Environmental ecotoxicology of heavy metals contaminants in the Dostbagloo alteration area, Ardabil province

Oxidation of sulfide-mineralized zones during weathering intensifies by the biological and chemical reactions, and the released acidic mine drainage (AMD) mobilizes toxic and heavy elements from the parent rock and concentrates them in soil or water environments. The village of Doustbaglu is located in a mountainous area to the northwest of Meshgin-Shahr city, which has numerous farmlands overlooking the extensive alteration zones. Field studies indicate that, unfortunately, skin and liver diseases, as well as cancer are prevalent in the area. The importance of knowledge of heavy metal enrichment in soil resources and the high potential of the Doustbaglu area for the production of agricultural and horticultural crops and its direct relationship with human health reveals the necessity of conducting this study to evaluate heavy metal contamination and identify possible sources.

In this study, the total concentration and bioavailability of heavy metals including As, Cd, Cu, Cr, Pb, Sb, Ni, and Zn in 70 surface soil samples were evaluated by ICP-MS analysis. Calculation of contamination rates of soil samples was done using different environmental indices including modified contamination index, soil heavy metals ecological risk index, pollution load index, and Nemerow’s index.

The results of the mCd index showed a high degree of contamination of Cu, Cr, Cd, Pb, Sb, Ni, Zn and as in most samples. High values of the ecological risk index (up to 2076.9) indicated the level of serious contamination risk of some samples. The pollution load index (PLI) in 10 samples showed PLI values <1 indicating no contamination of the samples, but in other samples, high loads of heavy metal contamination were observed in the soil of this area. According to Nemerow’s index, Cu, Pb, Sb, As, and Cd were highly contaminating. Statistical analysis of data and calculations of correlation coefficients, cluster analysis, and PCA test (VARIMAX rotation) revealed a positive and significant correlation between elements such as Pb with Cr, As and Sb, Ni with Cr, Cd and Zn and a negative correlation with arsenic. Therefore, it is estimated that these elements have a similar and predominantly geogenic origin.

Based on the results of geo-environmental indices, all eight studied elements showed high ecological risk potential and significant contamination occurrence in stream sediments and surface horizons of the Doustbaglu district.