Contamination assessment of heavy metals in the soils around Khouzestan Steel Company (KSC) (Ni, Mn, Pb, Fe, Zn, Cr)

Soil plays a vital role in human life as the very survival of mankind is tied to the preservation of soil productivity (Kabata- Pendies and Mukherjee, 2007).
The purpose of this study is the assessment of heavy metal contamination (Zn, Mn, Pb, Fe, Ni, Cr) of the soil around the Khuzestan Steel Complex.
For this purpose, 13 surface soil samples (0-10 cm) were taken. Also a control sample was taken from an area away from the steel complex. The coordinates of each point were recorded by Global Positioning System (GPS). The samples were transferred to the laboratory and then were air dried at room temperature for 72 hours. Then they were sieved through a 2mm sieve for determining physical and chemical parameters (soil texture, pH, OC), and a 63-micron sieve for measurement of heavy metal concentration. pH was measured using a calibrated pH meter at a 2: 1 mixture (soil: water), and soil texture was determined using a hydrometer. The amount of organic matter was measured using the Valkey black method (Chopin and Alloway, 2007).
After preparation of the samples in the laboratory, the samples were analyzed using the ICP-OES method to assess concentration of heavy metals.
Measurement of heavy metals concentration was carried out at the Zar azma laboratory in Tehran. To ensure the accuracy of the analysis of soil samples, replicate samples were also sent to the laboratory.
In order to assess the heavy metal pollution in the soil samples, different indices including contamination factor (CF), contamination degree (Cd), anthropogenic enrichment percent (An%), and saturation degree of metals (SDM) were calculated.
In addition, the mean concentrations of heavy metals in soil samples were compared to the concentration of these metals in Control Sample and unpolluted soil standard.
Measurement of soil pH showed that the soil has a tendency to alkalinity. Also, soil texture is sandy loam (Moyes, 2011).
The results showed that the mean Organic Carbon in the soil sample is 1.03%, the higher amount of OC is related to soil sample numbers 7 and 11.
The mean concentrations of Ni, Pb, Zn, Mn, Fe and Cr in soil samples were 61.42, 19.90, 156.63, 443.63, 38762.63 and 127.58 (mg/kg), respectively.
The highest concentrations of manganese, chromium, zinc and lead were found in soil samples number 4 and 12. This is in agreement with the results of the saturation degree of metals so that, the highest values of saturation degree of metals were found for soil samples close to the factory, (i.e. 4 and 12). The SDM values decreased with distance to the factory. The highest contamination factor was obtained for soil samples which were taken near the steel factory (4 and 12).
Also, the highest contamination degrees were found for soil samples 4 (23.7) and 12 (14.1) while, the lowest values were obtained for soil samples 6 (6.35) and 10 (6.07).
The results of the contamination degree calculation, anthropogenic enrichment percent, as well as statistical analysis are consistent. It can be said that the origin of iron in study areas is related to anthropogenic and geogenic activites.
The results of anthropogenic enrichment percent, indicated that Lead, Manganese, and Zinc in the soil samples which were taken around the steel factory have an anthropogenic source. Moreover, the source of Chromium and Nickel is mainly geogenic.
The results showed that all variables are normally distributed. Three components originate with a cumulative variance of 79.55% for soil samples.
PC1 which explains 41.47% of the total variance can be defined as an anthropogenic component since Mn, Pb and Zn soil samples have the highest loading on PC1. As previously indicated, the concentration of these elements in the study area is mainly influenced by the steel industrial complex.
The PC2 represents 22.26% of the total variance, and is strongly associated with Ni, Fe can be defined as geogenic and anthropogenic component, as the variability of the elements seems to be controlled by parent rocks and human activities.
Cr was individually included in the PC3 whith 15.82% of the total variance. The distribution of Cr in the studied soils confirmed that it was derived from the parent materials of soil.
The highest concentrations were found at soil samples 4 and 12. Comparison of heavy metals concentration with unpolluted soil standard indicated that, concentrations of Cr, Zn, Fe, Ni and Pb is higher than that of unpolluted soil standard. In general, Manganese, Chromium, Zinc and Lead are the most important elements that are found in emissions of steel plants.
The soil samples near the steel plant and downwind direction have much higher pollution level.
The results showed that Mn, Pb and Zn is related to human activity and Cr have geogenic source and Fe and Ni have both geogenic and anthropogenic source in the study area in the city of Ahwaz.