Summary:
Chondrichthyes, as apex predators of marine ecosystems,with a long life span and large lipid rich livers, are susceptible to the accumulation of high levels of bioavailable pollutants like heavy metals, via trophic web. Their exposure at high levels of heavy metals could cause disfunctions or damage at their life circle and reproduction. Targeted or by-catch fishing pressure for their fins, reduces their biomass. With their global population in decline, the understanding of the size of exposure and the potential effects on their physiology,is very much of importance for future conservation management plans.
In this study, 33 big size (58-390cm) sharks of common, not so common and rare appearances, were collected; a) pelagic; 14 Prionace glauca, 2 Mobula mobular, 1 Isurus oxyrinchus b) semipelagic; 2 Alopias superciliosus, 5 Hexanchus griseus, 2 Odontaspis ferox, 1 Sphyrna zygaena, and c) benthopelagic or demersal: 1 Oxynotus centrina, 4 Heptranchias perlo, 1 Hexanchus nakamurai, in order to analyze heavy metal levels such as Hg, Al,V, Mn, Zn, Co, Cd, As, Cu, Cs, Fe, Pb, Ni, Cr in their tissues. Sharks were caught in Eastern Mediterranean.
The detection of metals in the sharks’ tissues in the case of Hg, performed by Atomic Absorption Spectrometry Cold Vapor, while the rest of the metals were examined by Inductively Coupled Plasma Mass Spectrometer with a spectrophotometry detector, after wet digestion of tissue samples.
According to analysis, the highest concentations were presented by As in muscle tissue in M.mobular (160Kg), (241,8 μg*g-1 w.w.), while the lowest presented by V in heart tissue of A.superciliosus (321cm), (0,0005 μg*g-1 w.w.). Liver tissue seems to be targeted by Cd and H.perlo (111cm) presents the highest concentration value (1,979 μg*g-1 w.w.).
Hg, tends to concentrate particularly in muscle tissue, albeit the highest values of Hg, appeared in liver tissue. Highest value in muscle tissue 15,28 μg*g-1 w.w. appeared in O.ferox (285cm), while the highest value generally in Hg, appeared in liver tissue 62,20 μg*g-1 w.w., in H.griseus (238cm). Factors like different species and tissues, appears to affect Hg concentrations. Size is positively correlated to the increase of Hg concentration.
Concentrations of metals, appears to differ in between species, sexes and tissues as well as with size and food path. Muscle tissue is much of an interest because of the consumption by humans. Other highest concentrations in this tissue were Fe (209 μg*g-1 w.w., M.mobular (160Kg)) and Zn (108,5 μg*g-1 w.w., M.mobular (160Kg)). Average concentrations of metals (Hg, Pb, Cd) that are toxic for human consumption, were above the suggested consumption limit by E.U (1, 0.5,0.5 μg*g-1 w.w.correspondingly) for Hg (3,04±3,46), albeit Pb and Cd were below E.U limits, (0,013±0,017 and 0,241±0,627 correspondingly).
