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The PCB Baby Studies -
Part 3
(PCB effects are summarized at the top of each study.)
The Canadian Hudson Bay Study---
PCB exposure through fish & marine mammal consumption
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decreased male birth length
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immune system suppression
A Canadian study of Inuit (Eskimo) women from Hudson Bay
indicated very high levels of PCBs and DDE in breast milk (Dewailly et
al. 1989). These results prompted an examination of the health status of
Inuit newborns (Dewailly et al. 1993a).
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Newborns --- Correlation analysis revealed a statistically
significant negative association between male birth length and levels of
PCBs, dioxins, furans, hexaclorobenzene, and mirex in the fat of mothers'
milk. No significant differences were observed between male and female
newborns for birth weight, head circumference, or thyroid-stimulating hormone.
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6 to 12 Months Later --- Immune system effects were
observed in Inuit infants who were believed to receive elevated levels
of PCBs and dioxins from their mother's breast milk; they demonstrated
a decline in the ratio of the CD4+ (helper) to CD8+ (cytotoxic) T-cells
at ages 6 and 12 months (but not at 3 months) (Dewailly et al. 1993b).
The Sheboygan River Study,
Wisconsin--- PCB exposure through fish consumption
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immune suppression --- increased infections
The Wisconsin Maternal and Infant Cohort Study on the Sheboygan
River also investigated the association of maternal exposure to toxic substances
and adverse health effects in infants (Smith 1984). The Sheboygan River
is a Superfund site contaminated due to dumping of PCB oil wastes.
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Newborns --- Results from this study indicated an
association between maternal serum PCB levels and the number and type of
infectious diseases suffered by their infants. The categories of infectious
diseases included colds, earache, and flu symptoms. The author concluded
that exposure to PCBs in the womb resulted in an increase in the number
of illnesses in infants during the first 4 months of life. However, the
design of this study prevented access to either umbilical cord blood or
infant serum acquired immediately after birth to analyze for the presence
of PCBs. Therefore, the issue of exposure was presumed and not actually
addressed. (Swain 1991).
PCB Effects on Fetal Tissue---
Laboratory Study
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thymus gland damage
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immune system suppression
| This study of human fetal tissue (grown in a culture
dish) found that one type of PCB (called TCB) causes atrophy of the thymus
gland and suppression of the immune system, the former possibly causing
the latter. Details: TCB (3,3',4,4'-tetrachlorobiphenyl) binds to the cytosolic
aryl-hydrocarbon receptor (AhR) and transforms it into a DNA-binding state.
The development of fetal thymocytes is severely affected by TCB and other
AhR-binding xenobiotics, leading to a skewed pattern of thymocyte maturation
stages. Murine thymocyte proliferation after exposure to TCB was studied
in fetal thymus organ culture (FTOC). C57BL/6 fetus thymic lobes from day
15 of gestation were explanted and grown for 2, 4, 6, and 8 days in organ
culture in the presence or absence of 3.3 microM TCB. Subsets of
thymocytes were defined by CD4 and CD8 surface markers, and their cell
cycle was analyzed by DNA staining with 7-amino-actinomycin D (7-AAD).
Exposure of fetal thymi in vitro to 3.3 microM TCB significantly reduced
the total number of thymocytes, and fewer thymocytes were in S/G2M phase.
The inhibition of cell proliferation induced by TCB treatment affected
mainly the CD4-CD8- (double-negative, DN) and CD4-CD8+ (single-positive,
SP) subsets, and these inhibition appeared mainly in more immature thymocytes,
i.e. DNCD3- and CD8+CD3- subpopulations, whereas no effect of TCB on CD4+CD8+
(double-positive, DP) cell proliferative activity was observed. Analysis
of the relation of cell proliferation and development of subsets in differentiating
fetal thymocytes suggests that TCB enhanced thymocyte differentiation into
mature CD8+ cells. (Lai et al, 1994) |
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The Lake Ontario Birth Study
--- New York --- PCB exposure through fish consumption
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PCBs were not associated with miscarriages (sudden fetal
death)
Spontaneous fetal death (SFD) has been observed following
exposure to PCBs in various mammalian species. SFD was assessed in relation
to consumption of PCB-contaminated Lake Ontario sport fish among 1,820
women from the New York State Angler Study, 1990-91. Fish consumption was
obtained from self-administered food frequency questionnaires and history
of SFD from live birth certificates. A group of 979 women who had never
eaten Lake Ontario sport were classified as unexposed [this may not be
an accurate assumption]; while 841 women reported various levels of exposure.
