Trihalomethane exposures from municipal water supplies and selected congenital malformations.
BACKGROUND
Concerns about potential health effects of trihalomethanes (THMs) have prompted investigations on whether infants whose mothers were periconceptionally exposed to drinking water containing THMs are at greater risk of congenital malformations.


METHODS
We used two large case-control maternal interview studies that were conducted among California deliveries from 1987 through 1991. One study comprised 538 infants/fetuses with neural tube defects (NTDs) and 539 nonmalformed control infants. The second study included an additional 265 infants with NTDs, 207 infants with conotruncal heart defects, 409 infants with orofacial clefts, and 481 control infants. Expert personnel from municipal water companies estimated THM levels for a particular residence and specific periconceptional time period using quarterly monitoring measurements. Estimates were also made for four individual THM levels and for the total THM level.


RESULTS
NTD risk in the first study was inversely associated with total THM exposure. Although the second study did not show the same inverse relationship for NTDs, there were no positive associations of NTDs or the other malformations with total THM as estimated from continuous models. Elevated risks were observed for the lowest category of exposure (1-24 ppb), but risks were either not substantially elevated or were imprecise for higher exposure levels. Thus no evidence was observed for an exposure-response relation.


CONCLUSIONS
Our results do not provide a clear pattern of association between THM exposure and risks of specific congenital malformations. Imprecise exposure measures coupled with a lack of information about other possible sources of THM exposure may have caused associations to be underestimated.
Shaw
Gary M
GM
March of Dimes Birth Defects Foundation, California Birth Defects Monitoring Program, Oakland, CA 94606, USA. gsh@cbdmp.org
Ranatunga
Dilrini
D
Quach
Thu
T
Neri
Eric
E
Correa
Adolfo
A
Neutra
Raymond R
RR
D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000453:epidemiology*; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007407:Interviews as Topic; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects / Q000706:statistics & numerical data*; D011247:Pregnancy; D011256:Pregnancy Outcome; D012307:Risk Factors; D022882:Trihalomethanes / Q000009:adverse effects / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000009:adverse effects / Q000032:analysis*; D014881:Water Supply
D022882:Trihalomethanes; D014874:Water Pollutants, Chemical