Abstract
PFASs include thousands of persistent chemicals which demonstrate the ability to bioaccumulate. PFOS, followed by PFOA, are the dominant PFASs in human samples. In the pre- and postnatal period many developmental windows exist in which the child has increased susceptibility for environmental factors. Identifying such critical windows of susceptibility in early development is vital as exposure during these windows may result in permanent adverse health effects. Few studies, however, have identified critical windows after the breastfeeding period. This is likely due to the challenges of getting accurate exposure estimates in this period. As multiple blood tests in young children and adolescents are inconvenient, and ethical considerations may prohibit taking them, a physiologically-based pharmacokinetic model that calculates PFAS exposure is necessary. Such models have been developed up to 2 years of age but are lacking for older ages. In order to do risk assessment of exposure to PFAS in older children, a model that can estimate the PFAS concentrations in children up to early adolescence, is urgently needed. In this work a two-generational physiologically-based pharmacokinetic model for PFOS and PFOA was developed. The model consists of maternal and child compartments to simulate the transfer to the child through breastfeeding, and then takes into account the child’s growth and chemical half- lives in the years up to early adolescence. To evaluate the model, 98 simulations were performed where actual concentrations were available in adolescent serum. Model predictions were based on the breastmilk concentrations, proportion of breastfeeding, body weight as well as the chemical parameters volume of distribution, half-life, milk:plasma- and cord:mother ratio. The actual concentrations of PFOS and PFOA in serum samples from adolescent children, were used to test the accuracy of the model. Results were also compared to reported concentrations from previous studies. The predicted concentrations for mothers’ plasma concentrations (based on breast milk measures) and total daily intake were higher than what has been reported in previous studies. Also, mothers predicted daily intakes were 4-fold and 2-fold higher compared to the children’s daily intake of PFOS and PFOA, respectively. The predictions for children’s plasma concentrations were not accurate on an individual level; however, the model can give indications of the concentrations on a group level. Additionally, the model can give an indication of PFOS and PFOA levels in infants and toddlers, as predictions were the best in this period, alongside already published models. Furthermore, our results add to the knowledge on PFAS levels in adolescents.