A river in Brazil is showing concerning signs. Scientists found antibiotics not only in the water, but also in the mud at the bottom and in fish that people regularly consume.

The study focused on the Piracicaba River in São Paulo. When researchers tested the samples from the river, they found several types of antibiotics. These likely originate from human activity, like wastewater from homes, farms and hospitals.

One finding stood out. A drug called chloramphenicol, which is prohibited in animals sold for consumption, was found in fish. This drug can be harmful to humans, yet it showed up in lambari fish, a common local food. As a result, people could be ingesting it without knowing.

The levels of pollution did not stay constant. During the rainy season, the river has more water, causing the antibiotics to spread out and become less concentrated. 

But during the dry season, when water levels fall, the opposite occurs. This is when the chemical’s level was found to be at its peak in both the water and the fish.

Another issue is where these drugs end up. Many of them settle into the sediment at the bottom of the river. Over time, they can resurface back into the water, restarting the cycle.

In response, researchers tested a floating plant called Salvinia auriculata as a potential solution. The plant was able to remove a large amount of antibiotics from the water in a short period.

At first, this seemed like a simple fix.

However, the results did not show the full picture. Although the plant reduced the amount of antibiotics in the water, it also made it easier for fish to take in what remained. Scientists think the plant may change the form of the drug, which affects how it moves through the environment.

“This shows that using plants as ‘sponges’ for contaminants is not a trivial matter,” a researcher said in a press release.

The impact on fish was serious. The antibiotic stayed in their bodies for more than 90 days and built up over time. It also caused damage at the DNA level, which could affect their health.

The plant did reduce some of this damage, but not fully. It was not a complete answer.

The findings also point to a bigger issue. This is not just about pollution in a river; it is also about what ends up on people’s plates. 

Scientists also warn that this kind of exposure can add to antibiotic resistance, making some infections harder to treat.