Perchlorate has no measurable effect on the body until it reaches levels of approximately 245 ppb or greater in drinking water, at which point it may begin to block some of the thyroid's iodide uptake. Below this "no-effect" level of 245 ppb, perchlorate has no measurable biochemical or biological impact on people. Adverse effects are not seen at perchlorate levels of 14,000 ppb or less.
Greer study. Healthy adult volunteers, including both men and women, consumed perchlorate in drinking water at various dose levels for 14 days. At the low dose, equivalent to 180-220 ppb, there was no detectable inhibition of iodide uptake by the thyroid. (The thyroid uses iodine to produce hormones essential to growth and metabolism.) There was no adverse change in thyroid hormone levels associated with any dose level. View Abstract
Crump study. This study of children and newborns shows "no health-effect" at levels of about 110 ppb.
Braverman study. Healthy male volunteers consumed perchlorate equivalent to either 1,500 or 5,000 ppb in drinking water for 14 days. There was approximately 10% and 38% inhibition of iodide uptake at the lower and upper levels, respectively. No adverse changes in thyroid hormone levels were observed at either level. View Abstract
PBPK (Pharmocokinetic) Model Studies. These studies, conducted in rats, were designed to describe and predict the movement and effects of perchlorate in the body. Among other things, they showed that the threshold for iodide uptake inhibition in rats was equivalent to 350 ppb perchlorate in drinking water for humans.