Impact on the environment from steel bridge paint deterioration using lead isotopic tracing, paint compositions and soil deconstruction

- Soil Pb values up to 1200 mg/kg below Pb painted bridge
- Microscopy & SEM characterised up to 6 different paint layers.
- Isotopes identified different sources of Pb including paint and gasoline.
- Multiple methods provide definitive answers.

Deterioration and repair of lead paint on steel structures can result in contamination of the ambient environment but other sources of lead such as from past use of leaded paint and gasoline and industrial activities can also contribute to the contamination. Using a combination of high precision lead isotopic tracing, detailed paint examination, including with scanning electron microscopy, and soil deconstruction we have compared paint on a steel bridge and bulk soil and lead-rich particles separated from soil. The majority of Pb found in the paint derives from Australian sources but some also has a probable US origin. The isotopic data for the bulk soils and selected particles lie on a mixing line with end members the geologically ancient Broken Hill lead and possible European lead which is suggested to be derived from old lead paint and industrial activities. Data for gasoline-derived particulates lie on this array and probably contribute to soil Pb. Although paint from the bridge can be a source of lead in the soils, isotopic tracing, paint morphology and mineralogical identification indicate that other sources, including from paint, gasoline and industrial activities, are contributing factors to the lead burden. Even though physical characteristics and elemental composition are the same in some particles, the isotopic signatures demonstrate that the sources are different. Plots using 206Pb/208Pb vs 206Pb/207Pb ratios, the common representation these days, do not allow for source discrimination in this investigation.

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