Assessment of Heavy Metals Contamination of Soil Particle Size Fractions in Different Land Uses of Baghan Watershed, Bushehr province, Iran

Watersheds are the sources of drinking water for cities and villages, and their pollution with heavy elements threatens the health of the inhabitants who use their water and agricultural products. Considering the importance of Baghan watershed in Bushehr province, the purpose of this study was to evaluate the contamination of soil particle size fractions (<63 and <2000 µm) by some heavy metals (Cd, Mn, Ni, Pb, Zn, Cu, and Fe) in three major land uses (range lands, croplands and orchards). Location of 120 surficial composite soil samples (0-20 cm) were determined using the Latin Hypercube technique on the topographical map. After pretreatment of soil samples, heavy metals were extracted by the Sposito method and measured using an atomic absorption spectrometry and geochemical pollution indicators including contamination factor (CF), geo-accumulation index (Igeo) and the pollution load index (PLI) were calculated. A significant increase in the concentration of Cu, Cd, and Fe has been observed by decreasing the particle size in different land uses. The contamination factor (CF) for particle sizes <2000 and <63 were ordered as Cd>Mn>Pb>Ni>Cu>Zn>Fe and Cd>Mn>Cu>Ni>Pb>Zn>Fe, respectively. The CF index indicates that the orchard soils for Cd were considerably polluted and for other metals moderatly polluted. Positive and significant amount of geo-accumulation index (Igeo) for Cd and Mn was observed for both soil particle classes in all land uses. Overall, the results of this study confirmed concentration of some heavy metals in smaller particles size. Comparing contaminants concentration of Cd and Mn in croplands and orchards soils with the range lands soils indicated anthropogenic effects on soil pollution. The results revealed risk of heavy metals in the watershed and necessity of reconsidering management policies.