Accumulation of heavy metals due to pollution of the environment, particularly in agricultural ecosystems, can cause serious deterioration of crop yield and quality. In this study, we assessed the effect of silicon on physiological, photosynthetic and stress-related aspects of cadmium toxicity in hydroponically grown maize plants (Zea mays L., hybrid Valentina). One concentration of silicon (5 mM) and two concentrations of cadmium (5 and 50 μM) added to the cultivation medium were tested. Cadmium alone led to a significant growth inhibition and negatively affected the content of total chlorophylls and the efficiency of photosystem II. Especially in roots, application of cadmium resulted in the accumulation of reactive oxygen species and consequent membrane lipid peroxidation. The supplementation of silicon successfully ameliorated the toxic effect of cadmium on maize plants and enhanced growth, some of the photosynthetic parameters and reduced the level of oxidative stress. In plants exposed to higher concentrations of cadmium silicon also reduced its accumulation, especially in roots. Changes in the accumulation of phenolic compounds may indicate the influence of silicon on this aspect of secondary plant metabolism and its importance in the detoxification of heavy metals.

A novel mesoporous, nanocomposite, magnetically separable adsorbent, namely activated alumina (γ-Al₂O₃)/ferrite (Ni₀.₅Zn₀.₅Fe₂O₄) microfibers have been successfully prepared by the sol–gel process. These nanocomposite γ-Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers are formed after calcination of the precursor at 450 °C for 3 h, and characterized with high aspect ratios and uniform diameters of 1–10 μm. In the nanocomposite γ-Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers, the spherical γ-Al₂O₃particles are homogeneously embedded on the microfiber. Their specific surface areas and magnetic properties are significantly influenced by the γ-Al₂O₃content and calcination conditions. With the designed γ-Al₂O₃mass fraction of 0.2 and the calcination temperature of 550 °C, the γ-Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers possess a high specific surface area of 118.3 m²/g and saturation magnetization (Mₛ) of 20.4 Am² kg⁻¹, respectively. The adsorption behaviors of the nanocomposite γ-Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers were examined using the Congo red and methyl blue dyes as the adsorbate. The adsorption kinetics, effects of the adsorbent dosage and solution pH, adsorption isotherms, and regeneration of the microfiber adsorbents were investigated. The pseudo-second-order model can be used to describe the adsorption kinetics. The resultant isotherm data are well fitted by the Temkin model, implying that the dyes adsorption on the γ-Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers is a multilayer adsorption combined with some degrees of chemical interactions. Considering the simple synthesis process, high adsorption and unique magnetic property, these mesoporous, magnetic, nanocomposite γ-Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers can be used as a highly efficient, fast, and convenient adsorbent for dyes removal.Highlights The magnetic mesoporous Al₂O₃/Ni₀.₅Zn₀.₅Fe₂O₄microfibers were synthesized. Adsorption kinetics and adsorption isotherms were investigated. The separation, regeneration, and adsorption efficiency were enhanced.

Nanoscale zero-valent iron (nZVI) was synthesized and used for the removal of Sb(III) and Sb(V) from aqueous solutions. Results showed that more than 90 % of antimony would be removed in 15 min and that all of antimony could be removed with appropriate nZVI dosage in 90 min. The influence of pH value and possible impurities was investigated. The pH of 4 was found as the optimum pH. Discussion and speculation about the mechanism were presented according to X-ray photoelectron spectroscopy and transmission electron microscopy data. A sheet-like structure was observed after a 90-min reaction, and antimony was detected on the surface by energy-dispersive X-ray spectroscopy. Both Sb(III) and Sb(V) partially reduced in the process. The presence of humic acid transformed the morphology of nZVI but barely influenced the removal efficiency. Competing ions showed diverse influence between Sb(III) and Sb(V). The overall results indicated that nZVI was an efficient and suitable material for the removal of antimony.

