Environmental Engineering Reference
In-Depth Information
4 weeks before birth [hazard ratio (HR) = 1.13; 95 percent con
dence interval (CI),
0.95
1.35]. However, women who depended on a governmental source of payment
for prenatal care were at increased risk when exposed at such levels late in gestation
(HR = 1.39; 95 percent CI, 1.06
-
1.81). In contrast, exposure to high levels of total
THMs during the second trimester and high exposure throughout pregnancy
resulted in a 15
-
18 percent reduction in risk for preterm delivery in this population.
In addition to the risk of preterm births, a published Birmingham University
study is even more disturbing: Hwang et al. (
2008
) suggest that drinking tap water
containing total THMs while pregnant may double the risk of serious health defects
in the unborn child. The authors conducted a population-based cross-sectional study
of 396,049 Taiwanese births in 2001
-
2003 using information from the Birth
Registry and Waterworks Registry. They compared the risk of eleven most com-
mon speci
-
c defects in four disinfection byproduct exposure categories based on
the levels of total THM representing (1) high (total THMs 20 +
g/L), (2) medium
μ
(total THMs 10
-
19
μ
g/L), (3) low exposure (total THMs 5
-
9
μ
g/L), (4) very low
exposure (0
g/L) as the reference category. In addition, they also carried out a
meta-analysis of the results from the present and previous studies focusing on the
same birth defects. In summary, their results show:
-
4
μ
(1) For the risk of ventricular septal defects, the adjusted odds ratio was 1.81, with
the 95 percent con
dence interval being 0.98
3.35 compared to the reference
-
category;
(2) For cleft palate, the adjusted odds ratio was 1.56, with the 95 percent confi-
-
2.41, compared to the reference category;
(3) Anencephaly is a birth defect in which a baby is born without a major portion
of the brain, skull, and scalp. The odds ratio for anencephaly was 1.96, with
the 95 percent con
dence intervals being 1.00
-
dence being 0.94
4.07, compared to the reference
-
category.
(4)
In the meta-analysis, their summary odds ratio for ventricular septal defects
was 1.59, with the 95 percent con
dence intervals being 1.21
2.07.
-
9.2.3 Changes in Blood Levels
It is interesting that research indicates that exposure to showering and washing may
be worse than drinking chlorinated water, if whole blood levels of THM are
measured (Backer et al.
2000
; Nuckols et al.
2005
). Backer et al. found that the
highest levels of THMs in the blood were found in people who took a ten minute
shower and the lowest levels were found in blood samples from people who drank 1
liter of water over a 10 min period. Drinking of one liter of water increased blood
THMs by less than 10 percent of the increase resulting from showering or bathing
for 10 min. Like other volatile organic compounds, there is evidence that the THMs
may bioaccumulate in the body (Ashley and Prah
1997
).
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