Researchers from the Center for Nuclear Energy in Agriculture at the University of São Paulo have detected traces of several antibiotic types in the Piracicaba River, one of São Paulo state’s primary waterways in Brazil. In the same study, they investigated how these substances accumulate in fish and assessed whether the common aquatic plant Salvinia auriculata could mitigate the pollution.
The project was led by Patricia Alessandra Evangelista, with funding provided by the FAPESP foundation. The researchers combined environmental monitoring with contaminant accumulation experiments, studies on genetic damage in aquatic organisms, and an evaluation of phytoremediation—a method of environmental cleanup utilizing plants. This integrated approach allowed them to assess ecological risks while simultaneously testing cost-effective strategies for combating pollution stemming from both medical and livestock sectors.
Samples were collected near the Santa Maria da Serra dam and the Barra Bonita reservoir, an area where pollutants from the entire Piracicaba River basin tend to congregate. This region receives treated wastewater, domestic sewage, agricultural runoff, and waste from fish and swine farming.
The scientists analyzed water, sediment, and fish during both the rainy and dry seasons. Their monitoring included 12 widely used antibiotics from the tetracycline, fluoroquinolone, sulfonamide, and phenol groups. According to Evangelista, the findings revealed a clear seasonality. “During the rainy season, concentrations of most antibiotics were below the detection limit. In the dry season, when water volume decreases and pollutants become more concentrated, various compounds were identified.”
Substance levels in the water were measured in nanograms per liter, while concentrations in sediment reached micrograms per kilogram. Certain compounds, including enrofloxacin and sulfonamides, were found in higher concentrations in the sediment compared to similar studies in other countries. As the authors explain, sediments act as a reservoir for these pollutants due to their high organic matter content and nutrient levels, including phosphorus, calcium, and magnesium. Over time, these antibiotics can re-enter the environment.
One of the most significant findings was the detection of chloramphenicol in lambari fish (Astyanax genus), sourced from local fishermen near Barra Bonita. Chloramphenicol is an antibiotic whose use in livestock farming is prohibited in Brazil due to its toxicity. It was only found during the dry season, with concentrations reaching tens of micrograms per kilogram. Given that fish from this area are frequently sold and consumed, the study indicated a potential pathway for this dangerous substance to reach humans through food.
Evangelista explained that chloramphenicol and enrofloxacin were chosen for laboratory experiments due to their ecological and medical significance. Enrofloxacin is widely used in livestock farming, including aquaculture, as well as in human medicine. Chloramphenicol, despite being banned for food-producing animals, is still used in humans and is considered an indicator of persistent pollution, according to SciTechDaily.
In addition to identifying pollution, the researchers examined whether Salvinia auriculata, a floating aquatic plant often considered a weed, could aid in water purification. In laboratory settings, the plant was exposed to enrofloxacin and chloramphenicol at concentrations near environmental levels, as well as at concentrations 100 times higher. Compounds labeled with radioactive carbon-14 were used to precisely track the movement of the substances.
The results indicated that Salvinia auriculata is highly effective at removing enrofloxacin from water. In experiments with higher plant biomass, over 95% of this antibiotic disappeared from the water within days, with a half-life reduction to approximately 2-3 days. The outcome with chloramphenicol was different; the plant removed only 30-45% of the substance, and its half-life ranged from 16 to 20 days, suggesting greater environmental persistence for this compound.
Autoradiography images revealed that both antibiotics primarily accumulated in the plant’s roots. This suggests that uptake through roots and retention in the root zone likely play the main role in the purification process.
Separately, the researchers investigated how fish absorb these substances. They found that a decrease in antibiotic concentrations in the water did not always lead to a reduction in their accumulation within fish. Enrofloxacin primarily remained dissolved in the water and was relatively quickly eliminated from lambari, with a half-life of about 21 days. Its bioconcentration factor was low, indicating a lesser tendency to accumulate in tissues. Chloramphenicol behaved differently, persisting in fish for much longer, exceeding 90 days, with a high bioconcentration factor indicating greater retention in tissues.
The presence of Salvinia auriculata also influenced how fish absorbed antibiotics. Although the plant reduced the levels of these substances in the water, in some instances, fish began to absorb them more rapidly. The researchers hypothesize that the plant might partially convert antibiotics into forms that are more readily taken up by aquatic organisms. Evangelista emphasized, “This shows that using plants as ‘sponges’ for pollutants is not a straightforward task. The presence of a macrophyte alters the entire system, including how an organism interacts with the contaminant.”
The team also tested whether the antibiotics induced genetic damage in fish. Chloramphenicol significantly increased DNA damage, including the formation of micronuclei and anomalies in blood cell nuclei. However, in the presence of Salvinia auriculata, the level of this damage decreased to nearly the levels observed in the control group. The plant did not show such a pronounced protective effect with enrofloxacin.
The researchers suggest that with chloramphenicol, the plant might either produce fewer genotoxic byproducts or release antioxidant compounds in the root zone that reduce oxidative stress in fish. The situation with enrofloxacin is different; it is a chemically more stable substance that can form persistent and potentially toxic degradation products, whose effects the plant does not neutralize.
The authors specifically highlight that Salvinia auriculata cannot be considered a complete solution to antibiotic contamination in water. The study revealed both the advantages and limitations of this approach. One of the main challenges is determining what to do with the contaminated plants after the purification process. If not removed and treated properly, they could reintroduce antibiotics into the water, becoming a new source of pollution.
Nevertheless, the results indicate that aquatic plants can be integrated into cost-effective, natural purification methods, particularly where expensive technologies like ozonation and oxidation are financially prohibitive. Evangelista stressed, “The research shows that the problem is real, measurable, and complex. Any strategy to combat it must consider not only pollutant removal but also its biological and ecological consequences.”
Co-author Waldemar Luiz Tornisiello added that the detection of antibiotic traces in the water, sediment, and fish of the Piracicaba River demonstrates the significant harm caused by human activities. He noted that antibiotic resistance in microorganisms can lead to the emergence of “superbugs” in the environment. He also mentioned that the study yielded positive findings regarding inexpensive natural solutions and provided a better understanding of aquatic ecosystem functions and how to mitigate damage using natural methods.
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