DETERMINATION OF POLYCYCLIC AROMATIC-HYDROCARBONS (PAH) AND THEIR METABOLITES IN BLOOD, FECES, AND URINE OF RATS ORALLY EXPOSED TO PAH CONTAMINATED SOILS

Polycyclic aromatic hydrocarbons (PAH) have become an ubiquitous upper soil component as a consequence of industrialization involving a mult itude of combustion processes. Ingestion of PAH contaminated soil is c onsidered to be a major exposure route, specifically for small childre n living on these soils. Health risk assessment is based on extrapolat ions from data obtained via studies performed with pure chemicals. Add itionally it is assumed that after oral intake all PAH present in the soil will be absorbed by the human body. Interactions with the soil ma trix, however, may modulate the bioavailability of PAH. In this study, we examined the absorption and excretion of PAH in rats orally expose d either to industrially contaminated soils or pure model compounds as anthracene, pyrene and benzo(a)pyrene (B[a]P). The model compounds an d the metabolites, 1-hydroxypyrene (1-OH-pyrene) and 3-hydroxybenzo(a) pyrene (3-OH-B[a]P), were measured in blood, feces or urine by means o f HPLC with fluorescence detection. Because of rapid biotransformation only minimal levels of unmetabolized anthracene, pyrene and B[a]P in blood could be detected. The pharmacokinetic parameters were nonlinear and suggestive of enterohepatic cycling. Only low levels of the compo unds were excreted unchanged in feces whereas the levels of the metabo lites were considerably higher in feces and urine. These results indic ate that the dosed PAH are largely absorbed by the gastrointestinal tr act, subsequently metabolized and excreted as metabolites via urine an d feces. Significant differences between the soil-treated group and th e pure mixture-treated group could be observed; the soil-treated group showed higher fecal excretion of unchanged pyrene (0.5 versus 0.2% of the original dose) and B[a]P (1 versus 0.3%), lower excretion of 1-OH -pyrene in feces (5.1 versus 17.0%), and lower excretion of 1-OH-pyren e in urine (0.2 versus 3.4%). The fecal excretion of 3-OH-B[a]P betwee n the two groups was similar (8.8 versus 8.8%). These results suggest that the soil matrix is capable of reducing the absorption of at least pyrene. Therefore, exposure risk assessment models assuming complete bioavailability of soilmatrix-bound PAH probably overestimate the endo genous dose.