Isotopic record of lead in Singapore Straits during the last 50 years: Spatial and temporal variations

Abstract

The spatial and temporal variations of Pb were reconstructed from three corals along an east–west transect of the Singapore Straits — in proximity to one of the largest emerging Asian cities and one of the world's busiest ports. In addition to establish the variation in seawater Pb concentration, sources of Pb were also investigated via Pb isotopes in seawater and corals and compared with the isotopes in local aerosols and other potential Pb sources. The annual variation of Pb in Singapore corals seems to be related to local annual precipitation while the decadal-scale variation may be related to the long-term development of the region. The decrease of Pb/Ca in coral after 2005 coincided with the regional phasing out of leaded gasoline. The 206Pb/207Pb ratios in Singapore corals rose from as low as ~1.166 during the 1960s to ~1.189 by the late 1990s, and fluctuated between 1.180–1.198 from the late 1990s to 2010. 206Pb/207Pb in recent Singapore corals was elevated relative to Singapore atmospheric aerosols (~1.147, which is typical of urban aerosols throughout the southeastern Asian and Indonesian region). The linear distribution of 206Pb/207Pb vs. 208Pb/207Pb in triple isotope plots suggests two end-member mixing between the aerosol–Pb as a low 206Pb/207Pb end-member and an unidentified source with higher 206Pb/207Pb. Possible high 206Pb/207Pb sources include: surface runoff from imported south Chinese Pb, crustal materials from riverine inputs (sediments and suspended matter) or land reclamation, and vessels/dockyard activities.