Scientists yesterday warned that pregnant women might be risking birth defects in their babies or miscarriage through exposure to high levels of potential cancer-causing agents in indoor swimming pools.
They called for detailed studies into the effects of by-products from chlorination on the health of swimmers, particularly mothers-to-be who were regular users of public baths.
The warning came amid rising fears over a possible link between such chemicals and the wellbeing of women and their babies, although the researchers conceded "evidence so far seems to be inconsistent and inconclusive".
Mark Neiuwenhuijsen, of Imperial College, London, one of the scientists, said concentrations of the chemicals should be "reduced as far as possible ... while maintaining effective control against waterborne microbiological disease".
The study, reported in the journal Occupational and Environmental Medicine, concentrated on levels of the by-products in 44 samples collected from eight London pools in the summer of 2000. When chlorine is added to water as a disinfectant, it reacts with organic matter such as skin cells and body care products, to form disinfectant by-products or DBPs, of which the most common are trihalomethanes (THMs), components that can vaporise from water into the atmosphere. The most common THM is chloroform which has been identified as a potential cancer causing agent.
The researchers found total organic matter was three times higher in swimming water than tap water while levels of chloroform was more than 20 times higher. They found higher THM levels were linked to higher water temperature and higher numbers of people in the pools. The amounts varied day to day but were generally higher than reported in other European studies
They did not measure actual uptake of THMs by swimmers but said other research indicated that a one hour swim would produce a chloroform dose around 141 times higher than a 10 minute shower. Swimmers could also absorb it in different ways, through the skin, swallowing water and breathing it off the water surface as it evaporated.
Dr Neiuwenhuijsen said: "Swimming pools could be a major pathway for the uptake of trihalomethanes among pregnant women who go swimming often. Further work should be carried out to assess the importance of these relatively high concentrations on potential health risks."
