Relative bioavailability of soil-bound polycyclic aromatic hydrocarbons in goats

This study aimed at determining the relative bioavailability (RB) of three soil-bound PAH model compounds (phenanthrene [PHE], pyrene [PYR] and benzo[a]pyrene [BaP]) in four lactating goats. RB was estimated by comparing the urinary or milk excretion of the major mono-hydroxylated metabolites of PAHs after ingestion of PAH spiked-soil and -oil feeds. A series of three increasing doses were orally administered in order to estimate the dose response of the two different matrices. The results of this study reveal that urinary excretion prevailed compared to milk excretion (30-fold higher). The recovery rate of mono-hydroxylated metabolites of PAHs in urine and milk indicate that PYR was absorbed at a minimum level of 36%. 3-OH PHE excreted in urine suggests a minimal absorption of at least 5% for PHE. 3-OH BaP remained under the limits of detection and quantification and no RB could be calculated for this compound. RB of soil-bound PYR compared to PYR in oil was 61% and 50% in milk and urine, respectively. Thus, a significantly reduced RB of PYR in soil has been shown. On the other hand, no significant differences were observed between oil and soil for urinary 3-OH PHE (RB = 100%). These results show that the soil matrix significantly reduces the bioavailability of certain PAHs. The decrease of bioavailability seems to be dependent on the compounds, i.e. higher for PYR than for PHE. This study also suggests that soil ingestion should be taken into account in risk assessment studies.