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About this book. Explores the latest science on dioxins and other POPs, and their impact on human health. Now in its third edition, Dioxins and.
Table of contents
- DOSE RESPONSE MODELING FOR 2, 3, 7, 8-TETRACHLORODIBENZO-P-DIOXIN | Science Inventory | US EPA
- Dioxins: an overview.
- ISBN 13: 9780471433552
- Account Options
In collaboration with the Vietnamese government, Hatfield Consultants monitored environmental hazards, including heavy metals and organochlorines in the soil of the area surrounding Da Nang airbase, reporting that dioxins are prominent among the hazardous chemicals found there [ 2 ].
They were recruited at birth by obstetricians at district hospitals in Thanh Khe and Son Tra. The criteria for recruitment of mothers at the hospitals were as follows: i mothers must have resided in one of the study districts for a period encompassing at least the duration of their pregnancy; ii mothers must have given birth to full-term babies; and iii there must have been no complications during childbirth.
A total of mother—infant pairs were enrolled at baseline, including mothers that gave birth in the Thanh Khe district hospital in and 82 mothers that gave birth in the Son Tra district hospital in Subsequently, follow-up examinations were conducted at 4 months, 1 year, and 3 years after birth. Of mother—infant pairs at baseline, Fifty-three pairs did not receive a follow-up assessment because they moved to other areas or were absent on test days.
DOSE RESPONSE MODELING FOR 2, 3, 7, 8-TETRACHLORODIBENZO-P-DIOXIN | Science Inventory | US EPA
Thus, the final sample for the analysis included children and 66 children from Thanh Khe and Son Tra districts, respectively , which represented No significant differences were found regarding characteristics or breast milk dioxin levels between participants and drop-outs, or included and excluded participants. Written informed consent to participate in the survey and to publish data was obtained from all mothers according to a process reviewed and approved by the Health Department of Da Nang City.
Information was collected from mothers age, residential history, parity, smoking habits of the mother and other family members, alcohol consumption, education, and family income and the children age at the assessment, gestational weeks, and gender. Physical parameters of the children, including weight, height, and head and abdominal circumferences, were measured at birth and 5 years, and mean SD of measurement values are shown in Table 1.
A breast milk sample was collected from each nursing mother 1 month after birth by hand expression with the assistance of a midwife or medical worker.
The methods and results of dioxin analysis have been described previously [ 3 , 8 ]. Values of congeners with concentrations below detection limits were set to half the detection limit. The examiners were blinded to exposure levels and previous neurodevelopmental outcomes of each subject. During the Movement ABC-2 testing, 5 children refused to cooperate and the final sample for analysis of coordination movement included children, although all children were participated KABC-II.
The MD scale assesses skills such as posting coins, threading beads, and drawing trails. The Bal scale assesses skills such as one-leg balance, walking with heels raised, and jumping on mats. For the total Bal score, we added the three Bal subscale scores.
Dioxins: an overview.
Cognitive functions used in the present study included conceptual thinking, face recognition, number recall, triangles shape matching , word order, pattern reasoning, and hand movements. Scores for conceptual thinking, face recognition, triangles, pattern reasoning, and hand movements for 5-year-olds, and scores for four of these subscales excluding pattern reasoning for 4-year-olds were combined to provide a NVI score. SPSS software Version The concentrations of dioxins in breast milk were base logarithmically transformed to improve normality.
Single variable tests were used to test significant difference among exposure groups. The results split by gender are shown in Table 1. Additionally, there was no significant difference in Movement ABC-2 scores among the three TCDD exposure groups in children of any gender data not shown. Subsequently, NVI scores were compared between the three TCDD exposure groups in children of 5 years or older, as NVI score is assessed differently in 5-year-olds, including the pattern reasoning assessment.
The cutoff of 2. In boys, face recognition scores were lower in the high TCDD exposure group, but this difference was not significant. These results suggest that decreased pattern reasoning scores were the biggest contributor to decreased NVI scores in boys.
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We used the guidebook for each assessment to define cutoff values for being at risk of neurodevelopmental impairment. For the Movement ABC-2, this was the 15 th percentile of the general population 67 points [ 15 ]. These rates were significantly higher compared with children at no risk for impairment Table 5. However, none of these effects were found for girls.
Indeed, children with DCD often show delays in achieving motor milestones when they are younger [ 19 ]. The Movement ABC is a widely used test of motor skills for school-age children, and is also used to detect motor outcomes of children exposed to environmental pollutants. Roze et al. These motor effects may arise from a common mechanism in the brain, as high TCDD exposure has previously been shown to increase autistic traits at 3 years of age [ 11 ].
