environmental impacts of natural contaminants and mining activities on the surface and agricultural soils in the aq-darreh river watershed, takab, west azerbaijan province, nw iran

the concentrations of potentially toxic elements (as, sb, and hg) and some trace elements in 36 topsoil samples and 18 agricultural soil samples were measured at the aq-darreh river watershed, nw iran. based on the results of the chemical analysis and comparing them with different standards, it seems that the soils of the aq-darreh river watershed are polluted with as and sb. this pollution results from geochemical background (natural contamination) and mining activities. geochemical background values in topsoil and agricultural soils were estimated for as (429.7 ppm and 98.8 ppm), sb (79.02 ppm and 3.98 ppm), and hg (356 ppb and 2596 ppb). this research also indicates that mining activities have played a significant role in soil pollution and increasing as, sb and hg concentration in topsoils and as and sb in agricultural soils. results of sequential leaches and xrd analyses of both soil types showed that most of the as concentration is bound to amorphous iron hydroxides in soils, while sb and hg are bound to resistant minerals such as stibnite and cinnabar. clay and carbonate minerals have a lower adsorption of these pollutant elements in both topsoil and agricultural soils.