Estimation of Relative Bioavailability of Lead in Soil and Soil-Like Materials Using Young Swine

Veterinary Medical Diagnostic Laboratory, College of Veterinary Medicine, University of Missouri, Columbia, Missouri, USA.
Environmental Health Perspectives (Impact Factor: 7.98). 09/2006; 114(8):1162-71. DOI: 10.1289/ehp.8852
Source: PubMed


In this article we summarize the results of a series of studies that measured the relative bioavailability (RBA) of lead in a variety of soil and soil-like test materials. Reference material (Pb acetate) or Pb-contaminated soils were administered orally to juvenile swine twice a day for 15 days. Blood samples were collected from each animal at multiple times during the course of the study, and samples of liver, kidney, and bone were collected at sacrifice. All samples were analyzed for Pb. We estimated the RBA of a test material by fitting mathematical models to the dose-response curves for each measurement end point and finding the ratio of doses that gave equal responses. The final RBA for a test material is the simple average of the four end point-specific RBA values. Results from 19 different test materials reveal a wide range of RBA values across different exposure materials, ranging from 6 to 105%. This variability in RBA between different samples highlights the importance of reliable RBA data to help improve risk assessments for Pb in soil. Although the RBA value for a sample depends on the relative amounts of the different chemical and physical forms of Pb present, data are not yet adequate to allow reliable quantitative predictions of RBA from chemical speciation data alone.

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    • "However, the Pb RBA could be wide-ranging not only due to very different methods used to assess RBA but also due to the nature of soils and source of Pb contamination. For example, Casteel et al. (2006) demonstrated that RBA of Pb using a swine model ranges from 1 to 90 %: 1 % for galena-enriched soil, 6–90 % for samples from on-site location , and 27–75 % for samples from residential areas. Li et al. (2015) and Li et al. (2014) reported that Pb RBA (mouse model) ranged from 51.4 to 60.5 % for farming soils, 30.8 to 84.3 % for smelter soils, 7 to 26 % for mining soils, and 29.1 to 60.1 % for house dusts, respectively. "
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    ABSTRACT: Bioaccessibility to assess potential risks resulting from exposure to Pb-contaminated soils is commonly estimated using various in vitro methods. However, existing in vitro methods yield different results depending on the composition of the extractant as well as the contaminated soils. For this reason, the relationships between the five commonly used in vitro methods, the Relative Bioavailability Leaching Procedure (RBALP), the unified BioAccessibility Research Group Europe (BARGE) method (UBM), the Solubility Bioaccessibility Research Consortium assay (SBRC), a Physiologically Based Extraction Test (PBET), and the in vitro Digestion Model (RIVM) were quantified statistically using 10 soils from long-term Pb-contaminated mining and smelter sites located in Western Australia and South Australia. For all 10 soils, the measured Pb bioaccessibility regarding all in vitro methods varied from 1.9 to 106 % for gastric phase, which is higher than that for intestinal phase: 0.2 ∼ 78.6 %. The variations in Pb bioaccessibility depend on the in vitro models being used, suggesting that the method chosen for bioaccessibility assessment must be validated against in vivo studies prior to use for predicting risk. Regression studies between RBALP and SRBC, RBALP and RIVM (0.06) (0.06 g of soil in each tube, S:L ratios for gastric phase and intestinal phase are 1:375 and 1:958, respectively) showed that Pb bioaccessibility based on the three methods were comparable. Meanwhile, the slopes between RBALP and UBM, RBALP and RIVM (0.6) (0.6 g soil in each tube, S:L ratios for gastric phase and intestinal phase are 1:37.5 and 1:96, respectively) were 1.21 and 1.02, respectively. The findings presented in this study could help standardize in vitro bioaccessibility measurements and provide a scientific basis for further relating Pb bioavailability and soil properties.
    Full-text · Article · Dec 2015 · Environmental Science and Pollution Research
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    • "The real uptake (i.e., absorption) of Pb via dust ingestion is greatly dependent on the solubility (i.e., bioaccessibility) of Pb in the gastrointestinal system [18] [19] [20]. Due to the complex, time consuming and cost prohibitive nature of vivo assays [21], the oral bioaccessibility of Pb in soil/dust matrix has been usually predicted by various in vitro methods, such as dilute HCl extraction [22] and physiologically based extraction test (PBET) [19] [20] [23]. The PBET introduces digestive enzyme and pepsin into extraction solutions and mimics sequentially the chemical conditions in the gut and intestine and thus may provide valuable mechanistic information on the Pb mobilization from dust in the gastrointestinal tract [20]. "
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    ABSTRACT: In this study, ground surface dust samples from two contrasting areas, a former zinc smelting area in Guizhou Province and a common urban district in Wuhan city, Hubei Province, China, were assessed for in vitro Pb bioaccessibility using a physiologically based extraction test (PBET). Extremely elevated concentrations of Pb (220-6348mg/kg) and other trace metals were observed in the zinc smelting area. While moderate high metal concentrations (79-1544mg/kg of Pb) in the urban dusts were attributed to various urban activities, coal combustion and traffic emissions. Lead bioaccessibility in the stomach-phase varied from 17.6 to 76.1% and no significant difference was found between industrial and urban dust samples. Compared with the stomach-phase, Pb bioaccessibility in the more alkaline intestinal-phase was considerably lower (1.2-21.8%). A significantly negative correlation was found between dust Ca concentrations and Pb bioaccessibility in the intestinal-phase, suggesting that Ca plays an important role in reducing the bioaccessible Pb in the intestinal-phase. The estimated Pb exposure based on gastric bioaccessible Pb was 13.9 and 1.8μg/kgday for children living in the industrial and urban areas, respectively, accounting for 85% and 41% of their corresponding total Pb exposure. Copyright © 2015 Elsevier B.V. All rights reserved.
    Full-text · Article · Apr 2015 · Journal of hazardous materials
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    • "Therefore, from a physiological perspective, rodents are not the best model for oral exposure in humans. Swine have emerged as a promising model for human oral exposure to contaminants due to similarity in gastrointestinal anatomy and physiology, down to the cellular level, and as such, have been commonly used as models for a variety of compounds (Roos et al., 2002; Casteel et al., 2006; Budinsky et al., 2008). Additionally, swine have similar nutritional requirements to humans, ensuring that compounds will be absorbed in similar quantities, and at a similar rate (Patterson et al., 2008). "
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    ABSTRACT: Humans are constantly exposed to contaminants in the environment, which may lead to changes in physiological processes by altering enzyme activities that could affect bioavailability. However, bioavailability estimates are typically made from a single exposure to an animal model, which may lead to overestimating bioavailability. This study uses juvenile swine to model human exposure to benzo[a]pyrene (BaP) and anthracene in certified reference material (CRM), spiked soil, spiked food, or spiked corn oil after one and seven days of dosing. Area under the curve (AUC) was calculated after one and seven days of exposure for both BaP and anthracene for each exposure media. Whereas there were significant differences in AUC between different media, there were no significant changes in AUC after sub-chronic exposure to BaP or anthracene. Average BaP bioavailability for CRM, spiked soil, spiked food and corn oil was 71%, 0.72%, 0.03% and 0.97% respectively. Average anthracene bioavailability was 1.7% and 43% for corn oil and CRM respectively. Anthracene was not detected above background in swine exposed to spiked food and spiked soil. Thus, this study indicates that exposure media impacts bioavailability, but there is no statistical evidence that sub-chronic exposure affects systemic exposure.
    Full-text · Article · Nov 2014 · Science of The Total Environment
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