LIVER MICROSOMAL LEVELS OF CYTOCHROME P450IA1 AS BIOMARKER FOR EXPOSURE AND BIOAVAILABILITY OF SOIL-BOUND POLYCYCLIC AROMATIC-HYDROCARBONS

The bioavailability of soil-bound polycyclic aromatic hydrocarbons (PA Hs) for mammalian species was studied with rats fed with a diet contai ning contaminated soil preparations. The extent of cytochrome P450IA1 (CYP1A1) induction in the liver correlated with the amount of 5- and 6 -ring PAHs in the soil samples but not with the total PAH content. Oth er cytochromes P450 were much less affected by the soil-contaminants. The highest induction of CYP1A1 was obtained with a sample containing 274 mg 5- and 6-ring PAH/kg soil, resulting in a nearly 360-fold incre ase in the ethoxyresorufin deethylase (EROD) activity. In a semilogari thmic plot, a linear correlation was found between the 5- and 6-ring P AH concentration in the soil and the microsomal CYP1A1 content. As a m odel for the action of intestinal fluids, soil samples were extracted by bile acid solution. In these experiments, the selectivity in the so lubilization of individual PAHs parallels that of toluene extraction, although the yield is lower than the latter and varies with the soil s ample. The bioavailability of PAHs for microorganisms, but not for mam mals, was shown to be considerably reduced in the presence of high tot al organic carbon (TOC) values of the soil samples. This may have impl ications for decontamination strategies, diminishing the effectiveness of biological decontamination in cases with high TOC values. The data suggest that CYP1A1 induction in rats is a parameter that may be usef ul in risk assessments of contaminated soils for mammalian species.