Interseasonal variability in biomarkers of exposure in fish inhabiting a southwestern Australian estuary

Abstract

The Swan-Canning Estuary, in southwestern Australia, undergoes distinct seasonal changes, with freshwater discharge predominant in the winter (wet) season and low flow with high salinity predominant in the dry summer season. To investigate seasonal variability in biomarkers of exposure in fish, black bream (Acanthopagrus butcheri) were collected from seven sites in the Swan-Canning Estuary in winter 2000 and in summer 2001. No interseasonal or intersite differences in serum sorbitol dehydrogenase concentration were found, indicating the measured mixed-function oxygenase (MFO) enzymes were not influenced by liver damage. The ethoxyresorufin-O-deethlyase (EROD) activity of the postspawning females was higher in summer than in winter but was significantly lower than that in males in both seasons, suggesting estradiol suppression in females. Sexual differences in ethoxycoumarin-O-deethylase (ECOD) activity were not evident in either season. Both EROD and ECOD activities and polycyclic aromatic hydrocarbons (PAH) biliary metabolites had significantly different patterns of induction between seasons. The ratio of naphthalene-type to benzo(a)pyrene-type biliary metabolites was significantly higher in summer, indicating the sources of petroleum hydrocarbons were petrogenic compared to in winter, when the source was a mixture of pyrogenic and petrogenic PAHs. There was no upstream or downstream gradient of response in any biomarker in either season, demonstrating that there were multiple sources of contaminant input into the estuary. Although winter biomarker levels were triggered by the discharge runoff from major roads and drains, summer biomarker levels appear to have been related to recreational boating use on the estuary.