Mercury Contamination and Dynamics in the Sediment of the Second Songhua River, China

Abstract

The Second Songhua River (SSR) was subjected to a large amount of mercury discharge from petrochemical industries in Jilin City from the 1960s to 1980s. The objectives of this study were to investigate the spatial and temporal change of mercury concentration in the sediments of the river and to assess Hg pollution in sediment employing enrichment ratio. Bottom sediments sampled in 2005 were digested with various acids followed by analysis by atomic fluorescence spectrometry for Hg, ICP-MS for Cd, Pb and Sc, and ICP-OES for Co, Cr, Cu, Zn, Mn, Ni, P, Pb, Sb, Ti, V, Al, Fe, Mg, Ca, Na, and K, in order to measure the total concentrations of these elements in the sediments. Results indicated that mercury concentrations in the sediments were strongly related with distance from the historic industrial point source, decreasing at an exponential rate from 1.27 mg kg⁻¹ at Jilin City to 0.01 mg kg⁻¹ at downstream Haerbin City. In addition, mercury concentration decreased from 16.8 mg kg^{− 1} y⁻¹ in 1974 to 0.09 mg kg⁻¹ y⁻¹ in 2005 in the sediments at effluent discharge site, and from 0.006 mg kg⁻¹ y⁻¹in 1974 to 0.004 mg kg⁻¹ y⁻¹ in 2005 at Songyuan City 257 km downstream. In the sedimentary sections of the river, deeper sediments contained higher concentrations of mercury as compared to the surface sediments, suggesting discharges of higher levels of mercury in the past and its subsequent burial over the years by less polluted sediments. Background concentrations of mercury in the surface sediments, reconstructed by tracer Sc, were 0.011 to 0.018 mg kg⁻¹. Enrichment ratios of Hg in the sediments of SSR was 5 to 75, indicating moderate to extreme pollution, while the sediment of Songhua River is less contaminated, with enrichment ratios of 0.9 to 1.5. At present, the previously accumulated and buried mercury in sediments may not significantly affect water quality of the SSR, but might pose a potential ecological risk to aquatic and amphibian animals. Natural attenuation seems to be an economic remedial choice for these sediments.

Keywords:

• Second Songhua River
• sediment
• mercury
• contamination
• dynamics

Acknowledgements

This research was financed by the National Basic Key Research Program of China (2004CB418502) and the National Natural Science Foundation of China (40671002). Partial financial support for C. Lin by SRF for ROCS, SEM and Beijing Normal University is gratefully acknowledged. B. Yan at Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, provided help during part of the field sampling. We gratefully acknowledge the constructive detailed comments by three anonymous reviewers.

Notes

¹Ref: reference material.

²RE%: percent relative error.

³CV%: coefficient of variance.

⁴Max: maximal value.

⁵Min: Minimal value.

⁶One measurement.

¹Distance to discharge site of effluent from petrochemical complex of Jilin city.