You are here:
In Vitro, in Vivo, and Spectroscopic Assessment of Lead Exposure Reduction via Ingestion and Inhalation Pathways Using Phosphate and Iron Amendments.
Citation:
Kastury, F., E. Smith, E. Doelsh, E. Lombi, M. Donnelley, P. Cmielewski, D. Parsons, Kirk G. Scheckel, D. Paterson, M. de Jonge, C. Herde, AND A. Juhasz. In Vitro, in Vivo, and Spectroscopic Assessment of Lead Exposure Reduction via Ingestion and Inhalation Pathways Using Phosphate and Iron Amendments. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 53(17):10329-10341, (2019). https://doi.org/10.1021/acs.est.9b02448
Impact/Purpose:
Impairment of cognitive and neurological development due to childhood Pb exposure is well documented and can occur at blood Pb concentration (PbB) as low as 3 µg/dL. The two significant pathways for Pb exposure in humans are incidental ingestion of soil or surface dust and inhalation of re-suspended dust or airborne particulate matter with <10 µm in aerodynamic diameter (PM10). Following the ingestion of soil and surface dust, Pb may be solubilized in the acidic conditions of the stomach (pH 1.5-2.5) and subsequently absorbed by passive and facilitated diffusion via the divalent metal transporter in the duodenum and ileum of the small intestine (pH 7). Similarly, upon inhalation of re-suspended dust, Pb may be solubilized in the surfactants and epithelial lining fluid (pH 7.4) of the lungs. Solubilized Pb may be rapidly absorbed via the air blood barrier into the systemic circulation. However, approximately 90% of inhaled particles may be cleared from the lungs by the mucociliary escalator within 24 hours and swallowed, and then continue to be solubilized and absorbed in the gastro-intestinal (GI) tract. Children are the most at risk of being adversely affected via incidental ingestion or inhalation of soil/dust because of their higher occurrence of hand-to-mouth activities as well as their increased respiratory frequency, leading to a higher deposition fraction of fine particulate matter (< 4 µm) in the respiratory tract. Reduction in Pb bioavailability (Pb absorption into the systemic circulation) using soil amendments (e.g. phosphates, metal oxides, clay minerals) has been argued to be a cost effective risk minimization strategy compared to other remediation strategies including phyto-extraction or soil removal, replacement, washing and capping. In particular, phosphate amendments may reduce Pb bioavailability by promoting the formation of poorly soluble Pb-phosphate species [e.g. pyromorphites (Pb5(PO4)3X, where X = OH, Cl, or F) and Pb3(PO4)2], as demonstrated in human and animal feeding studies. A recent study demonstrated that the effects of Pb immobilization using phosphate and iron amendments may be sustained for as long as 16 years after application. However, the efficacy of Pb immobilization depend on site-specific soil chemistry, Pb speciation and choice of amendment. This study aimed to determine the efficacy of P and Fe amendments in reducing Pb exposure via ingestion and inhalation pathways using smelting/mining impacted soil. To achieve this aim, Pb impacted soil from Broken-Hill (Australia) was treated with soil amendments with Pb bioaccessibility and bioavailability assessed in ingestible and inhalable fractions. Additionally, changes in Pb speciation in pre- and post-bioaccessibility residuals was determined using X-ray absorption spectroscopy (XAS), Pb dynamics following in-vivo inhalation exposure was assessed in the lungs and GI tracts using X-ray Fluorescence Microscopy (XFM), while Pb speciation following inhalation exposure was assessed in situ using X-ray Absorption Spectroscopy.
Description:
This study compared lead (Pb) immobilization efficacies in mining/smelting impacted soil using phosphate and iron amendments via ingestion and inhalation pathways using in vitro and in vivo assays, in conjunction with investigating the dynamics of dust particles in the lungs and gastro-intestinal tract via X-ray fluorescence (XRF) microscopy. Phosphate amendments [phosphoric acid (PA), hydroxyapatite, monoammonium phosphate (MAP), triple super phosphate (TSP), and bone meal biochar] and hematite were applied at a molar ratio of Pb:Fe/P = 1:5. Pb phosphate formation was investigated in the soil/post-in vitro bioaccessibility (IVBA) residuals and in mouse lung via extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structures (XANES) spectroscopy, respectively. EXAFS analysis revealed that anglesite was the dominant phase in the ingestible (<250 μm) and inhalable (<10 μm) particle fractions. Pb IVBA was significantly reduced (p < 0.05) by phosphate amendments in the <250 μm fraction (solubility bioaccessibility research consortium assay) and by PA, MAP, and TSP in the <10 μm fraction (inhalation-ingestion bioaccessibility assay). A 21.1% reduction in Pb RBA (<250 μm fraction) and 56.4% reduction in blood Pb concentration (<10 μm fraction) were observed via the ingestion and inhalation pathways, respectively. XRF microscopy detected Pb in the stomach within 4 h, presumably via mucociliary clearance.
URLs/Downloads:
DOI: In Vitro, in Vivo, and Spectroscopic Assessment of Lead Exposure Reduction via Ingestion and Inhalation Pathways Using Phosphate and Iron Amendments.
Free access through PubMed Central