Analyses were stratified by gravidity; and smoking and maternal age were
controlled. No significant increase in risk for SFD was seen for lifetime
PCB exposure based on species-specific PCB levels, years of fish consumption,
current or lifetime estimates of kilograms of fish consumed. A small risk
reduction was seen with increasing years of fish consumption for women
with four or more pregnancies (odds ratio = 0.97; 95% confidence interval
= 0.94-0.99). These findings do not support an increased risk of SFD with
consumption of PCB-contaminated sport fish. (Mendola, 1994) Note:
no PCB blood or tissue samples were taken, therefore PCB exposures or non-exposures
were assumed, and this could skew the results.
The New York Prematurity Study---
at background PCB exposure levels
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no association between PCBs and premature births
Maternal serum levels of DDE and polychlorinated biphenyls
(PCB) and their congeners were compared for 20 women who had a spontaneous
preterm delivery and 20 matched women who had delivered at term at Mount
Sinai Medical Center in New York between October 1990 and August 1993.
Since no substantial case-control differences were evident, these findings
do not indicate that increased DDE or PCB levels are associated with spontaneous
preterm birth. (Berkowitz et al, 1996) Small sample size, at background
levels of PCBs.
The Baltic Sea Study, Sweden---
PCB exposure through fish consumption
The purpose of this study was to assess reproductive outcomes,
especially birthweight, and the consumption of fatty fish from the Baltic
Sea, contaminated with persistent organochlorine compounds, including PCBs,
among women from the Swedish east coast. Groups of fishermen's wives from
the Swedish east and west coasts were established and linked to the Swedish
Medical Birth Register for 1973-1991; 1501 children were born in the eastcoast
group and 3553 in the westcoast group. Comparisons were made with regional
populations and between the groups. Dietary interviews were made with 69
randomly selected women from the groups and 69 referents. The women interviewed
from the east- and westcoast groups ate locally caught fish more than twice
as often as their referents. Compared with the regional population, the
women in the eastcoast group gave birth to an increased number of infants
with low birthweights (< 3000 g), whereas the opposite was seen in the
westcoast cohort. Infants in the eastcoast cohort had significantly lower
birthweights than infants from the westcoast cohort (median 3530 versus
3610 g, P < 0.001). Even after adjustment for potential confounders,
eastcoast affiliation showed an increased risk for low birthweight (odds
ratio 1.44, 95% confidence interval 1.18-1.76). The effect was more conspicuous
for boys (odds ratio 1.95) and heavy smokers (odds ratio 3.00). The present
data support, but do not prove, an association between a high consumption
of contaminated fish from the Baltic Sea and an increased risk for low
birthweight. (Rylander et al, 1995)
The New York Occupational
Study --- occupational PCB exposure
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shorter gestation period
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lower birth weight
An occupational health study conducted in New York also investigated
the relationship of PCB exposure to birth weight and gestational age in
356 infants of mothers occupationally exposed to PCBs during the manufacture
of capacitors in upstate New York. Two groups of women were investigated:
a) the direct exposure group (worked in job areas with direct exposure
to PCBs during the manufacturing process) and b) indirect or low exposure
group.
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Newborns --- The results included a decrease in gestational
age (6.6 days) and a reduction of birth weight (153 grams) in infants of
mothers directly exposed to PCBs, when compared with infants of other mothers
employed in the same facility but not directly exposed to PCBs. (Taylor
et al, 1984)
The researchers conducted a follow-up study of 405 women
in this occupationally exposed population. Estimated serum total PCB levels
in women with direct-exposure jobs were more than four-fold higher than
for women in indirect-exposure jobs. After adjustment for confounding variables
a significant decrease was found in birth weight and gestational age associated
with higher PCB levels in the mothers. These results were similar to the
earlier findings reported by the Jacobsons. (Taylor et al, 1989) The authors
also stated that the magnitude of these effects was quite small and the
clinical significance of these results was questionable.
