Mercury speciation in China's coastal surface seawaters

Abstract

Mercury contamination of ocean ecosystems is one of many problems in the global environment. In this paper, mercury speciation for surface seawaters sampled from nine coastal sites of China was performed. Speciation analysis of total particulate mercury (HgT)P, total dissolved mercury (HgT)D, monomethylmercury (MMHg)D, dimethylmercury (DMHg)D, mercuric ion (Hg2+)D and mercuric chlorocomplexes ( )D was carried out by cold vapor atomic fluorescence spectrometry (CVAFS) after separation and preconcentration with thiol cotton fiber (TCF) and anion-exchange resin columns. The concentration of (HgT)D ranged from 25.3 to 41.1 ng/L. The concentration of dissolved inorganic mercury was in the range of 12.8–24.7 ng/L, which averaged 55.9% of the total dissolved mercury. Dissolved mercuric chlorocomplexes ( )D appeared to be the principal speciation, averaging 45.7% of total dissolved mercury. The concentration of (MMHg)D was higher in coastal seawaters collected in Beidaihe (2.55 ng/L) and Huludao (2.36 ng/L). In other costal water samples, the concentration of (MMHg)D ranged from 0.23 to 0.86 ng/L. A significant inverse correlation was observed between (MMHg)D and dissolved oxygen content. Labile inorganic mercury (II) was probably the most likely substrate for mercury methylation. The highest concentration of dissolved DMHg (0.136 ng/L) was detected in seawater sampled in Xiamen. Particulate mercury constituted 51–90% of the total mercury. The enrichment ability of the suspended particle matter for dissolved mercury was calculated to be 0.5 × 103 to 2.1 × 103. The particulate mercury varied from 12 to 63 ng/g, and the variations were positively correlated with the suspended particle matter concentrations, whereas a negative correlation was observed with salinity. Particulate mercury originated mainly from river inputs.