Soil science
N. Sahraei; A. Landi; S. Hojati; Edoardo Pasolli
Abstract
Introduction
In recent years, soil contamination with potentially toxic elements (PTEs) has become a major problem in most parts of the world. PTEs are naturally generated from the pedogenesis in the soil and are formed mainly by rock weathering. Nevertheless, the natural content of metals, i.e., Cr, ...
Read More
Introduction
In recent years, soil contamination with potentially toxic elements (PTEs) has become a major problem in most parts of the world. PTEs are naturally generated from the pedogenesis in the soil and are formed mainly by rock weathering. Nevertheless, the natural content of metals, i.e., Cr, Zn, Ni, Pb, Cd, used to be low in the soil, but due to anthropogenic activities such as industrial emissions, atmospheric transportation, sewage irrigation, and application of pesticides and fertilizers, there is an increase in the content of PTEs. PTEs in soil are one of the most important environmental pollutants due to their toxicity, durability, easy absorption by plants and long half-life. Therefore, the assessment of soil health is very important for the sustainable development of agriculture and the rehabilitation of soils contaminated with PTEs. The present study was conducted to quantify PTEs pollution for soil environmental assessment using a flexible approach based on multivariate analysis and using pollution indicators in a part of the central lands of Khuzestan province.
Materials and Methods
For this purpose, in February 2021, 200 surface soil samples (0-10 cm) were taken using stratified random sampling. The collected soil samples were cleaned by removing plant materials and other pebbles, and air dried, powdered, and sieved by using a 2 mm sieve size. The interest in soil's physical and chemical properties i.e., pH was determined with a digital pH meter. Soil textural particles were measured by the hydrometer method, soil organic carbon (SOC) content was estimated by following Walkley and Black method, bulk density (BD) was measured by the Clod method, and total metal content was determined using the aqua-regia solution digestion method and analyzed using Inductively Coupled Plasma-Optical Emission spectrometry (ICP-OEC). The level of Pb, Ni, Zn, Cr pollution was estimated based on environmental indicators including contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), pollution index of individual metals (PI), and modified pollution index of individual metals (MPI). Multivariate statistical methods including correlation analysis, cluster analysis (CA), and principal component analysis (PCA) were used to find the source of metals in the soil. All statistical methods were performed using SPSS (26 version) software.
Results and Discussion
Measurement of soil pH showed that the soil of the studied area tends to alkalinity. Also, the soil texture in this area is loam. The results showed that the SOC in these soil samples is 0.71%, and the range of EC (between 0.18 and 60.5 dS/m) indicates the distribution of saline and non-saline soils in the studied area. The total average concentration of Zn, Ni, Cr, and Pb were 60.26, 50.96, 50.38, and 12.67 mg/kg, respectively. The order of average for heavy metals was Zn> Ni> Cr> Pb. The highest amount of standard deviation and concentration changes were observed in Zn and Pb elements. These two elements also showed a high degree of variation coefficient in the studied area, which can indicate the high impact of human activities on the content of these elements. The results obtained from the application of multivariate statistics showed that there is a positive correlation between the elements such as Zn, Ni, and Pb in the study area, indicating that these metals probably have the same source. Whereas the absence of correlation of Cr with these elements indicates a separate source for this element compared to Pb, Zn, and Ni. There was also a strong relationship among these elements based on the PCA and CA classification. Based on the multivariate statistical analysis the source of pollution for the metals studied was mainly from both anthropogenic and geogenic activities. The results showed that the soil samples taken from the study area are in the low pollution category based on the individual element indices of CF and Igeo, but in the moderate pollution class based on the EF index. In addition, the evaluation based on the cumulative and multi-element indices of PI and MPI showed that 100% of samples have high pollution.
