total PCBs (p < 0.05) and higher chlorinated PCBs (p < 0.01). In incubated sediments, significant reduction of extractable PCBs and toxicity was observed at the end of the fifth year (p < 0.05). Addition of humic acid promoted the reduction of extractable PCBs and toxicity in sediment. These results will help us to better understand the risk caused by PCBs in regional contaminated sediments over time and also provide us a possible method to enhance the reduction of extractable PCBs in contaminated sediments.

China is one of three global hotspots for nitrogen (N) deposition, which has concerned scientists and the public. While previous studies on N deposition in China have focused on its composition, spatial pattern, and interannual dynamics, its monthly dynamics in different regions remain unclear, hindering our ability to evaluate its ecological effects. Therefore, we obtained monthly wet N deposition data from196 sites after continuous network observations and published data in China and analyzed the monthly dynamics of NH₄⁺–N, NO₃⁻–N, and dissolved inorganic N (DIN=NH₄⁺−N+NO₃⁻–N) deposition fluxes on site, regional, and national scales. We observed that the deposition fluxes of NH₄⁺–N, NO₃⁻–N, and DIN in China showed clear monthly patterns and regional differences. In Northern China, wet N deposition predominantly showed a unimodal trend, whereas in Southern China, it revealed a bimodal trend or irregular fluctuations. During 2000–2016, NH₄⁺–N, NO₃⁻–N, and DIN deposition fluxes were estimated as 9.09, 6.12, and 15.21 kg N ha⁻¹ year.⁻¹, respectively. Our findings enhance our understanding of atmospheric wet N deposition, and can serve as a reference for N deposition simulation experiments in different regions, and for generating long-term N deposition data for model optimization. Regional differences in the monthly dynamics of wet N deposition should be emphasized to accurately evaluate its ecological effects on terrestrial ecosystems in different regions.

Sustainable agriculture ensures food security and prevents starvation. However, the need to meet the increasing food demands of the growing population has led to poor and unsustainable agricultural practices, which promote environmental degradation. Given the contributions of agricultural ecosystems to environmental pollution, we investigated the impact of the agricultural ecosystem on environmental pollution in China using time series data from 1960 to 2014. We employed several methods for econometric analysis including the unit root test, Johansen test of cointegration, Granger causality test, and vector error correction model. Evidence based on the long-run elasticity indicates that a 1% increase in the emissions of carbon dioxide (CO₂) equivalent to nitrous oxide from synthetic fertilizers will increase the emissions of CO₂ by 1.52% in the long run. Similarly, a 1% increase in the area of harvested rice paddy, cereal production, biomass of burned crop residues, and agricultural GDP will increase the carbon dioxide emissions by 0.85, 0.63, 0.37, and 0.22%, respectively. The estimated results indicate that there are long-term equilibrium relationships among the selected variables considered for the agricultural ecosystem and carbon dioxide emissions. In particular, we identified bidirectional causal associations between CO₂ emissions, biomass of burned crop residues, and cereal production. Graphical abstract ᅟ

This work investigates the degradation of Reactive Gray BF-2R dye (a blend of reactive yellow 145, reactive orange 122 and reactive black 5 dyes) using UV/H₂O₂, Fenton, and photo-Fenton-advanced oxidative processes, with artificial sunlight and UV-C radiations. The photo-Fenton process employing UV-C radiation was the most efficient under the conditions studied. The ideal conditions for the degradation of the dye, determined using a factorial design 2³ and a study of the concentration of hydrogen peroxide ([H₂O₂]), were [H₂O₂] equal to 40 mg L⁻¹, iron concentration [Fe] of 1 mg L⁻¹, and pH between 3 and 4. The Chan and Chu non-linear kinetic model predicted the kinetic data with a degradation of over 98% for color and 68% for aromatics after 60 min. The behavior of the chemical oxygen demand fitted the first-order kinetic model well, with a degradation of 64% after 60 min. The Multilayer Perceptron 7-11-2 artificial neural network model enabled to model the degradation process of the aromatics and accurately predict the experimental data. Toxicity tests indicated that the post-treatment samples were non-toxic for Escherichia coli bacteria, and Portulaca grandiflora and Basil sabory seeds. However, they inhibited the growth of Lactuca sativa seeds and Salmonella enteritidis bacteria. The photo-Fenton process with UV-C radiation degraded the dye studied efficiently and the degradation percentages were, on average, 7% and 5% higher for color than those observed when employing the Fenton and UV/H₂O₂ processes, respectively. With the aromatic, however, they were 84% and 62% higher, thus justifying the use of this process.