A Comparative Study on Speciation and Availability Risk of Toxic and Potentially Toxic Elements in Different Groups of Sediments in the Dar-E-Allo Copper Mine, SE Iran

Abstract

ABSTRACT The present study has been performed to evaluate the prospective effects of toxic and potentially toxic elements (TPTEs) on different groups of sediments in mining area. Fractionation of metal and metalloid elements (As, Cd, Co, Cu, Fe, Mo and Zn) was studied using a modified Community Bureau of Reference (mBCR) sequential extraction procedure in the sediments collected at five sedimentary systems. Compared to natural background values the enrichment factor (EF) of TPTEs follow the order of Cu > Mo > Cd > Zn > Co > As > Fe. Comparison with sediments quality indicators (including: sediment pollution index (SPI), pollution load index (PLI), and modified contamination degree (mCd)) revealed, that leached sediment containing secondary phases (S5 and S6), sediments containing ferric compounds (S7 and S8) and then evaporitic deposits (S9) are considered as the most contaminated sediment with a high to ultra-high degree of contamination, Subsequently based on the average indices values for sedimentary systems, the descending order is as follows: S5> S4 > S2 > S3 > S1. This issue confirm that sedimentary systems of mining area are heavily contaminated by toxic and potentially toxic elements and were not found within the guideline acceptable values. The potential ecological risk index (PERI) revealed a very high risk level for Cu with a peak in sediments containing sulfide phases. Speciation results in the investigated sediments indicated that the labile form has a considerable role in the release of all TPTEs except for Mo, Fe, and to somewhat As. Accordingly, based on the risk of elements bioavailability, the descending order is as follows: S9 > S4 > S5 > S6 > S7 > S3 > S8 > S2 > S1. X-ray diffraction (XRD) analysis confirmed the presence of lithogenic minerals with low bioavailable elements in the samples (S1, S2, S3, S4, S7 and S8) and secondary minerals with high bioavailable elements in samples (S5, S6 and S9). Multivariate statistical analysis (Pearson’s correlation analysis, PCA, and CA) suggested that the sources of TPTEs contamination were mainly anthropogenic along with the geogenic sources in the study area.