Oral bioavailability of benzo[a]pyrene (B[a]P) in 19 soils was measured using a juvenile swine model. These soils include 12 surface samples and 7 subsurface samples collected from 12 sites in Australia covering major soil types. The B[a]P-spiked soils (50 mg/kg) were aged for 90 days at 60% water holding capacity. Following ageing, the soils were air-dried, homogenized and then dosed to juvenile swine at a rate of 1.25 g/kg body weight with food in triplicates. Bioavailability of B[a]P was measured by the area under the plasma concentration of B[a]P curve (AUC) over 24 h after dosing. Freshly spiked silica sand was used as a reference material to calibrate dose-responses and calculate the relative bioavailability (RB). Two solvent extraction methods were used to measure the B[a]P extractability (i) an exhaustive extraction using dichloromethane and acetone (DCM/Ace, v: v = 1:1) facilitated by sonication and (ii) a mild extraction using butanol (BuOH) vortex for 50 seconds. The relative bioavailability of B[a]P in soils were generally below 60% in swine, ranging from 21.1 ± 1.2% to 57.3 ± 8.6%, except for three soils, in which RB was not significantly different, and therefore high, from silica sand RB. The in vivo RB of B[a]P in soils showed no clear correlation with any simple soil parameter except for pore diameter (positively correlated, r = 0.53, p &lt; 0.05) when the three soils with high RB were excluded from regression. An index of carbon fraction considered recalcitrant as protected by fine particles in soil, fine particle associated carbon (FPAC; (Silt + Clay)/TOC), showed a strong negative correlation with RB in most of the surface soils (R2 = 0.87, p &lt; 0.001). The pore size fraction &lt; 6 nm also showed a strong negative correlation with RB in most of the surface soils (R2 = 0.86, p &lt; 0.001). Most of the outliers were from subsurface soils low in organic carbon demonstrating the influence of FPAC on bioavailability. The deviated actual data is likely related to the surface charges of the soils, where the nature of the soil mineral/carbon, pH and ions are all important. Extractability of B[a]P using DCM/Ace and BuOH ranged from 10.8 ± 0.8% to 75.2 ± 0.1% and 4.2 ± 0.2% to 56.7 ± 1.4% respectively. Despite the variation in RB, there was a strongly significant positive correlation between the DCM/Ace extractability and RB of B[a]P in all soils (R2 = 0.54, p &lt; 0.001, n = 19), indicating it is a good indicator for the potential risk of human exposure.

Correlation between solvent extractability and bioavailability of benzo(a)pyrene in 19 soils measured in juvenile swine

256th National Meeting (2018)

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