The effects of exposure duration and feeding status on fish bile metabolites: implications for biomonitoring.

Biliary metabolites of 2-chlorosyringaldehyde (2-CSA), the major chlorinated phenol found in chlorine dioxide bleached eucalypt pulp effluent, have been found to be sensitive biomarkers of effluent exposure in the sand flathead (Platycephalus bassensis). Before this method of biomonitoring can be applied in the field, the influences of exposure duration, depuration time, and fish feeding status on the level of this metabolite should be determined. In this study, sand flathead were exposed to a measured concentration of 0.3 microgram/1 of 2-CSA for 1, 2, 4, 8, 12, or 16 days. Fish previously exposed to 2-CSA were then held in sea-water alone for 1, 2, 3, 4, or 6 days. Fish were fed ad libitum throughout the experiment, and the fullness of the fish's stomach at the time of sampling was noted. There were no effects of exposure on biotransformation enzyme activities, either between exposure times or between the exposure and depuration periods. The major metabolite of 2-CSA, 2-chloro-4-hydroxy-3,5-dimethoxybenzylalcohol (2-CB-OH), was first detected in the bile of some fish sampled after 24 h of exposure, and the mean concentration of 2-CB-OH in the bile increased over the exposure period. The mean concentration (+/- SE) of 2-CB-OH in the bile was strongly influenced by fish feeding status, being 94 +/- 18 ng/ml bile in fish with empty stomachs and undetectable in fish with full stomachs. Bile volume was also influenced by fish feeding status, being greatest in fish with empty stomachs at the time of sampling. Results indicate that the feeding status of fish should be taken into consideration when using biliary metabolites as biomarkers of effluent exposure in the field, and methods to establish this are discussed.