The carbon balance of secondary dry tropical forests of Mexico’s Yucatan Peninsula is sensitive to human and natural disturbances and climate change. The spatially explicit process model Forest-DeNitrification-DeComposition (DNDC) was used to estimate forest carbon dynamics in this region, including the effects of disturbance on carbon stocks. Model evaluation using observations from 276 sample plots in a tropical dry forest in the Yucatan Peninsula indicated that Forest-DNDC can be used to simulate carbon stocks for this forest with good model performance efficiency. The simulated spatial variability in carbon stocks was large, ranging from 5 to 115 Mg carbon (C) ha⁻¹, with a mean of 56.6 Mg C ha⁻¹. Carbon stocks in the forest were largely influenced by human disturbances between 1985 and 2010. Based on a comparison of the simulations with and without disturbances, carbon storage in the year 2012 with disturbance was 3.2 Mg C ha⁻¹, lower on average than without disturbance. The difference over the whole study area was 154.7 Gg C, or an 8.5 % decrease. There were substantial differences in carbon stocks simulated at individual sample plots, compared to spatially modeled outputs (200 m²plots vs. polygon simulation units) at some locations due to differences in vegetation class, stand age, and soil conditions at different resolutions. However, the difference in the regional mean of carbon stocks between plot-level simulation and spatial output was small. Soil CO₂and N₂O fluxes varied spatially; both fluxes increased with increasing precipitation, and soil CO₂also increased with an increase in biomass. The modeled spatial variability in CH₄uptake by soils was small, and the flux was not correlated with precipitation. The net ecosystem exchange (NEE) and net primary production (NPP) were nonlinearly correlated with stand age. Similar to the carbon stock simulations, different resolutions resulted in some differences in NEE and NPP, but the spatial means were similar.

The comparative effectiveness for hexavalent chromium reduction and removal from irrigation water, using three selected plant species (Phragmites australis, Salix viminalis, and Ailanthus altissima) planted in soil contaminated with hexavalent chromium, has been studied in the present work. The above plant species were irrigated, in a continuous mode, with water, contaminated with 10 mg/L of hexavalent chromium. Hexavalent chromium and total chromium have been measured in all plant tissues species and in the drainage water. Total chromium removal from water was ranging from 56 % (Phragmites) to 70 % (Salix). After 360 days of growth, the chromium content of the contaminated soil dropped from 70 (initial) to 32, 36, and 41 mg Cr/kg₍dᵣy ₛₒᵢₗ₎, for Salix, Phragmites, and Ailanthus, respectively. Salix and Phragmites accumulated the highest amount of chromium in the roots (2,029 and 1,800 mg Cr/kg₍dᵣy ₜᵢₛₛᵤₑ₎, respectively), compared with 358 mg Cr/kg₍dᵣy ₜᵢₛₛᵤₑ₎for Ailanthus roots. Most of chromium was found in trivalent form in all plant tissues. Ailanthus had the lowest affinity for Crⱽᴵreduction in the root tissues. Phragmites indicated the highest chromium translocation potential, from roots to stems, while Salix indicated the highest chromium translocation from roots to leaves. Toxicity effects, expressed as root growth rate inhibition, indicated that Salix is the most chromium-tolerant species, with Ailanthus in the antipode.

The distribution of selected elements in individual fractions of organic matter from anthropogenically contaminated soils was investigated. The attention was paid especially at Hg. Furthermore, contents of S, Mg, Mn, Fe, Cu, Zn and Pb were also measured. The decomposition of organic matter to particular fractions was carried out by the resin DAX-8. Ten soil samples were collected, and the Advanced Mercury Analyzer (AMA-254) was used for the determination of the total Hg content. The two highest Hg values reached up to the concentration 10.5 mg kg⁻¹, and in the highest one, it was almost 29 mg kg⁻¹. In each extract, mercury was measured by inductively coupled plasma mass spectrometry (ICP-MS), for other elements, inductively coupled plasma optical emission spectrometry (ICP-OES) was applied. Results of the analysis show that the Hg content bound to the humic acids is inversely proportional to the content of Mg, Mn, Fe and Cu. However, this dependence was not confirmed by the samples with the mercury content above 10 mg kg⁻¹. In the case of fulvic acids, the relationship between Hg and S was observed and has again an inverse character.

