جستجوی مقالات مرتبط با کلیدواژه "cadmium availability" در نشریات گروه "آب و خاک"

Cadmium (Cd) contamination has been a widespread concern in paddy soils because of its subsequent transfer to the food chain. Biochar amendment is proposed to stabilize Cd in the contaminated soils. However, the pristine biochar shows limited functionality towards Cd sorption in practice. Recently, Mg-modified biochars have attracted much attention for their low toxicity. These biochars are coated by MgO or Mg(OH)2 precipitates during the pyrolysis process. Magnesium chloride (MgCl2)-modified biochars have been used widely in the removal of heavy metals from the aqueous solutions. However, there is little literature about their performance in soils. The present study therefore was conducted to investigate the effects of application of unmodified and MgCl2-modified rice husk biochars on the kinetics and isotherms of Cd sorption in a calyey paddy soil.

The unmodified and MgCl2-modified biochars were produced from rice husk at 600°C. Some relevant characteristics of the produced biochars (including elemental composition, pzc, pH1:10, ash content and BET surface area) were determined. Moreover, the studied soil was taken from a paddy field (0-20 cm) in the Qaemshahr region of Mazandaran province. The biochars (< 0.5 mm) were added to the soil samples at three levels (0, 3, and 5% w/w) and the amended soils were incubated at 25°C for 45 days. Then, the kinetic experiments of Cd sorption at a concentration of 375 mg Cd/L at times of 0.25, 0.5, 1, 2, 4, 8, 16, 24 and 48 hours and the isothermal experiments of Cd sorption at concentrations of 50, 100, 150, 200, 300, 350, 400, 600 and 800 mg Cd/L were performed. In both kinetic and isotherm experiments, a 0.01 M KCl solution was used as the background electrolyte. Finally, the relevant kinetic and isotherm models were fitted to the sorption data and their parameters were calculated.

Biochar characterization indicated that modification with MgCl2 resulted in an increase of the O/C ratio (from 0.27 to 0.48) and pH (from 7.67 to 8.60). This modification also increased the H/C ratio (from 0.032 to 0.071) and the specific surface area (from 195.6 to 231.2 m2/g). As a result, the MgCl2-modified biochar was more hydrophilic and less carbonized than the unmodified one. Moreover, the characteristic peaks of the MgCl2-modified biochar (3700, 1428 and 500 cm-1) were present in its FTIR spectrum. The results revealed that about 74 to 89% of the Cd sorption by the soils occurred in times less than 2 hours. With MgCl2-modification, the sorption equilibration time was reduced from 48 hours to 24 hours. In contrast, the unmodified biochar had no considerable effect on the Cd sorption kinetics. Among the kinetic models, the Elovich model with lower SEE was the best to fit the Cd sorption kinetic data. The intra-particle diffusion model was not satisfactory for Cd sorption on the biochars. Freundlich model with lower SEE well described the Cd sorption isotherms. Application of 3% and 5% MgCl2-modified biochar increased the Freundlich KF parameter by 2.4 and 2.8 times as compared to the control. Moreover, the aforementioned treatments increased the heterogeneity parameter of the Freundlich model (n) from 3.48 to 6.08. The Temkin model could not reasonable fit the sorption data. In contrast, the unmodified biochar did not show any considerable effect on the Cd sorption capacity of the clayey soil used in this research. This finding means that the unmodified biochar could not improve the sorption performance of negatively charged soil clay particles.

According to the results obtained, it could be concluded that the Cd sorption behavior of the soil treated with unmodified rice husk biochar was similar to that of the untreated soil. Whereas, the MgCl2-modification improved both sorption rate and sorption capacity of the soil for Cd. Application of MgCl2-modified biochar improved the Cd sorption properties of a clayey soil with high intrinsic sorption ability. Thus, this may be a promising approach in remediation of Cd-contaminated paddy soils with the aim of reducing Cd mobility and availability. However, there is need to do more research to create awareness about the importance of biomass nature as well as pyrolysis temperature, the ratio of MgCl2 to biomass, the mechanism of Cd stabilization and the desorption of Cd from soils treated with MgCl2-modified biochars.

