A century long sedimentary record of anthropogenic lead (Pb), Pb isotopes and other trace metals in Singapore

Abstract

Reconstructing the history of metal deposition in Singapore lake sediments contributes to understanding the anthropogenic and natural metal deposition in the data-sparse Southeast Asia. To this end, we present a sedimentary record of Pb, Pb isotopes and eleven other metals (Ag, As, Ba, Cd, Co, Cr, Cu, Ni, Tl, U and Zn) from a well-dated sediment core collected near the depocenter of MacRitchie Reservoir in central Singapore. Before the 1900s, the sedimentary Pb concentration was less than 2 mg/kg for both soil and sediment, with a corresponding ²⁰⁶Pb/²⁰⁷Pb of ∼1.20. The Pb concentration increased to 55 mg/kg in the 1990s, and correspondingly the ²⁰⁶Pb/²⁰⁷Pb decreased to less than 1.14. The ²⁰⁶Pb/²⁰⁷Pb in the core top sediment is concordant with the ²⁰⁶Pb/²⁰⁷Pb signal of aerosols in Singapore and other Southeast Asian cities, suggesting that Pb in the reservoir sediment was mainly from atmospheric deposition. Using the Pb concentration in the topmost layer of sediment, the estimated atmospheric Pb flux in Singapore today is ∼1.6 × 10⁻² g/m² yr. The concentrations of eleven other metals preserved in the sediment were also determined. A principal component analysis showed that most of the metals exhibit an increasing trend towards 1990s with a local concentration peak in the mid-20th century. Keywords: Pb; Pb isotopes; Heavy metals; Southeast Asia; Singapore; Sediment