“We were able to unequivocally detect significant quantities of a subtype of the algal toxin, known as “prymnesins”, in samples taken from various parts of the Oder,” stated Dr Elisabeth Varga, a researcher from the University of Vienna who carried out the analysis at the university’s Mass Spectrometry Centre. “We know from previous research on this algal toxin that the toxin is strongly bound to the algae. When this specific algae species is present in very large quantities, as is the case in the samples from the Oder, it must also be assumed that the toxin concentration is very high. Since all of the samples were taken at an advanced stage of the algal bloom, a direct connection with the fish and mollusc kill can be assumed,” explained Elisabeth Varga. However, there is still a need for further research on the toxicity of prymnesins, she added, and it has not yet been fully clarified which other groups of organisms may be affected apart from fish and molluscs. This is also true for potential effects on the human organism.
Scientists are in the process of determining the exact quantity of the toxin from the biomass samples of the alga and the water samples taken, but this procedure is more time-consuming and technically complex. “Prymnesins are very specific organic compounds, with up to 107 carbon atoms, as far as is known. Although these compounds can, in principle, be measured by advanced mass spectrometers, in practice only a few laboratories in Europe analyse them, partly because there is little need to investigate them,” explained Dr Stephanie Spahr, leader of the Organic Contaminants research group at IGB. There are no analytical standards for these toxins available anywhere in the world. For this reason, the toxins were unambiguously classified using previously characterised strains that had been cultivated at the University of Copenhagen (Per J. Hansen’s research group) and characterised at the Technical University of Denmark (Thomas O. Larsen’s research group) in the context of international projects.
Prymnesium parvum from the Oder river near Hohenwutzen, August 15, 2022 | Photo: Katrin Preuß/IGB
“The Oder is currently suffering from an extreme mass development of planktonic algae. Prymnesium parvum is highly dominant in all samples; in the Oder, this alga accounts for at least half of the total algal biomass, and even after being diluted by the influx of the river Warta, it still stands at 36 per cent. To my knowledge, such a mass development has never been observed before in our freshwaters. The phenomenon was probably made possible by salt discharges, copious amounts of nutrients, high water temperatures, and long residence times in barrages and in the developed river,” noted IGB scientist Dr Jan Köhler, leader of the Photosynthesis and Growth of Phytoplankton and Macrophytes research group.
“Now what is missing is the genetic characterisation of the algal strain. More than 50 strains of Prymnesium parvum have been described; they differ greatly in terms of their environmental requirements and toxin production. The toxins are currently classified into three groups, with each group consisting of more than ten different toxins; this poses a significant challenge when it comes to determining them,” stated Jan Köhler.
“We are now immediately contacting the competent authorities so that the research results can be integrated into new measurement campaigns and programmes,” remarked IGB scientist Dr Tobias Goldhammer, leader of the Nutrient Cycles and Chemical Analytics research group. This way, further developments on the Oder can be better monitored, he added. “The elevated salinity levels we measured in the samples occur more frequently in the Oder; they are triggered by industrial pollution in the upper reaches. Consequently, if salt levels do not decrease and we continue to experience excessively hot and dry summers, such toxic mass developments could occur again in the future,” emphasised Tobias Goldhammer.
The IGB has been researching and working on the Oder for decades, especially on river ecology and fish species communities. In addition, the institute coordinates the reintroduction programme of the Baltic sturgeon in the river basin. Therefore, researchers became active with their own investigations and followed the trail of a strong toxin that can be formed by the algae species Prymnesium parvum. The IGB was already able to detect this alga in masses in water samples from the Oder on Wednesday.