By Caroline Majewski, Publishing Associate: Researcher and Writer at Save the Water™ | May 21, 2025
Edited by Joshua Awolaye, Publishing Associate, Editor at Save the Water™
In a new study, a team looked at the “intrinsic biological defence of brown trout against chemical pollution in a stream with a low-dilution factor” (Koubova et al., August 2025, para. 1). In short, they looked at the responses of the fish in polluted water due to a sewage treatment plant discharge.
Why Trout?
Because they live in various locations, brown trout are a good way to test how pollution would affect them. Trout’s habitats are streams, rivers, and lakes (fresh and brackish waters) around the globe, including:
- Europe
- Northern Africa
- Western Asia
In the study, the scientists compared a control group upstream of a sewage treatment plant to a downstream group. In particular, this takes place in a headwater, which usually has low dilution, making the pollution effects more significant. After a specified time had passed (6, 14, and 24 weeks), they sampled the trout.
Pollution Concerns
Excess nutrients from sewage are one of the ways pollution happens.
While this study took place in a tributary of the Blanice River (in the Czech Republic), many places are experiencing similar concerns. Moreover, the environment was at an increased risk of pollution because of the continual release. In addition to the trout having a widespread habitat, they are also widely known to bioaccumulate contaminants.
What the Trout Can Tell Us: Results
When tested, the waters downstream were found to have higher micropollutants, androgenicity, and estrogenicity. Additionally, an increased endocrine disruption in males was also seen.
The study results show the impacts of micropollutant mixtures. This contamination contains different micropollutants:
- Bacteria
- Viruses
- Harmful chemicals
- Excess nutrients
Organisms have a defense system, which includes a set of biological responses to chemicals. Thus, this helps them on a cellular level and aids in biological homeostasis. Moreover, because of these concerns, scientists also studied the relationship between chemical pollution and biological markers of the fish. Long-term exposure is tested at timed intervals using an in-vitro method. This resulted in oxidative stress, biomarker disruptions, and endocrine disruption.
This study looks at the biological effects on organisms because the pollutants can “trigger” molecular changes. Interestingly, they also found that there was a gradual acclimatization to the pollution. This means that over time, some of the ecological impacts were lessened.
Broadscale Impacts
Treatment facilities (in the United States) process over 34 billion gallons of wastewater a day.
Moreover, in the United States, regulations on sewage discharge are being deregulated. This could lead to an increase in the effects. It prohibits federal and state agencies from issuing permits that are considered ‘broad’ without violating water standards. On the other hand, wastewater is receiving stricter regulations in the EU.
Looking Toward the Future
One way of helping this is by upgrading waste plant technology. Although this requires a lot of money upfront, the benefits are good,and more efficient waste treatment. These new technologies are crucial to lowering runoff and its bad effects.
Furthermore, as individuals, there are still actions you can take. If you use a septic system, ensure the equipment is modern, effective, and that you’ve enough working knowledge. Lastly, follow the correct directions for disposing medications and other household items such as cleaners and fertilizers.
