Thyroid Threat

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October 30, 2006

Thyroid Threat: Proposed Standards Based Upon Inadequate Study

The six parts per billion (ppb) drinking water standard for perchlorate proposed by the state of California is based on the findings of a short-term study with a very small sample size, now known to be wholly inadequate to detect perchlorate-related health effects. The same is true for the drinking water standards proposed in New Jersey, the clean-up standard adopted by the US EPA, and to a lesser degree the drinking water standard recently adopted by Massachusetts.

This study supporting the California proposed standard, known as the "Greer study," dosed 37 healthy adults with perchlorate for just 14 days. [23] The study did not include any measurement of iodide status, which the CDC study has subsequently shown to be a key variable. And when US EPA analyzed the study design, the agency found that it did not have sufficient statistical power to detect effects at low doses due to the small number of individuals in each dose group. (The lowest dose group included only seven individuals &em; six females and one male.) [24, 25]

The authors averaged data within dose groups to claim that the lowest dose of perchlorate caused no effects on iodide uptake by the thyroid. Closer examination of the data, however, shows that four of the seven individuals did have perchlorate-related reductions in iodide uptake. [16] With the CDC study in hand, we now know that these effects occur in the population, particularly in iodine deficient women, and that the proposed California standard would not protect the public health.

Sources: [1, 12, 27]