Thousands of fish have been dying in the Oder for days. The cause is still not clear. We spoke to engineer Dennis Peupelmann about possible causes.
Mr Peupelmann, thousands of fish have been dying in the Oder for a few days. Just yesterday Poland announced they are banning mercury as a cause of death. On the German side, Brandenburg’s Environment Minister Axel Vogel (Greens) spoke of “increased salt loads in the Oder” – what should we understand by that?
In this case, increased salt loads mean that the mass of pollutants per unit of time is higher than normal. In concrete terms, this means that a wave of pollutants is currently sloshing through the Oder.
Salts don’t sound very dangerous at first. What’s the deal with the salt wave?
Salt isn’t just the kind of salt we use in the kitchen. Salt compounds also include other substances. Roughly speaking, these are compounds of cations and anions. Aluminum salts or ammonium salts, for example, are very harmful compounds if they get into the water in large quantities. There are limit values for the content of substances in water that are considered harmless and are the same for all bodies of water in the EU.
Chemists say that there are no toxic substances, only the dose makes the poison. With the currently massive effects in the Oder, it can be assumed that a fairly large amount of salt got into the river if increased salt pollution is responsible for the fish kill.
Dennis Peupelmann is an environmental engineer and has already worked with water values in various places. Among other things, he was responsible for the evaluation and monitoring of water values in various projects in India. In his thesis at the University of Kassel, he also devoted himself to water research. Here he examined the values in a Hessian river.
Catastrophe in the Oder: Type of contamination can provide information about the origin
Where could these come from?
The most likely source of salt contamination is agriculture. Fertilizers and other substances used there have a high salt content. But of course the chemical industry or other branches of industry can also be considered. I consider improper waste disposal by private individuals to be rather unlikely due to the extreme effects. The type of substance could provide more precise information about its origin. Unfortunately, nothing more precise is known here.
Aluminum salts are often used in the textile industry, for example. For other contaminants such as mercury or lead, the source could be in the metals industry.
Environment polluted: Big fish also die in the Oder
Could there be other reasons for the fish deaths in Oder?
When fish die, it is very often due to insufficient or altered oxygen levels in the water. This can also be influenced by external influences such as heat or drought. Hot water can hold much less oxygen than cold water. The Oder currently has a temperature of 23.9 degrees (measured in Frankfurt an der Oder), which is definitely not yet in a range that could be dangerous for the fish. However, the concentration of salts or other pollutants naturally increases when the water level drops due to high temperatures. The Oder currently has a rather low flow rate, i.e. a low water level. My data is currently only from the German side, the Polish side has published few or none at all.
Actually, most of the fish found in Germany are quite robust when it comes to fluctuations in oxygen content. Depending on the size of the fish, salt or other toxins have a different effect on the animals, similar to how poison affects humans. Catfish and other large fish have also died in the Oder, which shows how extreme the current burden must be.
How do you assess the danger for the Baltic Sea?
The Baltic Sea naturally has a higher salinity than the Oder. As a result, if it were a matter of salt pollution, the effects would be far less than in the Oder itself. In addition, it is of course extremely diluted by the size of the Baltic Sea. Therefore, I assess the danger for the Baltic Sea as very low. (Interview: Lucas Maier)