Investigating the factors affecting the concentration of lead and cadmium in different points of the Sejzi desert emphasizing the distribution of biological soil crusts

Heavy metals are one of the most common pollutants that enter the environment due to industrial activities in human societies and endanger the health of organisms and humans over time. Recently, to decrease negative effects of heavy metals in the environment, the use of bio sorbents produced from industrial and agricultural wastes has been replaced by other methods as a low-cost method. Other biological methods, such as the establishment of some plant species that have the potential to absorb heavy metals, have had acceptable results in the areas around industrial estates or metal mines. Based on Researches' results in other parts of the world, biocrusts play an important role in the uptake of heavy metals and soil purification. Biocrusts are a close community of lichens, mosses, algae, and other soil microorganisms that affect the basic processes of the soil ecosystem. In this study, some of the soil properties and cadmium and lead concentrations in different parts of the Sejzi plain of Isfahan province were investigated and the effect of biological crusts on the concentration of pollutants was investigated.

After measuring acidity, electrical conductivity, organic carbon, soil texture, lead, and cadmium concentrations, the relationship between the distribution of biocrusts with soil properties and cadmium and lead concentrations was investigated by principal component analysis. Then, using one-way ANOVA, the most important effective features are identified. Based on Duncan's test, the mean values of soil properties measured in five villages located in Sejzi plain were compared with each other at 95% probability level, and finally, the soil of points of Sejzi plain with higher cadmium and lead concentrations were determined.

According In all studied sites, the average absorbable lead was more than 80 mg/kg (permissible level). The amounts of cadmium were measured at Fasaran and Sejzi at 2.8±0.6 and 2.38±0.18 mg/kg, respectively, that had been exceeded it's permissible level (2 mg/kg). Also, the results of the principal component analysis showed that in the first component, which is 67.4% of the total variance of the data, the correlation between the percentage of silt was 0.438 and the percentage of sand was measured -0.451. In the second component, which is justified about 48.6% of the total variance of the data, the correlation coefficient of the values of cadmium and lead were estimated 0.388 and -0.438, respectively. The comparison of soil properties in different places showed that the average values of soil salinity, organic matter, silt percentage, cadmium and lead are different in those places.

The high concentration of lead and cadmium levels in areas without biocrusts, including Sajzi and Fesaran, were mainly due to human mismanagement and construction of factories, mines, and roads. Also, some intrinsic properties of soil, such as soil texture were effective in the distribution and establishment of biological crusts.