Lead isotope signatures and source identification in urban soil of Baoshan district, Shanghai

Two soil cores were collected from the Yuepu Park and a vegetable field near the Yunchuan Road in Baoshan district, Shanghai. Particle size, Pb content and Pb stable isotopic ratios were measured to examine Pb contamination status and its source. The results indicate that Pb concentration in the vegetable field soil and Yuepu park soil varies from 17.2 mg·kg^-1 to 34.8 mg·kg^-1 and 17.5 mg·kg^-1 to 36.5 mg·kg^-1, respectively. The observed Pb isotopic ratios of vegetable field samples vary from 0.827 to 0.849 for ²⁰⁷Pb/²⁰⁶Pb, and 2.082 to 2.101 for ²⁰⁸Pb/²⁰⁶Pb, while those of Yuepu Park samples range from 0.839 to 0.848 and 2.089 to 2.097, respectively. Pb content, its enrichment factor (EF) and Pb stable isotopic ratios increase upward in both soil cores. EF values of surfacial (top 10 cm) vegetable field samples and park samples are mostly greater than 1.5, suggesting that higher Pb contents in topsoils are caused by anthropogenic activities. Compared with previous reports on Pb isotope signatures of different environmental materials in Shanghai, Pb isotopic ratios in the two soil cores are between those of Yangtze River intertidal sediments and the dust of coal combustion, and those of soil samples with EF>1.5 are closer to the isotopic ratios of coal combustion dust. It indicates that topsoil in the Baoshan district is contaminated by dust derived from coal combustion.