Distribution, accumulation and mobility of mercury in superficial sediment samples from Tianjin, northern China

Abstract

Seventeen sediment samples at three representative sites (the Yuqiao Reservoir, the Haihe River and the Haihe River Estuary) in Tianjin, northern China, were analyzed to investigate the pollution status, accumulation and mobility of mercury (Hg). The results show that the Haihe River has to be considered as moderate to strongly contaminated with Hg (2 < mean I_geo = 2.35 < 3), where total Hg contents were ca. 3 to 24 orders of magnitude greater than the regional background value. The sediments collected near a coal-fired power plant in an urban area were found to have very high Hg concentrations, which were significantly related to Hg emissions from coal-fired utility boilers. In the Yuqiao Reservoir, the surface sediments have to be considered as unpolluted with Hg (mean I_geo = −0.05 < 0) and the Haihe River Estuary sediments have to be considered as unpolluted to moderately polluted with Hg (0 < mean I_geo = 0.18 < 1). Sediment-bound Hg in the Yuqiao Reservoir and the Haihe River Estuary was found to be predominantly associated with the organo-chelated phase of the sediment (38.3% and 50.5%, respectively). However, unlike the Yuqiao Reservoir and the Haihe River Estuary, Hg in the Haihe River sediments existed mainly as sulfide Hg and elemental Hg, which accounted for 54.2% and 30.7% of total Hg, respectively. The availability of this element seemed restricted. The majority of Hg contamination in the Haihe River sediments had been attributed to historic and modern atmospheric deposition and Hg released from the Haihe River sediments didn't seem to be an important pollutant pathway into the Haihe River Estuary. The results provide new insights into Hg contamination in this region.