The concentrations, fluxes, enrichments and chronologies of potential harmful elements in sediment cores from Bohai Bay, North China

To reflect the historical changes, the vertical profiles of concentrations, enrichment factors and burial fluxes of potential harmful elements (PHEs: Ga, Ge, Mo, In, Sn, Sb, Te, Tl, Bi, W and V) were determined in two sediment cores collected from Bohai Bay. Sediment accumulation rates and chronologies were obtained from Pb-210 activity-depth profiles. Two sediment accumulation rates in core 2 were observed: a higher rate of 4.78 mm/year before the 1960s and 2.93 mm/year since then. The sediment accumulation rate in core 6 was 2.82 mm/year. The PHE concentrations and burial fluxes exhibited an obvious variation with the depth due to the natural and anthropogenic inputs. Especially, the higher concentrations and burial fluxes of PHEs occurred in the 1960s and 1980s, matching the large runoff and industrial development. Enrichment factors (EFs) of PHEs were computed in order to evaluate their potential sources. Results showed that the EFs of Sb, Te and Bi were higher than 1.5, revealing the anthropogenic inputs; however, the EFs of other PHEs were lower than 1.0, indicating the natural inputs. Moreover, the high EFs of Sb, Te and Bi appeared in the surface or subsurface layers, indicating that the extent of anthropogenic contamination enhanced in recent years. Sequential extraction technique was used to study the ecological risks of PHEs. Results revealed that the ecological risks of Mo, Te and Bi in both cores and Sb and W in core 2 were medium due to their high availability in the exchangeable and carbonate-bound fractions.