Antibiotics are powerful, life-saving medicines that fight bacterial infections by killing bacteria or stopping them from multiplying. They work by targeting specific bacterial components, such as cell walls or protein synthesis, without harming human cells. They are ineffective against viral infections like cold or flu, and their misuse can lead to antibiotic resistance. PharmaTimes Editor, MORGAN NWANGUMA writes that while Nigerian researchers have identified extensive and unfettered and repeatedly wrong use of antibiotics in the aquaculture sector, scientists at the Centre for Nuclear Energy in Agriculture at the University of São Paulo, Brazil are equally sounding an alarm concerning the amount of antibiotic residues they found in fish.
The first modern antibiotic, Salvarsan, was introduced in the early 1900s, followed by the breakthrough of penicillin in 1928, which transformed medicine by treating infections that were previously fatal. In the course of actions, they can be bactericidal (killing bacteria) or bacteriostatic (stopping bacteria from multiplying); when misused however, they can become poisonous to the human body.
Today, recent research reports say that antibiotics are quietly building up in rivers and fish, and even natural cleanup methods may bring unexpected consequences.
It has been found that antibiotics are accumulating in a major Brazilian river, particularly during the dry season when lower water levels make pollution more concentrated. They also detected a banned antibiotic in fish sold for food, raising concerns about possible human exposure. A common aquatic plant however, showed potential for removing some of these chemicals from the water, but it also changed the way fish absorbed them, creating new risks.
Here in Nigeria research conducted between 2021 and 2026 highlights that antibiotic residues are contaminating the food chain and posing serious public health threats. In the course of the study, scientists were able to identify widespread, unregulated, and often inappropriate use of antibiotics in the aquaculture sector, resulting in significant antibiotic residues in seafood, particularly catfish – and the development of antimicrobial resistance (AMR).
In a major research finding, scientists at the Centre for Nuclear Energy in Agriculture at the University of São Paulo (CENA-USP) identified several classes of antibiotics in the Piracicaba River, an important waterway in São Paulo state of Brazil. Their study, published in Environmental Sciences Europe, showed that these substances are present not only in the river water but also in fish living there. The team also investigated whether Salvinia auriculata, a common aquatic plant in the region, could help reduce contamination.
The research in Brazil was led by Patrícia Alexandre Evangelista with support from FAPESP. It combined environmental monitoring, studies of how pollutants accumulate in living organisms, tests for genetic damage in aquatic life, and plant-based experiments aimed at removing contaminants. This broader approach gave researchers a clearer picture of both the scale of the pollution and possible strategies for addressing contamination linked to human and veterinary drug use.
Pollution sources and seasonal trends
Samples were collected near the Santa Maria da Serra dam, close to the Barra Bonita reservoir, where pollutants from across the river basin tend to collect. The area receives contaminants from treated sewage, household wastewater, fish farming, pig farming, and agricultural runoff.
The researchers analyzed water, sediment, and fish during both the rainy and dry seasons. They monitored 12 widely used antibiotics from groups including tetracyclines, fluoroquinolones, sulfonamides, and phenols. “The results showed a clear pattern of seasonality. During the rainy season, most antibiotics had concentrations below detection limits. In the dry season, however, when water volume decreases and contaminants become concentrated, different compounds were detected,” says Evangelista.
Measured concentrations ranged from nanograms per liter in water to micrograms per kilogram in sediment. Some antibiotics, including enrofloxacin and several sulfonamides, were detected in sediment at levels higher than those reported in comparable studies around the world. Because the sediment contains high amounts of organic matter and nutrients such as phosphorus, calcium, and magnesium, it can act as a reservoir for these compounds, storing them and potentially releasing them back into the environment over time.
Prohibited antibiotic discovered in fish
“One of the most significant findings of the study was the detection of chloramphenicol in lambari fish (Astyanax sp.) collected from local fishermen in the Barra Bonita region. The researcher states that, “Chloramphenicol is an antibiotic whose use in livestock is prohibited in Brazil precisely because of the risks associated with its toxicity.”
This substance was detected only during the dry season, at concentrations of tens of micrograms per kilogram. Because lambari fish are widely eaten in the region, its presence raises concerns about possible human exposure to antibiotics through food.
