Rocket Science: Chapter 2: A Perchlorate Primer

Perchlorate consists of an atom of chlorine surrounded by four atoms of oxygen. It occurs as ammonium, potassium, magnesium or sodium salts. These perchlorate salts bind weakly to soil particles and are not significantly broken down in the environment. (EPA 1998.) In water, however, perchlorate salts are extremely soluble and highly mobile, migrating faster and farther than many other water contaminants. Together, these properties make perchlorate a particularly persistent and problematic pollutant once it contaminates groundwater.

Perchlorate salts are used in a variety of products as diverse as electronic tubes, car air bags, leather tanning and fireworks. Perchlorate was once used as a medical treatment for patients with severe hyperthyroidism, before serious side effects all but discontinued its use in the 1960s. (EPA 1998.) It is still used on a very limited scale in medicine for diagnosis and imaging. But perchlorate's main use is as an explosive propellant: Ninety percent of the perchlorate produced goes into solid rocket fuel for Air Force missiles and the NASA space shuttle. (EPA 1998.)

Large-scale production of perchlorate began in the 1940s and expanded along with the growth of the postwar military-industrial complex. In recent years perchlorate production reached almost 20 million pounds annually, but it fluctuates depending on demand by the military and the space program. For decades the two major perchlorate manufacturers have been American Pacific Corp. of Las Vegas and Kerr-McGee Corp. of Oklahoma City. American Pacific gained sole control of the industry in 1998 when Kerr-McGee sold its perchlorate operations to its rival for $39 million. In fiscal 2000, American Pacific reported income of $4.25 million on sales of $67.4 million, with about 70 percent coming from sales of perchlorate to aerospace and defense contractors.

Since the early 1950s, manufacture of perchlorate was centered at the American Pacific and Kerr-McGee plants outside Las Vegas, both in areas that drain into Lake Mead. In 1988, a series of explosions destroyed the American Pacific plant, leaving two people dead, more than 300 injured and a 400-foot crater in the desert. American Pacific built a new facility near Cedar City, Utah; in 1997 an explosion there killed one worker and critically injured another.

Perchlorate impairs normal thyroid function because it is taken up preferentially by the thyroid gland in place of idiode. The thyroid gland is therefore deprived of iodide, a necessary nutrient which it is designed to concentrate; and without iodine, thyroid hormone is inactive. As a result, perchlorate can disrupt the delicate balance of hormone levels in the body which are crucial for healthy metabolism, growth and development.

This effect has been known for decades, but recent research has found that perchlorate can affect human thyroid hormone levels at extremely low concentrations. Furthermore, studies have shown that perchlorate's effect on the thyroid may extend to thyroid cancer. Yet despite the numerous studies that have been conducted on the health effects of perchlorate, critical gaps in scientific understanding remain - most critically, studies that address the neurological development of fetuses and infants and studies that examine the possible concentration and transfer of perchlorate in breastmilk.

Perchlorate's effect on thyroid function was discovered in 1952 and has been confirmed by a series of studies since then. (Stanbury and Wyngaarden 1952; Kessler and Krunkemper 1966; Lampe et al. 1967; Brown-Grant and Sherwood 1971; Gauss 1972; Mannisto 1979.) Scientists also discovered perchlorate's pronounced effects on developing animals very early on. Studies in the 1950s showed that perchlorate could pass through the placenta and affected fetuses more seriously than adults. (Postel 1957; Brown-Grant and Sherwood 1971.)

Until the mid-1960s, perchlorate was used to treat a severe hyperthyroidism condition known as Graves' disease. Reports of adverse effects of perchlorate treatment began to appear in the medical literature in the early 1960s. Although some of these reactions were minor, such as skin rashes and nausea, there were also numerous reports of patients suffering from fatal reactions or severe side effects where blood cell production was seriously compromised or failed outright. (Southwell and Randall 1960; Hobson 1961; Johnson and Moore 1961; Fawcett and Clarke 1961; Krevans et al. 1962; Gjemdal 1963; Sunar 1963.) One study found that eleven of 76 severely ill Graves' disease patients treated with perchlorate suffered at least moderate and sometimes fatal hematological side effects. (Barzilai and Sheinfeld, 1966.)

