Assessment of Soil on Some Heavy Metals and its Pollution in Roodsar-Iran

Increased concentrations of heavy metals in the air, soil, or water threatens human health both directly and ...


Introduction
Over the past several decades, industrial activity in the mining and smelting sectors has caused serious environmental pollution by heavy metals on a global scale. Increased concentrations of heavy metals in the air, soil, or water threatens human health both directly and indirectly via accumulation in the food chain. In countries with high ecological awareness the risk of acute exposure has been minimized thanks to the enforcement of restoration laws and policies. The risk of chronic effects, however, is still there [1][2][3][4][5][6][7][8][9][10][11][12][13].
Heavy metals are chemical elements whose relative density is greater than 5gdm -³. Heavy metals are classified as essential microelements which include Cu, Fe, Mn, Zn, Mo, Ni and potentially toxic or nonessential elements as Cd, Cr, Pb, Hg and As. In soil coming through rain, dust and soot. Plants can also be deposited heavy metals from deeper soil layers in upper layer. Also, fertilization of soil comes a certain amount of heavy metals. However, major anthropogenic sources of soil pollution with heavy metals are intense traffic, metal industry, mining, organic and mineral fertilizers and municipal waste. Environment region of Guilan in Iran is several decades exposed to emissions of heavy metals and other pollutants emitted from metallurgical and thermal power plants [5][6][7]. It is known that atmospheric deposition of heavy metals due to soil in which maximum reserve in relation to other components of environment.
Usually linger for years in upper layer and very difficult to amounts of soil [1,[8][9][10][11]. Heavy metals can accumulate in large quantities in soil and can cause multiple ecological consequences of which are considered major polluters of environment [5,12,13].

Experimental Sections
a. Conducted an experiment had two objectives which are: To analyze heavy metals in soil samples using different digestion methods to determine most effective methods, b. To assess soil contamination by comparing results of limit values of heavy metals as defined in the Regulations that are defined [14,15]. soil [16][17][18]. Reducing size of primary sample of size suitable for laboratory work was carried out after primary sample dried 24h at 105°C, chopped and sieved. Samples were prepared in two ways: wet and dry digestion [5,17,19,20]. In wet digestion are used two types of reagents, table 1. Samples were prepared with super pure acids. In both cases, 1 g sample was added 10 ml of reagent. When digestion is carried sediment diluted with distilled water to 50ml.

Results and Discussion
Results of analysis of investigated heavy metals in soil defined location are given in Table 1. From results, Table 1, it is evident that as best method of sample preparation using wet digestion with HCl: HNO 3 =3:1. Above method is a standard method for preparation and analysis of soil samples, standard ISO 11047:2000.
Examining influence of soil depth on content of heavy metals, Table 1, it is evident that content of all investigated heavy metals slightly decreases with increasing depth, which is to be expected [21,22]. Results of many studies show that highest concentrations of heavy metals detected exactly at depth 0-5 cm, because greatest amount of heavy metals after arrival and migration in soil to retain a depth of 5cm [3,5,6,13]. Metal transport is not only dependent on physiochemical properties of metals but mostly on physical and chemical properties of soil, like for example: soil organic matter content, clay fraction content, mineralogical composition, pH, and more, all of which collectively determine binding ability of soil [8,12,17,19]. Based on results in Table 1 can be concluded that contents of Pb, Ni, Cr and Cu in almost all samples, prepared using three techniques of preparation, in both investigated depths, significantly higher than limit value. It is therefore necessary to take measures to reduce emissions of heavy metals from primary metallurgical plants and soil remediation measures for protection of human health [4,7,12,17].

Conclusion
For analysis of heavy metals in soil, as a method of sample preparation is best to use a wet digestion with HCl:HNO 3 =3:1.
Examining influence of soil depth on content of heavy metals it is evident that content of all investigated heavy metals slightly decreases with increasing depth, which is to be expected. Contents of Pb, Ni, Cr and Cu in almost all tested samples of soil at the region of Roodsar was significantly higher than limit value [23][24][25][26][27].