Metal contamination in sediments of the western Bohai Bay and adjacent estuaries, China

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Abstract

Twelve sediment cores were collected in July 2007 in open waters of western Bohai Bay, the Port of Tianjin, and the adjacent estuaries of the Haihe and Yongding Rivers. While overall concentrations of trace metals at incremental depths in these cores met the Marine Sediment Quality (GB18668-2002) criteria of China, the magnitude of both metal enrichment factors (EF) and geoaccumulation indices (Igeo) suggested that pollution with Ag, Cd, Cr, Cu and Zn was occurring in the estuaries and Port. Risk analysis also suggested that Ag and Ni concentrations were sufficiently elevated as to cause adverse biological effects in the study area. Although metal concentrations in western Bohai Bay were of less concern, a positive relationship between EF values and excess 210Pb activity for several metals suggested that their concentrations were increasing over time.

Introduction

Rapid economic growth in coastal China has resulted in environmental degradation, habitat loss and alteration, and has placed new pressures on the nation’s coastal resources (Zhang et al., 2007, Zhang et al., 2009, Feng et al., 2008). Heavily industrialized, China’s third largest urban center Tianjin, has not been immune to these issues (Ye, 1991, Fan, 1992). Historically, the city served as the “gateway” to Beijing and was considered the most important industrial center in northern China (Chang et al., 1992). While that status had eroded over time, the recent renewal of the Beijing–Tianjin metropolitan corridor has done much to improve the economic status of northern China and the surrounding Bohai Region (Wei and Jia, 2003). Part of the newly created infrastructure, the Port of Tianjin, the largest in nation, has a constructed surface area of 0.6 km2 and a shoreline of 125 km, and is a designated national “hub” for international trade (Wei and Jia, 2003, Lu et al., 2009). The adjacent Bohai Sea serves as the receiving waters for about 36% of the wastewater and 47% of the solid pollutants released in China (Wang and Wang, 2007). Its 16000 km2 western most segment Bohai Bay, encompasses Tianjin, Hebei and Shandong provinces, and is one of the most important enclosed coastal seas in Asia (Ye, 1991). Rapid port expansion, new commercial development and urbanization along tributaries emptying into the Bay contribute pollutants to the receiving waters (Fan, 1992). Despite its assimilative capacity, Bohai Bay has experienced substantial water and sediment quality degradation in recent decades (Ye, 1991). For example, 1 × 109 tons of wastewater is discharged annually into the Bay exacerbating eutrophication, harmful algal blooms, and acute and chronic toxicity including instances of fish and shellfish mortality (Ye, 1991, Fan, 1992, Tao et al., 2001, Wang et al., 2004). Numerous persistent organic pollutants, and trace metals are also transported into this region through direct discharges and/or loading from adjacent tributaries (Wang and Wang, 2007).

Elevated concentrations of metals in estuarine sediments and organisms are a well-documented environmental concern (Timothy, 2000, Klimmek and Stan, 2001, Blackmore and Wang, 2004, Podgurskaya et al., 2004, Cheung and Wang, 2005, Cravo and Bebianno, 2005, Falco et al., 2006, Feng et al., 2008). Although there are indications that Bohai Bay has become increasingly contaminated with metals in the past 20 years (Zhao and Kong, 2000, Zhang, 2001), the available data are restricted to localized inshore areas and lack spatial resolution. There is need to expand the spatial and temporal coverage of sediment sampling in the area to better understand the transport and fate of these contaminants, and their potential ecosystem impacts for management purposes. Here, we report on trace metal (Ag, Cd, Cr, Cu, Ni, Pb and Zn) concentrations in sediments of western Bohai Bay, the urbanized Haihe and Yongding River estuaries, and the Port of Tianjin to assess the potential for metal impacts on the environment, and to examine trends in metal concentrations with time. A focused study of this type serves to inform decision-makers on the sources, transport and distribution of sediment associated contaminants and their potential ecological impacts in the region. The results will also be applicable to science-based policy formulation, and to ecosystem restoration/rehabilitation practices.

Section snippets

Field work

Sediment cores, ranging in length from 40 to 100 cm, were collected with a custom designed 10-cm inner diameter gravity corer fitted with prewashed polyethylene liners at 12 sampling stations in western Bohai Bay, and within the Port of Tianjin and the local estuaries of the Haihe and Yonding Rivers during July 24–26, 2007 (Fig. 1; Table 1). Once retrieved, all cores were sectioned into 2 cm increments for the first 20 cm, and at 5 cm intervals thereafter. The outer layer of each core section

Sediment metal concentrations

As expected, metal sediment concentrations at the 12 study area locations varied widely, with individual ranges recorded as: 2.22–4.14% for Fe; 0.194–2.10 mg kg−1 for Ag; 0.093–0.252 mg kg−1 for Cd; 38.2–79.8 mg kg−1 for Cr; 17.8–78.9 mg kg−1 for Cu; 26.5–45.4 mg kg−1 for Ni; 18.3–30.7 mg kg−1 for Pb; and 61.6–156 mg kg−1 for Zn, respectively (Table 3).

Contamination assessment

Metal enrichment factors (EF) were also broadly distributed: EFAg = 2.0–15; EFCd = 0.63–2.0; EFCr = 0.77–2.0; EFCu = 0.77–2.8; EFNi = 0.67–1.5;

Discussion

To reduce the potential for bias and to better characterize the likelihood for adverse environmental effects in western Bohai Bay and vicinity, several metrics for comparing risks to ecosystem health were adopted in this study: 1) sediment quality criteria (GB18668-2002), 2) metal enrichment factors (EF) and geoaccumulation index (Igeo), and 3) the effects range-low (ERL) guidelines (Müller, 1979, Müller, 1981, Sinex and Helz, 1981, Salomons and Forstner, 1984, Sinex and Wright, 1988, Long

Conclusions

We observed that sediment quality in western Bohai Bay and its adjacent coastal areas generally meets primary Chinese Marine Sediment Quality (GB 18668-2002) criteria. Potential impacts of metals in western Bohai Bay outside of the Port of Tianjin appeared to be low as judged by all three metrics employed in this study. The western Bohai Bay is generally unpolluted by Cd, Cr, Cu, Ni, Pb and Zn. However, the land-based anthropogenic impact on the coastal environment exists as suggested by the

Acknowledgements

This international collaborative research is jointly supported in part by US New Jersey Sea Grant (Project # 6560-0000, H. Feng) and China Tianjin Science and Technology Committee (Project # 06YFGHHZ01500). We would like to sincerely thank Captain Min Li and Firstmate Baoju Zhang of R/V Jihaiyu 1002 for their cooperation in the field work. Thanks are extended to Haiming Shi, JiangboTu and other scientific staff in Tianjin Marine Environmental Monitoring and Forecasting Center for their

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