Chlorination has been the major means of disinfecting drinking water in Taiwan. The use of chlorinated water has been hypothesized to lead to several adverse birth outcomes, including low birth weight and preterm delivery. We performed a study to examine the relationship between the use of chlorinated water and adverse birth outcomes in Taiwan. The study areas included 14 chlorinating municipalities (CHMs), which were defined as municipalities in which [is greater than] 90% of the municipal population was served by chlorinated water, and 14 matched nonchlorinating municipalities (NCHMs), defined as municipalities in which [is less than] 5% of the municipal population is served by chlorinated water. The CHMs and NCHMs were similar to one another in terms of level of urbanization and sociodemographic characteristics. The study population comprised 18,025 women residing in the 28 municipalities who had a first parity singleton birth between 1 January 1994 and 31 December 1996 and for which complete information on maternal age, education, gestational age, birth weight, and sex of the baby were available. The results of our study suggest that there was no association between consumption of chlorinated drinking water and the risk of low birth weight. Key words: chlorination, disinfection by-products, drinking water, infants, low birth weight. Environ Health Perspect 108:765-768 (2000). [Online 30 June 2000] http://ehpnet1.niehs.nih.gov/docs/2000/108p765-768yang/abstract.html
The economy and effectiveness of chlorine in killing waterborne organisms has made water chlorination a tremendous public health success worldwide. However, chlorination of water can produce trace amounts of by-products such as trihalomethanes (THMs), which are carcinogenic organic halogenated contaminants of water chlorination (1--3). A number of epidemiologic studies have focused on the possible associations between the consumption of chlorinated drinking water and cancer mortality or incidence (4--15). Most studies have shown positive associations between the use of chlorinated drinking water and colorectal and bladder cancer risk.
Recently, several epidemiologic studies have examined the associations between the consumption of chlorinated water and adverse pregnancy outcomes (16--24). These studies found associations between chlorination and risk of spontaneous abortion, infants being small for gestational age, having low birth weight, or displaying specific birth defects. These studies considered a wide range of populations and regions but have been mainly carried out in the United States. The present study was carried out because few epidemiologic studies have been conducted outside the United States (21,23). There was a need for additional studies using new independent data from other populations, so we undertook the present study in Taiwan to explore further the association between adverse birth outcomes and the use of chlorinated water. This paper is one in a series of studies to assess the hazard potential posed by exposure to chlorinated drinking water.
Materials and Methods
Selection of study municipalities. Taiwan is divided into 361 administrative districts, which are referred to here as municipalities. We excluded from the analysis 30 aboriginal townships and 9 islets that encompassed different lifestyles and living environments; we also excluded the 12 municipalities of the city of Taipei because of Taipei's distinctly more urban character and larger population than other municipalities in Taiwan. This elimination left 310 municipalities.
Chlorination has been the major means of disinfecting drinking water in Taiwan. Chlorine is currently added to approximately 75.8% of the nation's drinking water. The current Taiwan water system is rather simple. Residents obtain their drinking water either from the public drinking water supply systems served by the Taiwan Water Supply Corporation or from nonmunicipal sources. The major sources of municipal water supplies are almost all surface waters and are treated with chlorine. The nonmunicipal sources are mainly privately owned wells (groundwater) and are unchlorinated.
In this study, we classified an individual municipality as a chlorinating municipality (CHM) if [is greater than] 90% of the municipal population was served by chlorinated …