Scallop shell-Fe₃O₄ nanoparticles were synthesized by co-precipitation and hydrothermal methods. The removal efficiency of RB5 was studied as a function of pH, adsorbent dosage, initial RB5 concentration, ionic strength, and temperature. Coating of Fe₃O₄ nanoparticles onto Scallop shell was identified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and energy dispersive X-ray (EDX) analysis. Maximum adsorption was obtained at pH 3. The removal efficiency of RB5 was increased with increasing adsorbent dosage. However, it was decreased with increasing initial RB5 concentration, temperature and in the presence of any anions. Adsorption kinetic study revealed that the pseudo-second order model better described the removal rate than the pseudo-first order model and intra-particle diffusion model. Adsorption isotherm was analyzed by both Langmuir and Freundlich equation. Experimental result was well described by the Langmuir equation. Maximum adsorption capacity was estimated to be 1111.11 mg/g. Thermodynamic studies indicated that the adsorption of RB5 onto Scallop shell-Fe₃O₄ nanoparticles was an endothermic (∆H = 178.14 KJ mol⁻¹) process. The negative values of free energy (∆G) for the adsorption indicated that adsorption of RB5 was spontaneous reaction. Adsorption activity of RB5 by Scallop shell-Fe₃O₄ nanoparticles was maintained even after six successive cycles.

This paper presents the efficacy of zero-valent iron nanoparticles (ZVINs), magnetic iron oxide nanoparticles (MINs), zero-valent iron nanoparticles/sugarcane bagasse (ZVIN-SB) composite and magnetic iron oxide nanoparticles/sugarcane bagasse (MIN-SB) composite in immobilizing chromium present in tannery sludge. The optimized values for the immobilization of chromium by the adsorbents were found to be 48 h, 100 g/kg and 7, respectively, for time, adsorbent dosage and pH. The maximum uptake capacity was found to be 429.75, 539.25, 587.25 and 625.8 mg/kg, respectively, for ZVIN, MIN, ZVIN-SB and MIN-SB. The desorption study of the unamended sludge and sludge amended by ZVIN, MIN, ZVIN-SB and MIN-SB was carried out with three different desorbing media (0.1 N HCL, DIW and 0.1 N NaOH). It was found that the cumulative concentration of leachate chromium was more in basic condition than in neutral and acidic conditions. In column studies, the concentration of leachate chromium attained 0 mg/L at 24, 15, 18 and 14 pore volumes, respectively, for the sludge amended by ZVIN, MIN, ZVIN-SB and MIN-SB. The experimental adsorption data fitted well with pseudo-first-order kinetics. The zero-order kinetics accurately predicted the experimental desorption capacity (q ₑ) of the sludge amended by ZVIN, MIN, ZVIN-SB and MIN-SB. The Fourier transform infrared spectroscopy (FTIR) analysis showed that the amine, carboxyl, iron compounds, etc. present in the adsorbents were the chief causes for the immobilization of chromium. The X-ray diffraction (XRD) analysis of the sludge showed the presence of trivalent chromium compounds at a higher concentration.

The changes in the availability of selected elements (Ca, Mg, K, Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) 16 years after amphibolite treatment were studied in the root zone of spruce (40 and 80 cm from the stem base) using the diffusive gradient in thin film (DGT) technique. The effective concentrations of some of the tested elements significantly increased (Ca (34 %), Mg (31 %), K (65 %), Al (143 %), Fe (242 %), and Pb (27 %)) in 80 cm distance from the stem, whereas the total and the water-soluble concentrations of the elements did not differ from the control. The changes in effective concentrations of the elements in soil were related to higher vitality of the trees on amended soil in contrast to the control.

Long-term fire retardant (LTR) use for forest fire suppression and/or prevention purposes can result in chemical leaching, from soil to the drainage water, during the annual rainfall period. Also, wildland fires can have an impact on the leaching of various chemicals from treated forest soils. Large quantities of ions in leachates, mainly due to ammonium (one of the major LTR components) soil deposition, could affect the groundwater quality. The alteration of pH, total hardness (TH), and electrical conductivity (EC) values in leachates mainly due to nitrogen-based LTR application (Fire Trol 931) was investigated in this laboratory study. The values of pH, TH, and EC were measured in the resulting leachates from pots with forest soil and pine trees alone and in combination with fire after a simulated rainfall period. pH, TH, and EC values in leachates from all treated pots were significantly greater than those from control pots.