The New York Ecologic
Epidemiologic Study --- at background PCB exposure levels
A much weaker ecologic epidemiologic study was conducted
within the Great Lakes drainage basin of upstate New York (Kagey and Stark,
1992) to study whether "maternal residence within the Great Lakes drainage
basin from 1968-1987 adversely impacted birth weight, gestational age,
and congenital anomaly rates of their offspring." In defining the exposure
area as the Great Lakes drainage basin, it was assumed that potential exposure
to contaminants was through inhalation of specific contaminants that evaporated
from the lakes, consumption of sport fish, home garden produce, and drinking
water from the lakes or sources within the basin. Results: the mean birth
weight of infants born within the Great Lakes drainage basin was comparable
to the mean birth weight of infants born outside the basin: 3,313 versus
3,319 grams, respectively. However, mothers residing in counties directly
adjacent to the Great Lakes gave birth to infants who weighed 28 grams
less than infants born to mothers who resided in nonadjacent areas. The
study found no differences in gestational age. Differences in congenital
anomaly prevalence rates were also difficult to detect because of changes
in coding and reporting practices over time. The authors concluded that
the two major limitations of ecologic epidemiologic studies were the lack
of individual measurements on PCBs or other exposure or outcome, and the
inability to control for confounding variables.
The Wasserman Study---
at background PCB exposure levels
This study found a positive correlation between higher PCB
concentrations in the mother and lower birth weight babies. (Wasserman
et al 1982).
The Green Bay Study, Wisconsin---
at background PCB exposure levels
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increased birth weight
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no adverse effects at low PCB exposure
Another Wisconsin Maternal and Infant Study examined Great
Lakes fish consumption and reproductive outcomes in Green Bay (Dar et al.
1992), at the mouth of the Fox River, a nominated Superfund site due to
serious PCB contamination from 7 paper and paper- recycling companies.
In this prospective study 1,112 women who were seen at the time of a positive
pregnancy test were asked to complete a questionnaire on fish consumption,
health and reproductive history, and other relevant issues, and to provide
blood samples for PCB analysis. After the pregnancy, the following reproductive
outcomes were abstracted from hospital labor reports and measured: fetal
wastage and stillbirths, birth weight, birth length, head circumference,
ponderal index, and birth weight percentiles for live births.
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Newborns --- The typical negative associations between
birth size measures and confounding variables, (i.e., consumption of caffeine
and alcohol, and smoking) were found. Birth size was positively associated
with gestational age, birth order, weight gain during pregnancy, male babies,
and rural residence. However, contrary to expectations, a positive association
was found (p<0.044) between birth size and PCB exposure (via sport fish
consumption) for most mothers (the exception being those mothers who gained
more than 34 pounds during pregnancy).
Serum PCB levels were performed on 106 women in this group,
and a positive correlation (Pearson p = 0.666) was found between the amount
of Lake Michigan fish mothers reported to consume and their PCB serum levels
(Dar et al. 1992). The PCB concentration was based on the sum of 13 individual
congeners; only 5 of 13 PCB congeners were identified in maternal serum.
Also, only 23 percent of the study group had PCBs above the detection limit
of 0.6 ng/ml for each congener. Additionally, the consumption of highly
contaminated sport fish was very low in this group. The authors concluded
that the Green Bay mothers were exposed to very low levels of PCBs, compared
with exposures in other studies (e.g. Fein et al. 1983,1984). This low
estimated level of exposure does not appear to have had a negative effect
on birth size. The authors also suggest that if adverse reproductive effects
occur in infants because of maternal fish consumption, perhaps there is
a threshold effect below which there are no negative effects.
Additional criticisms of this study: the mothers
were middle-class or more affluent women who visited area clinics and would
be better-educated about PCB risks. They ate very few or no local fish.
