Risky bismuth: Distinguishing between lead contamination sources in soils

Abstract

In a broad environmental study in St. Joseph County, Indiana, elemental data from ∼2000 soil samples and ∼800 paint samples were collected with X-ray Fluorescence (XRF) spectroscopy. The observed lead concentrations were compared to other elemental concentrations in these data. A strong correlation between lead and bismuth concentrations was observed in a subset of the soil samples and in nearly all of the paint samples, with lead levels approximately 150 times higher than bismuth. However, some soil samples contained lead with no bismuth present. Since most lead sources likely contain bismuth as an impurity from refining of native lead ore, but leaded gasoline does not contain any bismuth impurities due to the manufacturing process of tetraethyl lead, it may be possible to distinguish environmental lead sources by XRF. To test if leaded gasoline could be the source of lead in the subset of soil samples containing no bismuth, leaded paint samples were analyzed with Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES), which confirmed the presence of bismuth in leaded paint. Aviation gasoline, which contains tetraethyl lead, was also analyzed by ICP-OES to confirm the absence of bismuth in leaded gasoline. This discovery suggests that XRF can be used to rapidly distinguish different legacy lead contamination sources from one another. For low lead concentrations, elemental measurements of bismuth by ICP-OES can be used in environmental forensics to distinguish leaded gasoline contamination from other sources of lead.