Maternal exposure to dioxins [polychlorinated dibenzo- p -dioxins ( PCDDs ) and dibenzofurans (DFs)] during pregnancy is known to affect infant growth and neurodevelopment in humans and animals. The aim of this study was to investigate the relationship between newborn size and the concentration of dioxin isomers in breast milk and to subsequently evaluate the potential toxicity of each dioxin isomer among mothers living in sea coast areas who are at a high risk of contamination due to a high consumption of fish.

A total of 75 milk samples were obtained within 1 month of delivery from Japanese mothers living in the coastal areas of the Japan Sea. The relationships between the levels of seven dioxins and ten furan isomers in maternal breast milk, measured by high-resolution-gas chromatography/mass spectrometry, and the birth size of newborns, which is related to fetal growth, were investigated after adjustment for confounding factors.

The concentrations of 1,2,3,6,7,8-HxCDD (hexachlorodibenzo- p -dioxin), 2,3,4,7,8-PeCDF (pentachlorodibenzofuran), 2,3,4,6,7,8-HxCDF, and three dioxin toxic equivalent (TEQ) levels ( PCDDs -TEQ, PCDFs-TEQ, and total-TEQ) in maternal breast milk were inversely correlated to newborn length even after adjustment for gestational weeks, infant sex, and maternal age and height. These isomers were abundant among the 17 isomers tested and reflected the TEQ levels. Only 2,3,7,8-tetrachlorodibenzo- p -dioxin ( 2,3,7,8-TCDD ), the most toxic isomer, was negatively correlated with newborn head circumference, even after adjustment for gestational weeks, infant birth weight, and other confounding factors.

Based on our results, fetal growth may be influenced by maternal total exposure to dioxins, but only exposure to 2,3,7,8-TCDD would appear to possibly affect fetal head size during pregnancy.