Distribution, sources and ecological risk of trace elements and polycyclic aromatic hydrocarbons in sediments from a polluted urban river in central Bangladesh

Abstract

To assess the spatial and layer-wise distributions of 26 elements (Na, Al, Mg, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Sb, Co, Ba, Zn, Rb, Cs, La, Ce, Sm, Eu, Yb, Ta, Hf, Th and U) as well as the spatial distributions of polycyclic aromatic hydrocarbons (PAHs) in a polluted urban river (Turag, Bangladesh), benthic sediment samples from 11 different sampling stations were analyzed. Concentrations of Ti, Cr, Mn, Zn, Rb and Cs ranged from 2330 to 5490, 23–116, 186–4298, 34–7345, 77–186 and 2.19–12.0 μg.g−1(dw), respectively, whereas concentrations of ∑PAHs ranged from 45.8 to 1901 with an average value of 432 μg.kg−1(dw) in surface sediments. Geo-accumulation index, enrichment factor and pollution load index were used to assess the contamination level. Among the 26 elements, Zn is identified as the major elemental contaminant which shows significant layer-wise variations (RSDs: 21.7–221 %) at all sampling sites. Similarly, Cr, Mn, Ti, V, Fe and Co show layer-wise variation in some specific sampling sites which invokes variable contamination flux over the industrialization and/or urbanization period. Principal component analysis (PCA) and correlation study ascertained several anthropogenic sources for heavy metal contaminations. Although rare earth elements (La, Ce, Sm, Eu and Yb) seem to have crustal origin, their layer-wise variations are assumed to represent the sediment response toward the pollution load. Integrated study based on the diagnostic ratios and PCA depicted that pyrolytic origins mostly govern the PAHs distributions. Sediments quality guidelines (SQGs) indicated that the highest potential ecological risks occurred for Zn and fluorene at some specific sampling sites.