Evaluating the Concentration of Heavy Metals in Downstream Area of Southern Waste Landfill in Kermanshah

Affected by the change of land-use pattern, soil pollution has become an important environmental issue in developed and developing countries.  Heavy element pollution, as a kind of soil pollutant, is really dangerous due to their high toxicity and persistence in the environment. In the current study, the extent of pollution to heavy elements in downstream area of southern waste landfill of Kermanshah city was investigated. In this research, 208 soil samples (from 0 to 20 cm depth), were collected with 50 meters distances systematically from downstream area of waste landfill. The spatial pattern of variables was investigated through calculating experimental variograms and fitted models using geostatistics.  The mean concentrations of Fe, Mn, Cu and Zn in downstream area of waste landfill are 4077, 943, 41.8 and 102 mgkg⁻¹ respectively. The spherical model was recognized as the best model to describe the spatial variability of total heavy metals. Total content of Fe, Mn, Cu and Zn showed a strong spatial dependence. According to the ordinary kriging maps, the total concentration of elements in the central parts of the study area is less than the other parts. This is probably due to the lower slope of the central region and consequently the lower infiltration. The concentration of elements in the southeastern towards the northeast High slope of the area is the result of the adjacency to the waste landfill and also the higher steepness in this part. The findings indicated a long-term progressive trend soil pollution, thus it is necessary to halt latex infiltration either towards the soil or vertically ground water. The results showed a long-term progressive trend in soil pollution. Considering population growth, waste production rate, distance from the city center, and other factors determining the location of landfill, it is suggested to reconsider positioning waste landfill scientifically. Furthermore, some services such as waste separation in the source, waste recycling in the source, and composting would be inevitable.
Extended Abstract
1-Introduction
Soil is not only a means of plant growth or a pool for the disposal of undesirable substances but also a transmitter of many pollutants to the atmosphere, surface water, groundwater and plants. Soil pollutants can indirectly harm human health through water supply and the food chain. Heavy metals and their compounds are naturally found everywhere in the soil environment. Heavy metals generally refer to metals having a density greater than 5 grams. cm-3 such as Cadmium (Cd), Chromium (Cr), Mercury (Hg), Lead (lead), Copper (copper), Zinc (zinc), Manganese (Mn) and Nickel (Ni). Heavy metals in urban soil may be due to various human activities such as vehicle emissions, industrial discharges, and other human activities such as waste incineration and soil contamination. The spatial distribution maps of heavy metals is very important to control risk. Therefore, the present study aimed to evaluate some heavy metal concentrations in the downstream area of ​​South Kermanshah landfill.
2-Materials and Methods
 In this research, 208 soil samples (from 0 to 20 cm depth), were collected with 50 meters distances systematically from downstream area of waste landfill. Besides, 15 samples were taken randomly from adjacent area (with similar geological characteristics) as background soils. Total concentration analyses of the mentioned elements were conducted based on standard procedures. The normality of the soil heavy metal concentrations was assessed using Kolmogorov-Smirnov (K-S) test. Kriging is based on the assumption that the parameter being interpolated can be treated as a regionalized variable. The GS+ (v.5.3) software was used to calculate the spatial pattern of variables investigating fitted geo-statistics models. The Kriging method was used to estimate the concentration value of the unobserved points. Mapping was done applying the ArcView CIS 10.2 software.
3-Results and Discussion
 The results show that the mean concentrations of Fe, Mn, Cu and Zn in downstream area of waste landfill are 4077, 943, 41.8 and 102 mgkg⁻¹ respectively. Total concentration of elements were higher than the respective values in background soils. The increase in the mane of heavy metals concentrations in waste landfill soils is in the order of Zn ˃ Cu ˃Mn ˃ Fe in comparison with the corresponding background values. The coefficients of variation (CV) was relatively small for all the soil heavy metals. The concentration of soil heavy metals had CV % values between 15 and 31, which indicated slight variability in the study area. The findings from K-S test showed that soil concentration of Fe, Cu and Zn in the study area was distributed normally, although the Mn concentration is distributed normally. The results showed that the spherical model was the best model to describe the spatial variability of total heavy metals. Total content of heavy metals showed a Strong spatial dependence. Moreover, the analysis of variograms showed that structural component of spatial dependency dominates randomized component. According to the kriging maps, elements concentrations in the central parts of the study area is less than the other parts. This is probably due to the lower slope of the central region and consequently the lower waste leachate infiltration. The higher concentrations of elements in the southeastern towards the northeast slope of the area is the result of the adjacency to the waste landfill and also the higher steepnes in this part. The kriging estimation variances were calculated and delineated for all three elements; the delineations indicated that variances were raised in the margins of the study area among the samples where, the density of sampling decreased. The Mean Estimation Error (MEE) and Root Meam Square Error (RMSE) values ​​of heavy metals concentrations showed that the ordinary Kriging is an appropriate method to interpolate and map heavy metals concentrations in downstream area of Kermanshah waste landfill.
4-Conclusion
According to the values of the ranges of heavy metal concentration effect, the sampling distance was precise. The concentration of heavy metals in soils has increased under the influence of waste leachate in comparison with background soils and Zn has the highest increase. Results showed a long-term progressive trend in soil pollution. The results showed a long-term progressive trend in soil pollution. Considering population growth, waste production rate, distance from the city center, and other factors determining the location of landfill, it is suggested to reconsider positioning waste landfill scientifically. Furthermore, some services such as waste separation in the source, waste recycling in the source, and composting would be inevitable.