Scientists have found a significant association between the use of chlorine dioxide as a disinfectant in the domestic water supply and the incidence of severe congenital heart defects in infants, writes Steve Farrar.
Although other factors such as maternal illness, smoking and obesity contribute to the risk, the researchers believe the problem should be taken seriously.
Marie Cedergren, an obstetrician at Linköping University Hospital in Sweden, and colleagues who worked on the study are talking with Swedish regulatory authorities about possible action to minimise the threat.
The scientists obtained details of 58,669 women in the county of Östergötland from Swedish health registers and cross-referenced these with information on the composition of the municipal drinking water each individual was exposed to between 1982 and 1996.
During this time, 753 infants were born with serious cardiac defects that proved fatal or required surgery.
The comprehensive data available in Sweden enabled Dr Cedergren's team to compare details of the drinking water content with the health impact on unborn children.
Most domestic supplies are chlorinated using a variety of procedures to rid the water of disease-causing micro-organisms.
The scientists found that the presence of one group of chemicals - the trihalomethanes - had a statistically significant link to the risk of an infant having a serious congenital heart condition if the mother drank the water during her pregnancy.
These substances are byproducts formed when chlorine dioxide reacts with natural organic matter during one of the chlorination procedures. Other approaches, such as using hypochlorite to disinfect supplies, were not associated with such risks.
The findings are published in the journal Environmental Research .