The events that unfolded in early August 2022 along the Oder River in Germany sent shockwaves through the environmental science community. Tons of dead fish, mussels, and snails were discovered floating on the river, revealing the devastating impact of an environmental disaster. The cause of this catastrophe was quickly identified as a deadly combination of factors including excessive salinity, high water temperatures, low water levels, and an influx of nutrients and wastewater. These conditions triggered a bloom of the brackish water algae Prymnesium parvum, which produced the lethal algal toxin prymnesin.
A team of scientists led by the Helmholtz Center for Environmental Research (UFZ) sprang into action to investigate the extent of the damage and analyze water samples collected from the affected areas. Their research, published in Nature Water, revealed that high concentrations of organic micropollutants played a significant role in exacerbating the harmful effects of prymnesin. The study found that the environmental disaster in the Oder River resulted in the loss of up to 60% of fish biomass and up to 85% of mussel and snail biomass.
In response to the crisis, the UFZ established an interdisciplinary working group that included researchers from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), the University of Veterinary Medicine in Vienna (Vetmeduni), and the University of Birmingham. Together, they conducted extensive water sampling along the Oder, analyzed poisoned fish, and evaluated the samples to determine the presence of micropollutants. The primary goal of their research was to assess the impact of these pollutants on aquatic organisms and investigate the potential threat posed to human health.
The Analysis of Micropollutants
The researchers identified more than 120 organic micropollutants in the water samples, with substances like tris(1-chloro-2-propyl)phosphate, hexamethoxymethylmelamine, and 1H-benzotriazole showing the highest concentrations. While most of these pollutants were likely discharged from sewage treatment plants, others such as 2,4-dichlorophenol and chlorotoluron originated from industrial and agricultural sources, respectively. The study revealed that while the concentrations of these chemicals were not alarmingly high, their combination with algal toxins posed a significant threat to aquatic organisms.
To quantify the risk posed by the detected micropollutants, the researchers utilized a risk quotient (RQ) analysis. The RQ is calculated as the ratio between the measured concentration of a pollutant and its predicted no effect concentration (PNEC), with values exceeding 1 indicating potential harm to aquatic life. The mixture risk quotients (RQmix) obtained from the study ranged from 16 to 22 at various sampling sites, signifying a substantial risk to aquatic organisms from the pollutants present in the Oder River.
The Impact on Aquatic Organisms
Laboratory experiments conducted by the research team demonstrated the adverse effects of the chemical cocktails extracted from the water samples on algae, water fleas, and zebrafish embryos. The neurotoxic effects of these pollutants, when combined with the prymnesins found in the river, further highlighted the detrimental impact on aquatic organisms. Through in vitro assays and high-throughput screening, the researchers were able to determine that prymnesins played a dominant role in the neurotoxic effects observed, although the micropollutants also contributed to the overall toxicity.
The findings of this research shed light on the complex interactions between pollutants and algal toxins in aquatic environments like the Oder River. The study underscores the pressing need for comprehensive monitoring and mitigation strategies to protect vulnerable ecosystems from similar environmental disasters. As the researchers continue to investigate the long-term effects of pollution on aquatic life, it becomes clear that concerted efforts are required to safeguard the health and sustainability of our rivers and waterways.