Thursday, February 24, 2005

Perchlorates in Breast Milk

In the past few days, there have been a few stories about "Rocket Fuel in Breast Milk", a melodramatic reference to measured levels of perchlorates in human and cow's milk. Perchlorates are used in rocket fuel, fireworks, and explosives. They occur naturally, and are also made commercially. There are industrial sites where there is significant perchlorate contamination. This raises an obvious question: Did the perchlorate in breast milk come from rocket fuel contamination (or from any other industrial process)? And is it something to worry about?

Perchlorate Chemistry

Perchlorate is made up of a chlorine atom surrounded by 4 oxygen atoms- a tetrahedral structure- and it is properly called an ion, since it has a net charge (of -1, in this case), though it's just called perchlorate in the news. It is very reactive because in it, chlorine is highly deprived of electrons. Perchlorate will wrench the electrons from other compounds to satisfy this deficit, causing strong and often abrupt chemical changes. Organic chemists that I know tend to be wary of perchlorate salts, because they can detonate (hence their uses in explosives). However, the amount and form of perchlorate found in water supplies isn't a detonation hazard. It is a hazard to health because it interferes with iodide use in the thyroid gland.

Perchlorate in the Environment

There appears to be a lot of contamination near chemical plants that used perchlorates. The contamination dilutes quickly as one gets farther from the source. The contaminant is essentially diluted to zero when measured perchlorate falls to the naturally occurring level.

In some cases, at least, the natural backround level is not well known and has only recently been measured- an interesting example is in Texas- and found to be surprisingly high in an area where there is no obvious anthropogenic source (up to 20 parts per billion) . Researchers at Texas Tech have found that both lightning and ultraviolet radiation can generate perchlorates from sodium chloride, i.e. table salt. This makes conclusions about what is background and what is contamination harder, but perhaps not impossible.

Environmental Chemistry is not my forte, but this is interesting enough to spend some time researching, and I will post what I find. At this stage, I am ignorant of what is known about perchlorates and their natural distribution in the environment, to say nothing of what sort of health effects can be expected at a given exposure level. I have a lot to find out. Sounds like fun.


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