This mighty molecule is getting a lot of press lately. Lawyers are salivating and Google ads are beginning to proliferate. The EPA is collecting studies and asking for a review by the National Academy of Sciences. The stakes are very large. Bob Krieger says much of the alarm is 'alarmist'. He says, essentially, that microgram levels of the contaminant passing through the human body are scarcely enough to raise the attention of toxicologists. So are we talking about micrograms?
Larry Ladd has some useful information:
In 2002 the US EPA submitted a proposed reference dose of 1 part-per-billion (ppb) for perchlorate in drinking water. This was based on perceived changes in infant rat brain structure at a dose equivalent to 300 ppb for a 150 pound human adult or as low as 45 ppb for a bottle-fed infant. Increased skin irritability in mice ears, suggesting some sort of immune system effect, was found at a dose about four times higher.Recent research at Texas Tech suggest that tadpoles exposed to as little as 5 ppb perchlorate are more likely to not properly develop fore-legs. Amphibian metamorphisis is notoriously sensitive to thyroid hormone disruption. Regulators are waiting for additional research to confirm these surprising results. The majority of reviewers in an external peer review this year seemed to think a reference dose in the 3 to 10 ppb range was justified by the evidence, and a minority of the reviewers thought the standard should allow higher concentrations.
Current standards in various states reflect this range:
For further information, contact the scientists conducting the government investigation of environmental perchlorate at http://www.clu-in.org/studio/perchlorate_060402/
- A Superfund site in Massachusetts currently requires well shutdown at 1.5 ppb perchlorate, but wells are voluntarily being shutdown and replaced at 0.4 ppb.
- Superfund sites in California require shutdown at 4 ppb; state regulators in California and Texas also recommend public notification and regulatory investigation of perchlorate in any drinking water source containing 4 ppb.
- Arizona has a 14 ppb standard, while Nevada and New York enforce 18 ppb standards.
Some folks here in California are now afraid of lettuce. In that story we have 'detectable levels'.
A bit more sensible is this document. It's interesting to note that going in, potential lawsuit respondants are listed front and center.
What seems reasonable to me is for someone to quickly demonstrate how tapwater can be reduced to the 4ppm standard and make such methods readily available. While I was impressed by Krieger's audio presentation and his comparison of how perclorate is transient in the body like iodide, this kind of information is not linked. It may be that uptake of perchlorate into the thyroid can be blocked as radioactive iodine is with potassium iodide. And while everybody doesn't know that, there are clearly commercially available prophylactics. Making such alternatives available, if they can be shown viable is vastly preferable to the screaming litigation that looks almost inevitable from here.
We'll keep an eye open.