Chemical transformations of lead compounds under humid conditions: implications for bioaccessibility
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This short communication documents chemical transformations caused by weathering of two Pb compounds that commonly occur in house dust. Chamber experiments were designed to simulate humid indoor environment conditions to determine whether Pb compounds undergo chemical transformations influencing bioaccessibility. Reference compounds of Pb metal (12 % bioaccessibility) and Pb sulfate (14 % bioaccessibility) were subjected to an oxygenated, humidified atmosphere in closed chambers for 4 months. X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) spectroscopy were used to characterize the main Pb species, and the change in Pb bioaccessibility was determined using a simulated gastric acid digestion. At the end of the weathering period a small amount of Pb carbonate (9 % of total Pb) appeared in the Pb sulfate sample. Weathering of the Pb metal sample resulted in the formation of two compounds, hydrocerussite (Pb hydroxyl carbonate) and Pb oxide, in significant amounts (each accounted for 26 % of total Pb). The formation of highly bioaccessible Pb carbonate (73 % bioaccessibility), hydrocerussite (76 % bioaccessibility), and Pb oxide (67 % bioaccessibility) during weathering resulted in a measurable increase in the overall Pb bioaccessibility of both samples, which was significant (p = .002) in the case of the Pb metal sample. This study demonstrates that Pb compounds commonly found in indoor dust can ‘age’ into more bioaccessible forms under humid indoor conditions.
KeywordsLead Speciation Transformation Bioaccessibility XANES XRD
Funding for this project comes from Health Canada’s Chemicals Management Plan (CMP2 Research Fund ref. no. CRRS/SDRC 4500267169). XANES spectroscopy was conducted at the beamline X-11A at the National Synchrotron Light Source, which is supported by the US Department of Energy, under contract number DE-AC02-98CH10886. Dr. Kumi Pandya’s help during the experimental run is gratefully acknowledged. The Geological Survey of Canada Mineral Library (Ottawa, Canada) is thanked for the leadhillite donation. The authors thank Marc Chénier, Christine Levesque (Health Canada, Ottawa), Ted MacKinnon, and Derek Smith (CANMET-MMSL, Ottawa) for their precious technical support and contribution.
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