Schmidt, Wiebke (2008) Untersuchungen zur Schwermetall-Kontamination von Aalen (Anguilla anguilla) aus verschiedenen Habitaten. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 83 pp.

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Abstract

For several decades the European eel (Anguilla anguilla) has suffered a dramatic decline in recruitment and stock size. Same hypotheses on the cause of this decline have been proposed, including the effects of high fishing pressure, the loss of habitats, the climate change and the increasing pollution. Within the contaminations causing toxicological problems, heavy metals, like mercury and arsenic, still play an important role due to their persistence and accumulation. Both mercury and arsenic mainly act as neurotoxin to fishes. The present study reports on the mercury and arsenic contamination of European eels in four different habitats in Schleswig-Holstein, Germany. Concentrations of total mercury were determined by cold vapour atomic absorption spectrophotometry (PERKIN ELMER 1100) in muscle tissue of 109 eels from the river Eider, the Plöner See, the Baltic Sea near Fehmarn and the North Sea (by Helgoland). The average total mercury concentration was at its lowest (0.72 mg/kg dry mass) in the Eider river. Mean concentrations in eels collected from the Plöner See were at 1.56 mg/kg dry mass. A mean concentration of 1.37 mg/kg dry mass was found in eels from the Baltic Sea near Fehmarn. The highest concentration of total mercury was measured in eels from the North Sea (1,79 mg/kg dry mass). In comparison, mercury concentrations [mg/kg dry mass] differ significantly (p < 0.05) between yellow eels from the Eider and the North Sea. No differences were found between silver eels from the Plöner See and the Baltic Sea. Correlations between mercury concentration [mg/kg dry mass] and fish length [cm] were found for the limnic habitats, Plöner See and Eider. No relationships could be detected concerning both factors for eels coming from the Baltic Sea and the North Sea. Furthermore there were no correlations between mercury concentration [mg/kg dry mass] and fat fraction [%] in any of the investigated eels. 17% of the silver eels from the Baltic Sea exhibited mercury levels in muscles that exceed the legal limits (1 mg/kg fresh weight) established by the European Commission. In addition, mercury content higher than 1 mg/kg fresh weight was detected in 14% of the silver eels from the Plöner See. For one yellow eel (5%) from the North Sea the legal limit was exceed. Additionally, total arsenic concentrations were determined by graphite fumace atomic absorption spectrometric measurement (PERKIN-ELMER Zeeman 5100) in muscle tissue of 80 eels from the river Eider, the Baltic Sea and the North Sea. The lowest average total arsenic concentration was measured in eels from the river Eider (0.31 mg/kg dry mass). A mean concentration of 0.98 mg/kg dry mass was found in eels from the Baltic Sea. The average concentration was at its highest (3.34 mg/kg dry mass) in eels of the North Sea by Helgoland. By comparing the arsenic contamination of the habitats, significant differences (p < 0.05) were found between arsenic concentrations in eels from the Eider and individual eels coming from the Baltic Sea and also the North Sea. Furthermore, concentrations differ in eels from the Baltic Sea in comparison to specimen from the North Sea. No correlations were found between fish length [cm] and arsenic concentration [mg/kg dry mass] in any of the investigated habitats. The present study shows that yellow eels are useful indicators for mercury contamination. In addition, there is a need for further investigations to clarify the sources of the mercury and arsenic contamination. The sale of eels from the Plöner See should be prohibited to protect consumers.

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