Correlation between lead speciation and inhalation bioaccessibility using two different simulated lung fluids

Abstract

This study investigated the relationship between lead (Pb) speciation determined using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy in <10 μm particulate matter (PM₁₀) from mining/smelting impacted Australian soils (PP, BHK5, BHK6, BHK10 and BHK11) and inhalation exposure using two simulated lung fluids [Hatch's solution, pH 7.4 and artificial lysosomal fluid (ALF), pH 4.5]. Additionally, elemental composition of Pb rich regions in PP PM₁₀ and the post-bioaccessibility assay residuals were assessed using a combination of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) to provide insights into how extraction using simulated lung fluids may influence Pb speciation in vitro. Correlation between Pb speciation (weighted %) and bioaccessibility (%) was assessed using Pearson r (α = 0.1 and 0.05). Lead concentration in PM₁₀ samples ranged from 782 mg/kg (BHK6) to 7796 mg/kg (PP). Results of EXAFS analysis revealed that PP PM₁₀ was dominated by Pb adsorbed onto clay/oxide, while the four BHK PM₁₀ samples showed variability in the weighted % of Pb adsorbed onto clay/oxide and organic matter bound Pb, Pb phosphate, anglesite and galena. When bioaccessibility was assessed using different in vitro inhalation assays, results varied between samples and between assays, Pb bioaccessibility in Hatch's solution ranged from 24.4 to 48.4%, while in ALF, values were significantly higher (72.9-96.3%; p < 0.05). When using Hatch's solution, bioaccessibility outcomes positively correlated to anglesite (r:0.6246, p:0.0361) and negatively correlated to Pb phosphate (r: -0.9610, p:0.0041), organic bound Pb (r: -0.7079, p: 0.0578), Pb phosphate + galena + plumbojarosite (r: -0.9350, p: 0.0099). No correlation was observed between Pb bioaccessibility (%) using Hatch's solution and weighted % of Pb adsorbed onto clay/oxide and between bioaccessibility (%) using ALF and any Pb species. SEM and EDX analysis revealed that a layer of O-Pb-Ca-P-Si-Al-Fe formed during the in vitro extraction using Hatch's solution.

Keywords: ALF; Dust; EXAFS; PM10; Pb; Simulated lung fluid.

Fig. 1.

Concentrations of total (mg/kg) and bioaccessible Pb (%) in mining/smelting impacted PM₁₀ following extraction using Hatch’s solution (A) and ALF (B) for 24 h.

Fig. 2.

Correlation between Pb bioaccessibility (%) and Pb speciation (weighted %) of anglesite, Pb phosphate, organic matter bound Pb and Pb adsorbed onto clay/oxide in PM₁₀ using Hatch’s solution (left) and ALF (right). Lead bioaccessibility and speciation data from Kastury et al. (2018a, ; ; PP₂₀₁₈, SH15, CMW and BH) were included in correlation analysis.

Fig. 3.

Correlation between Pb bioaccessibility (%) and speciation (weighted % of Pb phosphate + galena + plumbojarosite) in PM₁₀ using Hatch’s solution (left) and ALF (right).

Fig. 4.

Scanning electron microscopy of PP PM₁₀ particles using backscatter mode (left) and analysis of elemental composition using Energy dispersive X-ray spectroscopy (right). A: PM₁₀ particle before bioaccessibility assay, B: PM₁₀ particle in post bioaccessibility assay residual after extraction using Hatch’s solution for 24 h, C: PM₁₀ particle in post bioaccessibility assay residual after extraction using ALF for 24 h.