They weren’t from the highly exposed lower-income families who use Fox
River fish for subsistence. This study also did not test the babies for
changes in behavior or intelligence. Also, the 13 PCB congeners chosen
for analysis were not the most toxic types of PCBs, and the blood samples
with no PCBs detected were not properly factored into the statistical analysis.
Because so few women in the study ate fish, the researchers resorted to
reworking the exposure categories for low, medium and high PCB exposure
--- which resulted in them ranking one meal every month or two as "high
exposure." In a Catholic town like Green Bay with a traditional Friday
Night Fish Fry, this would not be considered heavy fish consumption.
The Duesseldorf Germany
Study--- at background PCB exposure levels
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neurological damage --- reduced cognitive development, reduced
prespeech level of articulation, reduced mental and psychomotor abilities
Several studies were conducted on up to 171 mother-infant
pairs in Duesseldorf to determine the effects of regular background
levels of PCB contamination. The studies sampled for a very limited
set of PCB types, and found PCB effects only associated with elevated PCBs
in breastmilk fed to the babies.
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At 7 Months --- Results from the German (Duesseldorf)
cohort covering 171 healthy mother-infant pairs are given. The sum of PCB
congeners 138, 153 and 180 (sigma PCB) in cord plasma and maternal milk
was used to describe neonatal PCB exposure. Mean sigma PCB-concentrations
were 0.55 ng/ml in cord plasma and 427 ng/g fat in breastmilk. This report
covers the Bayley II mental (MDI) and psychomotor development index (PDI)
as well as the Fagan Test of Infant Intelligence (Visual Recognition Memory)
taken at 7 months of age in relation to neonatal sigma PCB. After confounder-adjustment
significant negative associations were found between sigma PCB in milk
and MDI (P < 0.05), whereas the other associations proved insignificant.
(Winneke et al, 1998)
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At 7 Months --- The possible effects of PCB-exposure
on prespeech development were explored. Data were collected in 163 seven
months olds from the Duesseldorf area. PCB-concentrations (138, 153 and
180) were measured in cordblood and maternal milk. Vocalizations were video
recorded for 10 minutes. Based on nonvegetative comfort utterances only,
the total time of vocalization (i.e. Articulation Activity: AA) and the
Articulation Level (AL) were determined. AL was judged by a 5-point Behaviorally
Anchored Rating Scale with category representing the lowest and category
5 the highest level. Prototypes were checked to fulfill the requirements
of the corresponding category by high resolution FFT-spectrography, band-limited
analysis, and listening. AL-scoring was based on comparison with prototypes.
Interrater reliability was r = .98 for AA and r = .95 of AL. PCBs in milk
and AL were negatively associated (r = -.17; p = .06 two-tailed). The result
suggest, that - using PCB-exposure as an environmental model - the level
of articulation as a highly reliable measure might be a sensitive indicator
for a subclinical delay of development. (Wiener et al, 1997)
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2.5 Years Old --- Associations between environmental
exposure to PCBs and mental and psychomotor development were examined.
Data were collected at age 30 months in 140 children from the Duesseldorf
area. PCB-concentrations (138, 153, 180 and sigma of congeners) were measured
in cord plasma and maternal milk (two weeks' samples). At age 30 months
mental and psychomotor abilities were examined using the Bayley Scales
of Infant Development (BSID II). After control for relevant confounders
no significant association was found between PCBs (sigma and single congeners)
measured in cord plasma and the BISD II, but significant negative associations
occurred between PCBs in breastmilk (sigma of congeners) and the BSID II
mental and psychomotor scales. Additionally, negative associations between
PCB congeners 138 and 180 on the one hand and the BISD II scales on the
other were statistically significant, too. These results suggest, that
child development at this age is negatively influenced by neonatal PCB
exposure. Background PCB concentrations are associated with poorer cognitive
and psychomotor functioning in young children. (Walkowiak et al, 2000)
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3.5 Years Old --- Developmental effects of environmental
