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 A novel socio-ecological approach helps identifying suitable wolf habitats
17.02.2017 | Universität Zürich

nachricht New, ultra-flexible probes form reliable, scar-free integration with the brain
16.02.2017 | University of Texas at Austin

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Biocompatible 3-D tracking system has potential to improve robot-assisted surgery

17.02.2017 | Medical Engineering

Real-time MRI analysis powered by supercomputers

17.02.2017 | Medical Engineering

Antibiotic effective against drug-resistant bacteria in pediatric skin infections

17.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>