Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Eels extinct from dioxin


Embryonic development is already disturbed at concentrations 10 times lower than the norm for human consumption.

Dioxin-like contaminants such as PCB’s are probably playing a key role in the extinction of the eel. Embronyic development in this species is halted at dioxin concentrations 10 times below the levels for human consumption. This discovery was made by a team of biologists, led by Guido van den Thillart, who are conducting research in Leiden into the sexual maturity and reproduction of the eel. To date, the search for the causes of the reduction in the numbers of eels have concentrated mainly on quantitative factors, such as over-fishing. The researchers published their findings on 1st March in the journal ’ Naturwissenschaften’.

The eel is on the point of extinction. Since the fifties, the number of eels has declined sharply. The influx of elvers, young eels which swim from the ocean up river, in recent years is less than 1% of the level in 1950. It was in the fifties that dioxins started to appear in the environment.

Hormone regulation
Dioxin-like contaminants are not just toxic, they also have a disruptive effect on hormone regulation and gene transcription mechanisms. It has been known for some time that this caused a considerable reduction in the fertility and reproduction of a large number of species of animals and it now appears that the eel is one of the species affected. Van den Thillart: ‘Only, this species seems to be more vulnerable’.

Sargasso Sea
To study the consequences of dioxins on eel embryos, the researchers dug up eels in the Grevelingen lake and in the Loire, which had just started their 5500 km journey, probably to the Sargasso Sea where they would eventually breed. Eels only become fully mature during the course of this journey. The researchers brought the eels to maturity in the lab, using hormone injections, and fertilized their eggs artificially. They measured the dioxin levels in the fat of the eels and followed the development of the embryos. Their conclusion was that there is a very strong negative correlation between embryonic development and the levels of dioxin-like substances. Even at dioxin concentrations 10 times lower than the norms for human consumption, embryonic development ceased; embryos suffered serious deformities and died.

Freshwater systems
Eels live on the beds of all freshwater systems from Norway to Morocco and Egypt. It is these seabeds in particular where there are high levels of dioxin contaminants. Within Europe, only Sardinia and the west of Ireland have lower concentrations than those measured in the biologists’ experiments. It can therefore be assumed that dioxins play a key role in the disappearance of the eel.

Yolk sac
Dioxins are stored in fat. The eel accumulates fat, which makes up about 20% of its body weight. This fat constitutes the eel’s reserves for the long journey to the Sargasso Sea where biologists believe reproduction takes place. Fat is in the first instance the fuel for swimming, but in the course of the journey, a great deal of fat finds its way into the egg cells of the females, explains Arjan Palstra. ’In these egg cells, first fat is accumulated, and then proteins. The fat and proteins then become the substance of the yolk sac of the larva.’

Palstra: ‘To date there was only evidence of quantitative causes of the decline in the eel population. Over-fishing is one example. But we are studying the quality of the silver eel, eels which are not yet mature. Silver eels leave the freshwater sites and swim across the ocean. We gradually learned that the quality of this species is declining. A particular virus seems to make silver eels anaemic once they have completed a considerable part of the journey and have expended a lot of energy. They also suffer from a parasite which damages their air bladder. And then you also have the high concentration of PCB’s in their fat, which drastically reduces their fertility.

Hilje Papma | alfa
Further information:

More articles from Life Sciences:

nachricht Biologists unravel another mystery of what makes DNA go 'loopy'
16.03.2018 | Emory Health Sciences

nachricht Scientists map the portal to the cell's nucleus
16.03.2018 | Rockefeller University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

Im Focus: Radar for navigation support from autonomous flying drones

At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.

Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

International Virtual Reality Conference “IEEE VR 2018” comes to Reutlingen, Germany

08.03.2018 | Event News

Latest News

Wandering greenhouse gas

16.03.2018 | Earth Sciences

'Frequency combs' ID chemicals within the mid-infrared spectral region

16.03.2018 | Physics and Astronomy

Biologists unravel another mystery of what makes DNA go 'loopy'

16.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>