A new study from researchers at the University of São Paulo has shed light on a growing environmental concern: the presence of antibiotic residues in freshwater systems, and their impact on aquatic life and potentially human health.
The research, conducted in Brazil’s Piracicaba River basin, found traces of multiple commonly used antibiotics in water, sediments, and fish. Scientists also explored whether a floating aquatic plant, Salvinia auriculata, could help reduce this contamination. The findings suggest it can—but not without complications.
Pollution Builds Up in Dry Seasons
The team, led by Patrícia Alexandre Evangelista, monitored samples from a region near the Santa Maria da Serra dam, where pollutants from across the river basin tend to accumulate. The area receives runoff from urban sewage, agriculture, aquaculture, and livestock farming.
Twelve antibiotics, including tetracyclines, fluoroquinolones, sulfonamides, and phenols, were tracked across both rainy and dry seasons. A clear pattern emerged: during the rainy season, most antibiotics were barely detectable, likely diluted by higher water volumes. In the dry season, however, concentrations rose significantly as water levels dropped and pollutants became more concentrated.
Sediments, rich in organic matter and minerals, acted as reservoirs for these compounds, storing them and potentially releasing them back into the environment over time.
Contaminated Fish Raise Health Concerns
One of the study’s most striking findings was the detection of chloramphenicol, a banned veterinary antibiotic, in lambari fish collected from local fishermen. The substance appeared only during the dry season, but at levels significant enough to raise concern.
Because this species is widely consumed in the region, researchers flagged a possible route of human exposure through food.
A Plant-Based Solution, With Limits
The study also tested whether Salvinia auriculata, a fast-growing floating plant often considered a nuisance, could help remove antibiotics from contaminated water.
In controlled experiments, the plant proved highly effective at absorbing enrofloxacin, eliminating more than 95% of it within days under certain conditions. Its performance was less impressive with chloramphenicol, removing only 30% to 45%, and over a longer period.
The antibiotics were found to accumulate mainly in the plant’s roots, suggesting that filtration and absorption at the root level play a key role.
A Complex Ecological Trade-Off
However, the picture is not straightforward. Even when the plant reduced antibiotic levels in the water, fish did not always benefit. In some cases, absorption rates in fish actually increased, possibly because the plant altered the chemical form of the antibiotics, making them easier for organisms to absorb.
Chloramphenicol, in particular, showed a strong tendency to persist in fish tissue, with a half-life exceeding 90 days. Enrofloxacin, by contrast, was eliminated more quickly and showed lower accumulation.
The study also examined genetic damage in fish. Chloramphenicol exposure led to increased DNA damage, but this effect was reduced when the plant was present, suggesting a possible protective role. No similar benefit was observed for enrofloxacin.
Not a Silver Bullet
Researchers caution against viewing Salvinia auriculata as a simple fix. While it can reduce antibiotic levels, it may also change how these substances behave in the ecosystem. There are additional concerns about how to safely dispose of contaminated plant biomass, which could otherwise reintroduce pollutants.
Still, the findings point to the potential of low-cost, nature-based solutions in regions where advanced water treatment technologies are not feasible.
Bigger Picture: A Growing Environmental Threat
The presence of antibiotics in rivers is more than just a local issue. It contributes to the broader global challenge of antimicrobial resistance, raising the risk of so-called “superbugs” emerging in natural environments.
As co-author Valdemar Luiz Tornisielo noted, the study underscores both the scale of human impact on ecosystems and the need for integrated solutions that consider not just pollutant removal, but long-term ecological effects.
In essence, the research reveals a problem that is measurable and widespread—and solutions that are promising, but far from simple.
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