Soil and water samples collected from Bijar area were analyzed in order to investigate arsenic contamination sources and their human risk potentiality assessment. Routine physical and chemical characteristics, iron oxides and arsenic contents were measured in 227 soil samples. Spatial variability of arsenic was calculated usinginverse distance weighting (IDW) to assess the arsenic contamination potential. Furthermore, the relationships between soil parent material, physico-chemical characteristics and the spatial distribution of arsenic were analyzed. Topsoil arsenic concentration showed significant correlations with clay (r = 0.77), sand (r = -0.45), silt (r = -0.48), Fe oxides contents (r = 0.65) and cation exchange capacity (r = 0.65) statistically. The highest arsenic concentrations were observed in the map delineations with higher clay, Fe₂O₃ and cation exchange capacities. Parent materials derived from Fe-rich igneous (or pyroclastic) rocks and mudstone (arsenic source parent materials) composed of significantly higher arsenic contents, compared to the rest parent material types. Spatial variability analyses demonstrated that considerable extent of the studied soils was potentially contaminated by arsenic. The distribution map of arsenic contaminated areas was rasterized by IDW which confirmed that arsenic contamination in the studied area originated from some specific point sources (arsenic bearing parent materials) and spread over the lower positions by water pollution and erosion-deposition processes.

Key words: Parent materials, IDW, Physicochemical characteristics.