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Chlorination by-products in tap water and semen quality in England and Wales
  1. Nina Iszatt1,2,
  2. Mark J Nieuwenhuijsen1,3,4,5,
  3. James Bennett1,
  4. Nicky Best1,
  5. Andrew C Povey6,
  6. Allan A Pacey7,
  7. Harry Moore8,
  8. Nicola Cherry9,
  9. Mireille B Toledano1
  1. 1MRC-HPA Centre for Environment and Health, School of Public Health, Imperial College London, London, UK
  2. 2Department of Genes and the Environment, Norwegian Institute of Public Health, Oslo, Norway
  3. 3Center for Research in Environmental Epidemiology (CREAL), Barcelona, Spain
  4. 4Municipal Institute of Medical Research Foundation (IMIM), Barcelona, Spain
  5. 5Center for Biomedical Investigation Network of Epidemiology and Public Health (CIBERESP), Barcelona, Spain
  6. 6Centre for Occupational and Environmental Health, Centre for Epidemiology, Institute of Population Health, Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK
  7. 7Academic Unit of Reproductive and Developmental Medicine, Department of Human Metabolism, The Medical School, University of Sheffield, Sheffield, UK
  8. 8Centre for Stem Cell Biology, University of Sheffield, Sheffield, UK
  9. 9Division of Preventive Medicine, University of Alberta, Edmonton, Canada
  1. Correspondence to Dr Mireille B Toledano, MRC-HPA Centre for Environment and Health, School of Public Health, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK; m.toledano{at}


Objectives Disinfection by-products (DBPs) have been associated with adverse semen outcomes in laboratory animals, although the evidence for trihalomethanes (THMs) is limited. Three small epidemiological studies found little evidence for an association between DBPs and adverse semen outcomes in humans. Using data from a large case–referent study (Chemicals and Pregnancy Study, Chaps-UK), we investigated the association between total THM (TTHM), chloroform and total brominated THMs and sperm concentration, percent motile sperm and motile sperm concentration (MSC).

Methods Chaps-UK recruited men from 13 fertility clinics in nine urban centres across England and Wales between 1999 and 2002. We linked modelled THM concentrations in water zones to semen quality data for 642 cases (men with low MSC) and 926 referents (other men investigated for infertility), based on the men's residence during semen sampling. We assessed risk of low MSC in relation to DBP exposure using continuous THM concentrations. A secondary analysis investigated continuous outcomes (MSC, sperm concentration and percent motile sperm).

Results In the case–referent analysis there was little evidence of elevated risk associated with chloroform, total brominated THM or TTHM concentration after adjustment (OR per 10 µg/L TTHM 1.01; 95% CI 0.91 to 1.12). Similarly, there was no significant effect of THMs on the continuous outcomes.

Conclusions In the largest study to date on DBPs in public water supplies, and semen quality we found that concentrations of THMs were not associated with poor semen quality. Large-scale investigation of other DBPs (eg, haloacetic acids) and other semen quality parameters (eg, sperm morphology and/or sperm DNA integrity) is recommended.

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