Conclusion
The present study concludes that the average values of Zn, Ni, Cr, and Pb were found to be below the guidelines set by the IEPA (Iran Environmental Protection Agency) as well as the Earth's crust values. The results indicate existing relationships among the studied variables, revealing that the heavy metals Zn, Ni, and Zn share the same source in the study area. Additionally, it was observed that the source of Cr is primarily geogenic in nature. These findings highlight the significance of utilizing multivariate statistical methods and pollution indicators in tandem, as they prove to be valuable tools for evaluating and quantitatively determining the potential pollution risk.
T. Mansouri; A. Golchin; J. Fereidooni
Abstract
Introduction: Soil contamination by heavy metals is one of the most important environmental concerns in many parts of the world. The remediation of soil contaminated with heavy metals is necessary to prevent the entry of these metals into the human food chain. Phyto-extraction is an effective, cheap ...
Read More
Introduction: Soil contamination by heavy metals is one of the most important environmental concerns in many parts of the world. The remediation of soil contaminated with heavy metals is necessary to prevent the entry of these metals into the human food chain. Phyto-extraction is an effective, cheap and environmental friendly method which uses plants for cleaning contaminated soils. The plants are used for phytoremediation should have high potential for heavy metals uptake and produce enormous amount of biomass. A major problem facing phyto-extraction method is the immobility of heavy metals in soils. Chemical phyto-extraction is a method in which different acids and chelating substances are used to enhance the mobility of heavy metals in soil and their uptake by plants. The aims of this study were: (a) to determine the potential of radish to extract Pb from contaminated soils and (b) to assess the effects of different soil amendment (EDTA and H2SO4) to enhance plant uptake of the heavy metal and (c) to study the effects of different levels of soil Pb on radish growth and Pb concentrations of above and below ground parts of this plant.
Materials and Methods: Soil samples were air dried and passed through a 2 mm sieve and analysed for some physico-chemical properties and then artificially contaminated with seven levels of lead (0, 200, 400, 600, 800 and 1000 mg/kg) using Pb(NO3)2 salt and then planted radish. During the growth period of radish and after the initiation of root growth, the plants were treated with three levels of sulfuric acid (0, 750 and 1500 mg/kg) or three levels of EDTA (0, 10 and 20 mg/kg) through irrigation water. At the end of growth period, the above and below ground parts of the plants were harvested, washed, dried and digested using a mixture of HNO3, HCl, and H2O2. The concentrations of Pb, N, P and K in plant extracts were measured. Statistical analysis of data was performed using MSTATC software and comparison of means was carried out using duncan's multiple range test.
Results and Discussion: The results showed that the effects of the type and rate of soil amendment and Pb levels of polluted soils were significant on dry weight and Pb concentrations of above and below ground parts of radish (p< 0.01). The dry weights of above and below ground parts of radish decreased as the Pb levels of polluted soils increased. By increasing the soil pollution level (1200 mg Pb/kg soil), the total dry weight of plant decreased by %47.3 which was probably due to phytotoxicity of lead and deficiency of several essential nutrients such as phosphorus. When the Pb levels of the polluted soils increased up to 400 mg/kg soil, the concentrations of Pb in above and below ground parts of the plant increased. But when the Pb levels of the polluted soils were higher than 400 mg/kg soil, the Pb concentration in above ground part of the plant decreased but in below ground part of the plant significantly increased. The decrease in Pb concentration in above ground part of radish was probably due to formation of insoluble lead complexes in soil. the use of soil amendments increased the concentrations of Pb in above and below ground parts of radish. The Application of EDTA increased the concentration of Pb in aerial part of radish more than the application of H2SO4. Also, the application of EDTA and H2SO4at low concentrations increased dry weight of plant since, the availability of micro- and macro elements enhanced and plant uptake of nutrients increased. But at the high concentrations of these amendments the increased availability of lead caused the reduced plant growth due to phytotoxicity. But the ability of the low level of sulfuric acid to absorb lead was more than EDTA. An antagonistic effect between phosphorus and lead uptake was also observed.
