Vertical distribution and contamination assessment of heavy metals in sediment cores of ship breaking area of Bangladesh

Vertical heavy metal profiling reflects the history of the deposition of metals and helps to understand the characteristics of accumulation in various layers of the sediment. Nevertheless, no previous studies in Bangladesh had focused on the vertical distribution of heavy metals in core sediments. In this study, vertical distribution, contamination level and potential ecological risks of six heavy metals (Zn, Cu, Pb, Cr, Ni, Mn) from the core sediment of ship breaking were assessed and compared with the non-ship breaking area of Bangladesh. The concentration (µg/g) of heavy metals in the 0–10 cm (surface), 10–20 cm (middle) and 20–30 cm (bottom) of sediment cores was as follows, respectively: Zn (35.54–100.68, 37.27–258.02, 42.78–66.45); Cu (16.38–75.25, 30.64–92.02, 34.99–52.98); Pb (4.84–132.08, BDL–204.48, BDL–23.51); Cr (14.57–42.13, 25.31–42.71, 15.26–36.34); Ni (4.02–42.23, 4.94–43.70, 4.40–43.13); Mn (198.74–764.16, 257.77–980.50, 255.62–856.44). The heavy metal content of core sediment from the shipbreaking region was substantially higher than that of non-shipbreaking area. Except for Ni, heavy metal content was highest in the middle layer, followed by the upper and lower layers of the sediment core. Contamination exponents such as enrichment factor, contamination factor and geo-accumulation index (Igeo) revealed contamination by Zn, Cu and Pb while potential ecological risk factor ( E r i ) and risk index suggested low ecological risk by studied heavy metals except for Pb. Correlation matrix, cluster analysis and principal component analysis indicated that all studied heavy metals could have similar anthropogenic origins.