VietNamNet Bridge – A study by Vietnamese and Japanese experts has found that dioxin continues to affect the neurodevelopment of pre-school children in contaminated areas of Viet Nam, due to perinatal dioxin exposure.

A medical worker cares for a child affected by dioxin at a medical facility in Da Nang's Hoa Vang District. — Photo: VNA/VNS

The experts studied 176 mother and child pairs in the central Vietnamese city of Da Nang between 2008 and 2015.

Tran Ngoc Nghi, a Vietnamese PhD student in Japan and co-author of the study, stated that large quantities of herbicides were sprayed in Southern Viet Nam during military operations by the US Armed Forces between 1961 and 1971.

Da Nang, a former major US airbase during the war, is considered to be a dioxin contamination hot-spot, due to the huge amount of herbicide stored and spilled in the area.

Previous studies conducted by the authors revealed that the levels of dioxin in breast milk of mothers residing near hot-spots were significantly higher compared with mothers living in unsprayed areas.

The research suggests perinatal dioxin exposure, both prenatal by placental transfer and postnatal through subsequent breastfeeding. This may contribute to adverse neurodevelopment effects later in the child's life.

Their previous epidemiological studies showed that perinatal dioxin exposure has considerable adverse effects on the growth and neurodevelopment of children from birth to the age of 3 years.

The new study extended the follow-up period of preschool children to 5 years after birth, analysing its influence over motor coordination and cognitive ability.

In the study, 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).

Subjects were divided into three groups (high, moderate and low exposure groups) according to TCDD and TEQ-PCDDs/Fs levels in the breast milk.

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).

The study found that 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.

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 neurodevelopment skills.

These results suggest different impacts on motor coordination and higher cognitive ability, respectively. Moreover, high TEQ-PCDDs/Fs exposure combined with high TCDD exposure may increase the risk of autistic traits combined with developmental coordination disorders.

A longer follow-up study of the present cohort is needed to clarify whether the effects of dioxin on neurodevelopment will continue to be evident in school-age children.

The study was approved by the Institutional Ethics Board for Epidemiological Studies at Kanazawa Medical University. It was jointly supported by the Japan Society for the Promotion of Science Asian Core Program and the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research and Challenging Exploratory Research.

VNS