Distribution, enrichment, and potential toxicity of trace metals in the surface sediments of Sundarban mangrove ecosystem, Bangladesh: a baseline study before Sundarban oil spill of December, 2014

The distribution, enrichment, and ecotoxicity potential of Bangladesh part of Sundarban mangrove was investigated for eight trace metals (As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) using sediment quality assessment indices. The average concentration of trace metals in the sediments exceeded the crustal abundance suggesting sources other than natural in origin. Additionally, the trace metals profile may be a reflection of socio-economic development in the vicinity of Sundarban which further attributes trace metals abundance to the anthropogenic inputs. A total of eleven surficial sediment samples were collected along a vertical transect along the freshwater–saline water gradient. The sediment samples were digested using EPA 3051 method and were analyzed on ICP-MS. Geo-accumulation index suggests moderately polluted sediment quality with respect to Ni and As and background concentrations for Al, Fe, Mn, Cu, Zn, Pb, Co, As, and Cd. Contamination factor analysis suggested low contamination by Zn, Cr, Co, and Cd, moderate by Fe, Mn, Cu, and Pb while Ni and As show considerable and high contamination, respectively. Enrichment factors for Ni, Pb, and As suggests high contamination from either biota or anthropogenic inputs besides natural enrichment. As per the three sediment quality guidelines, Fe, Mn, Cu, Ni, Co, and As would be more of a concern with respect to ecotoxicological risk in the Sundarban mangroves. The correlation between various physiochemical variables and trace metals suggested significant role of fine grained particles (clay) in trace metal distribution whereas owing to low organic carbon content in the region the organic complexation may not be playing significant role in trace metal distribution in the Sundarban mangroves.