The Relationship Between Exposure To Drinking Water Disinfection By-products And Human Male Semen Quality

Part I Associaiton between exposure to THMs in tap water and semen qualityObjective:To examine the associaiton between exposure to trihalomethanes (THMs) in tap water and semen quality, using the levels of THMs in water distribution systems and personal information on routine water-use activities as external exposure surrogates.Methods:In this part we conducted a prospective study. We recruited324men who lived in a water treatment plant in Wuhan, China and presented to the Reproductive Center of a larger hospital to seek semen examination. We evaluated the participants’THM exposure based on the spatial and temporal variability of four individual THM [chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and bromoform (TBM)] concentrations in tap water measured within90days preceding semen collection, personal information on ingestion and showering/bathing and the uptake factors of THMs. Multivariable linear regression was used to assess the associations of different routes of THM exposure via ingestion and showing/bathing with semen quality.Results:Multivariate linear regression analysis showed that TTHM, TCM and Br-THM uptakes via ingestion were associated with significant or suggestive decreasing trends in sperm concentration (P for trend=0.01,0.03and0.05, respectively) and sperm count (P for trend=0.02,0.05and0.09, respectively). In addition, we found that the third quartile of TCM uptake via showering/bathing was associated with declined sperm linearity compared with the first quartile of TCM uptake via showering/bathing (β=2.28%,95%CI:-4.44,-0.11). Conclusion:In this part our results suggested that THM exposure via ingestion may be associated with decreased sperm concentration and sperm count.Part II Associaitons of baseline blood THMs with semen parameters and serum total testosteroneObjective:To further examine the association of expsoure to drinking water THMs with semen quality and serum total testosterone, using baseline blood THMs as internal biomarkers.Methods:In this part we conducted a cross-sectional study. We recruited401men who presented to the Reproductive Center of a larger hospital in Wuhan, China to seek semen examination. We measured THM concentrations in morning whole blood to assess internal doses of baseline THM exposure, using solid phase micro-extraction-gas chromatography. Multivariable linear regressions were used to assess the associations of baseline blood THMs concentrations with semen parameters and serum total testosterone levels.Results:Multivariate linear regression analysis showed that the second tertile of blood BDCM level was associated with decreased sperm count (β=-0.13million,95%CI:-0.22,-0.03) compared with the lowest tertile of blood BDCM level; the second tertile of blood DBCM level was associated with declined sperm linearity compared with the lowest tertile of blood DBCM level (β=-4.74%,95%CI:-8.07,-1.42). In addition, suggestive dose-response relationships were also observed between elevated blood TCM or TTHM concentration and decreased sperm concentration (both P for trend=0.07), and between elevated blood DBCM concentration and decreased serum total testosterone (P for trend=0.07).Conclusion:In this part our results further suggested that elevated THM exposure may be associated with decreased sperm concentration, sperm count, and serum total testosterone.Part Ⅲ Assocaiton between urinary TCAA levels and semen qualityObjective:To examine the association between expsoure to drinking water disinfection by-products (DBPs) and semen quality, using urinary trichloroacetic acid (TCAA) as internal biomarkers.Methods:In this part we conducted a large-scale cross-sectional study. We recruited2009men who presented to the Reproductive Center of a larger hospital in Wuhan, China, to seek semen examination. We measured TCAA in urine as a biomarker of exposure to DBPs in chlorinated drinking water, using gas chromatography. Multivariate logistic and linear regression models were used to examine the relationship between urinary TCAA levels and semen quality.Results:Multivariate logistic regression analysis showed that men in the second and fourth quartile had an increased OR of having below-reference sperm concentration (OR=1.79,95%CI:1.19,2.69and OR=1.51,95%CI:0.98,2.31, respectively), men in the second and third quartile had an increased OR of having below-reference sperm motility (OR=1.46,95%CI:1.12,1.90and OR=1.30,95%CI:1.00,1.70, respectively), and men in the second quartile had an increased OR of having below-reference sperm count (OR=1.62,95%CI:1.04,2.55) compared to men with the lowest quartile of urinary TCAA levels. Similar results were also found in the continuous outcomes.Conclusion:In this part our results suggested that ingestion of exposure to drinking water DBPs may contribute to decreased sperm concentration, sperm count, and sperm motility in humans.