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, ...
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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.
siros sadeghi; Shahin Ostan; Nosratollah Najafi; Mostafa Valizadeh; Hassan Monirifar
Abstract
Introduction: Heavy metal contamination not only adversely affects the chemical properties, availability of nutrients and biological activity of the soils, but also causes serious risk to the human health from entering the food chain. Cadmium as an unnecessary heavy metal is highly toxic to plants. Cadmium ...
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Introduction: Heavy metal contamination not only adversely affects the chemical properties, availability of nutrients and biological activity of the soils, but also causes serious risk to the human health from entering the food chain. Cadmium as an unnecessary heavy metal is highly toxic to plants. Cadmium toxicity inhibits plant growth and even death. Metabolic processes such as photosynthesis and cellular respiration are disturbed due to cadmium toxicity. Among the heavy metals, zinc is an important nutrient in many biological processes such as photosynthesis, activity of antioxidant enzymes, proteins, hormones and other activities. Because of the similar chemical behavior of cadmium and zinc, interaction between the two metals is of interest to many researchers.
Materials and Methods: In this study, to investigate the interaction effects of cadmium and zinc on shoot and root dry matter and chemical composition of corn (Zea mays cv. single cross 704), a factorial experiment as a randomized complete block design in triplicate with eight levels of cadmium (zero, 0.5, 2.5, 5, 10, 20, 40 and 80 mg Cd kg-1) and eight levels of zinc (zero, 5, 25, 50, 100, 200, 400 and 800 mg Zn kg-1) was conducted in a loamy sand soil under greenhouse conditions. After 60 days, the plants were harvested and dry weights of shoots and roots were determined. Moreover, after wet digestion, the concentrations of cadmium, zinc, iron, manganese and copper in these tissues were determined by flame atomic absorption spectrometry (Shimadzu-6300).
Results and Discussion: Treatments with 800 mg Cd kg-1 showed symptoms of cadmium and or zinc toxicity at early stages of the growth. These plants died after 10 to 20 days of germination. The results showed that the cadmium and zinc interactions on shoot and root dry weights were significant. At 0.5, 2.5, 20 and 80 mg Cd kg-1 (except for Cd0.5-Zn25), application of 5 to 50 mg Zn kg-1 increased shoot dry weight. Higher levels of zinc supplementation exhibited adverse effects. At 5 and 10 mg Cd kg-1, supply of 5 to 100 mg Zn kg-1 was associated with an increase in shoot dry weight, but shoot growth was reduced at higher zinc levels. At 40 mg Cd kg-1, application levels of 5 to 200 mg Zn kg-1 increased shoot dry weight, whereas 400 mg Zn kg-1 showed adverse effects. Moreover, the cadmium and zinc interactions on chemical composition of corn were significant. Based on the results, at low levels of cadmium, zinc supplementation at each level increased the shoot and root cadmium concentrations, while at high levels of cadmium, low and high zinc supply caused a decrease and increase in the shoot as well as root cadmium concentrations, respectively. The concentration of a particular trend was observed on the shoot and root. Supplementation of zinc at each level of cadmium (except for 80 mg Cd kg-1), first increased and then decreased the iron concentration of shoots and roots. Application of zinc at each level of cadmium decreased manganese and copper concentrations in shoots and roots.
Conclusions: According to the results, the ecological tolerance of corn to zinc was found to be 800 mg Zn kg-1. Also, the application level of zinc with positive effect on shoot dry weight increased with an increase in cadmium level. At all levels of cadmium, supplementation of zinc at medium levels prevented the accumulation of cadmium in shoots, while high and low levels of zinc intensified the cadmium accumulation. The highest accumulation of cadmium in roots was occurred at highest level of zinc. Zinc supplementation at each level of cadmium first increased and then decreased iron concentration in shoots and roots. However, zinc supply at each level of cadmium decreased copper and manganese concentrations in shoots and roots. As a conclusion, zinc at low levels diminished toxic effects and accumulation of cadmium, meanwhile high levels of zinc not only did not control cadmium but showed deleterious effects. The critical level of poisoning for cadmium in aerial parts of both plants in lower density in the soil (up to 90 mg kg-1 ) showed very little changes, but in higher density, it decreased in brassica napus and increased in zea mays. The critical level of poisoning on the aerial parts of both plants showed very little change with increasing the total density of cadmium in the soil.
