Distinct contamination indices for evaluating potentially toxic element levels in stream sediments: a case study of the Harsit Stream (NE Turkey)

This paper revealed that the level of certain potentially toxic elements (PTEs) can be reflected in stream and terrace sediments from Harsit Stream in Northeast Turkey. The potential toxicity of these elements was established by determining and interpreting the enrichment factor (EF), contamination index (Pi), ecological risk index (E-r(i)), modified hazard quotient (mHQ), hazard quotient (HQ), and hazard index (HI). The distribution of PTEs in the sediment samples was non-uniform along the different sites of the stream. The change in concentration was attributed to the release of these elements from different sources (agricultural activities, industrial activities, and gasoline discharges). Results indicated that the stream sediments were locally contaminated by the following PTEs: Pb, As, and Cd based on EF values; Cu, Pb, Zn, As, Cd, and Hg based on Pi; Pb, Cd, and Hg based on E-r(i); and Pb, As, Cd, and Hg based on mHQ. According to the HQ and HI values of Pb, risks were posed to human health especially to children. Meanwhile, terrace sediments were locally contaminated as follows: Zn and As based on EF; Cu, Pb, Zn, As, and Cd based on Pi; and Zn and Cd based on E-r(i). The HQ and HI values of As were found to be > 1, suggesting a high chance of health risk to children. The PTE levels and the local distribution pattern revealed that agricultural activities, industrial functions, and gas stations along the stream were probable sources of toxic element contamination in sediments from the Harsit Stream. These findings can help evaluate the potential toxicity risks affecting living organisms.