Applications of elemental fingerprinting for population discrimination and biomonitoring potential assessment of Rutilus kutum from the Southern Caspian Sea

In this research, the potential use of five hard parts (otolith, scale, eye lens, dorsal spine, vertebral bone) of Rutilus kutum for populations discrimination and biomonitoring as well as their usability as biological archive in the southern Caspian Sea was investigated. Two soft tissues (muscle and liver) were also analyzed for assessment of the possible risk of consumption and use as biomonitoring tool, respectively. A total of 60 specimens were collected using beach seine from three sampling sites (adjacent to the estuaries of the rivers Sefidrud, Tajan and Grorganrud, respectively) in the Southern Caspian Sea in May 2016. In total, the levels of 13 major and trace elements in the samples (the seven soft and hard tissues) was measured using PIXE (Proton Induced X-ray Emission) and µ-PIXE methods. Minor similarities among the tissues were observed in the case of eye lens (for P, S and Zn) and liver (for Cl, Fe and K). There were no significant relationships between the elements and biological characteristics (weight, total length and standard length). Based on the results, it seems that all the studied hard parts, except for eye lens, may offer alternatives for biomonitoring of Ca, Cl, Fe, K and S in the southern Caspian Sea. Considering Sr level in otolith, no significant differences could be found between the sampling sites 2 and 3. So it can be concluded that the specimens collected from the two sites are probably from the same population. Similar results were also obtained based on the results concerning K accumulation in scale. It can be concluded that scales may provide an alternative structure to otolith for stock discrimination of R. kutum in the southern Caspian Sea. Among the 10 elements that were detectable in the muscle using the PIXE method, only in the case of four of them (i.e. Zn, Cu, Fe and Mn) maximum allowable concentrations for human consumption have been defined, which in all the cases the mean concentrations in the present study were far below the recommended limits.