Metalaxyl, an important phenylamide fungicide, is widely used for controlling fungal diseases caused by pathogens of the orders Peronosporales and Pythiales. Under laboratory conditions, metalaxyl was applied to soil samples at the recommended field rate (1×FR) and double of recommended field rate (2×FR) for two and three times. Soil subsamples were taken at 0, 1, 3, 7, 14, 28, and 45 days after the last application of metalaxyl for determination of metalaxyl residues and 7, 14, 28, and 56 days for enumeration of cultivable microorganisms and DGGE profile of soil microbial community. Soil incubation experiments revealed that metalaxyl was degraded faster in the third application than in the second application of the fungicide, half-lives of metalaxyl decreasing from 16.2 to 9.9 days for recommended field rate and 22.1 to 20.0 days for double of recommended field rate. Soil bacterial and fungal populations decreased in the first 14 days and then recovered to the control levels; population of actinomycetes did not alter in the first 28 days but increased at the end of the experiment after the second application. However, after the third treatment, temporary increase in soil bacteria population, nonsignificant inhibition effect on fungal population, and obvious stimulation effect on actinomycetes number were observed. DGGE results showed that successive inputs of metalaxyl altered the bacterial community structure. There were differences in the persistence and effects of metalaxyl on microbial community between the second and the third metalaxyl treatments.

The current work reports on the degradation of glycerol aqueous solution via photocatalytic-Fenton technique. The CuFe₂O₄ photocatalyst was synthesized via sol-gel method and its physicochemical properties were characterized. The as-synthesized photocatalyst possessed Brunauer-Emmett-Teller (BET)-specific surface area of 104 m²/g. The large BET-specific surface area was also corroborated by the field-emission scanning electron microscopy (FESEM) images which showed porous morphology. In addition, the XRD pattern showed that the visible light-active component, CuFe₂O₄, was successfully formed with band gap energy of 1.58 eV determined from the UV-Vis diffuse reflectance spectroscopy. Significantly, it was determined from the blank run study that the visible light was an integral part of the photoreaction. Without the visible light irradiation, glycerol degradation was low (<4.0 %). In contrast, when visible light was present, the glycerol degradation improved markedly to attain 17.7 % after 4 h of visible light irradiation, even in the absence of CuFe₂O₄ photocatalyst. This can be attributed to splitting of H₂O₂ into hydroxyl (●OH) radical. In the presence of CuFe₂O₄ photocatalyst, the photocatalytic Fenton degradation of glycerol has further enhanced to record nearly 40.0 % degradation at a catalyst loading of 5.0 g/l. This has demonstrated that the CuFe₂O₄ was capable of generating additional hydroxyl radicals to attack the glycerol molecule. Moreover, this degradation kinetics can be captured by Langmuir-Hinshelwood model from which it was found that the adsorption constant related to H₂O₂ was significantly weaker compared to the adsorption constant of glycerol.

Calcium nitrate and a lanthanum-modified bentonite (Phoslock®) were investigated for their ability to control the release of phosphorus from contaminated sediment. Their effectiveness and mode of action were assessed using microcosm experiments by monitoring the variation of physiochemical parameters and phosphorus and nitrogen species over time following the treatment for 66 days. Phoslock® was more effective reducing phosphorus in overlaying water and controlling its release from sediment. Calcium nitrate improved redox condition at the sediment-water interface and temporally reduce phosphorus in overlaying water but phosphorus level returned back in a long run. Phosphorus fractionation suggested that Phoslock® converted mobile phosphorus to more stable species while calcium nitrate increased the fractions of mobile phosphorus species. Phoslock® generally showed no effect on nitrogen species. Whereas calcium nitrate temporally increased nitrate, nitrite, and ammonium concentrations but their concentrations quickly reduced likely due to the denitrification process. Results suggested that Phoslock® can be more effective in controlling the release of phosphorus from sediment than calcium nitrate. However, calcium nitrate can improve the redox condition at the sediment-water interface, which may provide other benefits such as stimulating biodegradation.

