| Abstract
| - Perchlorate, thiocyanate, and iodine excretion in urine and milk of 13 breastfeeding women was investigated and the results were interpreted by a model of parallel/competitive transport of these species by the sodium iodide symporter. For each species i, we assumed physiological homeostasis, where iT,in equals the corresponding total excretion in urine and milk (ie,u + ie,m). The fraction of the total excretion that appeared in milk fi,m was measured and ranged from 0.394−0.781, 0.018−0.144, and 0.086−0.464 for perchlorate, thiocyanate, and iodine, respectively. The corresponding median values were 0.541, 0.053, and 0.177, respectively. The selectivity factors of perchlorate over iodide transport, and thiocyanate over iodide transport, defined as fPC,m/fI,m, and fSCN,m/fI,m, respectively, were 3.14 ± 1.20 and 0.27 ± 0.26 while PCT,in, SCNT,in, and IT,in among individuals varied 4.9, 5.0, and 8.4×, respectively. These transport selectivities are an order of magnitude lower than those indicated by in vitro studies, suggesting that the impact of both these anions on inhibiting iodide transport in milk may have been overestimated in the extant literature. On the other hand, our results showed that 12 of 13 infants did not have an adequate intake of iodine as defined by the Institute of Medicine and 9 out of 13 infants were likely ingesting perchlorate at a level exceeding the reference dose suggested by the National Academy of Science panel.
- Selectivity factors for perchlorate and thiocyanate transport over iodide at the mammary NIS may be lower in real subjects than that reported in vitro.
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