We examined the root production of a set of Fagus crenata (Siebold’s beech) saplings grown in an infertile immature volcanic ash soil (VA) and another set in a fertile brown forest soil (BF) with both sets exposed to elevated CO₂. After the saplings had been exposed to ambient (370–390 μmol mol⁻¹) or elevated (500 μmol mol⁻¹) CO₂, during the daytime, for 11 growing seasons, the root systems were excavated. Elevated CO₂ boosted the total root production of saplings grown in VA and abolished the negative effect of VA under ambient CO₂, but there was no significant effect of elevated CO₂ on saplings grown in BF. These results indicate the projected elevated CO₂ concentrations may have a different impact in regions with different soil fertility while in regions with VA, a higher net primary production is expected. In addition, we observed large elevated CO₂-induced fine-root production and extensive foraging strategy of saplings in both soils, a phenomenon that may partly (a) adjust the biogeochemical cycles of ecosystems, (b) form their response to global change, and (c) increase the size and/or biodiversity of soil fauna. We recommend that future researches consider testing a soil with a higher degree of infertility than the one we tested.

The capacities of a biosurfactant producing and polycyclic aromatic hydrocarbon (PAH) utilizing bacterium, namely, strain 1C, isolated from an Algerian contaminated soil, were investigated. Strain 1C belonged to the Paenibacillus genus and was closely related to the specie Paenibacillus popilliae, with 16S rRNA gene sequence similarity of 98.4 %. It was able to produce biosurfactant using olive oil as substrate. The biosurfactant production was shown by surface tension (32.6 mN/m) after 24 h of incubation at 45 °C and 150 rpm. The biosurfactant(s) retained its properties during exposure to elevated temperatures (70 °C), relatively high salinity (20 % NaCl), and a wide range of pH values (2–10). The infrared spectroscopy (FTIR) revealed that its chemical structure belonged to lipopeptide class. The critical micelle concentration (CMC) of this biosurfactant was about 0.5 g/l with 29.4 mN/m. In addition, the surface active compound(s) produced by strain 1C enhanced PAH solubility and showed a significant antimicrobial activity against pathogens. In addition to its biosurfactant production, strain 1C was shown to be able to utilize PAHs as the sole carbon and energy sources. Strain 1C as hydrocarbonoclastic bacteria and its interesting surface active agent may be used for cleaning the environments polluted with polyaromatic hydrocarbons.

Selenium is an essential trace element for many organisms, including humans, but it is bioaccumulative and toxic at higher than homeostatic levels. Both selenium deficiency and toxicity are problems around the world. Mines, coal-fired power plants, oil refineries, and agriculture are important examples of anthropogenic sources, generating contaminated waters, and wastewaters. For reasons of human health and ecotoxicity, selenium concentration has to be controlled in drinking-water and in wastewater, as it is a potential pollutant of water bodies. In this regard, in the present study, the ability of sunflower (Helianthus annuus L.) to tolerate and accumulate selenium was assessed in hydroponic culture as a model of rhizofiltration system. Selenium content and the chlorophyll parameters of sunflower plant treated using different concentrations of selenium in two forms of sodium selenite and sodium selenate were measured to clarify (1) the response of sunflower to selenium tolerance capacity and (2) the relationship between selenium, chlorophyll fluorescence parameters, and photosynthetic pigments contents. The results showed that selenium content in sunflower plants significantly increased by increasing added selenium levels. Furthermore, Chl a and b were not impaired after 3 weeks from selenium exposure up to 3 mg L⁻¹ for both selenite and selenate. Moreover, sunflower plants have a high selenium tolerance capacity for hydroponic clean-up. Translocation of selenate from sunflower roots to shoots was easier comparing with selenite in concept of phytoremediation processes.

A new combined difenoconazole and fluxapyroxad fungicide formulation, as an 11.7 % suspension concentrate (SC), has been introduced as part of a resistance management strategy. The dissipation of difenoconazole and fluxapyroxad applied to apples and the residues remaining in the apples were determined. The 11.7 % SC was sprayed onto apple trees and soil in Beijing, Shandong, and Anhui provinces, China, at an application rate of 118 g a.i. ha⁻¹, then the dissipation of difenoconazole and fluxapyroxad was monitored. The residual difenoconazole and fluxapyroxad concentrations were determined by ultrahigh-performance liquid chromatography tandem mass spectrometry. The difenoconazole half-lives in apples and soil were 6.2–9.5 and 21.0–27.7 days, respectively. The fluxapyroxad half-lives in apples and soil were 9.4–12.6 and 10.3–36.5 days, respectively. Difenoconazole and fluxapyroxad residues in apples and soil after the 11.7 % SC had been sprayed twice and three times, with 10 days between applications, at 78 and 118 g a.i. ha⁻¹ were measured. Representative apple and soil samples were collected after the last treatment, at preharvest intervals of 14, 21, and 28 days. The difenoconazole residue concentrations in apples and soil were 0.002–0.052 and 0.002–0.298 mg kg⁻¹, respectively. The fluxapyroxad residue concentrations in apples and soil were 0.002–0.093 and 0.008–1.219 mg kg⁻¹, respectively. The difenoconazole and fluxapyroxad residue concentrations in apples were lower than the maximum residue limits (0.5 and 0.8 mg kg⁻¹, respectively). An application rate of 78 g a.i. ha⁻¹ is therefore recommended to ensure that treated apples can be considered safe for humans to consume.

