How Much Uncertainty Is There in the Perchlorate Database?
Both the NAS (2005) and the U.S. EPA (2002a) applied a 10-fold intrahuman uncertainty factor, acknowledging that the critical study examined a small number of healthy, iodine-replete adults. Perchlorate effects on iodine uptake and thyroid hormone status may be more dramatic in pregnant women who are already somewhat iodine deficient, a high-risk scenario that is not uncommon (Azizi et al. 2003; Kibirige et al. 2004). Unlike the U.S. EPA’s 2002 assessment (U.S. EPA 2002a), the NAS’s assessment did not apply any other uncertainty factors. One dissenting member of the NAS committee thought that an additional uncertainty factor of 3-fold should be applied to account for additional issues. We believe that a database uncertainty factor of 3- to 10-fold is warranted based upon key data gaps as follows. Potential for greater toxicity to newborns from lactational exposure. Perchlorate is actively transported into breast milk, where relatively high levels have been reported in the United States
