Effect of household boiling on ciprofloxacin and enrofloxacin residues in cow milk from Dhaka, Bangladesh: paired HPLC-UV screening and dietary exposure assessment
A study of 120 cow milk samples from Dhaka, Bangladesh, found that while 15 minutes of household boiling significantly reduced ciprofloxacin and enrofloxacin residue levels, it failed to bring the vast majority of contaminated samples below the EU maximum residue limit, leaving dietary exposure risks largely unchanged.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
In many parts of the world, milk is a daily staple, a white liquid packed with protein and calcium that feeds families and fuels growth. Yet, the journey from a cow to a glass is fraught with invisible risks. Farmers often use antibiotics to treat sick animals, a necessary practice to keep herds healthy, but if these medicines are not managed with strict timing, traces can remain in the milk sold for human consumption. These leftover drugs, known as residues, pose a silent threat: they can trigger allergic reactions, disrupt the natural balance of bacteria in the human gut, and contribute to a growing global crisis where bacteria become immune to the very medicines designed to kill them. While boiling milk is a common household ritual in places like Bangladesh, believed to kill harmful germs, it is less clear whether this heat can also destroy these stubborn chemical traces.
A team of researchers in Bangladesh set out to investigate this specific question, focusing on two common antibiotics found in dairy cows: ciprofloxacin and enrofloxacin. They gathered 120 samples of raw cow milk from twelve different collection points around the capital city, Dhaka. To understand the true effect of home cooking, they did not just test the milk as it came from the farm. Instead, they took each sample and split it in two. One half was tested immediately as raw milk, while the other half was boiled in a pot on a stove for fifteen minutes, mimicking the way many families prepare their daily drink. The researchers then used a precise laboratory technique to measure the amount of antibiotic residue in both the raw and the boiled versions, comparing the results side by side to see if the heat had made a difference.
The findings revealed a landscape where these antibiotics are widespread. In the raw milk, the researchers detected at least one of the two antibiotics in nearly every sample they tested. When they looked at the combined amount of both drugs, the average concentration was roughly 195 micrograms per kilogram. This level is significantly higher than the safety benchmark used by the European Union, which sets a limit of 100 micrograms per kilogram for the total of these two substances. The study showed that this high level of contamination was not an isolated incident but a common occurrence across the regions sampled, with the vast majority of raw milk exceeding the safety threshold.
When the researchers turned their attention to the boiled milk, the results offered a mix of hope and reality. The boiling process did work to lower the levels of the antibiotics. On average, the combined amount of the two drugs dropped to about 180 micrograms per kilogram, a reduction that was statistically significant. This suggests that the heat did break down some of the chemical compounds or altered their concentration. However, this decrease was not dramatic enough to solve the safety problem. Even after boiling, the number of samples that remained above the safety limit barely changed. While the raw milk had about 92.5 percent of samples exceeding the limit, the boiled milk still had 90 percent of samples above that same line. In other words, while the heat reduced the amount of drug present, it did not bring the high-risk samples down to a safe level.
The study also looked at how much of these residues a person might actually consume. Using national data on how much milk people drink, the researchers calculated a risk score for adults and children. For an average adult, the estimated daily intake of these antibiotics, even from the contaminated milk, remained below a level considered dangerous. However, when they ran the numbers for a small child weighing only 10 kilograms, the risk score rose above the safety threshold, suggesting that young children could be more vulnerable to the effects of these residues. This calculation relied on the assumption that children drink the same amount of milk as adults, a conservative estimate that highlights a potential risk even if the exact daily habits of children are not fully known.
Regional differences also played a role in the findings. The researchers found that the levels of antibiotics varied from one area to another, with some locations showing higher concentrations than others. Yet, when they tried to pinpoint exactly which areas were significantly different from the rest, the data became too scattered to draw a firm conclusion about specific hotspots. This suggests that the issue is widespread and likely driven by common practices across the dairy supply chain, such as how long farmers wait after treating a cow before milking it, rather than being confined to a single neighborhood or farm.
Ultimately, the research paints a clear picture of a complex food safety challenge. Boiling milk at home is effective at killing bacteria and making the liquid safe from microbial infection, but it is not a magic cure for antibiotic residues. The heat reduces the amount of these drugs slightly, but it leaves the majority of contaminated samples still well above safety limits. The study concludes that the solution does not lie in the kitchen pot, but rather in the dairy farm. To truly protect consumers, the focus must shift to better veterinary oversight, ensuring that farmers follow strict waiting periods after treating animals, and improving the monitoring of milk before it ever reaches the collection points. Until these upstream measures are strengthened, boiling remains a necessary step for hygiene, but it cannot be relied upon to remove the chemical traces of modern animal husbandry.
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