The plant may transform antibiotics into forms more easily taken up by fish
Along the Piracicaba River in São Paulo state, a quiet accumulation of pharmaceutical residues in water, sediment, and edible fish has brought into focus a tension as old as industrial civilization: the hidden costs of what we discard into shared waterways. Researchers from the University of São Paulo have found chloramphenicol — a banned antibiotic — in lambari fish consumed by local communities, tracing a contamination pathway that moves from farm waste and treated sewage through river sediment and into human bodies. The discovery is not merely a local environmental footnote but a reminder that prohibition on paper does not equal absence in practice, and that ecosystems carry the memory of human choices long after those choices are made.
- A banned antibiotic is showing up in fish people are actually eating — not in trace abstractions, but at concentrations that represent a measurable route of human exposure.
- Dry seasons act as a kind of reckoning: when river water drops, contaminants concentrate, and the sediment bed releases what it has quietly stored, turning seasonal drought into a pollution event.
- Chloramphenicol persists in fish tissue for over ninety days and accumulates strongly, meaning the contamination does not flush out quickly — it lingers in the food chain.
- A floating aquatic weed, Salvinia auriculata, can strip more than ninety-five percent of one antibiotic from water within days, but paradoxically may make fish absorb contaminants faster — cleanup is not as simple as adding plants.
- Fish exposed to chloramphenicol showed significant DNA damage, including abnormal blood cell nuclei, signaling that the ecological harm extends to the genetic level of living organisms in the river.
In the river basin surrounding São Paulo's Piracicaba River, scientists have mapped a slow-moving contamination crisis years in the making. Researchers from the University of São Paulo sampled water, sediment, and fish near a dam and reservoir where treated sewage, agricultural runoff, and waste from livestock farming all converge. What they found was a seasonal pattern with a troubling rhythm: during rainy months, most of the twelve antibiotics tested fell below detectable levels, but when dry season arrived and water volume shrank, concentrations spiked. Sediment — rich in organic matter — was acting as a long-term storage reservoir, holding antibiotics and releasing them back into the ecosystem over time.
The most alarming finding was chloramphenicol, an antibiotic banned in Brazilian livestock farming because of its known toxicity. It turned up in lambari, a small fish widely sold and eaten in the region, at concentrations reaching tens of micrograms per kilogram during dry months. This created a direct, measurable pathway from contaminated water to human consumption. Chloramphenicol was studied alongside enrofloxacin — a drug common in animal agriculture and human medicine — because both persist in the environment and carry significant health implications.
The research team also tested whether Salvinia auriculata, a floating aquatic plant typically treated as a nuisance weed, could help clean up the pollution. Using radioactively labeled compounds to track antibiotic movement precisely, they found the plant removed over ninety-five percent of enrofloxacin within days when sufficient biomass was present. Chloramphenicol proved far more stubborn, with only thirty to forty-five percent removal and half-lives stretching to twenty days. Both antibiotics concentrated primarily in the plant's roots.
Yet the picture grew more complicated when fish were introduced. Lowering antibiotic levels in water did not always reduce how much fish absorbed — and the presence of Salvinia sometimes accelerated uptake, suggesting the plant may transform antibiotics into forms more readily absorbed by aquatic life. Chloramphenicol also caused measurable DNA damage in fish, including abnormal cell nuclei, though this damage decreased when Salvinia was present — possibly because the plant reduces toxic byproducts or releases antioxidant compounds.
The lead researcher was careful to frame Salvinia not as a solution but as a potential tool within a broader strategy. Contaminated plant material must be properly removed or it simply returns the pollution to the water. Still, in regions where advanced treatment technologies are financially out of reach, nature-based approaches like this could play a meaningful supporting role. The study's larger message is that antibiotic contamination in the Piracicaba River is real, ecologically complex, and already touching the people who live and eat along its banks.
In the Piracicaba River basin of São Paulo state, Brazil, researchers have uncovered a troubling accumulation of antibiotics in water, sediment, and the fish that local people eat. Scientists from the Center for Nuclear Energy in Agriculture at the University of São Paulo discovered residues of multiple antibiotic types in samples collected near the Santa Maria da Serra dam and Barra Bonita reservoir—areas where treated sewage, agricultural runoff, and waste from fish and pig farming converge. The work, led by Patrícia Alexandre Evangelista and published in Environmental Sciences Europe, combined environmental monitoring with laboratory experiments to measure not just the presence of these drugs, but their movement through the ecosystem and their biological effects.
The pattern that emerged was stark and seasonal. During rainy months, most of the twelve antibiotics tested—including tetracyclines, fluoroquinolones, and sulfonamides—fell below detectable levels. But when the dry season arrived and water volume dropped, the picture inverted. Contaminants became concentrated. Different compounds surfaced in the water at nanogram-per-liter concentrations, while sediment held them at microgram-per-kilogram levels. Some compounds, including enrofloxacin and sulfonamides, accumulated in sediment at concentrations higher than those documented in comparable studies worldwide. The sediment, rich in organic matter and nutrients, acts as a storage depot—holding these antibiotics and potentially releasing them back into the environment over time.
