|Organochlorine and heavy metal residues in harbour seals from the Wadden Sea and their possible effects on reproduction|
Reijnders, P.J.H. (1980). Organochlorine and heavy metal residues in harbour seals from the Wadden Sea and their possible effects on reproduction. Neth. J. Sea Res. 14(1): 30-65
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
Chlorine; Heavy metals; Reproduction; Phoca vitulina Linnaeus, 1758 [WoRMS]; ANE, Wadden Sea [Marine Regions]; Marine
As the harbour seal population in the Dutch Wadden Sea decreased significantly and its pup production is too low compared to the more stable population in Schleswig-Holstein, Germany, it is tried to correlate this with an assumed inverse trend of contaminants residue levels in seal tissues. Dead stranded animals are collected in both areas and blubber, liver, brain and kidney are analyzed for PCB, o,p'-DDT, p,p'-(DDT+DDE+TDE), dieldrin, aldrin, endrin, endosulfan, α-HCH, β-HCH, γ-HCH, HCB, QCB (pentachlorobenzene), HEPO, total mercury and methyl mercury, selenium and bromium. High levels of all contaminants except bromium occurred together in the seals. An equimolecular relationship is found for mercury and selenium but not for bromium. A clear cut correlation is also demonstrated for PCB and total DDT in blubber and kidney. The main metabolite present in the DDT family is DDE. Deposition of contaminants is generally lower in juvenile seals reaching a certain plateau level in older ones. The highest ratios of methyl mercury to total mercury are found in juveniles. The residue levels already present in stillborn pups indicate transplacental transport of all organochlorines and metals analyzed. Differences in residue levels between Schleswig-Holstein and Denmark on one hand and The Netherlands on the other revealed higher values for the latter, especially PCB levels in Dutch adult seals are a tenfold higher. Increase of PCB and total DDT residue levels with age is present in Dutch seals but absent in the Schleswig-Holstein and Danish specimens. The conclusion is drawn that the observed decrease in the reproductive success of the Dutch seal population correlates strongly with the high concentrations of PCB's in the tissues. The information indicative for the ability of these compounds to interfere with mammalian reproduction leads to the hypothesis that PCB's will be responsible for the low rate of reproduction in the Dutch seal population.