Thallium concentrations and sources in the surface sediments of Bohai Bay

The Tl concentrations and chemical speciation were determined in the surface sediments of Bohai Bay to evaluate its biogeochemical characteristics. The total Tl concentrations were in the range of 0.506–0.770 μg/g and correlated significantly with clay and total organic carbon (TOC) contents, suggesting that the grain size and TOC were major factors controlling Tl distribution. The sequential extraction performed to indicate Tl speciation and availability in Bohai Bay sediments suggested that Tl occurred mainly in the residual fraction and Tl came mainly from natural input. In the non-residual fractions, Fe–Mn oxide and organic matter fractions accounted for the main portions, suggesting that the labile Tl adsorption was dominated by Fe–Mn oxides and organic matter. In addition, according to our estimate, about 2.7 t/yr and 0.16 t/yr of Tl reached Bohai Bay via rivers and atmosphere, respectively.