# Essential Trace Elements in Three Species of Dolphins Stranded in the Croatian Part of the Adriatic Sea from 1995 to 2013

## TL;DR

This study measured copper and zinc levels in dolphin tissues over 18 years to understand their health and environmental impact in the Adriatic Sea.

## Contribution

The study provides a long-term baseline of essential trace element concentrations in three dolphin species, revealing trends and thresholds relevant to conservation and toxicology.

## Key findings

- Copper and zinc concentrations showed a declining trend across all tissues over the study period.
- Liver and kidney tissues had the highest copper levels in bottlenose dolphins, while skin showed the highest zinc levels.
- Element concentrations were positively correlated within and across tissues, and with body size metrics.

## Abstract

Trace elements are widespread in the environment and are considered essential when their absence leads to impaired biological function. This study investigated the concentrations of two essential trace elements—copper (Cu) and zinc (Zn)—in the tissues of three toothed whale (Odontoceti) species: bottlenose (Tursiops truncatus), striped (Stenella coeruleoalba), and Risso’s dolphins (Grampus griseus), found deceased in the Croatian part of the Adriatic Sea between 1995 and 2013. A total of 190 individuals were examined, comprising 159 bottlenose, 25 striped, and 6 Risso’s dolphins. Copper and zinc levels were quantified in liver, muscle, kidney, skin, lung, spleen, and fat tissues using inductively coupled plasma optical emission spectrometry (ICP-OES). Positive correlations in element concentrations were observed both across individuals within the same tissue type and between different tissues within the same individual. Overall, a decreasing trend in trace element concentrations was observed across all tissues over the study period. These results provide a valuable baseline for future toxicological and ecological studies, and contribute to the ongoing conservation efforts for dolphin populations in the Adriatic Sea.

Trace elements are widely distributed in the environment and are considered essential when their deficiency leads to impaired biological function. This study aimed to quantify concentrations of two essential trace elements—copper (Cu) and zinc (Zn)—in the tissues of three toothed whale (Odontoceti) species: bottlenose (Tursiops truncatus), striped (Stenella coeruleoalba), and Risso’s dolphins (Grampus griseus) found deceased along the Croatian coast of the Adriatic Sea between 1995 and 2013. A total of 190 individuals were analyzed, comprising 159 bottlenose, 25 striped, and 6 Risso’s dolphins. Concentrations of Cu and Zn were determined in liver, muscle, kidney, skin, lung, spleen, and fat tissues using inductively coupled plasma optical emission spectrometry (ICP-OES). The highest Cu concentrations were observed in the liver and kidneys of bottlenose dolphins, followed by striped and Risso’s dolphins. Zn concentrations were the highest in the skin of bottlenose and striped dolphins, whereas the liver exhibited the highest levels in Risso’s dolphins. In 14 bottlenose and 2 striped dolphins, Cu and Zn concentrations in liver tissue exceeded critical thresholds typically regulated by homeostatic mechanisms. Regression analysis indicated significant relationships between element concentrations, and both body length and body mass. In addition, trace element concentrations were positively correlated across individuals within the same tissue type, as well as among different tissues within the same individual. Overall, Cu and Zn concentrations exhibited a declining trend over the studied period across all tissue types. These findings provide important baseline data for future ecotoxicological investigations and contribute to conservation strategies for cetacean populations inhabiting the Adriatic Sea.