Maja Đokić: Determination of essential element levels in tissues of toothed whale (Odontoceti) from the Adriatic sea. Faculty of chemical engineering and technology, University of Zagreb, Zagreb.



In the marine environment, elements originate from natural and anthropogenic sources. Marine mammals accumulate elements in tissues mainly via the diet, and their bioaccumulation depends on the species, the element and the characteristics of the tissue. The aim of this study was to determine the concentrations of essential trace elements in the tissues of three species of toothed whales (Odontoceti): bottlenose (Tursiops truncatus), striped (Stenella coeruleoalba) and Risso’s (Grampus griseus) dolphins.

There is little data on the concentrations of essential metals in dolphin tissues. In this study, essential metal concentrations were correlated with tissue type, body length, age, dolphin species, sex and location of finding the carcasses. Also, the physiological range of elements was determined. Increased levels of certain elements allowed for the assessment of causes of pollution in a given area or determination of possible source of human activity that indicated the excessive use of this element and its expansion into the marine system.

The study examined a total of 190 dolphins: 159 bottlenose, 25 striped and 6 Risso's dolphins found in the Croatian part of the Adriatic Sea in the period from 1995 to 2013. The essential elements cobalt, chromium, copper, manganese and zinc were determined in the liver, muscle, kidney, skin, lung, spleen and adipose tissues using inductively coupled plasma–optical emission spectrometry (ICP-OES).

In more than 50 % of the examined tissues, the cobalt concentration was 0.001 mg/kg in all three dolphin species. Chromium concentrations greater than 1 mg/kg were determined in only 16 tissue samples. Of these, 15 were bottlenose dolphins, and only one was striped dolphin. Manganese concentrations in all examined tissues of three dolphin species were in the expected range for marine mammals, less than 7 mg/kg wet weight. The concentrations of copper and zinc outside the critical homeostasis controlled ranges (copper 3–30 mg/kg, zinc 20–100 mg/kg) in the liver were determined in 16 individuals, (14 bottlenose and 2 striped dolphins). There were no deviations from the critical zinc and copper ranges in the liver of the Risso’s dolphins.Among 16 dolphins outside the critical homeostasis controlled ranges, 12 had concentrations of copper and zinc above the critical concentrations, all of which had been found in the southern part of Croatian waters of Adriatic Sea. The assumption is that elevated concentrations of copper and zinc in the liver are the result of pollution of the marine environment, in this case the Adriatic Sea.

Statistically significant positive correlations were found between element concentrations in muscle, liver and kidney tissues. A slight negative correlation wasdetermined for cobalt and copper concentrations in muscle. The strongest correlations were found between copper and zinc in liver and kidney. This suggests that their role in the formation and function of the key enzymes for metabolism is synergistic rather than antagonistic as described in the literature.

The obtained results are the first significant study of the concentration ranges of these elements in the three dolphin species of the Adriatic Sea over two decades. The results may provide directions for future research and new guidelines for preserving the dolphin population in the Croatian part of the Adriatic Sea.

KEY WORDS: essential metals, dolphins, tissues, Adriatic Sea