An Investigation of Mercury Bioaccumulation and its Relation with Selenium in the Muscle and Liver Tissues of Milk Shark (Rhizoprionodon acutus)

Mercury and selenium concentrations were analyzed in the muscle and liver of milk shark (a dominant shark species in the Persian Gulf) from the coast of Bandar Abbas. A research project was designed to compare the level of accumulation Hg and its interaction with Se in milk shark. Hg concentration for each sample was determined by an Advanced Mercury Analyzer (LECO, AMA 254) and Se was assayed using a Graphite Furnace Atomic Absorption Spectrophotometry (Perkin Elmer 3030).The average ±S.D. of Hg and Se in the muscle and liver tissues were (0.06±0.02, 0.09±0.02 µg/g wet wt) and (0.53±0.16, 0.31±0.05 µg/g wet wt) respectively. A positive correlation between mercury concentration in the muscle and liver tissues with weight and length variables were statistically significant (p<0.05).The average of Hg and Se in liver tissue was significantly more than in muscle tissue (p<0.05). In this study, approximately 45% of the liver samples showed levels above the limit established by WHO and FAO. The accumulation of Se in the muscle and liver of milk shark showed a positive correlation with Hg concentration. The molar ratio of Se: Hg in the both tissue were above 1.0. These results suggest a detoxifying mechanism of Se through Se-Hg complexes. In this study, the mean Se-HBV in the muscle is positive; therefore Se concentration is sufficient for detoxification of Hg. In this index, 27% of the liver samples were negative.