Tracing of xenobiotic contamination in water with the aid of fish bile metabolites: a field study with caged rainbow trout ( Salmo gairdneri)

Abstract

Caging experiments were conducted using juvenile rainbow trout ( Salmo gairdneri) in a lake area receiving chlorine-bleached kraft pulpmill effluents (BKME) from a single discharge pipe. The trout were exposed for 10 and 15 days at four locations downstream (1, 4, 6 and 11 km) and at one reference location upstream (2 km) from the effluent pipe. Water, blood and bile samples were collected and analysed for concentrations of seven resin acids (RA) and eight chlorophenolic (CP) compounds. The activities of UDP-glucuronosyltransferase (UDP-GT) were measured in the livers of the experimental trout. Several physicochemical features and concentrations of RA and CP in water show that the experimental area formed a gradient system which was correlated with the concentrations of BKME in the water. The concentrations of free RA and CP in the blood plasma and bile of the caged trout were also distance related. This pattern was even more apparent in the total concentrations of conjugated RA and CP in the bile. The approximate bioconcentration factors in the trout plasma were 10 2 to 10 3 for RA and CP relative to the levels in the water. The hepatocellular concentration step, which involves conjugative biotransformations, further increased concentrations by a factor of 10 2 to 10 3. The overall gradient between the concentration of the parent compound in the water, and its metabolites in bile, thus approximated 10 5 for RA and, in some cases, even approached 10 6 for CP. 15 days of exposure, the activity of UDP-GT in trout livers was significantly increased at distances between 4–11 km from the source of BKME. We conclude that establishment of the pattern of metabolically converted xenobiotics in the bile of caged rainbow trout is both a sensitive and (semi)quantitative way to assess low levels of contamination in recipient waters.