Many of the chemicals identified are ones people are likely to encounter through everyday exposure, including food, drinking water, and the environment. Until now, most were not believed to interfere with bacteria at all.

Links to Antibiotic Resistance Raise New Concerns

When gut bacteria are exposed to these chemical pollutants, some change how they function in an attempt to survive. In certain cases, this adaptation also makes the bacteria resistant to antibiotics such as ciprofloxacin. If similar changes occur inside the human body, infections could become more difficult to treat.

The study was led by researchers at the University of Cambridge and involved testing 1076 different chemical contaminants on 22 species of gut bacteria under laboratory conditions.

Pesticides and Industrial Chemicals Among the Most Harmful

The chemicals shown to damage gut bacteria include pesticides such as herbicides and insecticides commonly applied to crops. Industrial compounds used in products like flame retardants and plastics were also found to be toxic to these microbes.

The human gut microbiome contains roughly 4,500 different types of bacteria that help keep the body functioning properly. When this delicate system is disrupted, it can contribute to a wide range of health problems, including digestive issues, obesity, weakened immune function, and effects on mental health.

Why Chemical Safety Testing Misses Gut Health

Current chemical safety evaluations typically do not account for the gut microbiome. This is because chemicals are designed to target specific organisms or processes, for example insecticides should target insects.

Using the data from their experiments, the researchers developed a machine learning model to help predict whether industrial chemicals — whether already in use, or in development — are likely to harm human gut bacteria. The findings and the new model were published in the journal Nature Microbiology.

Researchers Call for 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

There is currently limited information about how environmental chemicals directly affect the gut microbiome and, in turn, human health. The researchers say it is likely that gut bacteria are frequently exposed to many of the chemicals tested, but the exact amounts that reach the digestive system remain unclear. To better understand the risks, future studies will need to track chemical exposure throughout the body.

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 more is known, the researchers recommend simple steps to reduce exposure, such as washing fruits and vegetables before eating them and avoiding the use of pesticides in home gardens.