New porous carbonaceous adsorbents were prepared from an oily sludge generated in a fuel oil storage tank using pyrolysis with and without activation by KOH at 600 °C. The pore characteristics of the activated carbonaceous adsorbent (AC), due to the formation of micropores and mesopores structure, were considerably better than those of non-activated carbonaceous adsorbent (NA). The adsorption of Cd from aqueous solutions on the produced carbonaceous adsorbents was optimized using the Taguchi method. Under optimum conditions, the Cd adsorption efficiency for the NA and AC was obtained to be 77.7 and 98.2 %, respectively. The initial concentration and the adsorbent dose were the most significant factors affecting the removal of Cd by NA and AC, respectively. The adsorption data for the AC were well fitted by the Langmuir, Freundlich, and Redlich-Peterson isotherms models. The regeneration and reuse of the adsorbents in the three cycles of Cd adsorption-desorption were possible. The carbonaceous adsorbents had acceptable efficiency for the removal of Cd from a mine wastewater. Based on the obtained results, the oily sludges available in huge amounts in the petroleum industry proved to be a potential precursor resource for the production of the porous carbonaceous adsorbents, particularly for application in the wastewater treatment.

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.

The influence of long-term exposure to background pollution on the response and recovery of the invasive species Corbicula fluminea to ammonia stress was investigated using a multi-marker approach. Wild clams of the tidal freshwater areas of two estuaries of the NW Iberian coast with different levels of pollution, the estuaries of Minho river (reference) and of Lima river (contaminated), were collected and exposed individually to different treatments: 8 and 14 days in dechlorinated tap water (DTW), 8 and 14 days in 1 mg L⁻¹of ammonia (AM), and 8 days in AM followed by 6 days in DTW. After each defined time (0, 8, and 14 days), the clams were sacrificed and the activity of the enzymes glutathione S-transferase (GST), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), cholinesterase (ChE), octopine dehydrogenase (ODH), and the lipid peroxidation (LPO) levels were used as effect criteria. At the beginning of the bioassay, the clams from the polluted estuary presented significantly higher background levels of GST, CAT, GR, GPx, and LPO than those from the reference one indicating long-term exposure to oxidative stressors. In general, C. fluminea from both estuaries presented little sensibility to ammonia with no significant differences found between exposed and control clams for most of the biomarkers. That low sensibility of C. fluminea could be seen as advantageous for its invasion ability.

A study has been conducted to enhance fluoranthene degradation by combining biodegradation with hydrogen peroxide oxidation, as a chemical oxidant calcium peroxide has been used. The impacts of addition of calcium peroxide on microbial activity (phenol oxidase and acid phosphatase) as well as fluoranthene removal efficiency were investigated. It was observed that in the presence of calcium peroxide, the removal efficiency of fluoranthene on day 30 of the experiment was threefold higher as compared to a reference sample. It was found that the activity of phenol oxidase was stimulated on days 1, 7, and 14, by the presence of fluoranthene, whereas stimulation of the acid phosphatase activity in the samples of soil contaminated by fluoranthene was observed only after 14 days of the experiment. This may indicate that the induction period for this enzyme is longer compared with the induction period for phenol oxidase. The inhibition of the activity of both enzymes was observed in the presence of calcium peroxide.

Solar Photo-Fenton reaction, using FeSO₄ and H₂O₂, is an effective and energy-efficient advanced oxidation process (AOP) for degradation of pesticides. However, a major environmental concern is whether the net toxicity after the photo-Fenton process is within the tolerance limit of the aquatic plants and animals, since the unreacted pesticide and Fenton’s reagent may impart additional toxicity to the treated water. Here, we report the oxidative removal of dichlorvos pesticide in wastewater by solar photo-Fenton reaction along with the residual toxicity analysis of the treated water on an aquatic alga. It was found that at pH 3, dichlorvos, with an initial concentration of 6.9 × 10⁻⁵ mol L⁻¹, was observed to be fully degraded within a batch time of 120 min, though the corresponding reduction of chemical oxygen demand (COD) was about 53 % signifying incomplete mineralisation. In order to predict the transient concentration profiles of dichlorvos under different initial concentrations, a four-parameter mathematical model was formulated. Additionally, the resultant toxicity was also examined using a model blue-green alga Nostoc sp. Compared to the raw wastewater, the net biomass of chlorophyll-a was found to increase significantly. Respective estimate of the protein concentration also indicated the same trend. Therefore, sunlight-assisted photo-Fenton process may be regarded as an effective and safe technique for the treatment of pesticide-contaminated agricultural wastewater.