Heavy metal assessment in stream sediments from the rivers passing through the mining area

Stream sediment samples in two sizes of sand and clay/silt from the Chodarchay and Gilankesheh rivers which pass through the Chodarchay copper deposit, northwestern Iran, were measured for their metal concentrations using a sequential extraction procedure. The average concentrations of cadmium (18.22) in sediments from the rivers exceed the world average shale and continental upper crust values. Based on Geo-accumulation Index, cadmium is intensely elevated (in the clay fraction greater than 5 and in the sand fraction between 3 and 5), arsenic and lead are slightly elevated in a few stations and others are not-elevated. The zinc and copper values are almost equal to or lower than Geo-accumulation Index; thus, the sediments are unpolluted with respect to zinc and copper. Enrichment factor values confirm the risk of cadmium in the environment. Comparison of the mean heavy metal concentrations in the sediments with threshold effect concentration and probable effect concentration values shows that cadmium (clay/sand = 15.23/7.77) is higher than the threshold effect concentration and probable effect concentration values, while copper (13.41/7.71), lead (6.38/9.18), zinc (18.26/8.19), and arsenic (3.60/1.14) are lower than the threshold effect concentration values. The cadmium and lead could cause serious danger for river biota. Based on pollution intensity, sediment samples from both rivers are divided into low to highly enriched in lead, zinc, and copper, very high to intensely enriched in arsenic, and intensely enriched in cadmium and arsenic. The majority of metals are observed in the clay/silt fraction.