These results suggest that such exposure might increase the risk of motor coordination difficulties specifically. This might be caused by alteration of reaction time of visual processing due to impairment of myelination in the central nervous system [ 25 ]. Our results provide a new perspective on adverse health effects of perinatal dioxin exposure in preschool children, as increased risk for DCD resulting from dioxin exposure has not previously been reported.
To examine cognitive abilities of children, we used the NVI of KABC-II to derive a total global scale score, because only this scale was validated for a non-English-speaking population. This suggests that poor planning ability is related to increased TCDD exposure. Scores for face recognition were also lower in boys in the high TCDD exposure group, although the difference in scores was not significant compared with low TCDD groups. These findings suggest that poor cognitive ability observed in the present subjects might be similar to that in children with ASD, who have difficulties in planning and face recognition [ 26 ].
However, in the present study conducted at 5 years of age, boys in the higher TCDD group with a lower cutoff value of 2. Since testing for higher cognitive abilities is more appropriate at 5 than at 3 years old, we suggest that we have detected mild effects of dioxin exposure on cognitive ability in boys exposed to moderately increased TCDD. Future investigations are required to investigate whether the present cohort shows deficits similar to those in children with ASD in higher cognitive abilities, such as executive functions, including planning and theory of mind [ 27 ].
A Dutch cohort study of school-age children reported an inverse relationship between dioxin exposure and both visual motion processing and cognition [ 28 ], but no relationship between dioxin exposure and neurodevelopmental test results, including IQ [ 25 ].
ISBN 13: 9780471433552
This suggests that effects of dioxin exposure on cognitive functions in children might only be evident in specific higher brain functions. Consequently, they can only be detected by specific psychological tests and neurophysiological examinations, but not by general developmental tests.
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Therefore, we are planning to follow-up these children and assess alterations in specific higher cognitive functions, using neurophysiological tests such as EEG responses to visual and auditory stimuli. These results suggested that perinatal TCDD exposure influences social brain function, a higher brain function, that is also observed in children with ASD.
Moreover, Endo et al. These higher brain function deficits were indicated to be accompanied with alteration of neuronal activity in the medial prefrontal cortex and amygdala of the limbic system of mice brains [ 31 ]. These reports are consistent with our finding of lower cognitive scores in 5-year-old children with high TCDD exposure in the present study.
Further studies are required to determine the exact neuronal alterations in the brain, and effects on neuronal networks, particularly limbic system of the brain. Consistent with our previous studies of the birth cohort in Da Nang at 4 months [ 9 ] and 3 years of age [ 11 ], gender differences in the effects of dioxin on neurodevelopment were evident in the present study. Our results suggest that boys are more susceptible to dioxin toxicity than girls. The interaction between genes and the environment leading to early exposure to androgenic hormones is a potential etiological mechanism affecting sex-specific susceptibility to ASD [ 34 ].
An inverse association between testosterone levels in cord blood and maternal di 2-ethylhexyl phthalate exposure, a persistent organic pollutant, was reported in a Japanese birth cohort [ 35 ]. These results suggest that maternal dioxin exposure might influence testosterone levels of the fetus which play an important role in autistic traits in childhood. Recently, Winnike et al. They suggested that dioxins interact with the hypothalamic-pituitary-gonadal axis in the brain to induce endocrine-disrupter effects.
These results suggest that male susceptibility to the effects of dioxin on neurodevelopment might be mediated through an interaction of dioxins with the hypothalamic-pituitary-gonadal axis, consequently affecting androgenic hormone levels in the fetal brain. Our future studies following up these children will investigate associations between dioxin exposure and sexual dimorphism, in addition to cognitive abilities.
Although the Movement ABC-2 and KABC-II are useful tests for making independent quantitative judgments regarding motor coordination and cognitive ability, they have some limitations with respect to the present study. Therefore, we could not judge the developmental levels of individual children based on the scores obtained with this test.
However, we used their cutoff value to assess risk for movement difficulties, resulting in possible overestimation of children with possible DCD. Regarding KABC-II, it is possible that we overestimated the number of children at risk for cognitive impairment, albeit we used the NVI, which is validated for non-English-speaking populations. However, each test was performed by a single examiner who was well trained and followed specific instructions as described in the manual. Therefore, the comparison of test scores among the different exposure groups within the same population, to clarify associations between the levels of dioxin exposure and test scores of the test should be reliable.
These results demonstrate the considerable impact of perinatal dioxin exposure on neurodevelopment in boys at 5 years of age. A longer follow-up study of the present cohort in Vietnam is required to clarify whether the effects of dioxin on neurodevelopment will be evident in school-age children. The authors thank Dr. Tran Van Nhat, Dr. Clark, George W. Giesy, James P. Ludwig, Donald E. Michael Theobald, Richard E.