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Use of Routinely Collected Data on Trihalomethane in Drinking Water For Occup Environ Med 2001;58:447–452 447 Use of routinely collected data on trihalomethane Occup Environ Med: first published as 10.1136/oem.58.7.447 on 1 July 2001. Downloaded from in drinking water for epidemiological purposes T Keegan, H Whitaker, M J Nieuwenhuijsen, M B Toledano, P Elliott, J Fawell, M Wilkinson, N Best Abstract have been made to reduce high TTHM Objectives—To explore the use of rou- concentrations in the area. For chloro- tinely collected trihalomethane (THM) form and BDCM, the main THMs, the measurements for epidemiological stud- component between water zones was ies. Recently there has been interest in the greater than variation within water zones relation between byproducts of disinfec- and explained most of the overall exposure tion of public drinking water and certain variation. Variation between months and adverse reproductive outcomes, including seasons was low and showed no clear stillbirth, congenital malformations, and trends within years. The results indicate low birth weight. that routinely collected data can be used Method—Five years of THM readings to obtain exposure estimates for epide- (1992–6), collected for compliance with miological studies at a small area level. statutory limits, were analysed. One water (Occup Environ Med 2001;58:447–452) company in the north west of England, Keywords: chlorination byproducts; exposure; birth divided into 288 water zones, provided outcomes; routine data; trihalomethanes 15 984 observations for statistical analysis. On average each zone was sampled 11.1 times a year. Five year, annual, monthly, There is growing concern over the eVects of and seasonal variation in THMs were disinfection byproducts of chlorination on examined as well as the variability within human health. Early studies investigated links The TH Huxley School and between zones. between disinfection byproducts of chlorina- of the Environment, Results—Between 1992 and 1996 the total tion and increased risk of certain cancers, such Earth Sciences and THM (TTHM) annual zone means were as rectal, bladder, and colon cancer.1 More Engineering, Imperial less than half the statutory concentration, recent studies have focused on the possible College of Science at approximately 46 µg/l. DiVerences in Technology and eVects of disinfection byproducts of chlorina- Medicine, RSM Prince annual water zone means were within 7%. tion on certain reproductive outcomes, includ- Consort Road, London Over the study period, the maximum ing low birthweight, stillbirth, spontaneous SW7 2BP,UK water zone mean fell from 142.2 to 88.1 abortion, and congenital abnormalities. The http://oem.bmj.com/ T Keegan µg/l. Mean annual concentrations for indi- results from these studies have been mixed.23 M J Nieuwenhuijsen vidual THMs (µg/l) were 36.6, 8.0, and 2.8 Several of these reproductive epidemiologi- Small Area Health for chloroform, bromodichloromethane cal studies relied on crude exposure data. Some Statistics Unit, (BDCM), and dibromochloromethane used comparisons between water source Department of (DBCM) respectively. Bromoform data (ground v surface) and between water treat- Epidemiology and were not analysed, because a high pro- ments (chlorinated v non-chlorinated).45Oth- Public Health, portion of the data were below the detec- ers have used routinely collected total tri- Imperial College of tion limit. The correlation between halomethane (TTHM) measurements to form on September 30, 2021 by guest. Protected copyright. Medicine at St Mary’s, 6–9 London W2 1PG, UK chloroform and TTHM was 0.98, between exposure categories. More recent studies H Whitaker BDCM and TTHM 0.62, and between have attempted to measure individual exposure M J Nieuwenhuijsen DBCM and TTHM −0.09. Between zone with routinely collected THM measurements M B Toledano variation was larger than within zone combined with a measure of ingestion such as P Elliott variation for chloroform and BDCM, but number of glasses or water drunk per day.10–13 N Best not for DBCM. There was only little Misclassification of exposure as a result of North West Water, seasonal variation (<3%). Monthly varia- crude exposure assessment may lead to biased Thirlmere House, tion was found although there were no risk estimates, which makes it more diYcult to Lingley Mere, Great consistent trends within years. interpret the studies.14 Sankey, Warrington Conclusion—In an area where the TTHM Trihalomethanes (THMs), and many other WA5 3LP,UK M Wilkinson concentrations were less than half the disinfection byproducts of chlorination, are statutory limit (48 µg/l) chloroform formed when chlorine reacts with naturally Warren Associates, formed a high proportion of TTHM. The occurring organic substances present in water. 