Potential Relation Between Mercury Concentrations and Necropsy Findings in Cetaceans from sGerman Waters of the North and Baltic Seas

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Abstract

Concentrations of total mercury and methylmercury were analysed in muscle, kidney and liver samples from 57 harbour porpoises and three white-beaked dolphins, stranded or by-caught from the German waters of the North and Baltic Seas. Levels of total mercury ranged between 0.6 and 450 μg/g dry weight (dw) and of methylmercury between 0.2 and 26 μg/gdw. No differences in concentrations of either total mercury or methylmercury were observed between stranded and by-caught animals nor between males and females. However, a difference in mercury content of cetaceans from the North and Baltic Seas was found. A significant correlation between animal age and total mercury as well as methylmercury in all examined organs could be demonstrated.

Pathological, microbiological and parasitological studies were performed on the animals. The majority of pathological lesions were caused by helminths. Lesions characteristic of acute or chronic intoxication with mercury could not be found. However, there were significant associations between mercury levels and severity of lesions with respective to nutritional state of the cetaceans examined, demonstrated by means of polychotomous logistic regression for ordinal variables and adjusted for the effects of age and location.

Section snippets

Materials and Methods

In total, 57 harbour porpoises and three white-beaked dolphins were collected and examined between 1991 and 1993. Details on the sample compositions by location (North or Baltic Seas), origin (stranding or by-catch), sex and age are given in Table 1, Table 2.

Necropsies were performed on all 60 animals according to the protocol described in Kuiken and Hartmann (1993). The age was determined by counting the dentinal growth layers (Kremer, 1987). The nutritional state was judged from blubber

Mercury burden of cetaceans

The levels of total mercury in harbour porpoises ranged between 0.6 and 398 μg/gdw in muscle, 0.6 and 449 μg/gdw in liver and 0.5 and 160 μg/gdw in kidney. Methylmercury ranged between 0.2 and 18.3 μg/gdw in muscle, 0.2 and 26.0 μg/gdw in liver and 0.1 and 23.5 μg/gdw in kidney. Levels in wet weight are given in Table 3.

Because the mercury concentrations as well as the fraction of methylmercury may be influenced by location, origin, sex, age and organ, a multifactorial analysis of covariance (ANCOVA)

Conclusions

The investigations showed that harbour porpoises and white-beaked dolphins from German waters are carrying a significant burden of mercury. Since a correlation between animal age and total mercury body burden was observed, the results reflect a life-long exposure to this heavy metal. It is assumed that ingestion trough prey fish is the major source of mercury and especially of methylmercury. The higher mercury content in organs from harbour porpoises from the North Sea indicates that mercury is

Acknowledgements

The study was generously funded partially by the German Federal Ministry of Environment and the European Science Foundation. Microbiological results were performed by Dr Reinhard Weiss, parasitological analysis and analysis of stomach contents by Dr Roland Lick, age determination by Dr. Hartwig Kremer. We are grateful to Elsa Haubold, Dr. Christina Lockyer and Kai Abt for their constructive comments on the manuscript.

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    Present address: Deutsches Museum für Meereskunde und Fischerei, 18349 Stralsund, Germany.

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