Evaluation of Potentially Toxic Elements Pollution Indices in Rangeland Northwest of Chadegan city (Isfahan Province)

Today, the pollution of Rangeland soils by various destructive pollutants has become one of the human-environmental problems. Lacking proper management of organic matter discharge can also increase the concentration of salts, heavy metals, and pathogenic microorganisms. In this study, to investigate and measure the concentration of toxic elements, 128 soil samples of Chadegan region were selected to distinguish the concentration extent of these metals and also high-risk and polluted areas. Based on the obtained results in the sampled points, the average soil pollution by cobalt, copper, and chromium elements was observed which its origin can be considered as pollution with a geologic origin. The other elements observed in the soil have little enrichment or no pollution.

Soil pollution as a part of land degradation is caused by the presence of synthetic chemicals or other changes in the soil environment. The heavy metal pollution of soils has been very widespread and there is a risk of transmission of these toxic and accessible metals to humans, animals, and agricultural products. Heavy metals due to their non-degradability and physiological effects on living organisms are also very important in low concentrations. The soil pollution from toxic elements is different from water or air pollution because the toxic elements remain in the soil longer than the other parts of the biosphere and are more durable in the soil. The objectives of this study are to investigate the distribution of toxic elements and to assess the environmental pollution of a part of Chadegan’s soil which has been tried to be studied by using the accumulation land indices, pollution coefficient, pollution load, enrichment coefficient, heavy metals pollution zoning, and the statistical analyses.

In order to conduct this study, in-field inspections, 128 samples from the soil of the studied area have been taken from a depth of 30cm. After doing the initial preparation process, the samples up to the dimensions of less than four millimeters were firstly crushed by using the crusher machine in the laboratory and then pulverized in the disk mill up to 75 microns size (200 meshes). To weigh the samples, Teflon pipes were used in the 4-Acids Digest method.After weighing the samples in a Teflon tube; hydrochloride, pre chloridic, nitric, and chloride acids each added up to a certain amount and then all of them were placed in the Hot Box. After performing the complete digest operation, the samples were cooled at the ambient temperature and reached to sufficient volume with distilled water, and finally, the chemical analysis performed in the ICP-MS method by using Agilent Series 4500 machine made in the United Stutes. Due to the changes in the concentration of the elements in the soil of the region; Ba, Co, Sc, Pb, Y, Cu, B, Zn, Ni, Sr, Cr metals were selected. To determine and construe the extent of pollution of the soil samples studied; the enrichment factor, the pollution load index has been used here due to the concentration of the elements. The ArcGIS software was used to prepare the spatial distribution. Because Kriging methods (normal, simple, and discrete) have high potentials for determining the spatial distribution of the heavy metals of soil; hence they have been proposed as appropriate methods for interpolation and preparing the pollutants map.

The result of calculating the accumulation land index for the soil samples taken from different station show that Igeo extent of all elements is less than one or less than one or less than zero thus have little or no pollution. The result of the pollution coefficient analysis indicates that pollution is law and soil is non-polluted in all sampled areas except for some station that has low and average pollution in terms of cobalt, copper, and chromium elements. Regarding the pollution load index and due to the standard values of P.L.I; the soil of the studied area is free of pollution. The obtained results of calculating the enrichment coefficient of the studied soil samples show that apart from cobalt, chromium, copper, nickel, lead and zinc elements which have average enrichment and its origin can be considered as pollution with anthropogenic pollution; the rest of the present elements have low enrichment and are non-polluted. The zoning map of the concentration of the toxic elements from the area soil indicates that the elements of cobalt, nickel, copper, and strontium in the southwest of the region and also boron, barium, and yttrium elements in the southeast of the area have average to low concentration and the other elements have very low concentration. Based on histogram diagrams, the elements of boron, chromium, nickel, lead, strontium, and yttrium have symmetrical distribution and the elements of barium, cobalt, copper, and scandium have asymmetrical distribution and positive skewness.

According to the result of the accumulation land index, it was found that the studied soils have little or no pollution. The results of the pollution coefficient suggest that except for the elements of cobalt and lead which have average enrichment in some stations, the other elements have poor enrichment. The pollution load index shows that the studied samples have no pollution and also have appropriate concentration and this is while that the enrichment extent of cobalt, chromium, copper, and lead is near average and this enrichment extent can be considered as pollution with an anthropogenic origin.