PCB-exposure were examined in 121 children of the Duesseldorf group at
age 42 months. PCB-concentrations (138, 153, 180 and sigma of congeners)
were measured in cord plasma, breastmilk and infants plasma. Cognitive
functions were assessed using the Kaufman-Assessment Battery for Children
(K-ABC). The K-ABC consists of the Sequential (SEQ) and Simultaneous Processing
(SIM) subscales which are combined to form the Mental Processing Composite
(MPC). The neurological condition was assessed using the Neurological Optimality
(NOS) concept (Touwen/Hempel). After control for relevant confounders,
no significant associations were found between cordblood-PCBs (sigma) and
the K-ABC. As for breastmilk, significant negative associations were found
between sigma PCBs and the MPC and SEQ, respectively. Borderline negative
associations were found between PCBs (sigma) and SIM, whereas the association
with PCB 138 was significant. Regarding plasma from 42-months-old children,
significant negative associations were found between sigma PCBs and the
MPC. After control for sigma PCBs in cord plasma no significant effect
remained. Regarding the NOS, no significant PCB effects were found. These
observations corroborate negative associations between cognitive development
and neonatal PCB-exposure as reflected in early milk-samples. An additional
postnatal impact of background PCB-exposure is uncertain. (Wundram et al,
2000)
The New Bedford, Massachusetts,
Study --- PCB exposure through fish consumption
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neurological damage --- impaired visual memory
Researchers have been studying a group of mother-infant pairs
who live in four communities adjacent to a Superfund site, the New Bedford
Harbor and estuary in southeastern Massachusetts, known to be significantly
contaminated with PCBs. Out of 122 mothers, they identified four women
who had high breast milk levels of PCBs.
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Newborns --- Results of the preliminary data analyses
indicate that infant visual memory (assessed by the Fagan Test of Infant
Intelligence, which is predictive of cognitive performance in later childhood)
may be impaired by PCB exposures in the womb. (Korrick et al, 1998)
The estimated total PCBs ranged from 1,100 to 2,400 ng/g
milk fat in these four women, compared with an overall mean of 320 ng/g
milk fat for the total group. The PCB congener profile and history of one
of the four women was consistent with past occupational PCB exposures,
but the sources of PCB exposure for the other three women were not as easy
to identify. Environmental exposures such as those of fish consumption
were likely, whereas residence adjacent to a PCB-contaminated site was
considered an unlikely exposure source.
The Croatian Study ---
at background PCB exposure levels
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neurological damage --- impaired neurodevelopmental competencies
or inappropriate arousal reaction
Organochlorine compounds in milk were analyzed in samples
collected over a nine-year period (1987-1995) from 139 nursing mothers
whose children were hospitalized for various disorders. All samples contained
p,p’-DDE and PCBs; the median concentrations were 318 micrograms/kg milk
fat and 220 micrograms/kg milk fat resp. Higher levels were found in 12
mothers nursing children with impaired neurodevelopmental competencies
or an inappropriate arousal reaction. No difference was observed between
mothers nursing children with respiratory or gastrointestinal diseases,
urinary tract infections or other infectious diseases, anemias, prolonged
neonatal hyperbilirubinaemias or when children were with dermatological
findings, congenital malformations or healthy. (Krauthacker et al, 1998)
The Collaborative Perinatal
Project --- at background PCB exposure levels
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no intelligence loss in 7-year olds
This study evaluated prenatal PCB exposure in relation to
children's cognitive test scores in a large study. The Collaborative Perinatal
Project (CPP) was designed to identify determinants in neurological deficits
in children. Pregnant women were recruited from 12 US study centers from
1959 to 1966, and the children were followed until age 7. CPP third trimester
serum was analyzed for 806 women selected at random and for an additional
96 women whose children had either a low or high IQ score. Sera were assayed
for 11 specific PCBs at the Centers for Disease Control and Prevention.
