Distribution and Risk Assessment of Heavy Metals in Sediment from Bohai Bay, China

Abstract

Sediment core and porewater samples from the Western coastal tidal flat in Bohai Bay, China, were collected for meals and physical-chemical properties analysis. The vertical distribution characteristics of eight metals along the core was investigated based on 137Cs and 210Pb radionuclide dating. The chemical fractions of six metals (Cu, Pb, Zn, Ni, Mn and Cd) were also measured based on the modified European Community Bureau of Reference (BCR) sequential extraction procedures to better understand the mobility and bioavailability of these metals in the sediment. In addition, geoaccumulation index (Igeo) and risk assessment code (RAC) are used to assess risk status of these metals in the environment. 210Pb measurement indicates a sedimentation rate of about −1.87 cm∙year−1. The metals Cu, Zn, Pb and Ni show similar vertical distributions throughout the core, while Mn and Cd show different distribution patterns. Ni, Cu, Pb and Zn are strongly associated with the residual fraction while Mn and Cd are dominant in the acid-soluble fraction. According to the estimated diffusive fluxes, the Zn ions were the most mobilized, followed by Cu, Ni, Pb, and to a lesser extent Cd. The result of Igeo shows that Ni in sediments does not reflect any pollution, and Cu, Pb and Zn are in a level from unpolluted to modest polluted throughout the core. Mn and Cd have obvious anthropogenic sources. Based on the RAC, Cd and Mn pose a high to very high risk to the local environment, respectively, due to the significant percentage of exchangeable fraction. Clay content is significantly positively correlated with Ni, Cu, Al and Fe, and Cu, Pb, Zn and Ni might originate from the same sources or be influenced by similar geochemical processes. River runoff and atmospheric deposition are important sources for heavy metals, and since 1998, domestic sewage discharge might have had an important influence on the source of heavy metals (except for Cd and Mn).

An Ex-Situ Immobilization Experiment with Zn, Pb, and Cu in Dredged Marine Sediments from Bohai Bay, China

“…Tianjin Port, located in Bohai Bay, is the largest comprehensive port in Northern China, where large-scale dredging activities are carried out along the coastal areas every year [34,36]. It was reported that a total of 466 × 104 m 3 of dredged materials were dumped into sites adjacent to the Tianjin Port between 2012 and 2013, resulting in a negative influence on the marine ecosystem in Bohai Bay; therefore, great importance should be attached to this issue [34,37,38].…”

Two Approaches to Measure Trace Metals Fluxes at the Sediment–Water Interface: Sediment Porewater Profile and Benthic Incubation

“…However, information about the fluxes of trace metals at the sediment-water interface in Indonesian waters is still minimal. In other countries, metals flux observations have been carried out, such as in China (Duan et al 2019;Li et al 2020;Liu et al 2019;Ni et al 2017), Sweden (Frogner-Kockum et al 2020, France (Point et al 2007;Rigaud et al 2013), Italy (Emili et al 2016;Zago et al 2000), Spain (Santos-Echeandia et al 2009), Germany (Pohl et al 2004), and the United States (Kalnejais et al 2015). Through the positive or negative signs generated from the flux calculations, we could find out the direction of the metal movement in the sea.…”

“…Fluxes of dissolved metals between porewater sediment and overlying bottom water are driven by different concentrations in chemical composition on both sides (Berner 1976). The concentration gradient at the sedimentwater interface is used to calculate the outward flux from the sediment or inward flux to the sediment (Liu et al 2019). When metal concentrations in the uppermost porewater is higher compared with the dissolved metal concentrations in bottom seawater, it indicates that the benthic flux of metals will be released by sediments to overlying waters (Li et al 2020;Zhu et al 2016).…”

“…Redox geochemistry and diagenesis are processes that control the benthic fluxes in Vigo Ria (Santos-Echeandia et al 2009). Other locations in which the sediment porewater profile method has been used are Berre Lagoon, France (Rigaud et al 2013), Massachusetts Bay and Hingham Bay, United States (Kalnejais et al 2015), and Changjiang Estuary (Duan et al 2019), Jinzhou Bay (Li et al 2020), Bohai Bay (Liu et al 2019), and Daya Bay in China (Ni et al 2017).…”

The ex-situ immobilization experiment of heavy metals in dredged marine sediments from Bohai Bay, China

“…Tianjin Port, located in Bohai Bay, is the largest comprehensive port in Northern China, where large-scale dredging activities are carried out along the coastal areas annually [34,36]. It was reported that a total of 466×104m 3 of dredged materials were dumped into sites adjacent to the Tianjin Port between 2012 and 2013, resulting in a negative influence on the marine ecosystem in Bohai Bay, and therefore, great importance should be attached to this issue [34,37,38].…”