Update 11/2020: A new study by Lain, et. al suggest that the low levels of perchlorate found in the environment will not negatively impact IQ in children.
Perchlorate has a well-documented, scientifically-established “No Observed Effect Level” (NOEL) which, at 245 ppb, is above all but one documented exposure from drinking water in the US(1). No adverse health effects are expected to occur when humans are exposed to levels below the NOEL of any compound.
During more than 65 years of research into the human health effects of perchlorate, no studies have supported a finding that changes in IQ were caused by perchlorate exposure. EPA’s Biologically Based Dose Response (BBDR) model for perchlorate is an alternative that uses mathematical modeling to predict a possible effect where no supporting data exist. The use of this model in combination with one study based in a non-US population to suggest possible IQ effects is only theoretical and not supported by empirical evidence.
Additionally, the method to mathematically associate thyroid hormone change (which would not occur at levels below the NOEL) with changes in human IQ is overly conservative and unjustified because:
a. Other studies that reported no association were not taken into account.
b. The tests employed to measure changes in IQ lacked the sensitivity and specificity to conclude that any IQ change was occurring, especially distinctions between 1, 2, or 3 points.
c. The single study used in combination with the model relied on data from a non-US country where the typical iodine levels in the population are insufficient, as opposed to the US population which is typically considered iodine-sufficient. Most notable, this study did not evaluate perchlorate.
d. The conclusion of any adverse effects on neurodevelopment is inconsistent with the results of multiple animal studies conducted over many years at much higher doses where this possible effect was rigorously monitored and found to be nonexistent.
For perchlorate in drinking water, as with any other substance, it is the amount of exposure (the dose) that matters in assessing possible adverse effects. For example, too much vitamin C, or even too much oxygen, can be “toxic” at high doses, but the mere presence of these compounds doesn’t mean they pose a health risk. The same applies to perchlorate, where the adverse effect dose for humans has not even been identified after multiple years of clinical studies.
Adverse effects at the highest expected levels to be encountered in drinking water have only been theorized and are in fact counter to the established scientific literature.
1. US EPA Perchlorate Occurrence and Exposure (Updated UCMR 1 Data Set). The only water system above 90 ppb was in Puerto Rico with a value of 420 ppb at the time. EPA stated: EPA contacted the Puerto Rico Aqueduct and Sewer Authority (PRASA) in January 2019. PRASA personnel indicated that no updated monitoring data for perchlorate is available. PRASA personnel stated that the Utuado water system was significantly impacted by hurricane Maria and monitoring records from years prior to 2017 were lost.