CB PATTERN IN THE HARBOR PORPOISE - BIOACCUMULATION, METABOLISM AND EVIDENCE FOR CYTOCHROME-P450 HB ACTIVITY

Metabolism of chlorobiphenyls (CBs) was studied in harbour porpoise by comparing patterns of CB-X/CB-153 ratios in blood, brain, liver and b lubber with the patterns in herring, the main food source. The CBs wer e classified in five groups, based on the presence/absence of vicinal Ii-atoms (vic. Hs) in meta,para (m,p) and/or ortho,meta (o,m) position s and the number of ortho-Cl-atoms (ortho-Cls). Plots of CB-X/CB-153 r atios in porpoise tissue vs the ratios in herring appeared to be linea r for each CB group in all tissues. Slopes of these plots (metabolic s lopes) were used as quantitative indicators of metabolic activity. In this way, activity of PB-type isozymes of the P450 monooxygenase syste m was apparent: in contrast to existing literature data, harbour porpo ise appears to be able to metabolize congeners with m,p vie. Hs, even in the presence of more than 2 ortho-Cls. The presence of 3-MC-type (M C-type) isozymes was also detected. The metabolic slopes were also use d as basis for risk assessment. Due to their metabolism the most toxic non-ortho CBs were not present in the tissues at detectable levels. W e suggest a risk assessment approach which takes this into account. It is considered to be an alternative and more reliable basis for risk a ssessment than the use of toxic equivalent factors. The results suppor t the model of equilibrium distribution of CBs in harbour porpoise and the role of blood as central transport medium. The model has been dev eloped for persistent compounds; it appears to hold for metabolizable CB congeners as well.