Cognitive functioning was measured at age 7 using the Wechsler Intelligence
Scale for Children (WISC). Weighted likelihood estimation was used to examine
the association between total PCB levels and WISC IQ, while adjusting for
study center, maternal age, race, serum lipids, parity, socioeconomic status,
and education, and child's age, gender, head circumference at birth, and
breast feeding. Among those in the lowest exposure category (less than
1.5 ug PCB/L serum) the adjusted mean IQ score was 91.7 (standard error,
1.6) and in the highest category (greater than or equal to 5 ug/L) was
97.4 (1.6); the overall trend p (PCB continuous) was 0.2. These data provide
no support for the hypothesis that in utero exposure to background levels
of PCBs is associated with lower IQ scores at age 7. (This study sampled
for only 11 of the 209 kinds of PCBs and may have missed the types of PCBs
linked with IQ effects.) (Gray et al, 2000)
The Tobacco Smokers Study---
at background PCB exposure levels
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mother’s active or passive smoking increases baby’s PCBs
PCBs and hexachlorobenzene (HCB) are ubiquitous compounds
that have tumor-promoting properties if applied together with tobacco-specific
carcinogens. It was the purpose of this study to investigate whether parental
smoking by itself will increase the prenatal uptake of such organochlorine
compounds. With the informed consent of the parents, blood samples were
taken from 80 full-term newborns before the first oral feeding. Six types
of PCBs and HCB were analyzed with capillary gas chromatography. Information
about parental smoking behavior, the geographic origin of the parents,
and their actual and previous working places was recorded. The researchers
composed three study groups for statistical analyses: 12 active smoking
mothers, 33 passive smoking mothers, and 35 nonsmoking families. Babies
born to active smoking mothers had the highest PCB and HCB concentrations
compared with children of passive or nonsmoking mothers. These differences
were statistically significant for both PCBs and HCB. Newborns of passive
smoking mothers had higher PCB and HCB concentrations than children of
nonsmoking families but lower values than those of active smoking mothers.
It is concluded that active and passive maternal smoking increases a baby’s
burden with PCB and HCB. (Lackmann et al, 2000)
The Michigan Girls Study---
at background PCB exposure levels
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reduced long-term growth
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increased weight (body mass index)
Growth alterations are among possible delayed effects of
a baby’s environmental chemical exposure. Accidental contamination of the
Michigan food supply with polybrominated biphenyls (PBBs) led to the exposure
of more than 4000 individuals in 1973 and subsequent formation of the Michigan
PBB registry. This registry contains archived measurements of blood serum
PBB and the ubiquitous environmental contaminant, polychlorinated biphenyl
(PCB). These chemicals are suspected of disrupting endocrine function;
therefore, The researchers assessed current body mass index (BMI) and height
in 308 females 5 to 24 years of age born to exposed mothers. Daughters
were exposed to the chemicals in their mother’s womb and in many cases
through breastfeeding. In utero PBB exposure was estimated by using initial
maternal serum PBB and a model of PBB elimination. Initial maternal serum
PCB level was used as the estimate of PCB exposure since maternal PCB exposure
was ongoing. Self-reported weight and height were obtained by a mailed
questionnaire for daughters 5 to 17 years of age and by telephone interview
in daughters 18 years of age and older. The potential associations were
modeled with multivariate techniques. Modification of the associations
by exposure after birth was also assessed. The researchers did not find
an association between estimated in utero PBB and either current BMI or
height; however, estimated in utero PCB exposure above 5 parts per
billion was related to reduced current BMI. The addition of more PCBs through
breastfeeding after the girls were born appeared to make no difference.
While PBB results were null, this study provides evidence that a baby’s
exposure to PCBs in the womb may have long-term effects on growth. (Blanck
et al, 2000)
The Slovenia Study ---
PCB exposure through regional contamination
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enamel damage on baby’s permanent teeth
The aim of this study was to evaluate the effects of long-term
exposure to PCBs on developing tooth dental enamel in children. A total
of 202 8- to 14-year-old children who were pre- and post-natally exposed
to PCBs in the contaminated region of Bela Krajina, Slovenia, were studied.
202 controls from Brsljin were matched for age and sex. Risk assessment
was based on the concentrations of toxic PCB congeners in the diet. Levels
of PCBs in dentine were used to validate exposure. PCB levels were analyzed
by high-resolution gas chromatography. The prevalence of developmental
defects of enamel was assessed using the FDI Index. Developmental defects
of enamel in permanent teeth were found in 71.3% of exposed children,
compared to 49.5% in the control group. The enamel was abnormal in 21.9%
of the permanent index teeth of exposed children and in 12.7% of the control
children. The difference was statistically significant (chi(2) = 84.18;
p = 0.0019), mostly on account of demarcated opacities and hypoplasia.
