Perchlorate Debate

Last month, an article in Environmental Health Perspectives rehashed the “perchlorate debate”. It must have been a slow news day. . .

“. . . perchlorate in drinking water sources around the nation has drawn the attention of scientists and public health advocates who say that even small doses of the chemical threaten people’s health.”

Perchlorate has been drawing attention for many, many years now because it has been difficult for the U.S. Environmental Protection Agency to estimate a level in drinking water that protects public health. It’s hard to say why it’s drawing attention now.

The one new piece of information I gleaned from the article was that perchlorate controversy is going to be tossed in the lap of the National Academy of Sciences. That seems to be happening to EPA a lot these days. For the past 15-20 years they’ve been trying to develop scientifically-based health standards for dioxin and trichloroethylene, without success. Those chemicals are also going to the NAS. I don’t find that to be a comforting sign because it seems to reward indecisiveness and dithering by the agency.

What’s next if the NAS can’t provide some good recommendations? Take it to Congress? I can’t wait to see that: “quick, we need to put aside the war on terror so we can debate this drinking water standard for TCE”.

Looking at the Numbers

While the debate continues about a definitive protective level, EPA provides to its enforcement personnel interim guidance recommending perchlorate concentrations of 4 to 18 parts-per-billion (ppb) as action levels in groundwater supplies – these potentially represent targets for monitoring or groundwater cleanup. Marianne Lamont Horinko, the agency’s assistant administrator for the Office of Solid Waste and Emergency Response, encouraged agency personnel to “carefully consider the low end” of that range. [A quick aside: those drinking water concentrations correspond to the “provisional Reference Dose (RfD)” of 0.0001 to 0.0005 mg/kg-day, or milligrams of perchlorate ingested per kilogram of body weight each day. A discussion of what the Reference Dose means is a topic for another day, but here’s where you can go if you want to read ahead.]

For an agency project manager overseeing a groundwater cleanup at a Superfund site, “carefully consider the low end” of that range, sounds like the code for “direct the responsible party to use the low end of the range for a cleanup level unless they really hold your feet to the fire or threaten to sue us or something. . . .” Not the most systematic approach to risk management.

Perchlorate provides a good example in site cleanup of a process that is just transparent enough to unnerve the general public, but not sufficiently transparent to inform. EPA says that a concentration in drinking water from 4 to18 ppb is protective enough to use as a cleanup level (for now. . .). For those individuals who have not been dragged through the onerous process of developing a health-based action level, this brings up some good questions, such as “which is it, 4 or 18?” If 4 ppb is needed to protect against adverse health effects, then how can 18 ppb be protective? If 18 is ok, why do we need 4?

When EPA revised its health risk assessment for perchlorate in 2002, a protective level in drinking water dropped to 1 ppb. So now what’s the deal with using 4 and 18 as cleanup levels? Complicating matters a bit further, the state of California proposes in 2004 to use 6 ppb perchlorate as Public Health Goal (PHG), and eventually a drinking water standard. In practical terms, there is no difference between 4 ppb and 6 ppb as a cleanup level in groundwater, though that point is probably not obvious to most people. More about this chronology can be found here.

Clouding the issue further, EPA in 1995 proposed a drinking water action level of 32 ppb, which predates its 4 to 18 ppb recommendation. A few years ago, an exposure study performed with human volunteers showed that 200 ppb in drinking water represented a no-observed-effect-level for perchlorate in adults, which reportedly was argued as a protective level by industry. That level arguably doesn’t address the adverse effects of concern, which is interference with iodide uptake by the thyroid gland in pregnant women, with possible effects to neurological development in the fetus.

An industry-DOD group, the Perchlorate Study Group had, in a 24 May 2004 meeting with the National Academy of Sciences, presented recent unpublished research that preliminarily concluded that a perchlorate level of 110 ppb had no effect on pregnant women and infants. I haven’t seen where that value comes from, but the action level in drinking water that seems to make the best use of the considerable scientific database, and has been developed using a transparent process is 70 ppb. But with all of the zigzagging that has gone on, is anyone prepared to find it believable?

There was a thought process underlying each of these numbers, but when examined together, they show more of a regulatory and scientific muddle which doesn’t inspire a lot of confidence that there is a plan for addressing perchlorate-contaminated groundwater. Matters don’t look quite so distressing when the facts are ordered into a coherent narrative, but that doesn’t seem to have happened yet. The story in Environmental Health Perspectives is a good summary of the recent facts, but doesn’t address why perchlorate history looks like this, or what it means to people who live where there is perchlorate-contaminated groundwater.