Spatial and Temporal Variability of Some of Heavy Metals in Aerosols of Lenjanat Region, Esfahan

Heavy metals released from stationaryand mobile origins can be transported in water, air and soil and can be even absorbed by plants, animals and human bodies. Trace elements are currently of great environmental concern. Nowadays, one of the most important environmental problems is pollution of agricultural soils occurs by heavy metals due to human activities. Atmospheric subsidence is one of the main sources of these elements which can result from industrial activities, fertilizers, sewage sludge, compost and pesticides. Heavy metals mapping of the atmosphere dusts indicates the status of pollution and its intensity in industrial regions. This information can also be used as a guideline for better management and pollution control. This study was performed to investigate the spatial and temporal availability of heavy metals in atmospheric dusts of Lenjanat region, Isfahan where agricultural land is extensively surrounded by industrial activities like steel making factory (Esfahan), cement making factory (Sepahan and Esfahan) and Bamalead mine. Sampling was done from 60 points with the same altitude(three to six meters from the ground)and their location was recorded by GPS. Glass traps (1×1 m2) covered by plastic mesh (2 × 2 cmvents) were used to trap the dusts for four seasons of the year. Collected dust samples were passed through a 200 mm mesh screen size and the total weight of the dusts and the heavy metals content of Cd, Zn, Cu, Ni and Pbwere determined(with HNO3 60%). Data analysis was performed using Statistical 6.0 software. Analysis of spatial data via variogram was calculated and performed using Variowin, 2.2 software packages. After determination of the best fitting model, kriged maps of the total concentration of heavy metals were prepared by Surfer 8 software. The average concentrations of Zn, Pb and Cd in dust in most parts of the study area were much higher than the soil standard values and the maximum value was around the Zn and Pb mines. However, the concentrations of Cu and Ni were higher than the standard values only in some parts of the area. Comparison of the averages for different seasons showed that in most cases there were significant differences between the concentrations of the various elements. A significant correlation was observed among Pb, Zn and Cd concentrations in all seasons indicating similar origin of these elements. The average dust deposition rate in the summer was more than the other seasons. Moreover, in all seasons except the spring and fall, there was a significant difference between the average dust deposition rates. Kriged maps of Zn, Cd, and Pb showed that the maximum concentrations of these elements occurred near the Pb and Zn Bama mine and the concentrations of these elements decreased with increasingthe distance from the mine. The contamination was lower in the spring and higher in the summer. Based on the kriged maps, samplingfrom one seasononly can be used to assess the trend of element contamination but if the objective focuses on absolute heavy metals values, season strongly influences the results and interpretation from one season can be misleading. The determination of the amounts of dust and their heavy metal contents in different wind directions is recommended to identify the source of dusts and heavy metals. Results showed a significant difference among the mean values of dusts for the different seasons except for the spring and fall. The mean values of Pb and Cd in all seasons and Zn except for the spring were higher than the threshold values reported for the soils. A significant correlation was observed among the concentrations of some elements which may suggest their same origin. Interpretation of kriged maps showed that zinc and lead Bamamine in the region could be the main source of the contamination of Zn, Pb and Cd. According to quantitative calculations, a low accordance was observed for the pattern and the values of each element in different seasons. This can be related to the wind velocity and its direction, intensity of industrial and mining activities and also the amount of humidity of soil and air during the year. Interpretation of atmospheric data based on one season may be considerably misleading.