Hydrogen peroxide, a chemical previously associated with hair bleaching, has been pumped into the Kłodnica, a tributary of the Oder, to stem the return of golden algae – also known as prymnesium parvum – that has once again killed tons of fish. Poland is not alone in facing this challenge. According to a study published last year in the scientific journal Nature, algal blooms around the world have significantly increased in frequency and intensity.
What are algal blooms and why do they occur?
Algae are microscopic organisms found in oceans, lakes, and rivers. They are essential to aquatic ecosystems. However, when their blooms get out of control, some species—such as those found in the Odra and Kłodnica rivers—produce toxins that can be harmful to fish, humans, and other parts of the ecosystem.
Algal blooms occur due to a mix of environmental factors, including warmer temperatures. temperatureshigh light levels, and increased nutrients in water from agricultural waste and sewage systems. Some studies suggest that algal blooms are likely to increase as temperatures rise due to climate change.
The 2022 Oder fish die-off has been dubbed a “human-caused ecological disaster” as scientists have found that a key factor in the golden algae blooms was high water salinity caused by mine discharges coal and other industries into the river. Prymnesium does not produce clearly visible blooms. The first sign that something is wrong may be frantic or dead fish.
What impact can hydrogen peroxide have on the environment?
According to the Polish Ministry of Climate and Environment, hydrogen peroxide eliminated 90 percent of golden algae at the junction of the Gliwice Canal and the Kłodnica River.
This is not the first time that this bleach has been used to combat microorganisms: its effectiveness was also demonstrated in British tests in 2017. However, according to Christian Wolter, a scientist at the Leibniz Institute for Aquatic Ecology and Inland Fisheries in Berlin, this is the first time that Polish authorities have used it in a river, not in standing water.
The lesser evil?
The impact of using this chemical on the environment is not yet fully understood, says Jacek Engel, president of the Greenmind Foundation, Polish environmental NGO. Engel added that his colleagues are conducting research on the effects of hydrogen peroxide on other parts of the ecosystem, such as plankton, tiny organisms that are a key food source in water bodies.
In his opinion, the local impact on the ecosystem that the use of this chemical could have should be weighed against the greater evil that would be the spread of golden algae, “because, of course, it won't just kill Prymnesium parvum. It kills everything… but it still kills organisms in one specific place to save the entire Oder system,” Wolter explains.
Wolter added that Polish authorities have set up several monitoring points to measure how quickly hydrogen peroxide disappears and its impact on invertebrates, algae and fish.
As Elisabeth Varga, a scientist at the University of Veterinary Medicine in Vienna, explains, getting the right concentration of the chemical is key to avoid harming other organisms. “You have to find a concentration that is high enough to damage the microalgae and prevent their growth, but which is not too high to affect all other animals,” she points out.
According to British research, hydrogen peroxide decomposes after a short time and quickly becomes harmless. Tests also showed that “fish and macroinvertebrates were not harmed by the experiment.”
“Short-term measure”
– Hydrogen peroxide is a temporary measure – says Julios Kontchou, environmental toxicologist from Greenpeace Germany. – But it is not a solution to the problem we have in the Oder – he adds. The Polish Ministry of Climate also emphasized that the use of hydrogen peroxide was a measure used in a crisis situation. According to the German toxicologist, a key solution would be to lower the current threshold values of sewage that coal mines and other companies discharge into the river, because this significantly increases the salinity of the water.
It removes the effects, not the causes
The use of hydrogen peroxide is an example of combating symptoms, but not the primary problem, Wolter believes. “We know that prymnesium parvum is a brackish-water algae, and the main reason for its occurrence in the Oder is the salt content,” he noted.
According to research published last year by Greenpeace Polska, many tributaries of the Oder, which receive sewage from several hard coal mines, have water salinity higher than the Baltic Sea. Ecologists called this result “frightening” because the Oder is a freshwater river, while the Baltic is a saltwater sea.
– I would say the situation is similar to what we saw last year, and in some points even worse than 2022, Kontchou said, referring to the salt levels in the river. government has already announced plans to build establishments desalination to improve water quality in the Odra.
Ecologists: Leave the Oder to Nature
But German environmental group BUND and other organizations in Poland argue that protection of the Oder must go beyond measures to monitor and stop salt discharges and include keeping it as wild as possible, rather than treating it as a waterway for barges and tourist traffic.
There are many EU regulations concerning rivers, says Wolter. – The problem is their implementation. And this does not only concern Poland, but also other member states. Across Europe, 60 percent of rivers are not in a good ecological condition, says Wolter, adding that most German rivers do not meet the objectives of the EU Water Framework Directive, established to improve the quality of water in European water bodies.
While the International Commission for the Protection of the Oder against Pollution – a joint agreement between the Czech Republic, Germany and Poland – has become more involved in monitoring the river since the 2022 disaster, it could be empowered to take further action, Wolter believes.