Heavy metal enrichment and its ecotoxicological risk assessment in sediment cores from tropical backwater systems, Kalpakkam Coast, India

The vertical distribution of heavy metals in core sediments of two backwaters along the Tamil Nadu coast of India was investigated. The average concentration of heavy metals for Sadras backwater cores followed the sequence: Al>Fe>Mn>Cr>Zn>Pb>Ni>Cu>Co>Cd. The Edaiyur backwater core sediments also showed a similar sequence of metal content (Al>Fe>Mn>Cr>Zn>Ni>Pb>Cu>Co>Cd) with a minor change. Concentrations of all these metals during this study showed the following range: Al - 2.3–7.2 %; Fe - 0.99–5.4 %; Mn - 145.78–1108.22 ppm; Cr - 51.98–149.87 ppm; Zn - 29.85–239.68 ppm; Pb - BDL-155.59 ppm; Ni - 24.32–59.09 ppm; Cu - BDL-46.02 ppm; Co - 3.55–19.67 ppm and Cd - BDL-10.90. Core sediments showed considerable enrichment of Cr, Pb, and Cd with respect to the upper continental crust concentrations. Average values of Mn, Cu, Co, Ni, Zn, Al, and Fe were below the UCC concentrations. CF, EF, and Igeo showed relatively high Cr, Pb, and Cd contamination. Most of the PLI values were > 1 except for a few subsamples, indicating the polluted nature of the sediment. The mCD, however, showed two cores were relatively more contaminated than others. Average Cu and Zn concentrations were below TEL and ERL values, whereas metals such as Ni, Cr, Pb, and Cd were between TEL-PEL and ERL-ERM. The mean PEL quotient showed toxicity probability to organisms below 21%. Sadras backwater cores showed recent surface metal enrichment, whereas the Edaiyur backwater cores showed almost uniform vertical distribution, which was supported by multidimensional scaling analysis.