Determination of potentially toxic elements (PTEs) and an assessment of environmental health risk from environmental matrices

Okorie, Ikechukwu (2010) Determination of potentially toxic elements (PTEs) and an assessment of environmental health risk from environmental matrices. Doctoral thesis, Northumbria University.

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Abstract

A former industrial site now used for recreational activities was investigated for total PTE content, uptake of the PTEs by foraged fruits and mobility of the PTEs using single extraction such as HOAc and EDTA. In order to evaluate the health risks arising from ingestion of the PTE contaminated soil, the oral bioaccessibility using in vitro physiologically based extraction test (PBET) and tolerable daily intake (TDI) or mean daily intake (MDI) was used. The PBET simulates the transition of the PTE pollutants in the soil into human gastrointestinal system while the TDI or MDI is the mass of soil that a child would require to take without posing any health risk. In addition to the former industrial site, an investigation of the urban road dust from Newcastle city centre and its environs was undertaken with the view to looking into the PTE content, oral bioaccessibility and the platinum group elements (PGEs). Optimized microwave procedure was applied to 19 samples obtained from a former industrial site (St Anthony's lead works) in Newcastle upon Tyne. Of the range of PTEs potentially present at the site as a consequence of former industrial activity (As, Cd, Cr, Cu, Ni, Pb and Zn), the majority of top soil samples indicated elevated concentrations of one or more of these PTEs. In particular, data obtained using either inductively coupled plasma mass spectrometry (ICP-MS) or flame atomic absorption spectroscopy (FAAS) indicates the high and wide concentration of Pb on the site (174 to 33,306 mg/kg). Comparing the resulting PTEs data with UK Soil Guidelines Values (SGVs) suggests at least parts of the site represent areas of potential human health risk. It was found that Pb soil values exceeded the SGV on 17 out of the 19 sampling sites; similarly for As 7 out of 19 sampling sites exceeded the SGV. While for Cd and Ni the soil levels were below the stated SGVs. Samples of foraged fruits collected from the same site were also analysed for the same PTEs. The foraged fruit was gathered over two seasons along with samples of soil from the same sampling areas, acid digested using a microwave oven, and then analysed by ICP-MS. The foraged fruits samples included blackberries, rosehips and sloes which were readily available on the site. The concentration levels of the selected elements in foraged samples varied between not detectable limits and 24.6 mg/kg (Zn). Finally, the soil-to plant transfer factor was assessed for the 7 elements. In all cases, the transfer values obtained were below 1.00,except Cd in 2007 which is 1.00, indicating that the majority of the PTE remains in the soil and that the uptake of PTE from soil to plant at this site is not significant. The determination of total or pseudo total PTE content of soil is often insufficient to assess the risk to humans. A range of extraction protocols were applied to the 19 samples urban topsoils, and report on the correlations between pseudo total PTE content and results obtained following a physiologically-based extraction procedure (oral bioaccessibility), EDTA and HOAc extraction protocols (reagent-specific available fraction), for a broad range of PTEs (As, Cd, Cu, Cr, Ni, Pb, Zn). Results of the single-reagent extraction procedures did not, in general, provide a good indication of oral bioaccessibility but shows positive correlation with the pseudo total PTE content. The bioaccessibility data shows that considerable variation exists both spatially across the site, and between the different PTEs, but correlates well with the pseudo-total concentrations for all elements (r2 exceeding 0.8). One of the main objectives of this work is to show the role of bioaccessibility in generic risk assessment. Comparison of the pseudo-total PTE concentrations with SGV or generic assessment criteria (GAC) indicated that all of the PTEs investigated need further action, such as receptor exposure modelling. If we refine our generic risk assessment using the PTE bioaccessibility data then a very...

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