Seasonal responses of the mixed-function oxygenase system in the American oyster, Crassostrea virginica (Gmelin 1791), to urban-derived polycyclic aromatic hydrocarbons.

Mixed-function oxygenase (MFO) system components (cytochrome P450 and b5, "423 peak" and NADPH cytochrome c reductase) and body burdens of polycyclic aromatic hydrocarbons (PAHs) were determined seasonally in oysters, Crassostrea virginica (Gmelin 1791), collected from an undeveloped estuary (North Inlet, SC) and an urbanized estuary (Murrells Inlet, SC). All MFO system components monitored in oysters from North Inlet demonstrated seasonal variations; levels were lowest during October 1992. Whole oyster PAH tissue levels were always higher in Murrells Inlet oysters compared with North Inlet oysters. Seasonal variation of PAH body burdens was evident in oysters from Murrells Inlet; the highest levels occurred during April 1993. Differences between the two estuaries were seasonally evident in most oyster MFO system components. Reductase activity was highest at the most contaminated Murrells Inlet site during October 1992 and April 1993. This seasonal variation was positively correlated to that of their PAH body burdens. Cytochrome P450 content was also elevated at the most contaminated site during April 1993. These results suggest that reductase activity and cytochrome P450 content in Murrells Inlet oysters were induced by the high PAH body burdens during April 1993 and indicate their potential as molecular biomarkers of PAH contamination.