Spatial Distribution of Mercury Contamination in Soils around of Kerman Cement Plant

In recent decades, industrial and technological advancements have led to the gradual increase of heavy metal concentrations. As such, this phenomenon of heavy metals being present in the environment at high concentrations causes deleterious effects on various terrestrial creatures and human beings. Mercury (Hg) is one of the most toxic elements and can cause renal and neurotoxicity to humans and wildlife. It has been identified as a priority toxic substance in many countries. It is, however, rare to find information on Hg in soils from industrialized areas of Iran in literature. In order to ascertain the distribution of Hg, as well as the extent of contamination with Hg, and to provide policymakers with remediation measures for the affected soils, a study of surface soils was conducted in areas around of Kerman cement plant.

Soil samples were collected from the depth of 0 to 20 cm. 103 samples were taken and analyzed. Mercury concentration in soil samples were determined by atomic adsorption method coupled Graphite furnace. Statistical analysis and indices calculation were performed by SPSS and EXCEL, respectively, and distribution maps were prepared by kriging method in ArcGIS software. For evaluating pollution, Geoaccumulation index, enrichment factor and contamination factor were also calculated and interpreted.

The mercury concentration in soil samples ranged from 6.70 to 340.96 μg/kg, with a mean value of 164.06 μg/ kg. Mercury is naturally present in very low concentrations in the soil. The concentration of this element in soils ranges from 0.01 to 0.5 mg/kg around the world. The average Hg concentration in the earth crust is reported to be 80 μg / kg. In soils of the study area, the Hg concentration was higher than most of the reported values for soils worldwide and earth crust. This indicates that industrial activities have increased the concentration of mercury in the soil. In fact, the concentration of mercury more than the amount of earth crust indicates the onset of contamination due to various anthropogenic activities. The coefficient of variation of mercury concentration in the soil was 55%, which shows a high variability (CV≥ 35%) according to the classification proposed by Wilding et al. (19). The high variability coefficient shows the heterogeneous and non-uniform distribution of the property. Therefore, there is a high concentration of mercury in some areas of the study region. In other words, soil was affected by external factors in some areas. Based on the cleaning standards of soil for mercury in soils used for industrial purposes in some countries, all soil samples in the studied area have a much lower concentration of mercury than standard values. In other words, although the activity of the cement plant has increased the concentration of mercury in the soil, it can continue its industrial activity. The plant’s managers should, however, take a close look at the release of this metal and other pollutant. According to the results derived from Igeo, Hg was graded as unpolluted to moderately polluted. Low levels of contamination (CF <1) to significant contamination (3.00 ≤ CF <6.00) of mercury were observed based on the contamination factor. The results suggest that anthropogenic sources control the concentration of mercury in the soil. The average contamination factor more than one (CF> 1) indicates that the soils of this region have been exposed to mercury contamination. Spatial distribution map indicates that the highest concentration of mercury in the soil is between 200 and 341 μg/kg, which was observed around the factory and south-east of the region. Release of mercury in the environment is related to natural processes and human activities. Mercury release due to human activities is mainly due to combustion of fossil fuels, iron ore processing, steel industry and cement plants. Considering the high concentrations of mercury in the southeastern part of the region, the lower part of the plant, it seems that environmental factors such as the topography of the area may affect its distribution. The high concentrations of Hg were observed at low elevations, on the south side, and over the areas with relatively low slope gradients.

The results demonstrated that the concentration of Hg was higher than most of the reported values for soils worldwide and earth crust. This indicates that industrial activities have increased the concentration of mercury in the soil. According to the results derived from Igeo, Hg was graded as unpolluted to moderately polluted. In addition, the level of contamination was identified to be low to high, based on the contamination factor (CF). The spatial distribution map of the total concentration of mercury shows that the highest concentration of mercury was observed around the factory and to the south and southeast of the region. The high concentrations of this metal were at low elevations and on the south side of the catchment and in areas with relatively low slope gradients. It is concluded that although the concentration of this pollutant is not critical in the study area, due to the close proximity of the industrial area to the residential area, planning to control the release of this metal and other pollutants should be seriously considered.