A study of 762 healthy men and 4,146 semen analyses associated higher blood trihalomethane levels with lower semen volume and total sperm count.
Exposure timing during early sperm development may matter; the analysis also identified changes related to lipid metabolism and hormone synthesis.
Chemicals produced during drinking-water disinfection may be associated with male reproductive health, according to a new study.
The associations with lower semen volume and total sperm count were relatively pronounced for exposure 70–90 days before collection, drawing attention to environmental conditions months before a semen test.
An international team including Shanghai Jiao Tong University School of Medicine analyzed 4,146 semen samples from 762 healthy Chinese men. Higher blood trihalomethane concentrations were associated with lower semen volume and total sperm count. The findings appeared in Environmental Science & Technology in October 2026.
What are trihalomethanes?
Trihalomethanes (THMs) are disinfection by-products formed when chlorine-based disinfectants react with organic matter in water. Examples include chloroform and bromodichloromethane.
Exposure can occur through drinking water, inhaling compounds that evaporate during showers or baths, and skin contact. Their longer-term health effects have been studied, but the relationship between exposure timing and sperm development remains incompletely understood.
This study compared blood concentrations with semen results and also examined changes in seminal metabolites.
Associations with exposure 70–90 days before collection
The researchers examined blood THM levels in relation to semen volume and total sperm count across the 4,146 samples from 762 men.
Higher concentrations of some THMs, including chloroform and bromodichloromethane, were associated with lower volume and total count. These adverse associations were relatively prominent for exposure 70–90 days before semen collection.
That interval is relevant because sperm production and maturation take approximately two to three months. A semen test may therefore reflect health and environmental conditions months earlier, rather than only recent habits.
The findings suggest that early sperm development may be a vulnerable period for some environmental exposures. They do not prove that exposure 70–90 days earlier caused a reduction in sperm count.
Ninety metabolites linked to exposure and semen quality
To explore possible biological pathways, the team analyzed metabolites in seminal plasma—the fluid portion of semen that supports sperm survival and movement.
Ninety metabolites were associated with both THM exposure and semen quality. Statistical analysis identified 44 as potential mediators of the relationship.
Related pathways included unsaturated fatty-acid biosynthesis, steroid-hormone biosynthesis, arachidonic-acid metabolism and linoleic-acid metabolism. These metabolites statistically explained part of the observed associations.
The results suggest possible links with lipid and hormone-related processes involved in sperm production and maturation. Whether these metabolic changes actually cause lower sperm counts requires further investigation.
The study does not show that drinking tap water causes infertility
The findings should not be interpreted as proof that tap water itself causes male infertility.
Researchers measured blood THM concentrations, not the amount of tap water consumed. The study cannot establish how a particular amount of drinking water affects sperm count or whether filters or bottled water improve sperm health.
Participants were healthy men, and the study did not assess pregnancy success or infertility incidence. Although statistically significant associations were observed, lifestyle or other environmental factors may have contributed.
It would be inappropriate to use these findings alone to judge the safety of tap water in South Korea, or to conclude that ordinary tap-water use causes male infertility.
Looking at the months before trying to conceive
The study’s broader message is that sperm health is not determined solely by what happens on the day of testing or in the preceding few days.
Smoking, alcohol, obesity, inadequate sleep and excessive testicular heat are familiar considerations in male reproductive health. The findings suggest that environmental chemicals and their timing also warrant attention.
Because sperm development takes months, men preparing for pregnancy can review their health and environment at least two to three months beforehand. The study does not establish that reducing THM exposure alone restores sperm count or improves pregnancy rates.
The analysis encourages consideration of environmental conditions during sperm development alongside testicular and hormonal factors.
Sperm health develops over time. This work offers a research direction that considers preceding months of exposure as well as current semen results.
This article is based on “Trihalomethane Exposure, Seminal Plasma Metabolomics, and Semen Quality in Healthy Men: A Meet-in-the-Middle Approach,” by an international team including Shanghai Jiao Tong University School of Medicine, published in Environmental Science & Technology in October 2026. DOI: 10.1021/acs.est.6c06945.
This observational study cannot establish causation. Abnormal semen findings or suspected male infertility should be discussed with a urologist or fertility specialist.
The accompanying image was created using generative AI (ChatGPT, OpenAI); any people depicted are fictional.
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