Metal bioaccumulation in representative organisms from different trophic levels of the Caspian Sea

The bioaccumulations of metals Cu, Cd, Ni, Cr, Co, Mn, Zn and Fe were measured in bivalves, Cerastoderma glucaum, and four species of fishes including Alburnus chalcoides, Liza aurata, Rutilus frisii and Sander lucioperca from various trophic levels of the Caspian food web. The concentrations of Cd, Cr, Co and Ni in most samples of fish were below the detection limits; while the concentrations were detected in most samples of bivalve C. glucaum. The stable nitrogen isotope ratios varied among the samples from C. glucaum (δ15N=3.5 ‰) to S. lucioperca (δ15N=13.1‰). Among the four fish species, while the highest concentrations of Mn, Ni and Fe were observed in L. aurata, the lowest concentrations of Mn and Fe were observed in S. lucioperca. These species also had the lowest and highest trophic levels with an average of 3.3 and 4.2, respectively. No accumulation of metals with increase in body size was observed in muscles of species from different trophic levels. The comparison of metal concentrations with the health guidelines for human consumption showed that those intakes were lower than the legislated limits. While there was a strong relationship between trophic levels and body size of A. chalcoides and R. frisii, no significant slopes were observed between the total lengths (TLs) and the Ln concentrations of metals. It is necessary to determine metal concentrations in food resources of fish species, particularly in R. frisii that has significantly different δ15N in relation to body size