EPA Inspector General Concludes California’s Perchlorate Standard Too Low for Nation

The Environmental Protection Agency Office of Inspector General released a scientific analysis of perchlorate on April 19.  The IG report criticized EPA for relying on an “outdated single chemical risk assessment approach.”  Perchlorate is only one of several chemicals that stress the thyroid’s ability to uptake iodide.  The IG office conducted a cumulative risk assessment to evaluate the risk to thyroid function from multiple stressors.  Results from this analysis led the office to conclude that setting a drinking water standard lower than 25 ppb would “not provide a meaningful opportunity to lower the public’s risk.”

According to the report, addressing iodide deficiency in pregnant and nursing woman “appears to be a more effective approach… to reducing the frequency and severity of permanent mental deficits in children.”  This result is consistent with a 2005 NAS report on perchlorate that recommended “consideration be given to adding iodide to all prenatal vitamins.”

In 2005, EPA established a perchlorate reference dose (RfD) that if promulgated into a national drinking water standard would result in a maximum contaminant level of 25 ppb.  California’s drinking water standard for perchlorate is 6 ppb. 

A regulatory determination from EPA on whether or not to issue a national primary drinking water standard for perchlorate is anticipated some time this summer.

The full report is attached below.