This study evaluated the seed germination and dry mass accumulation of five plant species (Brassica napus L., Brassica rapa L., Celosia cristata L., Tagetes erecta L., and Calendula officinalis L.) grown in five mine tailings collected from Zacatecas, Mexico. Sampled mines were El Bote, Noria de San Pantaleon, Noria de Angeles, Vetagrande, and El Bordo-El Lampotal, in which Pb (3.9–69.7 mg kg⁻¹), As (0.7–26.2 mg kg⁻¹), Hg (0.05–0.10 mg kg⁻¹), and Au (0.01–0.02 mg kg⁻¹) were detected. The most abundant elements at each mine site were as follows: Pb and Au (3.9 and 0.023 mg kg⁻¹, respectively) for El Bote; As, Pb, and Hg (7.4, 6.1, and 0.10 mg kg⁻¹, respectively) for the Noria de San Pantaleon; Pb, As, and Hg (69.7, 26.2, and 0.08 mg kg⁻¹, respectively) for Noria de Angeles; Pb (20.8 mg kg⁻¹) for Vetagrande; and Pb (5.3 mg kg⁻¹) for El Bordo-El Lampotal. Both Noria de Angeles and Vetagrande mine tailings had high values of sodium, sulfates, and electrical conductivity, chemical properties that impaired seed germination and dry mass accumulation. Regardless the mining tailings, B. napus showed high seed germination (66 %), tolerance, growth, and total dry mass accumulation (0.041 g). Either B. napus or C. cristata has good potential for stabilizing or recovering metals from mine tailings.

A shortage in available water resources for rice production makes the evaluation of rice yield and greenhouse gas emission in response to drought caused by water scarcity vital. Here, we examined three forms of irrigation management (normal amount [NA], 70 % of NA [NA 70 %], and 30 % of NA [NA30%]) and two rice varieties (Oryza sativa L. cv. Hanyou 8 and Oryza sativa L. cv. Huayou 14) to determine their effects on CH₄ emission and rice yield in two rice growing seasons. Hanyou 8 is a variety of water-saving and drought-resistance rice (WDR), while Huayou 14 is a common rice variety with no known adaptation to drought conditions. NA 70 % reduced CH₄ emission by 30.3–53.3 %, and NA 30 % further depressed CH₄ emission by 51.0–76.7 % relative to NA in both seasons. However, NA 70 % and NA 30 % significantly decreased rice yield by 6.3 % (P < 0.05) and 10.1 % (P < 0.01), respectively, for Huayou 14 when compared with NA in the relatively dry season. Conversely, no differences in rice yield among different irrigation managements were observed for Hanyou 8 in both seasons, suggesting that Hanyou 8 is more drought-resistant than Huayou 14 in terms of rice yield. The results suggest that, to meet the water scarcity, the use of rice varieties with water-saving and drought-resistant traits may minimize rice yield loss and mitigate CH₄ emission in the rice-cultivated regions of the world.

Environmental pollution by pentachlorophenol (PCP) is a critical concern worldwide, and microbial bioremediation could constitute an ecologically friendly solution. The main objectives of this study were at first to clarify the factors, affecting the ability and efficiency of PCP biodegradation by the bacterium isolate P6, and secondly to optimize the condition of using P6 for PCP bioremediation. The PCP mineralizing bacterium was isolated from the contaminated forest soil of Tunisia, and it was identified as Citrobacter freundii (C. freundii), by using conventional and molecular characteristics. The HPLC and spectroscopic analysis were used to investigate the PCP degradation and the biomass formation by this isolate P6. The main results showed that P6 was able to degrade or to transform more than 98 % of 640 mg/l PCP afterwards 168 h in mineral salt medium (MSM). As well, the optimal aerobic growth conditions of P6 in MSM include essentially the range of pH (4 ≤ pH ≤ 9) and of temperature (25 °C < temperature < 30 °C). The addition of glucose as extra carbon sources has an effect to enhance the PCP biodegradation. On the other side, this isolate of C. freundii is capable to remove or transform around 95.33 % of PCP added in the sterilized soil suspension supplemented with PCP and adjusted to a final concentration of around 400 mg/l during 2 weeks of incubation at 25 °C. This last result argues in favor of the use of this strain P6 of C. freundii as a microbial tool of remediation of PCP-contaminated site.

