A lead isotopic study of the human bioaccessibility of lead in urban soils from Glasgow, Scotland

The human bioaccessibility of lead (Pb) in Pb-contaminated soils from the Glasgow area was determined by the Unified Bioaccessibility Research Group of Europe (BARGE) Method (UBM), an in vitro physiologically based extraction scheme that mimics the chemical environment of the human gastrointestinal system and contains both stomach and intestine compartments. For 27 soils ranging in total Pb concentration from 126 to 2160 mg kg− 1 (median 539 mg kg− 1), bioaccessibility as determined by the ‘stomach’ simulation (pH ~ 1.5) was 46–1580 mg kg− 1, equivalent to 23–77% (mean 52%) of soil total Pb concentration. The corresponding bioaccessibility data for the ‘stomach + intestine’ simulation (pH ~ 6.3) were 6–623 mg kg− 1 and 2–42% (mean 22%) of soil Pb concentration. The soil 206Pb/207Pb ratios ranged from 1.057 to 1.175. Three-isotope plots of 208Pb/206Pb against 206Pb/207Pb demonstrated that 206Pb/207Pb ratios were intermediate between values for source end-member extremes of imported Australian Pb ore (1.04) – used in the manufacture of alkyl Pb compounds (1.06–1.10) formerly added to petrol – and indigenous Pb ores/coal (1.17–1.19). The 206Pb/207Pb ratios of the UBM ‘stomach’ extracts were similar (< 0.01 difference) to those of the soil for 26 of the 27 samples (r = 0.993, p < 0.001) and lower in 24 of them. A slight preference for lower 206Pb/207Pb ratio was discernible in the UBM. However, the source of Pb appeared to be less important in determining the extent of UBM-bioaccessible Pb than the overall soil total Pb concentration and the soil phases with which the Pb was associated. The significant phases identified in a subset of samples were carbonates, manganese oxides, iron-aluminium oxyhydroxides and clays