Geochemical dispersal of thallium and accompanying metals in sediment profiles from a smelter-impacted area in South China

Thallium is a trace metal with a toxicity greater than that of Pb, Cd and Hg. This study complements the authors’ previous research, with main focus on contamination by Tl and accompanying metals (Pb, Zn, Cd, and Cu) in sediments from an area historically affected by Pb-Zn smelting in Shaoguan city (northern Guangdong Province, South China). In order to provide complex data on the geochemistry of anthropogenic Tl in sediments, total contents and geochemical fractionation of Tl and the other metals were comparatively studied for two different sediment profiles, core A from the Pb-Zn smelter outlet (a major Tl pollution point-source) and core B from the inlet of the North River (natural water courses near the smelter). Surprisingly high enrichment of Tl was observed across both depth profiles, with varying distribution patterns versus depth. Further comparison of Tl contents and its geochemical fractions in the upper, middle and bottom horizons of core A and core B, in combination with mineralogical phases of the sediments, clearly demonstrated both lateral and vertical mobility of Tl, due to complex processes such as mechanical disturbance/mixing, long-term alteration/dissolution of smelter-derived particles, and vertical migration of Tl through colloidal (or microparticle) transport with alumino-phyllosilicates and Fe/Mn (hydr)oxides. Relatively high abundance of Tl in the labile fractions of all selected sediments from both locations highlights a potentially significant environmental risk to the local ecological system in the near future.