Infant Exposure to Dioxin-Like Compounds in Breast Milk
A simple, one-compartment, first-order pharmacokinetic model is used to predict the infant body burden of dioxin-like compounds that results from breast-feeding. Validation testing of the model showed a good match between predictions and measurements of dioxin toxic equivalents (TEQs) in breast-fed infants, and the exercise highlighted the importance of the assumption of the rate of dissipation of TEQs in the infant. Five nursing scenarios were developed and evaluated within this modeling framework based on nursing duration: (1) non-nursing (i.e., formula only), (2) 6 weeks, (3), 6 months, (4) one year, and (5) two years. After nursing, the child is assumed to be exposed to background TEQ levels. It is further assumed that an infant weighs about 3.3 kg at birth and can be exposed to a total of 800 pg TEQ/day by consumption of breast milk, leading to an estimated body weight-based exposure of 242 pg TEQ/kg-day. After one year of breast-feeding, the exposure drops to about 18 pg TEQ/kg-day. This estimate considers declines in the concentrations of dioxins in mothers milk and infant body weight increases. This is significantly higher, on a body weight basis, than adult TEQ exposure, which are estimated to average about 1 pg TEQ/kg-day. For the 6 month and higher nursing scenarios, body burdens (expressed as a body lipid concentration) are predicted to peak at around 9 weeks at 44 ppt TEQ lipid. The formula-fed infants are predicted to have a body burden that peaks at less than 10 ppt TEQ lipid after the first year. These results compare to the current adult average body burden of 25 ppt TEQ lipid. Breast-feeding for 6 months or more is predicted to result in an accumulated exposure 6 times higher than a formula-fed infant during the infant's first year of life. After 10 years, the accumulated exposure is still twice as high for breast-fed infants than formula-fed infants. Over a lifetime, breast-feeding is predicted to result in an accumulated exposure that is 3% to 18% higher than that of a formula-fed infant, depending on the duration of breast-feeding.