PAH metabolites in bile, cytochrome P4501A and DNA adducts as environmental risk parameters for chronic oil exposure: a laboratory experiment with Atlantic cod.

In order to perform environmental risk assessments with regard to oil contamination in the sea, it is important to obtain knowledge about threshold levels for possible adverse effects in marine organisms. With this objective in mind, selected biomarkers were studied in Atlantic cod (Gadus morhua) chronically exposed to mechanically dispersed crude oil. The fish were exposed for 30 days in a continuous flow system to nominal concentrations of 0.06, 0.25 and 1 ppm North Sea crude oil. Fish were sampled five times during the exposure period. In addition, the 1 ppm group and the control group were sampled 1 week after the end of exposure. Polyaromatic hydrocarbon (PAH) concentrations in the seawater were analysed regularly by direct fluorescence and, at one occasion, by gas chromatography with mass spectrographic detection (GC/MS) measurements. Liver samples were analysed for parent PAH levels by means of GC/MS measurements, and PAH metabolites in bile were analysed by means of fixed wavelength fluorescence. Cytochrome P450 induction in liver was estimated by ethoxyresorufin-O-deethylase (EROD) activity, and hepatic DNA adducts were analysed by the 32P-postlabelling assay. The parent PAH concentrations in liver showed peak levels 3 days after the start of exposure, followed by a reduction towards the end of the experiment. In contrast, the PAH metabolites in bile and EROD activity showed generally increasing levels throughout the whole exposure period, indicating an increased biotransformation efficiency. The level of DNA adducts in the 1 ppm group showed a stable increase during the entire exposure period. Only a slight, non-significant decrease in DNA adduct levels was observed after 7 days of recovery in clean water. Exposure-dependent responses were observed for all three biomarkers. The lowest nominal concentration of dispersed oil in water, 0.06 ppm, corresponded to a measured total PAH concentration in the water of 0.3 ppb. Atlantic cod exposed to this concentration showed increased levels of PAH metabolites in bile and a slight induction of CYP1A, as well as formation of DNA adducts when compared with control fish. Particularly noteworthy is the detection of DNA adducts at such a low exposure concentration of oil in water, which, to our knowledge, is a novel finding. These dose-response data may serve as useful contributions when assessing environmental risk with regard to marine oil pollution.