Study and investigation of heavy elements in the soil of Zabol and Birjand cities

Study and investigation of heavy elements in the soil of Zabol and Birjand cities



Abstract



Introduction

One of the most significant environmental challenges today is soil pollution, which is particularly evident in developing countries. This issue has consistently been a focal point for urban and environmental officials. Soil, as a fundamental component of living ecosystems, is essential for sustaining life on Earth. In addition to its crucial role in life continuity, soils have a significant impact on evolution and even the formation of life. They serve as a primary source for generating societal wealth and play a vital role in development projects and community health initiatives. Today, the accumulation of heavy elements and soil pollution in agricultural lands is recognized as one of the vital issues in the field of environmental biology globally. This not only compromises the quality of agricultural products but also jeopardizes the sustainability of agricultural production. Entry of heavy elements into soil ecosystems occurs through human activities, and researchers believe that these pollutant sources may pose long-term risks to human health. This is because prolonged exposure to surface soils containing heavy metals can lead to serious health hazards through inhalation, ingestion, and skin absorption

Materials and Methods

The study areas in this research include two counties: Birjand in South Khorasan Province and Zabol in Sistan and Baluchestan Province. In this study, a systematic grid sampling method was used for soil sampling. A total of 90 samples were collected, with a distance of 200 meters between each sample on both sides of the road. The sampling depth was 0-25 centimeters. After sampling, the samples were transferred to the laboratory. Finally, 12 elements (Al, Mn, Fe, Cr, Zn, Ni, Ti, Co, Cd, Cu, As, Pb) were analyzed in the soil samples using the ICP-OES instrument model Varian 710-ES. Then, three indices, including Muller's Accumulation Index, Contamination factor, Cumulative pollution index and Enrichment Factor, were used to assess the contamination intensity of the soil samples. Pearson correlation matrix in R software was also employed to examine the relationships between heavy metals present in the soil samples from the cities of Birjand and Zabol.

Results and Discussion

The levels of metals present in the soil (concentration in the earth's crust) of Birjand city indicated high concentrations of lead, Nickel, Cadmium, Zinc, Copper, and Chromium related to human activities. According to the results obtained from the analysis of background soil samples, among the measured metals in Zabol city, the highest average concentration was related to aluminum and iron, while the lowest average concentration was related to nickel. The results of the Pearson correlation analysis for heavy metals in Birjand city showed that Copper, Zinc, and Arsenic have the highest negative correlation with other heavy metals, while the rest of the heavy metals had a positive correlation with each other. The results of the Pearson correlation matrix for the concentration of heavy metals in the soil of Zabol city also showed that there is mostly a negative correlation between most elements, while in other cases, they, the highest average concentration was related to aluminum and iron, while the lowest average concentration was related to nickel. The results of the Pearson correlation analysis for heavy metals in Birjand city showed that Copper, Zinc, and Arsenic have the highest negative correlation with other heavy metals, while the rest of the heavy metals had a positive correlation with each other. The results of the Pearson correlation matrix for the concentration of heavy metals in the soil of Zabol cit all have a positive correlation. Based on the accumulation index, it can be stated that the origin of pollution in Birjand city with chromium and lead is mostly anthropogenic. Additionally, the origin of other elements that were within the non-polluted range can be attributed to the earth's crust. On the other hand, in Zabol city, the accumulation index indicates pollution of the soil in the area with Nickel.

Conclusion

Based on the results of the study in the two cities of Zabol and Birjand, it can be concluded that the pollution status with heavy metals in these two cities differs significantly. Considering the correlation between heavy metals in soil samples from the cities of Birjand and Zabol, it was found that in Birjand, copper, zinc, and arsenic had negative correlations with other heavy metals, while the rest of the heavy metals had a positive correlation with each other. However, in Zabol city, most elements had negative correlations. Nevertheless, the strongest positive correlations were observed between titanium and iron, titanium and manganese, arsenic and lead, and manganese and cobalt. These results indicate differences in the pattern of heavy metal pollution between the cities, which may be attributed to local factors such as industrial activities, traffic, and fuel consumption.This study overall underscores the need for further actions to control and reduce heavy metal pollution in both cities.

Keywords: Heavy metals, accumulation coefficient, Pearson coefficient, soil pollution.