Parts of the Czech Republic received extreme loading of acid deposition from coal combustion in the second half of the twentieth century. Although associated Hg deposition was not directly measured, Hg deposition rates calculated from peat cores approach 100 μg m⁻² year⁻¹. We quantified the soil concentrations and pools of Hg with carbon (C), sulfur (S), and nitrogen (N)—elements closely associated with soil organic matter at five sites across the Czech Republic—four sites known for extreme deposition levels of S and N compounds in the twentieth century, and one site relatively less impacted. The site-specific means of O-horizon Hg concentrations ranged from 277 to 393 μg kg⁻¹, while means of Hg concentrations in mineral soil ranged from 22 to 95 μg kg⁻¹. The mean Hg/C ratio across sites increased from ∼0.5 μg Hg g⁻¹C in the Oi-horizon to ∼5 μg Hg g⁻¹C in the C-horizon due to the progressive mineralization of soil organic matter. The soil Hg/C increase was accompanied by a soil C/N decrease, another indicator of soil organic matter mineralization. Soil Hg/C also increased as soil C/S decreased, suggesting that Hg was stabilized by S functional groups within the soil organic matter. Mineral soil Hg pools (8.9–130.0 mg m⁻²) dominated over organic soil Hg pools (5.3–10.1 mg m⁻²) at all sites. Mineral soil Hg pools correlated more strongly with total soil S and oxalate-extractable Fe than with total soil C. Total soil Hg pools could be accounted for by a time period of atmospheric inputs that was short relative to the age of the soils. The cross site variability of Hg soil pools was not sensitive to the local Hg deposition history but rather related to the capacity of soil to store and stabilize organic matter.

Urban stormwater runoff is contaminated by nutrients that wash off of roadways, parking lots and lawns during storms. In-ground permeable filter systems that consist of carefully selected filter material have the potential to remove these nutrients from the run-off. In this paper, four filter materials, calcite, zeolite, sand and iron filings, were investigated using laboratory batch tests to evaluate their efficiency in the removal of nitrate and phosphate from the simulated stormwater at different initial concentrations under the same 24-h exposure time period. The range of removal for nitrate was from 39 % to 65 % for calcite, from 42 % to 77 % for zeolite, from 40 % to 70 % for sand, and from 74 % to 100 % for iron filings. The removal of phosphate ranged from 35 % to 41 % for calcite, 59 % to 100 % for zeolite, 49 % to 100 % for sand, and 73 % to 100 % for iron filings. The removal of nitrate is mainly attributed to electrostatic adsorption, except when iron filings were used as a filter material where additional processes such as electrochemical reduction, ligand complexation and precipitation may have contributed to the higher nitrate removal. Phosphate removal is also attributed to electrostatic adsorption in all filter materials; however, at higher phosphate concentrations, the precipitation process may be the dominant process for all of the filter materials except calcite. The Langmuir and Freundlich isotherms fitted the observed nonlinear adsorption results, but the mechanism of removal of phosphate changed from adsorption to precipitation at concentrations higher than 1 mg/l in zeolite, sand, and iron filings; therefore, the adsorption models are valid below this concentration limit. A typical application of these batch adsorption test results is presented in the design of a field in-ground permeable filter system.

The growing demand for new sources of water for irrigation has led to an increase in the practice of using treated wastewater in agricultural processes. Thus, in the present research, we have assessed the irrigation of a culture of eucalyptus with reclaimed wastewater. The sewage comes from domestic sources and was treated in a facultative lagoon. The culture of eucalyptus was assessed through plant diameter at breast height and total volume of wood produced. Soil contamination was determined through its salinization and the values of sodium adsorption ratio (SAR). The use of wastewater in irrigation has brought an increase of 82.9 % in productivity compared to traditional cultivation. This shows that in a same area of cultivation, practically double of the eucalyptus wood could be obtained and used in the most different industrial activities. In addition, it would prevent the entering of a large amount of nutrients in water bodies due to their recycling in the agricultural culture. In the period of 4 years of studies, SAR has always been below the values pointed by the literature as indicators of problems for the soil.

The simultaneous removal of phenol and ammonium using heterotrophic nitrifying-denitrifying bacterium Serratia sp. LJ-1 was investigated. The maximum removal rates of ammonium nitrogen and phenol were 1.08 ± 0.05 and 2.14 ± 0.08 mg L⁻¹ h⁻¹, respectively. The ammonium oxidation had much higher tolerance to phenol toxicity than that of the autotrophic nitrifying bacteria. The increase in phenol concentration led to an increase in ammonium oxidation rate under the phenol concentration of 600 mg L⁻¹. The increase in ammonium concentration caused an increase in phenol biodegradation rate under the ammonium nitrogen concentration of 150 mg L⁻¹. Maximum rates of phenol biodegradation and total nitrogen removal in the treatments with nitrification metabolite (nitrate or nitrite) as the sole nitrogen source were more than 30 % lower than those of the treatment with ammonium as the sole nitrogen source. Ammonium was removed through nitrification and subsequent aerobic denitrification while phenol was biodegraded through the ortho-cleavage pathway and subsequently mineralized. Since phenol often coexists with nitrogen pollutants, these findings have significant environmental implications in terms of the simultaneous removal of these contaminants.