A newly-published analysis of data used in two studies that California regulators have relied upon in proposing a revised public health goal (PHG) for perchlorate provides more science to refute the conclusions of those studies and, in so doing, raises additional questions about the validity of the proposed PHG. A PHG is the first step in setting a statewide drinking water standard.
On January 7, 2011, California’s Office of Environmental Health Hazard Assessment (OEHHA) proposed a perchlorate PHG of 1 part per billion (ppb) in drinking water. One ppb is roughly equal to a half teaspoon in an Olympic-sized pool. On December 7, 2012, OEHHA released a revised risk assessment in support of its previously proposed revision of the PHG. The proposal remains under consideration by OEHHA.
The two studies relied upon in proposing the lower PHG—Blount et al. (2006) and Steinmaus et al. (2007)—interpret data collected by the Centers for Disease Control and Prevention (CDC) for its 2001-2002 National Health and Nutrition Examination Survey (NHANES) to suggest an association between low levels of perchlorate exposure and decreased thyroid function.
However, at the time the Blount and Steinmaus papers were published, the NHANES dataset only reported two measures of thyroid function. Subsequently, CDC released additional measures for the 2001-2002 NHANES dataset which provided a more complete picture of thyroid function. An analysis of the enhanced NHANES dataset by Bruce et al. (2012) published in the peer-reviewed
Journal of Occupational and Environmental Health, reported no functionally relevant association between perchlorate exposure and thyroid function, contrary to the OEHHA conclusions.
Notably, the researchers in Bruce et al. did find a significant association between exposures to two other substances commonly found in foods, thiocyanates and nitrates. These substances act in the body in the same fashion as perchlorate, i.e., they contribute to iodine uptake inhibition (IUI). This suggests that regulating perchlorate in exclusion of other chemicals that have the same mechanism of action will not provide a public health benefit. In fact EPA’s Office of Inspector General estimates that the contribution of perchlorate to IUI is about 1% of the total contributed by other thyroid stressors, primarily nitrate, thiocyanate and iodine deficiency.
The Bruce paper was available in the published scientific literature before OEHHA released its revised draft PHG, yet it is not cited in OEHHA’s most recent PHG document. Further, OEHHA has so far not commented on how this new information will impact adoption of a final PHG. Because OEHHA is statutorily required to use the best available science in establishing public health goals, the Bruce findings should be considered by OEHHA in its evaluation of the need for a revised PHG for perchlorate.