Levels and variability of metals in soils of the province of Golestan (Iran).
Studying the concentration distribution of metals is necessary for soil pollution monitoring and maintaining environmental quality. To date, very little large-scale research has been performed to investigate metal contamination in developing countries. In this study, the content and spatial distributions of five metals (cadmium [Cd], copper [Cu], nickel [Ni], lead [Pb], and zinc [Zn]) were quantified based on 346 topsoil samples from 12 districts in the province of Golestan (northeast [NE] Iran). The concentration levels (mg/kg) of Cd, Cu, Pb, Ni and Zn varied from 0.02 to 0.36, 9.3 to 93.7, 6.8 to 44, 9.5 to 85.35, and 25 to 417.4, respectively. The average concentrations (mg/kg) obtained were as follows: Cd 0.12 ± 0.07, Cu 23.9 ± 9.07, Ni 34.88 ± 11.59, Pb 15.42 ± 5.81 and Zn 82.08 ± 30.87. Significant differences in the distribution of trace elements among districts were detected. The AzadShahr and BandarGaz districts displayed the highest metal concentrations. Greater metal values were obtained in the central, south, west, and NE areas, although Zn concentration was also high to the north of the province. Values of contamination factor and contamination degree indicated that the metal pollution level was on the order of Zn > Cd > Pb > Cu > Ni and that all of the metals belonged to a low or moderate pollution category. Ni and Cu levels derived from natural sources, whereas Cd, Pb, and Zn derived from anthropogenic activities with greater mean concentrations than reference concentrations.