Distribution and Forms of Copper, Zinc, Cadmium, Iron, and Manganese in Soils Near a Copper Smelter1

We examined the contamination of soil by copper, zinc, and cadmium with respect to distance from a copper smelter. The majority of contamination was in the immediate vicinity of the smelter. Between 30 to 60 percent of total Cd was exchangeable in MgCl2 solution, and the exchangeability was much greater than that of the other elements examined, including iron and manganese. Most of the Cu, Zn, and Mn were present in an oxalate-extractable fraction, but only small amounts were extractable by citrate-dithionite-bicarbonate (CDB) solution. This suggests that Cu, Zn, and Mn were more strongly associated with amorphous iron oxides, with only small amounts being occluded in crystalline iron oxides. Only Cu was appreciably associated with the soil organic fraction. The treatment of soils with sodium hyperchlorite prior to oxalate extraction appeared to be necessary to better estimate the amounts of Cu associated with the oxalate-extractable fraction. Without this pretreatment, the oxalate extraction could overestimate the amounts of Cu associated with this particular fraction possibly due to the dispersion of organically complexed Cu in the oxalate solution. The mobility of Cu, Zn, and Cd in the soils was limited, as evidenced by a sharp reduction in concentrations of the three elements with depth. Comparing subsoil concentrations of these elements with those from areas relatively unpolluted by smelter fallout revealed that Cd was more leachable than Cu or Zn under western Washington conditions.