The extent of the defects was also greater in the exposed group (chi(2)
= 61.3; p = 0.0001). No significant correlations were found between PCB
exposure and developmental defects in deciduous teeth (temporary baby teeth).
In conclusion, our results showed that long-term exposure to PCBs may cause
developmental defects of enamel. (Jan et al, 2000)
The Faroe Islands Study---
PCB exposure through fish & marine mammal consumption
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neurological damage --- memory and attention deficits
This study was designed to assess the neurological and behavioral
consequences for babies after exposure to methyl mercury in the mother’s
womb. The Faroe Islands are 18 separate small islands north of the British
Isles in the north Atlantic Ocean., with a population of about 50,000 people.
Fishing and whaling are important parts of their culture. Maternal exposure
to mercury was through consumption of fish and intermittent higher-level
exposure through pilot whale meat, while consumption of whale blubber also
resulted in the mothers’ exposure to PCBs. Analysis of the neurobehavioral
domains affected revealed impairment in attention, memory, and performance
on visuospatial tasks, auditory impairment, and to a lesser extent motor
impairment. For four of the eight tasks affected by MeHg exposure, impairment
was also correlated with in utero PCB exposure as measured by cord tissue
PCB levels (p less than .10). While MeHg-PCB interactions were not identified
in the statistical analyses, the study was not designed to optimize identification
of interactive effects. Cross-sectional studies in a smaller number of
children in the Amazon and Madeira by the same group of investigators,
in which average MeHg maternal hair levels were about twice as high those
in the Faroe Islands, identified auditory, visual, and/or visuospatial
deficits, with no evidence of deficits in attention or memory. While the
results of the cross-sectional studies must be interpreted with caution,
the data provide circumstantial evidence that some effects observed in
the Faroe Islands study may result from exposure to PCBs or PCBs plus methylmercury,
particularly when the pattern of effects identified in other PCB studies
are taken into consideration. (Rice, 2000)
PCBs and Mercury Combined Effects---
Laboratory Study
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PCBs and mercury together are more toxic than if present
separately
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PCBs reduced dopamine levels, and much more so when present
with mercury
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PCBs and mercury together increased free intracellular calcium
This isn’t a study on human babies, but it is significant
because it raises the possibility that PCBs may cause greater health damage
if other toxic chemicals such as mercury are present at the same time.
These New York researchers acknowledge that contaminated fish in the Great
Lakes "contain many man-made neurotoxicants, making it difficult to determine
which are responsible for observed deficits in children." Therefore, the
scientists did a series of experiments, using both striatal tissue obtained
from adult rats and cerebellar granule cells obtained from newborn rats,
to determine the active toxicants by initially comparing the neurotoxic
effects of two fish-borne contaminants --- PCBs and methyl mercury. Striatal
punch dopamine (DA) content was reduced in a dose dependent manner following
exposure to a commercial mixture of PCBs at media concentrations greater
than 10 ppm, but not following exposure to MeHg, at media concentrations
ranging from 4 to 14 uM. Decreases in DA content were significantly
greater than additive following exposure to both contaminants. In other
words, the combined toxic effects were more than just the sum of the individual
effects of PCBs or Mercury. Intracellular calcium concentrations in cerebellar
granule cells were determined using flow cytometry and the calcium sensitive
dye Fluo-4 and were elevated following exposure to the ortho-substituted
PCV congener 2,2' (1 to 10 uM) or MeHg (1 to 2.5 uM). The increases were
significantly
greater than additive following exposure to both contaminants. The
researchers suggest that: (i) the significant synergism between these two
contaminants may involve an elevation of free intracellular calcium and
(ii) fish-consumption guidelines may need to consider these interactions.
This study is important to us locally, because both PCBs and mercury are
found in high levels in Fox River sediment and Green Bay. In addition,
many commercial fish, even from the ocean, and most inland lake fish in
Wisconsin are contaminated with mercury. (Mercury is in the muscle tissue,
not the fat, so trimming fat off the fish doesn’t remove mercury.) (Seegal
et al, 2000)
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