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ABSTRACT
In 1995, the Agency for Toxic Substances and Disease Registry (ATSDR)
began data collection for a study of environmental exposure to volatile
organic compounds (VOCs) in drinking water and a variety of adverse pregnancy
outcomes at the U.S. Marine Corps Base at Camp Lejeune, Onslow County,
North Carolina. This study was undertaken following documentation that
environmental exposure to VOCs in drinking water had occurred in the past.
At that time, there was no evidence of an increased rate of adverse pregnancy
outcomes at Camp Lejeune. However, because fetuses tend to be more sensitive
to toxic chemical exposures and many pregnant women had resided in housing
areas supplied with contaminated water, it appeared prudent to research
the topic. This report describes
a study of past exposure to VOC-contaminated drinking water and mean birth
weight (MBW), small for gestational age (SGA), and preterm birth in residents
of base family housing at Camp Lejeune. The results were based on analysis
of live births to women residing in base family housing when they delivered
during the period January 1, 1968, through December 31, 1985. Birth certificates
were studied from 6,117 tetrachloroethylene (PCE)-exposed women, 141 short-term
trichloroethylene (TCE)-exposed women, 31 long-term TCE-exposed women,
and 5,681 unexposed women. The following potential confounders and effect
modifiers were evaluated: sex of infant, maternal and paternal ages, maternal
race, maternal and paternal education, military pay grade, maternal parity,
adequacy of prenatal care, marital status, and year of birth. The influence
of timing and duration of exposure on potential effects was also explored
by linking family base housing records to birth certificate data.
Preterm delivery was not associated
with VOC-exposure in any category. For most live births, including all
births to women younger than 35 years of age with no prior fetal deaths,
there was no association between PCE-contaminated drinking water and MBW
or SGA. For the group as a whole, infants whose mothers resided in PCE-exposed
areas weighed an average of 24 grams (g) less at birth than infants whose
mothers lived in unexposed housing. This difference was too small to be
biologically meaningful. After controlling for potential confounders, the
overall odds ratio (OR) for PCE and SGA was 1.2 (90% confidence limits
[CL]: 1.0, 1.3). These results provide reasonable assurance that PCE-contaminated
drinking water did not affect the birth weight of infants of mothers who
were younger than 35 years of age and had no medical history of fetal death;
this accounted for most base residents exposed to PCE.
Associations between PCE and the study outcomes were observed in two potentially susceptible subgroups: infants of mothers 35 years of age or older and infants whose mothers had histories of fetal deaths. For older mothers, the adjusted difference in MBW between PCE-exposed and unexposed births was -205 g (90% CL: -333, -78), and the adjusted OR was 4.0 (90% CL: 1.6, 10.2) for PCE exposure and SGA. In mothers who had previously had one or more fetal deaths, the adjusted OR for PCE and SGA was 1.6 (90% CL: 1.2, 2.1). In mothers who had previously had two or more fetal deaths, the differences in MBW and SGA between PCE-exposed and unexposed mothers were much larger, but the number of births to women in
this group was fairly small. Because
associations in these subgroups were not anticipated, these results should
be considered exploratory. They are, however, biologically plausible and
deserving of followup.
The TCE-exposed groups were both
small in number. The difference in adjusted MBW between the long-term TCE-exposed
group and the unexposed comparison group was -139 g (90% CL: -277, -1);
the OR was 1.5 (90% CL: 0.5, 3.8) for SGA and long-term TCE exposure. This
increase was entirely attributable to differences in male infants within
the long-term TCE-exposed group. Among males alone, the OR for SGA was
3.9 (90% CL: 1.1, 11.9) and the difference in MBW was -312 g (90% CL: -540,
-85). The short-term TCE-exposed group had a lower prevalence of SGA infants,
and MBW was slightly higher overall in this group compared with the unexposed
group.
The finding and magnitude of reduced
birth weight and increased SGA in males within the long-term TCE-exposed
group is potentially important. However, the small sample size considerably
weakened the evidence for a causal association. Although it is possible
to speculate on mechanisms by which such a sex-based difference might arise,
this difference was unexpected and could not be explained by known mechanisms
of TCE toxicity. These findings warrant followup in a larger TCE-exposed
population.
ATSDR had intended to analyze fetal
death data, but existing records were too incomplete to be useful. In addition
to the main analyses, several substudies were conducted and are presented
in Appendices A and B. Important conclusions from these substudies are
(1) the housing record data were complete and should have provided reasonable
information regarding length of exposure during pregnancy; (2) abstracting
medical records is feasible and might enrich the data quality for the subgroups
of study participants for which associations between VOC-exposure and MBW
and SGA were noted; (3) a limited amount of birth defects data was available
from the birth certificate. These data were inadequate for a formal evaluation
of associations between VOC exposure and birth defects. Alternative approaches
are recommended to study VOC exposure and birth defects if the question
remains an issue of public health interest.
VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER
AND ADVERSE PREGNANCY OUTCOMES
INTRODUCTION
The Agency for Toxic Substances
and Disease Registry (ATSDR) has a broadly defined legislative mandate
to prevent or mitigate adverse human health effects and diminished quality
of life resulting from exposure to hazardous substances in the environment.
Population-based research conducted to identify links between exposures
and specific adverse health effects is a necessary part of this mandate.
One exposure-disease relationship that warrants further investigation is
the association between volatile organic compounds (VOCs) in drinking water
and adverse pregnancy outcomes. Pregnancy outcomes are of particular importance
to populations residing on military bases because such populations include
a high proportion of reproductive-aged individuals.
OBJECTIVES
The primary objective of this retrospective
study was to explore potential associations between previous exposure to
VOCs in drinking water and three adverse pregnancy outcomes at the U.S.
Marine Corps Base at Camp Lejeune, Onslow County, North Carolina, where
tetrachloroethylene (PCE), trichloroethylene (TCE), and 1,2-dichloroethylene
(1,2-DCE) were found in drinking water supplies in the 1980s. The
three pregnancy outcomes were (1) reduced fetal growth, measured as decreased
mean birth weight (MBW) and small for gestational age (SGA); (2) preterm
birth; and (3) late fetal deaths. However, because of incomplete data,
this third outcome could not be determined.
Three secondary objectives of the study were (1) to validate the quality
of housing record information as it was used to assign exposure and duration
of exposure (see Appendix A); (2) to evaluate the feasibility and utility
of reviewing medical records to enhance the study's inferences (see Appendix
B); and (3) to gather existing information on birth defects (see Appendix
B). It was understood from the outset that the third and final objective
would be difficult to achieve because of the limited information regarding
birth defects available from birth certificates. Nonetheless, the potential
relationship between VOCs and birth defects is of such strong public health
concern that an attempt was made to evaluate all existing data.
This page last updated on November 22, 2000
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