Evangelista said chloramphenicol and enrofloxacin were chosen for detailed laboratory experiments because of their significance to both environmental and public health. “Enrofloxacin is widely used in animal husbandry, including aquaculture, as well as in human medicine. Chloramphenicol, on the other hand, is still used in humans despite being banned for food-producing animals and serves as a historical marker of persistent contamination,” she explains.
Can aquatic plants remove antibiotics?
The researchers also investigated whether Salvinia auriculata, a floating aquatic plant often regarded as invasive, could help clean contaminated water.
In controlled laboratory experiments, the plant was exposed to both environmentally relevant concentrations and doses 100 times higher of enrofloxacin and chloramphenicol. To track exactly how the antibiotics moved through the water, the plant, and fish, the team used carbon-14 radiolabeled compounds.
“The results showed the high efficiency of Salvinia in removing enrofloxacin. In treatments with higher plant biomass, more than 95% of the antibiotic was removed from the water within a few days. The half-life of the compound dropped to about two to three days. In the case of chloramphenicol, removal was slower and partial. The plant was able to remove 30% to 45% of the antibiotic from the water, with half-lives ranging from 16 to 20 days, indicating the greater persistence of the compound in the environment,” the researcher reports.
Imaging analyses showed that the antibiotics accumulated mainly in the plant’s roots, indicating that root absorption and filtration play an important role in removing them from the water.
One of the more striking findings was that reducing antibiotic levels in the water does not always mean fish will absorb less of them.
Enrofloxacin remained largely dissolved in the water and was cleared relatively quickly by lambari fish. It had a half-life of about 21 days and showed limited accumulation in tissues. Chloramphenicol behaved very differently. It remained in the fish for much longer, with a half-life of more than 90 days, and showed a much stronger tendency to accumulate in tissues.
The presence of Salvinia auriculata also changed these patterns. Although the plant lowered antibiotic concentrations in the water, it sometimes increased the rate at which fish absorbed them. One possible explanation is that the plant may alter the chemical form of the antibiotics, making them easier for fish to take up.
“This shows that 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,” Evangelista remarks.
DNA destruction in fish and possible defense
The research as well investigated genetic damage in fish. Chloramphenicol significantly increased DNA damage, as shown by changes in blood cells, including micronuclei and other abnormalities. However, when Salvinia auriculata was present, the damage declined and moved closer to the levels observed in the control groups. For enrofloxacin, the plant did not significantly reduce the genetic effects.
“The interpretation we propose is that, in the case of chloramphenicol, the plant may generate fewer genotoxic byproducts or release antioxidant compounds into the rhizosphere, reducing oxidative stress in the fish. On the other hand, enrofloxacin is chemically more stable and may produce persistent and potentially toxic metabolites whose action is not neutralized by the macrophyte,” the researcher comments.
Promise and limits of nature-based solutions
Evangelista said Salvinia auriculata is not a simple solution to antibiotic pollution. Although the plant shows promise, it also presents important challenges. One major concern is what happens after it absorbs contaminants. If the plant material is not properly removed and treated, the antibiotics could be released back into the environment.
Even so, aquatic plants may provide a low-cost, nature-based way to reduce pollution, particularly in areas where advanced treatment technologies such as ozonation and other oxidative processes are too expensive.
“The study shows that the problem is real, measurable, and complex. And any strategy to address it must consider not only the removal of the contaminant, but also its biological and ecological effects,” the researcher concludes.
Mounting ecological and public health anxiety
“The detection of antibiotic residues in the water, sediments, and fish of the Piracicaba River shows just how harmful human activities can be. The resistance of microorganisms to antibiotics can lead to the emergence of superbugs in the environment. The research yielded positive results with low-cost environmental solutions and enabled a better understanding of the integrated functioning of aquatic ecosystems and the use of effective natural techniques for impact mitigation,” says Valdemar Luiz Tornisielo, supervisor of Evangelista’s research as well as co-author of the report.
The radiolabeled molecules used in the research were made available by the International Atomic Energy Agency (IAEA).
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