California PHG for Perchlorate Diverges from National Academy of Science Recommendations; State Shows No Additional Health Benefits in Lower Health Goal Number

It’s unfortunate the Cal/EPA announcement of a PHG of 6 parts per billion (ppb) for perchlorate does not fully reflect the conclusions of an expert panel on perchlorate convened by the National Academy of Sciences (NAS). Most disappointing is that the state, in moving in a direction different from the NAS findings, has demonstrated no additional public health benefits.

NAS recommended a reference dose of 0.0007 milligrams per kilogram of perchlorate per day, which the U.S. EPA subsequently translated into a Drinking Water Equivalent Level (DWEL) of 24.5 ppb.

NAS explained their conclusions were based on a highly conservative, health protective and precedent-breaking approach. This is important because a PHG set below what NAS says is necessary may foster a mistaken public impression that perchlorate levels above the PHG are unsafe. Rather than working from the customary baseline of a No Adverse Effect Level, the NAS made the decision to work from the No Observed Effect Level of 245 ppb and then included an additional margin of safety it declared protective of the most sensitive subpopulations, including pregnant women and their fetuses, as well as newborns.

Setting the PHG is a preliminary step for developing a regulatory standard for drinking water, known as a Maximum Contaminant Level (MCL). To the extent California’s PHG is not based on the best available science, the resulting MCL could be unnecessarily restrictive and costly, forcing local governments to divert resources away from more pressing needs, while still not providing corresponding health benefits.