Interannual variability in fish biomarkers in a contaminated temperate urban estuary

During the past decade the Swan–Canning estuary, Western Australia, has shown signs of stress which has been attributed to high nutrient inputs. There is little information on the effect of nonnutrient contaminants on biota inhabiting the estuary. A suite of biomarkers was measured on black bream (Acanthopagrus butcheri) to determine whether annual variations in fish biomarkers exist in the wet (winter) and dry (summer) seasons. Serum sorbitol dehydrogenase showed no significant differences between years, indicating that measured mixed-function oxygenase (MFO) enzyme activities were not affected by annual variations in hepatic tissue damage. Ethoxyresorufin-O-deethylase activity was lower in female black bream than in male fish while ethoxycoumarin-O-deethylase activity was not influenced by gender. Biomarker levels measured at various sites confirm that major roads and drains are significant contributors of MFO-inducing chemicals into the Swan–Canning estuary. No consistent upstream or downstream gradient in biomarker response was identified. The ratio of naphthalene-type to benzo(a)pyrene-type biliary metabolites was linked to runoff from urban areas into the estuary. There was high annual variability in all biomarkers in both seasons, suggesting that biannual monitoring is required to evaluate the effect of contaminants on the biota in the estuary.