Physiological and proteomic responses in Mytilus edulis exposed to PCBs and PAHs extracted from Baltic Sea sediments

Stress responses in blue mussels (Mytilus edulis. L.) exposed to rganic pollutants were measured using several physiological measures and as changes in protein expression. Blue mussels from the Baltic Sea were exposed for 6 days in a flow-through system to two fractions of extracted Baltic sediments (containing primarily PAHs or PCBs) from one industrially impacted site and one off-shore site. Exposure to Aroclor1248 (a commercial PCB mixture) was included as a reference treatment. Physiological response was measured as changes in respiration, excretion, clearance rates and scope for growth. Of the physiological responses, only clearance rate and scope for growth in the Aroclor and impacted site PCB treatments differed significantly (p<0.05) from control organisms, perhaps due to a large variation among individuals. Seven proteins were observed, presumed to be from stress protein families (hsp60, hsp70 and hsp90) on one-dimensional electrophoresis gels. All protein levels, except three proteins, 62, 73 and 90 kDa, in response to PCB exposure from the industrial site, were significantly higher (p<0.05) in treated than in control organisms, suggesting the use of stress-inducible proteins as diagnostics in risk assessment. A wider sample of proteins was observed using two-dimensional gel electrophoresis. The presence or absence of protein spots compared to control organisms was used as an indication of stress. Between 23 and 76 proteins or spots were present and 15 to 23 absent compared to controls, and the results supported the physiological and one-dimensional gel results, suggesting that the mussels were indeed suffering from stress. The methods used here represent stress monitoring at two different levels of biological organization; the cellular- and the level of individual organisms. In this experiment the protein response showed less variation among individuals compared to the physiological parameters. The protein response, however, still suffers from the lack of interpretation into commonly used monitoring terms, which emphasizes the need for more knowledge of whether the response is a momentary reflection of exposure or an early warning of higher order effects.