Trace Pollutants In The Water: Which Clarification Techniques Help Fish?

Research team at the University of Tübingen is investigating how wastewater treatment plants should be upgraded to protect aquatic life

Pollutants in rivers and lakes can pose a threat to aquatic organisms, even in small lanes. This environmental issue has become more publicized in the past decade. The trace pollutants include residues from chemicals used in daily life such as dishwashing tablets, detergents or shower gels as well as from medicines, cosmetics or pesticides. The substances pass through domestic sewage in sewage treatment plants, where they can often not be completely restrained or degraded by conventional cleaning methods. About the purified wastewater, they are therefore registered in our waters. Under the direction of Professor Rita Triebskorn, a group of scientists from the Institute for Evolution and Ecology of the University of Tübingen investigated the effects of different clarification technologies on the health of fish. They conclude that, depending on the composition of the wastewater, it should be decided on a case-by-case basis which cleaning techniques can sustainably protect aquatic organisms. Her study was in the journalEnvironmental Sciences Europe released. 

In conventional wastewater treatment plants, waste water from private households and industry undergoes mechanical, biological and chemical purification stages. For some years, additional purification technologies, for example based on activated carbon or ozonation, have been increasingly used as the fourth purification stage. "As part of a study on Lake Constance, we were able to show that an additional activated carbon stage allows trace substances to be efficiently removed and that the health of the aquatic organisms in the receiving waters has thus improved significantly," says Rita Triebskorn. "So far, unfortunately, there are still relatively few studies on how the trace substance elimination affects long-term water ecosystems."

Standardized experimental conditions
In their comparative study, the researchers included three conventional wastewater treatment plants, one of which, the Langwiese sewage treatment plant on the district of Ravensburg, was additionally equipped with an activated carbon filter system during the course of the study. Above and below the discharge point of the treatment plant, they put crabs with rainbow trout into the water. "This has the advantage over the study of wild fish that we can standardize many of the fish's characteristics, such as age, nutrition and level of development. Thus, any effects on the health of the animals can be seen more clearly, "says the first author of the study Sabrina Wilhelm from the research team. On the one hand, she used established methods to investigate whether the nuclei of rainbow trout had increased genotoxic changes.

Decide on a case-by-case basis
"While we could not detect any negative effects of trace pollutants on the health of fish in one of the conventional treatment plants, the critical liver values ​​for rainbow trout below the second conventional plant were greatly increased," Sabrina Wilhelm summarizes the results. "Even at the Langwiese sewage treatment plant, we measured such negative effects before the upgrade." Here, the equipment of the system with the additional activated carbon filter significantly reduced both the fish's liver values ​​in question and genotoxic effects. 

"Investing in modern clarification techniques will benefit the water ecosystem, especially if conventional technologies do not sufficiently remove the pollutants," says Rita Triebskorn. "Depending on the composition of the wastewater, however, negative influences on aquatic organisms can also be reduced by optimized conventional purification." The bottom line is that it is worth investing in good wastewater treatment in order to sustainably protect our environment.