Geochemical fractions and phytoavailability of Zinc in a contaminated calcareous soil affected by biotic and abiotic amendments

Many studies have conducted to determine the best management practice to reduce the mobility and phytoavailability of the trace metals in contaminated soils. In this study, geochemical speciation and phytoavailability of Zn for sunflower were studied after application of nanoparticles (SiO₂ and zeolite, with an application rate of 200 mg kg^-1) and bacteria [Bacillus safensis FO-036b(T) and Pseudomonas fluorescens p.f.169] to a calcareous heavily contaminated soil. Results showed that the biotic and abiotic treatments significantly reduced the Zn concentration in the aboveground to non-toxicity levels compared to the control treatment, and the nanoparticle treatments were more effective than the bacteria and control treatments. The concentration of CaCl₂-extractable Zn in the treated soils was significantly lower than those of the control treatment. The results of sequential extraction showed that the maximum portion of total Zn belonged to the fraction associated with iron and manganese oxides. On the contrary, the minimum percent belonged to the exchangeable and water-soluble Zn (F₁). From the environmental point of view, the fraction associated with iron and manganese oxides is less bioavailable than the F₁ and carbonated fractions. On the basis of plant growth promotion, simultaneous application of the biotic and abiotic treatments significantly increased the aboveground dry biomass yield and also significantly reduced the CaCl₂-extractable form, uptake by aboveground and translocation factor of Zn compared to the control treatment. Therefore, it might be suggested as an efficient strategy to promote the plant growth and reduce the mobile and available forms of toxic metals in calcareous heavily contaminated soils.

Root-induced changes of Zn and Pb dynamics in the rhizosphere of sunflower with different plant growth promoting treatments in a heavily contaminated soil

Root induced changes are deemed to have an important role in the success of remediation techniques in contaminated soils. Here, the effects of two nano-particles [SiO₂ and zeolite] with an application rate of 200mgkg^-1, and two bacteria [Bacillus safensis FO-036b(T) and Pseudomonas fluorescens p.f.169] in the rhizosphere of sunflower on Zn and Pb dynamics were studied in greenhouse conditions. The treatments reduced the exchangeable Zn (from 13.68% to 30.82%) and Pb (from 10.34% to 25.92%) in the rhizosphere compared to the control. The EC and microbial respiration/population of the rhizosphere and bulk soil had an opposite trend with the exchangeable fraction of Zn and Pb, but dissolved organic carbon followed a similar trend with the more bioavailable fractions. As a result, the accumulation of Pb and Zn in the plant tissues was significantly (p < 0.05) reduced by the application of amendments, which might be due to the shift of the metals to immobile forms induced by the nature of the treatments and changes in the rhizosphere process. The empirical conditions of this research produced the intensification of the rhizosphere process because the findings highlight those changes in the rhizosphere EC, pH and dissolved organic carbon can affect the efficiency of zeolite/SiO₂ NPs and bacteria to immobilize Pb and Zn in the soil, depending on the chemical character of the metals and the treatments. Generally, the affinity of the biotic treatment for Pb was more than the abiotic and conversely, the abiotic treatment showed a higher ability to immobilize Zn than the biotic treatment.

Preparation and characterization of poly(acryl amide-coacrylic acid)/nay and Clinoptilolite nanocomposites with improved methylene blue dye removal behavior from aqueous solution

The nanocomposites of poly(acryl amide-co-acrylic acid) with NaY and Clinoptilolite were prepared using ammonium persulfate as an initiator and N,N′- methylene bis acryl amide as the cross-linker. The morphology was characterized by SEM and the structure of nanocomposite materials was studied with XRD and FT-IR that showed the interaction between porous materials and poly(AAm-co- AAc). Thermo gravimetric analyzer (TGA) curve shows that all the chain-extended poly(AAm-co-AAc) are stable up to 250 °C and maximum weight loss occurs at 890 °C. The TGA results indicated higher stability for poly(acryl amide-co-acrylic acid)/NaY and Clinoptilolite composites than poly(AAm-co-AAc). The adsorption and desorption behavior of methylene blue were investigated for nanocomposites. It was shown that poly(AAm-co-AAc)/NaY and Clinoptilolite nanocomposites have higher adsorption than NaY, Clinoptilolite and poly(AAm-co-AAc) alone. This effect was attributed to good interaction between the hydroxyl group in porous materials and carboxylic group in poly(AAm-co-AAc) with methylene blue.