Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Eels extinct from dioxin

13.03.2006


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’.

Elvers
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.’

Anaemia
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:
http://research.leidenuniv.nl/

More articles from Life Sciences:

nachricht Hunting pathogens at full force
22.03.2017 | Helmholtz-Zentrum für Infektionsforschung

nachricht A 155 carat diamond with 92 mm diameter
22.03.2017 | Universität Augsburg

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Pulverizing electronic waste is green, clean -- and cold

22.03.2017 | Materials Sciences

Astronomers hazard a ride in a 'drifting carousel' to understand pulsating stars

22.03.2017 | Physics and Astronomy

New gel-like coating beefs up the performance of lithium-sulfur batteries

22.03.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>