DOES PERCHLORATE REACT IN THE HUMAN BODY?

What's Known

It's well-established that at least 99% of large doses of perchlorate simply pass out of the human body unaltered. In a 2001 rat study, within 2 days 99.5% of a single radiolabeled dose of perchlorate passed through the rat's urine, although traces of the perchlorate lingered in the rat's skin for a week.

Children in the Ukraine living next to abandoned Soviet solid rocket installations have been reported to suffer from mysterious summertime rashes. In the laboratory absorption of ultraviolet light makes perchlorate much more likely to react with pure iron, although it's not clear if the same is true with the blood hemoglobin flowing through capillaries on the surface of the skin. Some tenative research on mice suggests drinking perchlorate at a concentration of 1000 ppb makes skin more reactive to other irritants.

The well-studied effects of perchlorate on the thyroid concern the passive blocking of iodide uptake. What is still unknown to the public is whether perchlorate consistently reacts with any human enzyme and/or acidic part of the body (e.g. gastric pits in the lining of the stomach or lacunae between osteoclasts and bone mineral). If perchlorate reacts, it would oxidize or "bleach" the human tissue around it and present a cancer risk.

Dr. Nancy Carrasco of the Albert Einstein School of Medicine in the Bronx is the head of the research team that cloned the Sodium Iodide Symporter (the NIS), the cell membrane molecule that concentrates iodide in the thyroid. It is primarily by disrupting proper function of the NIS that perchlorate adversely affects iodide uptake into the thyroid. At the 2002 EPA perchlorate peer review Dr. Carrasco observed that, contrary to the conventional wisdom, perchlorate's affect on the NIS does not appear to be totally reversible. Dr. Carrasco stated that her lab currently has a working hypothesis that perchlorate oxidizes a portion of the NIS.

If perchlorate does react systematically, at a low rate, with some particular part of the human body, then it's possible that the critical effect of perchlorate toxicology has not yet been identified. In such a scenario the ill effects of perchlorate toxicology might be more dependent on time rather than the size of the dose, especially if one of the reaction sites is in connective tissue like bone or cartiledge. For example, it would take six months for perchlorate to precipitate in all bone mineral in the skeleton, and another six months for that perchlorate to be completely exposed to acid from osteoclasts. The chances of perchlorate reacting are increased in an acid environment.

Potential risk factors include genetic dispositions (some enzymes have hundreds of structural variants), synergistic contaminants (metals that form compounds with which perchlorate in solution can spontaneously react such as rhenium and vanadium), other health conditions (peer reviewers have suggested that persons with some kidney abnormalities may not excrete perchlorate as efficiently as others), and even the amount of pressure applied to perchlorate embedded in connective tissue may increase the risk of perchlorate reacting.

It is interesting to note that the place with the most consistently high death rates for thyroid cancer and connective tissue sarcomas -- northern Minnesota's Mesabi range mining district -- has potential sources for both environmental perchlorate and rhenium/vanadium aerosol, and lies beneath the main path for pre-1964 Iodide-131 fallout from the Nevada Nuclear Test Site. Radiodide and perchlorate follow many similar pathways within the human body.

Metabolization studies need to be done to fully evaluate the risks of consuming perchlorate. A specialized metabolization study addressing the question of perchlorate reactability would probably involve test animal subjects consuming large doses of radioactively-labeled perchlorate (ClO4-), and then testing the animals' urine. If radioactive chloride (Cl-) or (ClO3-) are found in the urine in the part-per-billion range, then the potential exists that perchlorate is systematically reacting with some enzyme in the body. Further research would have to be conducted to determine if this reaction is random or concentrated. Random parts-per-billion reactions of perchlorate with bacteria in the human gut or human tissue should not present a significant health hazard.