Inorganic N fertilizer and irrigation water types on the C and N dynamics are poorly understood. This work aimed to evaluate the effect of different N fertilizer and irrigation water types on soil C and N mineralization. The farmland experiment was conducted with three types of N fertilizer (urea, ammonium sulfate, and slow-release urea) and drip irrigation with two types of water (groundwater and reclaimed water) for a summer maize-winter wheat crop rotation. Soil samples were collected from the experimental farmland for incubation experiments. The results showed that the average cumulative mineralization of soil C (incubation 20 days) and N (incubation 14 weeks) in different treatments ranged from 73.50 to 91.37 mg kg⁻¹ and 52.65 to 64.04 mg kg⁻¹, respectively. N fertilization significantly increased dissolved organic carbon (DOC), dissolved organic nitrogen (DON), soil organic carbon (SOC), and soil organic nitrogen (SON) contents in the soils, but N fertilizer and irrigation water types had no significant influence on them. Correspondingly, N fertilization significantly enhanced the mineralization of C by 14.14–21.22 % and N by 15.81–22.16 % in soils but no significant difference among different N fertilizer types. Compared with groundwater, reclaimed water irrigation enhanced the mineralization of C by 3.33 % and N by 1.01 %, but the difference was not statistically significant. The cumulative mineralization of C and N in soils after DOM removal average significantly decreased 9.83 and 14.83 %, respectively, which indicates that DOM plays an important role in soil C and N mineralization. Our results indicate that inorganic N fertilization promotes soil C and N mineralization, which may inevitably aggravate global warning. Reclaimed water irrigation had similar influence on soil C and N mineralization as groundwater irrigation; thus, we recommend irrigation with reclaimed water in water shortage areas.

Zero-valent iron has received considerable attention for its potential application in the removal of heavy metals from water. This paper considers the possibility of removal of zinc ions from water by causing precipitates to form on the surface of iron. The chemical states and the atomic concentrations of solids which have formed on the surface of zero-valent iron as well as the type of the deposited polycrystalline substances have been analyzed with the use of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The BET surface area, the pH at point of zero charge (pHPZC), the ORP of the solutions, and the pH and chemical concentrations in the solutions have also been measured. Furthermore, the paper also considers the possibility of release of zinc from the precipitates to demineralised water in changing physicochemical and chemical conditions. In a wide range of pH values, Zn ₓ Fe₃ ₋ ₓ O₄ (where x ≤ 1) was the main compound resulting from the removal of zinc in ionic form from water. In neutral and alkaline conditions, the adsorption occurred as an additional process.

A novel magnetic pyridinium-functionalized mesoporous silica adsorbent (Fe₃O₄@SiO₂@Py-Cl) was synthesized for nitrate removal from aqueous solutions. The adsorption performances were investigated by varying experimental conditions such as pH, contact time, and initial concentration. The adsorbent was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and magnetic hysteresis loops. The results showed that the adsorption equilibrium could be reached within 30 min and the kinetic data were fitted well by pseudo-second-order and intra-particle diffusion model. The adsorbent exhibited a favorable performance, and its maximum adsorption capacity calculated by the Langmuir isotherm model was 1.755 mmol/g. The nitrate adsorption mechanism was mainly controlled by the material through ion exchange of nitrate with chloridion, as determined by XPS. This study indicated that this novel pyridinium-functionalized mesoporous material had excellent adsorption capacity. Meanwhile, compared with other adsorbents, it could remove nitrate fast and easy to be collected by magnetic separation, showing great potential application for nitrate removal from aqueous solution.

Sediment, suspended particulate matter (SPM), water and clam Scrobicularia plana samples were collected in a temperate coastal lagoon with anthropogenic impact. Arsenic levels in sediments, SPM and water presented a spatial concentration gradient. A significant linear regression between arsenic levels in S. plana and SPM suggests particulate matter as the main route of arsenic exposure. Trend analysis showed that total arsenic concentrations in S. plana generally increased with size class, reflecting lifespan bioaccumulation. Despite being efficient in reflecting environmental contamination levels, results suggest that arsenic accumulation by S. plana may not be a passive process, given the proportionally lower accumulation in high contamination areas. Annual bioaccumulation rates ranged from 5.6 to 1 mg kg⁻¹ year⁻¹, suggesting a possible toxicity risk for individuals of the most contaminated area. Despite the absence of regulatory guidelines, food safety assessment highlighted possible adverse effects of consuming S. plana in most contaminated areas.

