Assessment of heavy metal contamination of soils impacted by a zinc smelter activity

Four metals (Cu, Zn, Pb and Cd) were assayed in soils within the impact zone of the Miasteczko Slaskie Zinc Smelter (southern Poland). The investigated area is afforested and has been subjected for a long time to intensive deposition of metal-bearing dusts. Soil pHKCl varied broadly from very acidic (pHKCl = 3.4) to slightly alkaline (pHKCl = 7.2). Organic carbon (Corg) content fluctuated within a large range, i.e., 5.5 - 66.4 g kg-1, whereas the cation exchange capacity (CEC) was in most cases markedly low (from 1.4 to 5.9 cmol(+)kg-1), with exception for two sites (C and D) exhibiting values of 26.8 and 15.1 cmol(+)kg-1, respectively. Total Zn, Pb and Cd contents exceeded manifold their respective levels in the Earth crust (reference value - RV)) as well as those suggested as background levels for Poland (BLP). The assessment of the contamination of soils by these metals was undertaken on the basis of geoaccumulation indices (lgeo), contamination factors Cl and degrees of contamination (Cdeg). The overall metal contamination represented practically two classes: low contamination for Cu; considerable to extreme contamination (in ascending order) for Zn, Cd, and Pb. The contribution (BLP-based assessment) of each metal to the degree of contamination index varied from 2.14 % (for Cu), via 26.33% (for Zn) to quite equally for Cd and Pb, both representing 35.22% and 36.32, respectively. It is worth pointing out that copper was the sole metal to threaten the least (Figure 1) the soils of the investigated ecosystem.