Abstract
Dioxin concentrations remain elevated in the environment and in humans residing near former US Air Force bases in South Vietnam. Our previous epidemiological studies showed adverse effects of dioxin exposure on neurodevelopment for the first 3 years of life. Subsequently, we extended the follow-up period and investigated the influence of perinatal dioxin exposure on neurodevelopment, including motor coordination and higher cognitive ability, in preschool children. Presently, we investigated 176 children in a hot spot of dioxin contamination who were followed up from birth until 5 years old. Perinatal dioxin exposure levels were estimated by measuring dioxin levels in maternal breast milk. Dioxin toxicity was evaluated using two indices; toxic equivalent (TEQ)-polychlorinated dibenzo-p-dioxins/furans (PCDDs/Fs) and concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Coordinated movements, including manual dexterity, aiming and catching, and balance, were assessed using the Movement Assessment Battery for Children, Second Edition (Movement ABC-2). Cognitive ability was assessed using the nonverbal index (NVI) of the Kaufman Assessment Battery for Children, Second Edition (KABC-II). In boys, total test and balance scores of Movement ABC-2 were significantly lower in the high TEQ- PCDDs/Fs group compared with the moderate and low exposure groups. NVI scores and the pattern reasoning subscale of the KABC-II indicating planning ability were also significantly lower in the high TCDD exposure group compared with the low exposure group of boys. However, in girls, no significant differences in Movement ABC-2 and KABC-II scores were found among the different TEQ-PCDDs/Fs and TCDD exposure groups. Furthermore, in high risk cases, five boys and one girl highly exposed to TEQ-PCDDs/Fs and TCDD had double the risk for difficulties in both neurodevelopmental skills. These results suggest differential impacts of TEQ-PCDDs/Fs and TCDD exposure on motor coordination and higher cognitive ability, respectively. Moreover, high TEQ-PCDDs/Fs exposure combined with high TCDD exposure may increase autistic traits combined with developmental coordination disorder.
Highlights
During military operations by the US Armed Forces between 1961 and 1971, large quantities of herbicides were sprayed in Southern Vietnam
High toxic equivalent (TEQ)-PCDDs/Fs exposure combined with high TCDD exposure may increase autistic traits combined with developmental coordination disorder
In both boys and girls, there was no significant difference in the characteristics of mothers or children among the three TEQ-PCDDs/Fs exposure groups, except for maternal age, which was significantly higher in the high TEQ-PCDDs/Fs group compared with the low exposure group
Summary
During military operations by the US Armed Forces between 1961 and 1971, large quantities of herbicides were sprayed in Southern Vietnam. One of these herbicides, Agent Orange, contained 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which is the most toxic dioxin congener of polychlorinated dibenzo-p-dioxins/furans (PCDDs/Fs). We recently reported that levels of TCDD and PCDDs/Fs in breast milk of mothers residing near hot spots were significantly higher compared with mothers living in unsprayed areas [3,4], suggesting perinatal dioxin exposure including high prenatal dioxin exposure by placental transfer from mothers and postnatal dioxin exposure through breastfeeding to their offspring. Since the brain is undergoing a variety of developmental processes during the perinatal period and is sensitive to neuro-toxins such as dioxins, prenatal exposure by maternal transfer may contribute to adverse neurodevelopmental effects in offspring which appear in later life [5]
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