By Morgan Nwanguma
A major new study has found that dozens of commonly used chemicals can harm beneficial bacteria in the human gut. Many of these substances, widely present in pesticides and everyday industrial products were previously assumed to be biologically harmless. When exposed to these chemicals, gut microbes can become stressed, and in some cases, develop resistance to antibiotics, raising fresh concerns about unseen impacts on human health.
In a large laboratory analysis, scientists tested 1,076 synthetic chemicals and discovered that 168 of them inhibited or completely halted the growth of bacteria essential to a healthy gut microbiome. These microbes play a critical role in digestion, immune function, and overall well-being.
Alarmingly, many of the harmful chemicals are ones people are routinely exposed to through food, drinking water, and the environment. Until now, most were not thought to interfere with living organisms at all.
New Links to Antibiotic Resistance
The researchers found that when gut bacteria are exposed to chemical pollutants, some adapt in ways that also make them resistant to antibiotics such as ciprofloxacin. If similar changes occur in the human body, this could make infections harder to treat and further complicate efforts to combat antibiotic resistance.
The study, led by scientists at the University of Cambridge, examined the effects of these chemicals on 22 species of gut bacteria under controlled laboratory conditions.
Pesticides and Industrial Chemicals among the Most Damaging
Among the most harmful substances were pesticides, including widely used herbicides and insecticides applied to crops. Industrial chemicals commonly found in products such as plastics and flame retardants were also shown to be toxic to gut microbes.
The human gut microbiome is made up of roughly 4,500 bacterial species that help maintain physical and mental health. Disrupting this complex ecosystem has been linked to conditions ranging from digestive disorders and obesity to weakened immunity and mental health challenges.
Gaps in Chemical Safety Testing
Current chemical safety assessments rarely consider effects on the gut microbiome, largely because chemicals are typically evaluated only for their intended targets – for example, insecticides are designed to affect insects, not bacteria in the human body.
Using their experimental data, the researchers developed a machine-learning model capable of predicting whether existing or newly developed industrial chemicals are likely to damage gut bacteria. The study and the predictive model were published in Nature Microbiology.
Scientists Demand a New Approach to Chemical Safety
Dr. Indra Roux, a researcher at the University of Cambridge’s MRC Toxicology Unit and the study’s first author, said: “We’ve found that many chemicals designed to act only on one type of target, say insects or fungi, also affect gut bacteria. We were surprised that some of these chemicals had such strong effects. For example, many industrial chemicals like flame retardants and plasticizers — that we are regularly in contact with — weren’t thought to affect living organisms at all, but they do.”
Professor Kiran Patil, senior author of the study and also based at the University of Cambridge’s MRC Toxicology Unit, added: “The real power of this large-scale study is that we now have the data to predict the effects of new chemicals, with the aim of moving to a future where new chemicals are safe by design.”
Dr. Stephan Kamrad, another researcher involved in the work, said: “Safety assessments of new chemicals for human use must ensure they are also safe for our gut bacteria, which could be exposed to the chemicals through our food and water.”
What Scientists Still Don’t Know About Real-World Exposure
Scientists still have limited insight into how environmental chemicals directly interact with the gut microbiome, and what that means for human health. While researchers believe gut bacteria are regularly exposed to many of these chemicals, the precise levels that actually reach the digestive system are not yet known. Closing this knowledge gap will require future studies that closely track how chemicals move through the body and accumulate in different tissues.
Patil said: “Now we’ve started discovering these interactions in a laboratory setting it’s important to start collecting more real-world chemical exposure data, to see if there are similar effects in our bodies.”
Until clearer evidence emerges, the researchers advise taking practical precautions to limit exposure – such as thoroughly washing fruits and vegetables before consumption and avoiding the use of pesticides in home gardens.
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