8 Prince Maurice results of the correlation analysis suggest They are generally the most common byprod- Court, Devizes, that TTHM concentrations provided a ucts. It is thought that THM concentrations Wiltshire SN10 2RT, good indication of chloroform concentra- vary both temporally and spatially.15 16 In the UK J Fawell tions, a reasonable indication of BDCM water company under study much of the supply concentrations, but no indication of is upland surface water, which has higher con- Correspondence to: DBCM. Zone means were similar over the centrations of THM precursors than water Dr M J Nieuwenhuijsen years, but the maximum concentrations drawn predominantly from aquifers. Surface [email protected] reduced considerably, which suggests that water sources are more likely to produce chlo- Accepted 14 March 2001 successful improvements in treatment rinated THMs, whereas treated water from www.occenvmed.com 448 Keegan, Whitaker, Nieuwenhuijsen, et al Occup Environ Med: first published as 10.1136/oem.58.7.447 on 1 July 2001. Downloaded from ground water sources can produce higher con- water are measured in samples from randomly centrations of brominated THMs. selected taps in each water zone. The sum of Water companies in the United Kingdom the concentrations of the four individual divide the area under their control into water THMs is the TTHM concentration. Under the supply zones, hydraulically defined in such a Water Supply (Water Quality) (1989) Regula- way that the quality of drinking water on entry tions, the water companies are required to col- to a zone would be the same for all consumers lect four samples/year/water zone. The statu- within that zone. These zones form the basis tory limit for TTHMs is 100 µg/l as a rolling 3 for monitoring the water quality of drinking month average. Exceedance of the limit water so they define populations of consumers requires monthly measurements to be taken to which routinely collected water data can be until the TTHM concentrations decrease. In related. The water in each water zone is tested many zones monthly measurements are taken a minimum of four times a year to comply with routinely for operational purposes. the TTHM regulatory standard. Of all the dis- infection byproducts, only THM concentra- WATER SUPPLY (OR COMPLIANCE) ZONES tions are currently regulated, although they are Water zones diVer in area, in the number of not the only class of disinfection byproduct people each serves, and in the volume of water suggested as having adverse reproductive passing through each per day. Small, rural eVects. Haloacetic acids, haloacetonitriles, and zones may serve 300 people 70 kl per day, acetonitriles have also been implicated.317 whereas others may deliver as much as 16 000 To assess the eVect of THM exposure kl per day to 50 000 people. The main water concentrations on certain reproductive out- sources in the area are Thirlmere and Ullswater comes, routinely collected quarterly (seasonal) in the Lake District. Only 6% of zones are sup- THM concentrations could be attached to a plied exclusively by groundwater. The number pregnancy trimester of women living in the of water zones may change. In north west Eng- water zone, but such exposure information land during 1992 there were 313 zones, in would generally be based on only one measure- 1993 316, in 1994 317, in 1995 and 1996 323. ment, and given the variation in exposure, that Some of the new zones were created whole, might be unreliable. Annual averages would whereas some were split from existing zones. It provide more precise THM means, but would was decided to omit the data from all zones be based on perhaps four measurements and created after 1992, from all zones created from might not reflect exposure for any 3 month existing zones, and from the zones from which period within that year. A 5 year average THM these were split. Only zones in which bounda- concentration would be based on more meas- ries and source did not change over the study urements (between 20 and 60), but might be period and for which 5 years’ worth of data insensitive to timing of exposures relevant to were available were included. For the statistical birth outcomes. analysis, this left 288 water zones supplied by The purpose of this study was to explore 194 treatment works, serving about 6.8 million routinely collected THM data for use in epide- people. http://oem.bmj.com/ miological studies and to determine the best measure of THM exposure. The specific aims LABORATORY ANALYSIS of this study were to examine; (a) the current Water samples were analysed by the water exposure concentrations of TTHM and indi- company with a capillary gas chromatograph vidual THMs in tap water in the north west with an electron captive detector. The detec- area, (b) the correlation between TTHMs and tion limit was 2.5 µg/l for all THMs. The water individual THM concentrations, (c) the vari- company runs internal and external quality ability of total and individual THM concentra- control tests and is accredited by the United on September 30, 2021 by guest. Protected copyright. tions between and within zones, seasons, Kingdom Accreditation Service (UKAS).
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