Levels of potassium perchlorate in excess of 4 parts per billion
(ppb) have been found in 317 out of 950 San Martin wells
tested.
Levels of potassium perchlorate in excess of 4 parts per billion (ppb) have been found in 317 out of 950 San Martin wells tested. The source of the contamination is a former highway flare manufacturing plant, Olin Corporation. Perchlorate is being found in the ground water south of the closed site: predictably, seeing as the watershed flows south from Cochrane Road.
South County residents are, naturally, concerned about possible perchlorate contamination of their drinking water. Perchlorate may interfere with iodide assimilation by the thyroid gland, which regulates metabolism, growth, and development, and hence is of particular concern for pregnant women and babies.
Like many residents, I have been devouring every word The Dispatch has printed on the plume, and particularly studying the colored glossy graphics with the circles and squares showing which wells have been contaminated and how badly.
But I couldn’t find the chemical formula for perchlorate, or what the safe level is for perchlorates in drinking water, or what methods are used to clean up perchlorate contamination of ground water. So I went onto the ‘Net, and found some things that seemed obvious upon reflection, and others that totally surprised me.
The chemical formula for perchlorate is ClO4, which in retrospect, I should have figured. After all, hydrogen peroxide is H2O2, water with an extra oxygen. Perchlorate is an anion, chlorate with an extra oxygen, (and VH would be appalled that I have forgotten so much chemistry.)
However, unlike hydrogen peroxide, perchlorate doesn’t spontaneously fizz apart into harmless constituent molecules. It requires a high activation energy to break it up into ClO3 and oxygen, but fortunately even more energy is released in the process, so the ClO3 and extra oxygen don’t spontaneously recombine.
The biggest surprise was that prior to 1997, no analytical measuring technique for measuring perchlorate levels lower than 400 ppb existed. A technique was invented to measure levels down to 4 ppb. Now that they could measure it, the EPA, in 1998, placed perchlorate on its Contaminant Candidate List, and began trying to figure out if it qualified as a contaminant. A year later, the EPA ordered water systems to begin monitoring to see if any perchlorate contamination existed.
And they found it: downstream of rocket fuel plants, down watershed from airbag plants, and in our case, down watershed from a flare factory. They even found a couple of places that seem naturally contaminated: high levels of naturally occurring perchlorates seeped into the water table. And state and federal agencies began to do research to determine the MCL, the maximum contaminant level.
But they haven’t yet figured out how much is dangerous. Intuitively, it seems that there must be a dangerous level, because perchlorate is used medicinally to treat hyperthyroidism, i.e. to lower the thyroid activity in people who have – well, hyperactive thyroids. And there are some small scale studies and some poorly controlled studies that seem to say there could be a danger in too much perchlorate intake. But how much is too much? No one knows.
No MCL has been established, not at the state level nor at the federal level. The EPA is working on it; the California Department of Health is working on it, and is mandated to have a MCL established later this year. And they also haven’t yet figured out whether iodide supplements would prevent the adverse effects, though again, intuitively it seems they should.
There are several possible processes for treatment and clean up, including biological reduction, electro reduction, anion exchange, and membrane filtration. My personal favorite is trees: several species, including willow, cottonwoods, and eucalyptus cinera, take up perchlorate and degrade it into ordinary old chloride, which we routinely add to drinking water to kill pathogens.
I couldn’t find any places that are actually using trees in any but small scale experiments. But there are a few treatment plants that use a layer of microorganisms and chemicals to degrade the perchlorates, which is almost as cool.
In sum, the science of detecting and cleaning up perchlorates is in its infancy. That’s why there are no firm answers yet. As soon as the EPA figures out what to do, we can start doing it. In the meantime, bottled water is on Olin Corp.
