Mullus surmuletus as a multiple biomarker for marine pollution

Abstract

The use of bioindicators to evaluate effects of chemical pollutants in the marine organisms constitutes a relatively new and efficient tool in the monitoring field. In the last two decades great advances have been made in this regard and various biomarkers have been determined as being ideal for pollution monitoring. However, due to species-specific differences in biological responses to different types of marine contaminants, very few studies have investigated the possibility of using a single species as a multiple biomarker of pollution. The present study has investigated the feasibility of using the fish Mullus surmuletus as such a multiple biomarker for organic as well as heavy metal contaminants. Fish were sampled from different sites on a seasonal basis over a period of one year starting in May (Spring) 1999 till March (Winter) 2000. The biomarkers investigated where EROD activity and MT induction. Mullus surmuletus proved to have a high response factor both in what regards EROD and MT monitoring. Choice of this species was based on its habitat preference (which is in-shore and thus close to the point of coastal pollution). When sampling was carried out in spring (the reproductive season), immature individuals were used so that sex-related fluctuations were avoided. The sites monitored included: Xghajra, which is exposed to pollution from Malta's major sewage outfall throughout the year; St.Paul's Bay, which is a touristic area exposed to potential marine contamination risks, especially during the summer months; St.Thomas Bay, which is a relatively clean area and only occasionally threatened by marine contaminants. Numerous studies before this have demonstrated the strong correlation of mixed function oxidase activity (and indicated through EROD activity) and polyaromatic hydrocarbons (PAHs) or polychlorobiphenyls (PCBs) in the environment. Similarly, other studies have also noted the elevated levels of MT (above normal homeostatic levels) when heavy metal pollution is present in the environment. Biomonitoring results in the present study have confirmed Xghajra as a site of both organic and heavy metal pollution. EROD activities in liver of fish sampled, were expressed in terms of two indices: Specific EROD activity (RPI), which measures the level of inducible proteins per mg of microsomal protein; and Total EROD activity (RP2) which measures the level of inducible proteins per mg of total liver tissue. The highest specific EROD activity value was recorded for fish sampled from Xghajra during the summer season Such samples had a mean Specific EROD activity value of 258.48 ± 90. 70 pmoles/min/mgprotein The lowest values recorded was 4.18 ± 1.71 pmoles/min/mgprotein. Such a value was recorded for samples obtained from the reference site (St.Thomas Bay). RP2 proved to have higher percentage induction than RPI. Hence, there is an indication that RP2 can be a better biomonitoring parameter than RPI for organic pollution monitoring. Studies on this matter are almost non-existent and this has to be confirmed by further studies. Highest MT induction levels were also recorded for samples obtained from Xghajra. Such fish were collected during the winter season and had an MT level of 403.5 ± 42.9 µgMT/gFW. The lowest MT level was (as expected) recorded for fish sampled from the reference site during the winter season Such samples exhibited an MT level of 92.5 µgMT/gFW. An apparent. trend in MT induction levels was obtained for fish sampled at St.Paul's Bay. This trend is possibly related to seasonal pollution that may be occurring at this site. The ecological significance of these results as well as the merits of using a single fish species as a multiple biomarker of pollution, are discussed.