Dichlorodiphenyltrichloroethane (DDT) is one of the persistent organic pollutants (POPs) that are highly toxic to the environment. Effective evaluation on the bioavailability of DDTs in soils is essential for risk assessment and soil remediation. The aims of this study were to verify the feasibility of the hydroxypropyl-β-cyclodextrin (HPCD) extraction method for predicting the bioavailability of DDT, dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE) in soils, and to examine the effect of HPCD on their biodegradation in different soils. Four soils were aged with a mixture of p,p′-DDT, o,p′-DDT, p,p′-DDD and p,p′-DDE (0.25 μg g⁻¹ for each compound) for 20 and 100 days, respectively. For each of the DDTs, a significant positive correlation between HPCD-extractable fraction and biodegradable fraction in each soil was observed. It was demonstrated that the amounts of HPCD-extractable p,p′-DDT and o,p′-DDT were not significantly different from the amounts that were degradable as assessed from their degradation by Enterobacter sp. LY402 (p > 0.05). Such 1:1 relationship between extraction and degradation was not obtained in the cases of p,p′-DDD and p,p′-DDE, as the amounts of degradable p,p′-DDD and p,p′-DDE were lower than the amounts that were extractable with HPCD. Additionally, the biodegradation of p,p′-DDT, o,p′-DDT, p,p′-DDD, and p,p′-DDE was inhibited in the presence of HPCD, which could be due to the binding of the compounds to HPCD, making them less available to access the bacteria for degradation. This study provides the possibility of using the HPCD extraction method to predict the bioavailability of p,p′-DDT and o,p′-DDT in soils. But when HPCD was used as an additive in the bioremediation of DDT-contaminated soils, it might have a negative effect on biodegradation.

Under various abiotic stresses, plants overproduce reactive oxygen species (ROS) such as superoxide anion (O₂•⁻), hydroxyl radical (OH•), and hydrogen peroxide (H₂O₂). When in excess, these highly reactive molecules cause oxidative stress, thus damaging proteins, lipids, and DNA. Therefore, plants evolved an enzymatic defense machinery that involves such enzymes as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APOX). Various plant families, species and even specimens differ in their ability to withstand the abiotic stress. A study has been undertaken to assess the differences in response to trace metals between two species: a resistant hyperaccumulator Indiana mustard (Brassica juncea) and a metal-sensitive pea (Pisum sativum). We observed that trace elements (Cu, Zn, Cd, Pb) changed the activity of antioxidative enzymes (SOD, APOX, CAT) and the rate of ROS generation. However, in the control plants and at a point 0′ of the treatment, we have noticed a large disproportion in the hydrogen peroxide level, with B. juncea maintaining naturally higher H₂O₂level (up to 40 times higher). We believe that this may be a distinguishing trait common to plants being resistant to oxidative stress.

The remediation of metal-impacted soils requires either the enhanced mobility (and capture) of the target analytes or their effective complexation/immobilisation. In this study, a range of ameliorants (activated carbon, bonemeal, bentonite and CaSx (calcium polysulphide)) were compared to assess their effectiveness in immobilising metals in soils. In addition to chemical analysis (pH and trace element analysis), microbial biosensors were used to assess changes in the water-soluble biotoxicity of metals as a consequence of ameliorant dosing. Management of soil ameliorants requires an enhancement of K d (solid/solution partition coefficient) if soil leachate is to meet predefined environmental quality standards. Of the ameliorants tested, CaSx was the most effective per unit added for both laboratory-amended and historically contaminated soils, regardless of the metal tested. At the ameliorant concentrations used to effectively immobilise the metals, the biosensor performance was not impaired. Microbial biosensors offered a rapid and relevant screening tool to validate the reduced toxicity associated with the ameliorant dosing and could be calibrated to complement chemical analysis. While laboratory-amended soils were a logical way to evaluate the performance of the ameliorants, they were generally associated with K d values an order of magnitude lower than those of historically contaminated soils.