Identification of historical lead sources in roof dusts and recent lake sediments from an industrialized area: indications from lead isotopes

Abstract

X-ray fluorescence and stable lead (Pb) isotopic analyses have been undertaken on dusts, known from microscopic investigation to contain significant quantities of industrially- and urban-derived particulate matter, present in the roof cavities of houses in the Illawarra region (N.S.W., Australia), with the objective of examining the historic record of Pb pollution. All investigated houses contained in excess of 250 μg g −1 Pb, with dwellings close to a copper smelter, in a large industrial complex including a major steelworks, containing higher (> 2500 μg g −1) Pb concentrations. The isotopic composition in the dusts, expressed here as 206Pb 204Pb , is relatively constant at 17.0, irrespective of dwelling age or distance from the industrial complex. Contamination of the dusts by Pb sourced from paint cannot explain the isotopic uniformity of the dust samples. Isotopic modelling indicates that the dusts contain Pb derived from the copper smelter, gasoline-air Pb and a minor contribution from coal-utilising sources. Lead loading was also investigated in the adjacent lagoon, which acts as a natural sink for particulate matter in the Illawarra region. Isotopic data and modelling indicate that one natural and four anthropogenic sources contribute to the Pb burden of this lagoon. The natural source consists of Permian rocks cropping out in the catchment area which have a 206Pb 204Pb of ∼ 18.7. The suggested anthropogenic sources are an old disbanded base-metal (Pb) smelter ( 206Pb 204Pb ∼ 16.2–16.3 ), the copper smelter ( 206Pb 204Pb ∼ 17.9 ), gasoline-air derived Pb ( 206Pb 204Pb ∼ 16.4–16.5 ) and industries utilising coal, for example the recently closed thermal coal-fired power station ( 206Pb 204Pb ∼ 18.9 ). The relative contributions of the base-metal (mainly lead) smelter and gasoline-air Pb in the sediment can only be partly assessed due to the isotopic similarity of these sources. Likewise the natural background and coal source (e.g. power station) contributions can only be estimated from historical data. Age estimations for sediment cores, using 137Cs, provide some control on these assessments. Near surface sediments in the lagoon have a relatively constant 206Pb 204Pb of 17.6–17.7, irrespective of sample location. Isotopic calculations, together with records of particulate matter pollution emissions, indicate a link between the Pb in roof dusts ( 206Pb 204Pb ∼ 17.0 ) and Pb contamination of the near surface (upper 20 cm) lagoonal sediments via a homogeneous, non-unique source of lead whose isotopic composition closely matches that of the dusts. Over the last 5 decades, atmospheric fallout of Pb-bearing particulate matter appears to have been the dominant pathway for addition of Pb to the lagoon and dwellings in the Illawarra region.