The most alarming discovery involved chloramphenicol, an antibiotic whose use in livestock has been prohibited in Brazil precisely because of its toxicity. Researchers detected it in lambari fish—small fish commonly sold and eaten in the Barra Bonita region—during the dry season, at concentrations reaching tens of micrograms per kilogram. This finding opened a direct pathway from contaminated water to human food and human bodies. Chloramphenicol was selected for deeper study alongside enrofloxacin because of their environmental persistence and health significance. Enrofloxacin is widely deployed in animal agriculture and aquaculture as well as human medicine. Chloramphenicol, though banned for food-producing animals, remains in use for human patients and serves as a marker of stubborn, long-lived contamination.
Beyond documenting the problem, the team tested whether Salvinia auriculata, a floating aquatic plant often dismissed as a nuisance, could help remediate the pollution. Using carbon-14-labeled compounds to track antibiotic movement with precision, researchers exposed the plant to both environmental concentrations and levels one hundred times higher. The results were mixed but encouraging for one compound. Salvinia removed more than ninety-five percent of enrofloxacin from the water within days when plant biomass was sufficient, cutting the antibiotic's half-life to two or three days. Chloramphenicol proved more resistant. The plant removed only thirty to forty-five percent, with half-lives stretching from sixteen to twenty days. Autoradiography images revealed that both antibiotics accumulated primarily in the plant roots, suggesting that root absorption and rhizofiltration drove the cleanup.
But the story grew more complicated when researchers examined how fish themselves absorbed these drugs. Lowering antibiotic concentrations in the water did not always reduce fish uptake. Enrofloxacin remained mostly dissolved and was eliminated relatively quickly by lambari fish, with a half-life around twenty-one days and a low bioconcentration factor—meaning it did not accumulate in tissues. Chloramphenicol behaved oppositely. It persisted in fish for more than ninety days and showed a high bioconcentration factor, indicating strong retention in tissue. The presence of Salvinia auriculata further complicated matters. Although the plant lowered antibiotic levels in water, fish sometimes absorbed the compounds more rapidly. Researchers suspect the plant may partially transform antibiotics into forms more readily taken up by aquatic organisms—a reminder that using plants as pollution sponges is not straightforward.
Genetic damage in fish provided another window into the toxicity. Chloramphenicol significantly increased DNA damage, including micronuclei formation and abnormalities in blood cell nuclei. When Salvinia auriculata was present, however, this damage dropped closer to control levels. For enrofloxacin, the plant offered no such protection. The researchers propose that Salvinia may generate fewer toxic byproducts from chloramphenicol or release antioxidant compounds that reduce oxidative stress in fish. Enrofloxacin, being chemically more stable, may produce persistent metabolites that the plant cannot neutralize.
Evangelista emphasized that Salvinia auriculata should not be mistaken for a complete solution. The study revealed both promise and peril. A critical concern is the fate of contaminated plant material. If not properly removed and treated, the plants themselves become pollution sources, releasing antibiotics back into the environment. Yet the findings suggest that aquatic plants could become part of affordable, nature-based cleanup strategies in regions where expensive technologies like ozonation and advanced oxidative treatment remain out of reach. The research demonstrates that antibiotic contamination in the Piracicaba River is real, measurable, and ecologically complex—and that any strategy to address it must account not only for removing the contaminant but for understanding its biological and ecological consequences.
Citas Notables
The detection of antibiotic residues in the water, sediments, and fish of the Piracicaba River shows just how harmful human activities can be.— Valdemar Luiz Tornisielo, supervisor of the research
Using plants as 'sponges' for contaminants is not a trivial matter. The presence of the macrophyte changes the entire system, including the way the organism comes into contact with the contaminant.— Patrícia Alexandre Evangelista
La Conversación del Hearth Otra perspectiva de la historia
Why does the dry season make this problem worse?
When water volume drops, the same amount of antibiotic gets concentrated into less water. It's like reducing the size of a container without removing what's inside—the density increases. Sediment also plays a role, trapping these drugs and potentially releasing them back over time.
So people eating these fish are actually consuming a banned antibiotic?
Yes. Chloramphenicol was found in lambari fish at measurable levels during dry season. These are fish that local people buy and eat regularly. It's a direct exposure route that wouldn't exist if the antibiotic stayed in the water.
The plant removed ninety-five percent of one antibiotic but only thirty percent of another. Why such a difference?
Chemistry matters. Enrofloxacin is more water-soluble and the plant roots can absorb it efficiently. Chloramphenicol is more persistent, more resistant to breakdown. The plant can capture some of it, but the compound's structure makes it harder to remove completely.
If the plant removes the antibiotic, doesn't that solve the problem?
Not entirely. The antibiotic doesn't disappear—it accumulates in the plant roots. If you don't carefully harvest and dispose of that contaminated plant material, you've just moved the problem. It could leach back into the water or soil.
Did the fish get healthier when the plant was present?
Complicated. For chloramphenicol, yes—the genetic damage in fish decreased when Salvinia was in the system. But for enrofloxacin, the plant didn't help. And in some cases, fish actually absorbed antibiotics faster when the plant was there, possibly because the plant was transforming them into forms the fish could take up more easily.
What does this mean for people downstream?
It means the contamination is persistent and moving through multiple pathways—water, sediment, fish, and potentially back again. There's no single fix. You need monitoring, you need to address the sources of pollution, and you need multiple cleanup strategies working together.