Chlorine-Treated Drinking Water Might Change Species Diversity in Gut Microbiota

In many parts of the world, drinking water is treated with chlorine to reduce potentially pathogenic microbes; however, chlorine-treated water could affect the gut microbiome, which flourishes when there is a diverse array of microbial species.

According to results from a recent murine study, chlorinated drinking water significantly reduced α-diversity in the guts of mice compared to unchlorinated drinking water. The results of this study, published in Science of The Total Environment, suggest that drinking chlorinated water can have direct and indirect effects on the gut microbiota, which could change its function.

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“It is possible that chlorination-induced shifts in the gut microbiota could be causal to gastrointestinal [GI] epithelial structure and function, as many of the bacteria significantly altered by chlorination have previously been linked with gut permeability and inflammation,”wrote the study authors.

There are few studies which assess acute or chronic exposure to chlorinated drinking water on GI microbiota in mice and humans (which share similar GI microbiota), so investigators conducted a study to evaluate it, specifically looking at the water’s effect on gut microbiota composition and function.

The team put mice into groups and fed them water with a chlorination agent (hypochlorous acid[HOCl] or 2-component-determined circulating immune complexes [TCIC]) or unchlorinated water (control) for 3 weeks. The investigators then evaluated the fecal bacterial microbiota using16S rRNA sequencing, which makes it possible to gain insight into gut microbiota diversity.

Chlorination changed the mice’s microbiota, regardless of the type of agent. While chlorine was shown to alter α-diversity in the gut microbiota, it was also shown to significantly impact community dissimilarities (β-diversity); both the HOCl and TCIC microbial communities were significantly different from one another, wrote the study authors.

Amplicon sequence variants (ASVs) reflect the abundance of different species in the gut after chlorination or exposure. After chlorination, species Lactobacillus ASV1, Akkermansiamuciniphila ASV7, and Clostridium ss1 ASV10 became more abundant, while strains Ileibacterium, valens ASV5, Desulfovibrio ASV11, and Lachnospiraceae UCG-006 ASV15 became less abundant.

“Drinking water chlorination impacted relative abundance of ASVs across all fecal samples… with overlapping but not identical changes induced by HOCl and TCIC, respectively,” wrote the study authors.

The authors noted that this study did not evaluate the impact of microbial changes (caused by chlorinated agents) on gastrointestinal function parameters, which include gut barrier function, gut permeability, and inflammation, or innate immunity in mice. Anecdotally, there is some evidence that significantly high levels of chlorine in tap water negatively altered the gut microbiota of mice at risk of colorectal cancer, but the study highlights the inconclusive effects of chlorine in drinking water.

Further studies can delve into the role of sex as a variable of microbial change. Other studies could also evaluate the gut microbial population of mice who are exposed to unchlorinated water after drinking chlorinated water or compare the effects of chlorinated water on the oral and fecal microbiota communities, according to the study authors. Moreover, studies are needed in humans to assess the health impacts.

“Differential abundance analysis…revealed microbiota changes [were] observable as a function of chlorinated drinking water administration, but translatability and health impact potentially relevant to human populations exposed to chlorinated drinking water remain to be addressed by future studies,” study authors wrote.

REFERENCE

Jandova J, Schiro G, Duca FA, Laubitz D, Wondrak GT. Exposure to chlorinated drinking water alters the murine fecal microbiota. Sci of The Total Environ. 2024. doi:10.1016/j.scitotenv.2024.169933