High-resolution depositional records of lead isotopes and polycyclic aromatic hydrocarbons in the Bohai Sea, China: Implications for a sediment footprint of anthropogenic impact

Abstract

Mercury (Hg), Lead (Pb) and its stable isotopes and polycyclic aromatic hydrocarbons (PAHs) were analyzed in a sediment box core obtained from the central Bohai Sea (BS) of northern China to trace anthropogenic input for the past century. The records of Hg, PAHs and Pb isotopic ratios revealed that the BS was clearly impacted by human activities from the early 1930s to the middle 1940s, possibly related to the acceleration of heavy industrialization in northeast China. Under rapid development and significant increase in fossil fuel consumption, pressure on the BS environment had obviously increased, as revealed by increasing concentrations of Hg, Pb, and PAHs from the early 1960s to late 1990s, with a synchronous decrease of 206Pb/207Pb isotopic ratios. The evolving trends in 206Pb/207Pb ratio, Hg, and PAHs were found to be decoupled since the early 2000s, possibly because of the significant improvement in environmental protection. Depositional records of Pb isotopic ratios with PAH compositions indicate a high-resolution sediment footprint of anthropogenic energy-consumption-based impacts around the BS over the past century, especially with the transformed emission sources from the leaded gasoline and combustion of coal before the 2000s to coal combustion and nonferrous metal smelting thereafter. The decreased records of sedimentary Pb have been widely found by around the world (e.g. North America, Southeast Asia and West Europe) after the ban on the leaded gasoline. However, this trend in China is reverse by the phasing out of leaded gasoline since the 2000s, possibly due to the recent accelerating development of nonferrous metal smelting and the continued increase in coal-dominated energy consumption.