Mercury distribution in sediment along urban–rural gradient around Shanghai (China): implication for pollution history

The increasing levels of heavy metals in the environment generally related with the rapid industrialization and urbanization. Mercury (Hg) is a global toxin with wide concerns, and China gradually becomes the main producer, consumer, and emitter of Hg in the world. However, few historical data are available on the occurrence of Hg in Chinese urban areas. Here, we collected 35 lake surface sediment samples from 35 public parks and 1 sediment core in the Luxun Park in Shanghai, a hyper-urbanization city in China, to determine the spatial and vertical distributions of total mercury (THg) and methylmercury (MeHg) and to explore the Hg pollution history with the industrial development. Higher concentrations of Hg and MeHg and greater Hg enrichment were found in urban areas compared with suburban area with the following order: central urban core area > developed urban area > developing urban area > suburban area. The THg concentration in the sediment core showed an increasing trend from 1876 to 2000 and a decreasing trend from 2000 to 2012, coinciding with the process of industrialization and urbanization in Shanghai. However, THg fluxes unceasingly increased from 1876 to present probably attributed to coal consumption in the suburban area and transportation agglomeration in the central urban core area. Unlike THg, no significant variations for MeHg with time and the maximum value (0.17 μg/kg) appeared in 1947. The methylation ratio of MeHg to THg in the sediment is pretty low, and more studies are needed to further understand the fate of Hg in the environment.