Organohalogenated contaminants in harbour porpoises

Determination of organohalogenated contaminants in liver of harbour porpoises (Phocoena phocoena) stranded on the Belgian North sea coast

Context of the study

The harbour porpoise is a vulnerable species in European waters. During the past decades the number of observations of this cetacean have decreased. Although observations along the coast of the Netherlands have increased since 1990, this trend is more likely to reflect a shift in distribution of harbour porpoises, than an actual increase of the population. One of the main threats to the harbour porpoise is accidental capture by fishing gear. High levels of contaminants, declining fish stocks and other anthropogenic stress factors (wind mills, sonar, shipping,... ) are also considered possible threats.

Content of the study

The study evaluates the occurrence of important organic contaminants in the harbour porpoise: one of the top predators in of the North Sea ecosystem. Harbour porpoises don't migrate on a large scale, which makes them a suitable indicator for local pollution. The study specifically evaluates the occurrence of PBDE's, PCB's and organoclorine pesticides. This study is based on liver samples of 21 harbour porpoises, which stranded along the Belgian coast between 1997 and 2000.

Results of the study

Organoclorine pesticides occured in low concentrations, while relatively high values of PCB's, PBDE's were measured. (PCB's averaged 36,4 µg/g, PBDE's averaged 2,3 µg/g). Comparison with other studies shows that the PCB concentrations are lower in harbour porpoises stranded along the Dutch and Belgian shorelines than in those stranded along the English shoreline. This might be caused by discharges of PCB's in the Rhine, Scheldt and Meuse rivers. Due to drainage from the rivers these compounds will be present at higher concentrations along the Belgian and Dutch coasts. Concentrations of DDT's (the most important organochlorine pesticide) are lower then those reported in 1991. This reflects the decline of DDT concentrations in the North Sea after the European ban in the 1970's.

Higher median concentrations of all examined contaminants have been found in adults. This is explained by the accumulation of these pollutants in the animals with increasing age. Differences in food preferences between adult and juvenile harbour porpoises may be an additional factor. Adult females showed lower average pollutant concentrations than adult males: during pregnancy females transfer these pollutants (which primary accumulate in body fat) through their milk (which contains 30-60% fat) towards their pups.

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