Trihalomethane levels in home tap water and semen quality

Background: Trihalomethanes (THMs) are byproducts of drinking water chlorination whose effects on semen quality have not been previously studied in humans. Methods: We examined the relationship of THMs to semen quality in 157 healthy men from couples without known risk factors for infertility. Total THM (TTHM) levels were assigned based on water utility measurements taken during the 90 days preceding semen collection. We analyzed continuous semen parameters in relation to total and individual THMs, adjusting for potential confounders by using repeated measures analyses. Results: TTHM level was not associated with decrements in semen quality. Percent normal morphology decreased and percent head defects increased at higher levels of an ingestion metric (TTHM multiplied by cold home tap water consumption). At the highest level of the ingestion metric (> 160 μg/L × glasses/day, which is equivalent to >2 glasses/day of water containing 80 μg/L) we observed a difference of -7.1 (95% confidence interval = -12.7 to -1.6) for percent morphologically normal sperm compared with the lowest level (≤ 40 μg/L × glasses/day). Of the individual THMs, bromodichloromethane exposure was inversely related to linearity (a motility parameter); we observed a small decrease (β = -0.09, SE 0.04) for every unit increase in bromodichloromethane. Conclusion: Although our study had a limited exposure assessment and a selective sample, our results suggest the need for further study of the effects of THMs on semen quality.