Lead isotope fingerprinting used as a tracer of lead pollution in marine sediments from Botany Bay and Port Hacking estuaries, southern Sydney, Australia

Anthropogenic lead has been released into environmental ecosystems via human activities; essentially from mining, smelting of lead, leaded gasoline and industrial activities. In order to explore the source apportionment and historic record of lead pollution in the marine sediments, concentration of lead was determined from the Botany Bay and Port Hacking estuaries, south of Sydney, Australia. Areas with the highest concentrations of lead in the sediment samples were analysed by inductively coupled plasma-mass spectrometry (ICP-MS) for lead isotopes to effectively identify the metal contamination source. In addition, other sediment samples were collected from cores at 40 cm depth to represent the natural background composition. The study found that the total lead in the tested marine sediments varied from 75.6 mg/kg to 582.2 mg/kg. The 206Pb/204Pb showed a decline towards the current surface sediment. Assuming that the natural background source of lead remains the same in terms of both isotopic signature and accumulation rate, the decline in 206Pb/204Pb indicated a rise in the contribution of old lead to the sediment, mainly from gasoline fumes (car and boat exhausts) and paint. This is because the samples came from close to water discharge points which have concentrated the catchment lead via stormwater runoff.