Article by Jo Macfarlane – Medical Correspondant – The Times
Pregnant women living in areas where tap water is heavily disinfected with chlorine nearly double the risk of having children with heart problems, a cleft palate or major brain defects, a new study found.
Scientists say expectant mothers can expose themselves to the higher risk by drinking the water, taking a bath or shower, or even by standing close to a boiling kettle.
The dangers comes from chemical by products in chlorinated water known as Trihalomethanes, or THMs, which can be absorbed through the skin. They can then pass into the womb.
THMs form because of a chemical reaction between chlorine and natural substances in the water.
They exist in mains water across Britain – but are highest in areas where more chlorine is added because the water quality is poor.
Earlier studies linked chlorine water to an increased risk of still birth, miscarriage, birth defects and bladder cancer. But this is the frst time that the risk has been narrowed down to specific birth defects.
Although a major study in 2007 by Imperial College, London, into births defects and THM levels in Britain uncovererd ‘little evidence’ of a link, the new research appears to contradict its findings.
A research team led by Professor Jouni Jaakkola of the University of Birmingham analysed the birth registry details of nearly 400,000 babies born in Taiwan between 2001 and 2003. Levels of Chlorine found in water there are similiar to those found in the UK.
Scientists compared the number of birth defects recorded by doctors to the leel of THMs in the drinking water in different areas.
The proportions of certain anencephalus, usually found in 0.01 per cent of births, rose to 0.17 per cent in high THM areas. Hole in the heart defects also nearly doubled from 0.015 per cent to 0.024 per cent. The number of cleft palates rose from 0.029 per cent to 0045 per cent in high THM areas.
Overall, the risks of having chidlren with these three defects increased by between 50 per cent and 100 per cent. there was also a slightly raised risk of urinary tract defects and downs syndrome.
The study appears in Environmental Health Journal.
The number of defects could be much higher as some are not detected until later in childhood.
THM levels across Britain vary widely even within one water company area. They range from 92 micrograms per litre in south Stafforidshire to just five in Hartlepool. Most areas have levels way above the high range in the Taiwan study. High levels were recorded in South West England, Yorkshire and North East Essex.
Prof Jaakkola said THMs should be cut because the biologial reasons for the defects were unknown.
He said “Our findings dont just add to the evidence that Chlorination may cause birth defects but suggest that exposure to chlorination may cause birth defects but suggest that exposure to chlorination by products may be responsible for some specific and common defects.