Long-term irrigation with recycled water (RW) that contains high salt may pollute groundwater. The HYDRUS-1D model was texted against soil water content and electrical conductivity (ECe) observed in a summer maize and winter wheat rotational field irrigated with ground water (GW) and RW; then, the risk for polluting groundwater in two regions of Beijing was evaluated. The comparisons indicated that the simulated soil water content and ECe values were generally in agreement with the field observations, indicating the reliability of HYDRUS-1D in soils irrigated with GW and RW. The regional prediction results of the proposed simulation model indicated that the average soil ECe at the bottom of vadose zones ranged from 0.400 to 0.896 dS m⁻¹, and the values in the Tongzhou and Daxing Districts irrigated with RW were 1.40 and 1.09 times, respectively, higher than that irrigated with GW over the next 50 years. Five risk indicators represent salt transporting time and values were used. The results of the proposed evaluation model showed that the risk scores ranged from 3.04 to 9.32. In the Tongzhou and Daxing Districts, the risk scores of RW irrigation for polluting groundwater were 1.06 and 1.08 times, respectively, higher than that GW irrigation. The risk scores of GW or RW irrigation for polluting groundwater in the Tongzhou District were 1.75 or 1.72 times, respectively, higher than that in the Daxing District. Considering the small risk difference between GW and RW irrigations, RW can be used in both regions. Due to the different vadose zone structures, the Daxing District is more suitable for RW irrigation. The long-term use of RW for irrigation should consider the salt content of RW and vadose zone structure.

The competitive/simultaneous adsorption of arsenite (As(III)) and arsenate (As(V)) onto ferrihydrite is one of main processes controlling the distribution of arsenic under oxidizing conditions in the natural environment. Adsorption reactions of As(III) and As(V) with ferrihydrite were investigated by employing a combination of batch adsorption experiments and Fourier transform infrared (FTIR) spectroscopy measurements in single and binary systems, i.e., both As species were present at the same time. Isotherm studies showed that the adsorption of As(III) in the binary system was less than that in single system, indicating that As(V) hindered As(III) adsorption. The presence of As(III) had almost no impact on As(V) adsorption at pH 5 in the binary systems. Freundlich model described the equilibrium data well (R ² > 0.94), and the adsorption affinity onto ferrihydrite was in the following order: As(III)-single > As(III)-binary > As(V)-single > As(V)-binary. Kinetic data of As(III) and As(V) from single and binary systems were both well described by pseudo-second-order equation (R ² > 0.98). FTIR showed that after adsorbing of either As species, a new peak occurred at 826 cm⁻¹ due to the formation of Fe-O-As bonds, indicating that competition between As(III) and As(V) could take place on the surface sites as a result of the formation of a similar surface complexes.

In this study, the decolorization of a dye solution via bio-Fenton process with in situ generation of H₂O₂ by enzymatic catalyzed oxidation of glucose was investigated. For this purpose, magnetite was synthesized and was used as the support for glucose oxidase immobilization. The particle size of the magnetite was estimated to be around 42 nm according to the obtained scanning electron microscope images. The magnetite crystal size was obtained approximately 26 nm by X-ray diffraction spectrum. Effective variables on immobilization were investigated. The best immobilization conditions were achieved at pH 6, temperature of 10 °C, glucose oxidase/support ratio of 1800 U/g, and time of 2.5 h. In these conditions, 450 U of glucose oxidase was immobilized per grams of magnetite. The immobilized glucose oxidase was used for the decolorization of acid yellow 12 in batch experiments. Decolorization conditions were optimized by response surface methodology. Four parameters including pH, temperature, glucose, and Fe²⁺ concentrations in five levels were investigated. The optimum conditions were obtained as follows: pH = 4.5, T = 29 °C, initial glucose concentration of 1.5 g/L, and Fe⁺² concentration of 1.4 g/L. Decolorization efficiency after 120 min at optimal conditions in the presence of 0.3 g immobilized enzyme (450 U/g) in 100 cm³ solution was observed to be equal to 62.27 %.