Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane diastereoisomers (alpha-, beta/-, and gamma-HBCD) were investigated in effluents from sewage treatment works, landfill leachates, sediments, and food web organisms of the North Sea basin. Residues were quantified by liquid chromatography-mass spectrometry. Both flame retardants were enriched in sewage sludges, where a maximum total (sigma) HBCD concentration of 9.1 mg/kg (dry weight; d.w.) was found; TBBPA was at levels of 102 microg/kg. Landfill leachates from The Netherlands showed up to 36 mg (sigmaHBCD)/ kg (d.w.). gamma-HBCD dominated isomeric profiles in sediments, and concentrations were elevated near to a site of HBCD manufacture. alpha-HBCD was the primary congener detected in marine mammals; however, very few samples exhibited TBBPA. sigmaHBCD ranged from 2.1 to 6.8 mg/kg (lipid weight; l.w.) in liver and blubber of harbor porpoises (Phocoena phocoena) and seals (Phoca vitulina). TBBPA levels in cormorant (Phalacrocorax carbo) livers were up to 1 order of magnitude lower compared to sigmaHBCD. HBCD in eels (Anguilla anguilla) from the Scheldt basin (Belgium) reflected the spatial distribution of concentrations in local sediments. This study shows evidence of HBCD bioaccumulation at the trophic level and biomagnification in the ascending aquatic food chain, and these findings justify risk assessment studies at the ecosystem level.
– Since the 1980s, the European eel Anguilla anguilla stock is in steep decline. Lipid reserves are essential to cover energetic requirements for silver eel migration and reproduction. Two large and independent data sets from Belgium and The Netherlands show an average one‐third decrease in fat contents of yellow eels over the past 15 years. Also Le Cren’s relative condition factor decreased. On the basis of the somatic energy reserves, reproductive potential of eels from various latitudes over Europe was estimated, assuming fat levels in yellow eel are indicative of those in silver eels. Only large individuals, females as well as males, with high lipid content seem to be able to contribute to the spawning stock. The decrease in fat content in yellow eels may be a key element in the stock decline and raises serious concerns about the chances of the stock to recover.
For some years now the parasitic swim bladder nematode Anguillicola crassus of the European eel Anguilla anguilla L., has been reported from several European countries. The enhre life history of this parasite has recently been elucidated in our laboratory. Young larvae leave the swim bladder of the host via the pneumatic duct and reach the water through the digestive tract. They are ingested by small copepods (Cyclopoida), which act as intermediate hosts. Larvae remain in the hemocoel until the copepods are eaten by the final host, the European eel. Larvae penetrate through the intestinal wall and reach the swim bladder where they develop into adults. When infected copepods are eaten by other small fish, such as carp Cyprinus carpio L. or ide Leuciscus idus L., larvae do not reach the adult stage. However, when larger eels feed on such facultative reservoir hosts, they too become infected.
European eel (Anguilla anguilla (L.)) stocks are in decline in most of their geographical distribution and their status is considered below safe biological limits. Recently, there is an increasing awareness that spawner quality might be an essential element in the decline of the species since pollution by bioaccumulating chemical substances may have a large impact on the reproduction success of the eel. This review gives an overview of the literature on the effects of contaminants on the European eel and on the consequences on the biology and fitness of the eel in order to document the role of pollution in its decline. A variety of contaminants have been found to affect the eel. These contaminants may cause disturbance of the immune system, the reproduction system, the nervous system and the endocrine system and effects were reported on several levels of biological organization, from subcellular, organ, individual up to even population level. More extensive research is needed in order to evaluate how pollutants are detrimental to eel populations. Getting a comprehensive overview of the quality (including contamination levels, biomarker responses, lipid content and condition) of the silver eel population all over Europe seems to be an essential and urgent objective for the European eel management.
Understanding the effects of pollutants on the genome is of crucial importance to preserve the evolutionary potential of endangered natural populations. The highly vagile European eel (Anguilla anguilla L.) has suffered a dramatic decline in recruitment since two decades, urging for a better understanding of the genetic impact of pollution. Its catadromous life history constitutes a model to assess local selection of pollutants on condition and genetic variability, as juveniles recruit in European rivers without appreciable pollution load or interfering genetic background. Because of its high fat content and local benthic feeding behaviour, the feeding stage is considered extremely prone to the bioaccumulation of pollutants. We studied the relationship between heavy metal bioaccumulation, fitness (condition) and genetic variability in the European eel. The muscle tissues of 78 sub-adult eels, originating from three Belgian river basins (Scheldt, Meuse and Yser), were examined for nine heavy metal pollutants (Hg, Cd, Pb, Cu, Zn, Ni, Cr, As and Se), while in total 123 individuals were genotyped at 12 allozyme and 8 microsatellite loci. A significant negative correlation between heavy metal pollution load and condition was observed, suggesting an impact of pollution on the health of sub-adult eels. In general, we observed a reduced genetic variability in strongly polluted eels, as well as a negative correlation between level of bioaccumulation and allozymatic multi-locus heterozygosity (MLH). Microsatellite genetic variability did not show any pollution related differences, suggesting a differential response at metabolic enzymes and possibly direct overdominance of heterozygous individuals.
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