In the past few decades, accumulation of heavy metals in soils has increased as a result of human activities. The objective of this study was to evaluate the effect of common reed nano-biochar and Fe-modified nano-biochar on cadmium (Cd) mobility and fractionation in a Cd-contaminated soil. This study was carried out in 1399-1400 as a factorial experiment based on a completely randomized design (CRD) with two factors including absorbent type (at four levels including biochar, modified biochar, nano-biochar and modified nano-biochar), and biochar application levels (0, 0.5 and 1% w/w) in three replications under laboratory conditions. After treatments’ application, the soil samples were incubated for 90 days. At the end of incubation period, Cd availability and fractionation were measured and Cd mobility factor was determined. The results indicated that with the application of all absorbents (especially at 1% w/w level), concentration of available Cd, exchangeable and Cd bound to carbonate fraction were significantly decreased, while Cd bound to Fe-Mn oxides, Cd bound to organic matter and residue fraction of Cd significantly (P<0.05) increased. The Cd availability in modified nano-biochar treatment (1%) decreased by 26.37 % compared to the control. Results also indicated that nano-biochar had a more significant impact than raw biochar on the immobilization of Cd and decrease its mobility in the soil. In addition, modified-biochar and nano-biochar had more efficiency than raw biochars on the Cd stabilization in the soil. In general, the results revealed that common reed nano-biochar and modified nano-biochar with FeCl2 can be suitable absorbent for stabilization of Cd in contaminated soils.

Soil, as an important component of terrestrial ecosystems, plant growth media, and a habitat of diverse living organisms commonly encounters a variety of abiotic stresses. Soil microorganisms play an important role in maintaining soil quality and functioning, since they are responsible for the decomposition of dead organic material, nutrient cycling and degradation of hazardous organic pollutants. Metal toxicity and salinity are the major abiotic stresses affecting soil microbial activity and community structure in many areas of the world, in particular arid regions. Salinity may prompt the negative influences of soil pollution on soil microbial activity. On the other hands, application of organic amendments to saline soils or toxic metal-polluted soils may alleviate the negative consequences of these two abiotic stresses on soil microbial activity and population.

This study was conducted under controlled laboratory conditions at Shahrekord University. The main aim of this study was to investigate the effects of salinity and plant residue as an organic amendment on concentrations of soluble elements, enzyme activity and substrate-induced respirations (SIR) in a calcareous soil polluted with cadmium (Cd) over a three-month incubation experiment. A factorial experiment with two levels of cadmium (0 and 30 mg kg-1), three levels of salinity (1.35, 7.5 and 15 dS m-1) and plant residue treatments (with and without alfalfa residue) was conducted using a completely randomized design with four replications. Using cadmium chloride salt, the soil was contaminated, and subsequently amended with alfalfa residue (1%, w/w). After thorough mixing of soil and plant residue, salinity treatments were applied using NaCl salt. To reactivate the microbial population and for the aging effect, soil moisture was set at 70% of field capacity, and containers were pre-incubated at room temperature for 4 weeks. The samples were then incubated at 25±1 oC for 98 days.

Increasing salinity levels resulted in an increase in soluble Na concentration, a reduction in soil enzyme activity and SIR, and a decline in the concentrations of soluble Ca, Mg and K. The harmful impact of soil salinity on microbial properties was much greater in Cd-polluted soils than unpolluted soils.

Results indicated that addition of plant residue reduced the negative impacts of salinity and Cd pollution stresses on soil microbial and enzyme activity, and that resulted in increases in the concentrations of water soluble elements.The findings of the current study confirmed that application of adequate organic amendments can decrease Cd toxicity, enhance substrate availability and maintain soil microbial and enzyme activity in saline and polluted soils with substrate limitation.

Any cadmium (Cd) contaminated soil might cause reduction in plants’ yield and increase the hazard of Cd-contaminated plants consumption by both human and animals. The research aimed to investigate the effect of EDTA chelate on Cd uptake in pot marigold (Calendula officinalis L.). A factorial experiment using randomized complete blocks was used in three replications. Treatments included application of 0(C0), 25(C25), and 50(C50) Mg ha-1 cow manure in a Cd polluted soil [ 0(Cd0), 5(Cd5), and 10 (Cd10) mg Cd kg -1 soil] and two rates of EDTA chelate (0 and 2.5 mmol kg-1 soil). Applying 2.5 mmol EDTA chelate caused significant increase in shoot Cd uptake by 21% and 25% in a Cd polluted soil (10 mg Cd kg -1 soil) treated with 25 and 50 Mg ha-1 cow manure, respectively. Also, addition of 2.5 mmol EDTA chelate caused an increase in the root and shoot bio-concentration factor. The results of this experiment showed that applying 2.5 mmol EDTA would increase the Cd availability, which could be considered as a factor that plays an important role in Cd remediation in soils treated with organic amendments.