Accumulation of heavy metals in Caspian seals (Phoca caspica)

Concentrations of heavy metals (Fe, Mn, Zn, Cu, Pb, Ni, Cd, Co, and Hg) were determined in the muscle, liver, and kidney of 42 Caspian seals and fishes collected from the Caspian Sea in 1993. Higher Mn and lower Fe and Cu concentrations were found in the liver in comparison with other marine pinnipeds. Lower Cu concentrations in the liver appear to be a common feature in small seals belonging to subgenus Pusa, which include ringed, Baikal, and Caspian seals. However, low Fe and high Mn in livers were specific to Caspian seal. Concentrations of toxic metals such as Hg and Cd were relatively low. Pinniped species can be divided into two groups, based on accumulations of Cd or Hg in the liver. Interestingly, it was found that Cd-accumulating groups feed on invertebrates, whereas the preferred diet of Hg accumulators is fish. Caspian seals seemed to belong to the Hg-accumulating group.Cd and Hg concentrations in the liver and kidney of young animals increased with age. Mercury concentrations in adult animals increased with age continuously, whereas Cd concentrations in adult animals decreased. This trend might be due to preferential feeding habits and shift in ratio of Hg and Cd in the diet ( i.e., invertebrates to fish).