Distribution of thallium in the Bohai Sea: implications for hydrodynamic forces and anthropogenic impact

Abstract

The distribution, sources, and fate of sedimentary thallium (Tl) in the Bohai Sea (BS) were studied on the basis of datasets of total Tl and chemical speciation of Tl in surface sediment samples. The Tl concentration exhibits a certain trend of accumulation in the fine-grained sediment, suggesting that the mud deposits are sinks for land-originated Tl and that the regional currents and tide systems play a key role in the sorting of sediment and accumulation of Tl in the BS. The low Tl enrichment factor and high proportion of Tl in the residual fraction indicated that Tl is mainly derived from a natural source, although the BS is under intense environmental pressure because of excess wastewater discharge. Local Tl contamination was observed at the Liuguhe River mouth, and this contamination does not extend to beyond the inner shelves of the BS because of the regional currents. The level of Tl in the nonresidual fraction is very low and is dominated by the level of Tl in the Fe-Mn oxide fraction, indicating that Tl exhibits low mobility and bioavailability in the BS. The correlations between Tl concentration and MnO and Fe2O3 and the relatively high level of Tl in Fe-Mn oxide fraction suggested that MnO and Fe2O3 influence the geochemical behavior of Tl in the BS. The oxidizable fraction of Tl is negligible, suggesting that total organic carbon (TOC) might not be a major factor influencing the accumulation of Tl in the BS, although there is a positive correlation between Tl and TOC in the samples.