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, 46 (23), 12806-13

Heterogeneous Atmospheric Chemistry of Lead Oxide Particles With Nitrogen Dioxide Increases Lead Solubility: Environmental and Health Implications

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Heterogeneous Atmospheric Chemistry of Lead Oxide Particles With Nitrogen Dioxide Increases Lead Solubility: Environmental and Health Implications

Jonas Baltrusaitis et al. Environ Sci Technol.

Abstract

Heterogeneous chemistry of nitrogen dioxide with lead-containing particles is investigated to better understand lead metal mobilization in the environment. In particular, PbO particles, a model lead-containing compound due to its widespread presence as a component of lead paint and as naturally occurring minerals, massicot, and litharge, are exposed to nitrogen dioxide at different relative humidity. X-ray photoelectron spectroscopy (XPS) shows that upon exposure to nitrogen dioxide the surface of PbO particles reacts to form adsorbed nitrates and lead nitrate thin films with the extent of nitrate formation relative humidity dependent. NO(2)-exposed PbO particles are found to have an increase in the amount of lead that dissolves in aqueous suspensions at circumneutral pH compared to particles not exposed. These results point to the potential importance and impact that heterogeneous chemistry with trace atmospheric gases can have on increasing solubility and therefore the mobilization of heavy metals, such as lead, in the environment. This study also shows that surface intermediates that form, such as adsorbed lead nitrates, can yield higher concentrations of lead in water systems. These water systems can include drinking water, groundwater, estuaries, and lakes.

Figures

Figure 1
Figure 1
SEM image and XRD powder diffraction of PbO particles. For comparison, XRD patterns of lead containing compounds and minerals, such as PbO (massicot), Pb metal, PbO (litharge), PbO2 (plattnerite), Pb3O4 (minium), PbCO3 (cerussite) and Pb3(CO3)2(OH)2 (hydrocerussite) are also shown.
Figure 2
Figure 2
Survey XPS data of as-received PbO and after exposure with NO2. Inset: N1s binding energy region after exposure to NO2 shows a new peak due to adsorbed nitrate species. See text for further details.
Figure 3
Figure 3
High resolution XPS data in the O1s, N1s, C1s and Pb4f binding energy regions of as-received PbO and after exposure to NO2 under various environmental conditions as noted in the left panel. For comparison, XPS data are also shown for a Pb(NO3)2 sample. The sloping background in the N1s region is from the intense Pb4d peak as seen in the survey spectra shown in Figure 2.
Figure 4
Figure 4
Quantification of the nitrogen product following adsorption on PbO after six consecutive exposures to NO2 for 30 min in the absence of water vapor (circles). Similarly, data following exposure to NO2 at various relative himidity is shown (squares).
Figure 5
Figure 5
ICP-OES measured Pb2+(aq) in solution from unreacted PbO particles and NO2 exposed particles for 24 h, with NO2 alone as well as NO2 and 8 Torr H2O mixture. Reactors contained solids loading of 50 g L−1. Uncertainties represent one standard deviation from triplicate experiments.

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