An assessment study of heavy metal distribution within soil in upper course of Zarqa River basin/Jordan

Levels of heavy metals are found in soils and waters of the major tributary valleys of the Jordan Valley. Heavy metal content in soils irrigated by treated waste water were measured for a 40 km reach of Zarqa River. Soil samples from eight different sites along the upper course of this river were analyzed to determine the concentration of selected heavy metals (CO, Cr, Cu, Pb, Ni, Zn). Silt forms the major component of the soils with an average of 54%. Clay fractions show an increase with depth from 17 to 41%. Trends in particle size distribution and metal contents were compared across sample sites. Samples contained moderate to considerable levels of Pb and Ni. Concentrations of Cu and Cr ranged between 33-59 and 65-90 ppm, respectively. These values represent a slight to moderate class of pollution. The concentration of Cr shows a decrease with depth and distance from the waste water plant. Cu, Zn, and Ni show increasing concentrations with depth but Pb and CO do not. The concentrations of the measured heavy metals increases near the waste water treatment plant but decreases with distance from the plant due to precipitation in the stream bed and dilution with stream water. This decline in metal content with distance from the treatment plant suggests that most metals reaching floodplain soils may derive from the same source. Although current metal concentrations are low to moderate, floodplain surface soils in this area should be regarded as a potential source for future heavy metal pollution downstream.