https://phys.org/news/2018-07-purification-techniques-healthier-aquatic-ecosystems.html

Standardized experimental conditions

In their comparative experiments the researchers looked at three conventional wastewater treatment plants – one of which, the Langwiese plant in the Ravensburg district, had an activated carbon stage installed during the study. The biologists placed cages into the water above and below the place where treated water from the plant flowed into the river. "Compared with the examination of wild fish, this has the advantage that we can standardize the fish characteristics such as age, diet and stage of development. This means we can better recognize any effects on the health of the animals," says team member and the study's corresponding author, Sabrina Wilhelm. Established methods were used to find out whether the rainbow trout cell nuclei showed signs of increased genotoxicity. And the livers of the fish were examined to determine whether they were having to work harder to remove or break down toxins.