Conclusion: The results of the experiment showed that the Radish plant had the ability to absorb and accumulate the high concentration of lead in its tissues and so can be used for the phytoremediation of lead-contaminated soils. The EDTA application had higher potential for enhancing lead mobility and phytoavailability than H2SO4, But the ability of the low level of sulfuric acid to absorb lead was more than EDTA. The rate of amendment also had a significant effect on phyto-extraction process and the process was adversely affected by high concentrations of the amendments.
seyed sajjad hosseini; Amir Lakzian; Akram Halajnia
Abstract
Introduction: Application of EDTA may increase the heavy metal availability and phytoextraction efficiency in contaminated soils. In spite of that, it might also have some adverse effects on soil biological properties. Metals as freeions are considered to be severely toxic, whereas the complexed form ...
Read More
Introduction: Application of EDTA may increase the heavy metal availability and phytoextraction efficiency in contaminated soils. In spite of that, it might also have some adverse effects on soil biological properties. Metals as freeions are considered to be severely toxic, whereas the complexed form of these metalswith organic compounds or Fe/Mn oxides may be less available to soil microbes. However, apart from this fact, some of these compounds like EDTA and EDTA-metal complexes have low bio- chemo- and photo-degradablity and high solubility in their own characteristics andable to cause toxicity in soil environment. So more attentions have been paid to use of low molecular weight organic acids (LMWOAs) such as Citric acid because of having less unfavorable effects to the environment. Citric acid increases heavy metals solubility in soils and it also improves soil microbial activity indirectly. Soil enzymes activity is a good indicator of soil quality, and it is more suitable for monitoring the soil quality compared to physical or chemical indicators. The aims of this research were to evaluate the changes of dehydrogenase, urease and alkaline phosphomonoesterase activities, substrate-induced respiration (SIR) and Pb availability after EDTA and citric acid addition into a contaminated soil with PbCl2.
Materials and Methods: An experiment was conducted in a completely randomized design with factorial arrangement and three replications in greenhouse condition. The soil samples collected from surface horizon (0-20 cm) of the Typic haplocalsids, located in Mashhad, Iran. Soil samples were artificially contaminated with PbCl2 (500 mg Pb per kg of soil) and incubated for one months in 70 % of water holding capacity at room temperature. The experimental treatments included control, 3 and 5 mmol EDTA (EDTA3 and EDTA5) and Citric acid (CA3 and CA5) per kg of soil. Soil enzymes activity, substrate-induced respiration and Pb availability of soil samples were determined by standard methods after 7, 14, 21 and 28 days of chelates addition.
Results and Discussion: The soil texture was loam and the indigenous Pb content was 25.55 mg kg-1. The soil pH was 7.4 and electrical conductivity of saturated extraction measured 2.5 dS m-1. The soil carbonate calcium was 14% and the content of organic carbon and essential nutrients were low. The results showed that EDTA3 and EDTA5 treatments increased Pb availability by 2.17% and 10% compared to control treatment but CA3 and CA5 treatments decreased it by 3.8% and 15.7% respectively. The Pb availability in control and EDTA5 treatments did not change during the incubation time. The available Pb concentration dropped sharply during the incubation time in EDTA3, CA3 and CA5 treatments. The reduction rates in CA3 and CA5 treatments were more than EDTA3 treatment. This may be due to the high stability and low biodegradability of EDTA than biodegradable chelators and low molecular weight organic acids. The results showed that urease and dehydrogenase activities were significantly reduced in EDTA3 and EDTA5 treatments compared to control treatment. Urease and dehydrogenase activities were decreased with the increase of EDTA concentration. Alkaline phosphomonoesterase activity was not affected by the EDTA3 and EDTA5 treatments. In CA3 and CA5 treatments, dehydrogenase and alkaline phosphomonoesterase activities significantly increased with increasing the concentration of citric acid. CA5 treatment showed a prominent effect on urease activity compare to CA3 treatment. The soil enzyme activities increased with incubation time. It seems that reduction in Pb availability causes an increase of soil enzymes activities. Significant negative relationships were found between soil enzymes activities and available Pb concentration (dehydrogenase activity (r=-0.906, P
