Perchlorate is an inorganic ion, analogous to chloride or sulfate, found in perchlorate salts. Perchlorates are used in explosives or as a component of rocket fuels and fireworks, because under the right conditions they are powerful oxidizing agents. They are manufactured mainly for use by the military and NASA. Over many decades of their manufacture, particularly in the Cold War years following World War II, perchlorate salts were dumped into waste ponds or discarded in other ways. Because perchlorates are quite soluble in water, they readily found their way into groundwater systems. In 2007 the General Accounting Office (GAO) reported the results of a national survey of sites identified as having a significant concentration of perchlorate in the water. Of the nearly 400 sites identified, 153 were public drinking water supplies, serving up to about 10 million people.
Is perchlorate dangerous? It appears that the only recognized source of potential risk implicates the thyroid. It turns out that perchlorate ion looks to the thyroid gland a lot like iodide ion, which is essential to its proper functioning. So if the perchlorate level in the body gets high enough, the perchlorate ion could block iodide from the place it needs to be, thus impairing proper thyroid function. However, the levels of perchlorate found in most water supplies do not pose a problem for adults. They could, however, be a health threat to very young children and pregnant women.
At the behest of environmental and public interest health groups, the National Academies of Science (NAS) convened a panel of experts to look at the issues. The committee of experts eventually recommended a reference daily dose, let’s call it REF-d, which they believed could be taken in over a lifetime without appreciable risk of deleterious effects. The experts also indicated that this level of exposure would not cause adverse effects on children or pregnant women.
On a couple of occasions, the Center for Disease Control (CDC) has reported on perchlorate to Congressional Committees. In 2007 the CDC reported that in a national survey of substances found in urine samples, all 2820 participants in the survey were found to have measurable levels of perchlorate. However, only a handful had levels exceeding the REF-d proposed by the NAS panel. So there seems to be little cause for great concern for the general population. However, children showed higher levels of perchlorate than adults. Further, for the 36 percent of women who had relatively low iodine levels in their urine, higher perchlorate levels were associated with lower levels of two key thyroid hormones. This is particularly significant for pregnant women, because low levels of thyroid hormones are associated with neurodevelopmental impairments in the fetus.
Perchlorate is largely a legacy pollutant. The plants that were built to manufacture it in the mid-twentieth century are largely closed, or if they still produce perchlorates operate with much stricter environmental rules than in the past. But there is a lot of perchlorate in the ground. One of the best-known cases concerns a plant in Henderson, Nevada, near Las Vegas, built under a U. S. Navy contract in the 1950s. The navy eventually sold the plant to an industrial firm and it passed some years later into the hands of Kerr-McGee Chemical company. The plant is no longer active but its operations over time left a huge amount of perchlorate salts in the ground around the plant. It’s a long story I needn’t recite here, but suffice to say that there is a continuing flow of perchlorate-laden water from around that plant into Lake Mead just above Hoover Dam, and thence into the Colorado river. All the water in that river system, used to provide drinking water and crop irrigation, from Hoover Dam to the Mexican border, contains varying levels of perchlorate, but generally in the range below about 15 parts per billion. The states that draw their water from the Colorado river at one stage or another have benchmark standards that vary from 1 part per billion for New Mexico to 4 parts per billion for California to 14 parts per billion for Arizona.
So shouldn’t the EPA be involved here? Well, the EPA doesn’t seem to have found this an interesting topic for investigation. In October of 2008 it announced that it would not regulate perchlorate in drinking water, arguing that “there is not a meaningful opportunity for health risk reduction”. The rationale is that perchlorate levels are low in most public drinking-water systems. The decision not to move toward setting a regulatory standard was happily received by governmental agencies such as NASA and Defense, which- in a perfect mimicking of industrial responses - detest having to divert money from new and exciting projects to the tiresome business of cleaning up messes left in the past. But it was not applauded by environmental and public health advocates such as Earthjustice. After much dithering, EPA has issued a new statement that says in effect that perhaps they moved too fast.
But what rhetorical firepower is delivered in dealing with these issues! In the winter 2008 issue of In Brief, Earthustice’s magazine, the article dealing with this topic is headed: “Rocket Fuel in your Drinking Water?” Other potent phraseology includes: “…toxic legacy of the cold water.” “Weapons makers will benefit at the expense of millions of Americans’ drinking water spiked with rocket fuel.” I’m a big fan and supporter of Earthjustice, but all this hyperbole seems a little over the top, in light of the National Academies report, and the work of the GAO and CDC.
Further, the story is more nuanced than Earthjustice’s perspective would suggest. Kerr-McGee began many years ago to clean up the Henderson, Nevada site, and has successfully sued the U. S. Government to pay for some of its share in the costs. In 2005 Tronox, the successor company to Kerr-McGee, received $20.5 million in a settlement with the government. By the end of 2005, Tronox has spent $122 million on the cleanup, and expected to spend considerably more in the following years. However, as reported by Cheryl Hogue in the August 18, 2003 issue of Chemical and Engineering News, the process of cleanup is necessarily slow; you can’t just suck all the contaminated water out of the ground and somehow purge it of perchlorate. The level in the water leaching into Lake Meade will more rapidly decline over time as a result of the cleanup, but there will be some perchlorate in the Colorado River for decades to come. Furthermore, because so much of the water is used in southern California for irrigation of crops, the lettuce, table grapes and other foods grown in the region that we all eat contain some level of perchlorate.
Clearly, we need more knowledge of the health effects of perchlorate in drinking water and the food supply. Here is a case where science can exercise an expert authority on an issue of broad public concern. Not easy to do when the issue is clouded with controversy and conflicting special interests. It’s also not easy to do when the funds for carrying out needed studies are not available. More urgently, all the agencies that can play a role, governmental and otherwise, should make sure that women who contemplate becoming pregnant or are pregnant understand the need to maintain a healthy level of thyroid activity. Public education is also one of science’s roles. We can inform people who are drinking water that has a relatively high level of perchlorate, to assuage needless fears and advise on what they should do to maintain good health.