Water chlorination and birth defects

Chlorination of drinking water that contains organic compounds leads to the formation of by products, some of which have been shown to have mutagenic or carcinogenic effects. As yet, too little is known about the possible ter atogenic effects on the human fetus. We linked the Norwegian waterwork regi stry, containing 1994 data on chlorination practice and color (an indicator for natural organic matter), with the Medical Birth Registry for 1993-1995 . The proportion of the population exposed to chlorination and a weighted m ean color number in drinking water was computed for each municipality. Amon g 141,077 births, 2,608 (1.8%) had birth defects, In a comparison between e xposed (high color; chlorination) and reference groups (low color; no chlor ination), the adjusted odds ratio was 1.14 (0.99-1.31) for any malformation , 1.26 (0.61-2.62) for neural tube defects, and 1.99 (1.10-3.57) for urinar y tract defects. This study provides further evidence of the role of chlori nation of humic water as a potential cause of birth defects, in a country w ith relatively low levels of chlorination byproducts.