Scientists did not begin to examine the potential health effects of perchlorate at low doses until recently. In 1995 the EPA found that laboratory animals developed thyroid disorders after two weeks of drinking perchlorate-laced water. (Caldwell et al. 1995; EPA 1998.) In a 90-day drinking water study, researchers found significant reductions of thyroid hormone levels from perchlorate doses more than 10 times lower than those consumed in the two-week test, but no lower dose was tested. (Springborn 1998.) The most recent study to suggest health effects from low-level exposure comes from Arizona, where last year the state health department found a significant increase in abnormal levels of a thyroid hormone in infants whose mothers drank perchlorate-tainted water from the Colorado River while pregnant. (Brechner et al. 2000.) The study compared newborns in Yuma and Flagstaff. Levels of perchlorate are undetectable in the drinking water in Flagstaff. But at the time the data was collected, Yuma's water, drawn from the Colorado, had perchlorate concentrations more than three times lower than the California action level and more than five times lower than the EPA's current provisional standard.

There have been a few studies which have shown no association between perchlorate exposure in humans and thyroid hormone levels (e.g. Li et al. 2000a, Li et al. 2000b, Lamm et al. 1999, and Crump et al 2000), but these studies were all sponsored by various industry groups with a stake in the outcome of EPA's scientific review of perchlorate, including the perchlorate manufacturer American Pacific and the aerospace giant Kerr-McGee. Researchers from the California Department of Health Services and a University of Massachussetts scientist on the EPA's peer review panel have pointed out serious if not fatal weaknesses in all but one (Crump et al.) of these studies (Hill et al. 2000, Zoeller 2001.), but at this point the EPA is still using them in its evaluation of perchlorate.

Perchlorate's risks are by far greatest to children. In adults, hypothyroidism causes a variety of adverse symptoms including fatigue, depression, anxiety, unexplained weight gain, hair loss and low libido. Although these symptoms can be serious, especially if left untreated, the consequences of depressed thyroid hormone levels on developing fetuses and infants can be devastating: In a developing fetus or infant, even temporary disruption of thyroid hormones can lead to permanent defects in the developing organism. (EPA 1998.)Thyroid hormones are crucial to proper development of many organ systems, including the nervous and reproductive systems. (Porterfield 1994, Jannini 1995.) The possible developmental effects of hypothyroidism include mental retardation, vision, speech and hearing impairment, deaf-mutism, spasticity, abnormal gait, delayed reflex development, impaired fine motor skills, and abnormal testicular development in males. (EPA 1998; Brechner 2000.) In older children, depressed thyroid levels have been associated with lower motivation to learn and attention deficit disorder. (Porter et al. 1999.)Probably the most important issue when considering the potential effects of perchlorate is the relationship between maternal and fetal thyroid hormone levels and neurolgical development. It has been known for decades that mild maternal hypothyroidism can cause reduced IQ in children (Man and Jones 1969). Recently, however, scientists have begun to recognize how sensitive neurological development is to maternal thyroid hormone levels. In fact, one study found that women whose levels of a particular thyroid hormone measured in the lowest 10 percent of the population during the first trimester of pregnancy were more than 2.5 times as likely to have a child with an IQ of less than 85 and five times as likely to have a child with an IQ of less than 70. This was true whether or not these women were clinically hypothyroid, and many of the women in this group had thyroid hormone levels considered to be in the normal range (Pop et al. 1999.) This is important because it means that perchlorate does not have to alter women's thyroid hormone levels dramatically to have critical effects.

Despite the well established connection between maternal thyroid hormone levels and neurological development of offspring, none of the studies performed to date have been designed to address this critical issue. (EPA 1999c.) Furthermore, the studies that have been done have been interpreted using a cancer model of risk assessment rather than a brain development model. Another critical question which has been so far overlooked is whether perchlorate is concentrated and passed on to an infant through breastmilk. Although this issue is always a concern when talking about drinking water contamination, it is of particular importance in the case of perchlorate because the same molecule which moves iodide into the thyroid gland is also present in breast tissue. (Tazebay et al 2000, Welcsh et al. 2000.) Since perchlorate interferes with this molecule, being taken up preferentially at the expense of iodide, it is likely that perchlorate would be concentrated in milk, while iodide would be present at lower than normal concentrations. (EPA 1999c.)

Perchlorate was suspected as a carcinogen as far back as 1966, when the first long term study on the effects of perchlorate in drinking water was performed. After two years of perchlorate consumption, more than a third of perchlorate-fed lab animals developed benign thyroid tumors, compared with none of the control animals. (Kessler and Krunkemper 1966.) Perchlorate does not directly cause cancer, but perchlorate-induced tumors result from changes in the thyroid caused by hormone interference. (Similar effects are seen with other thyroid hormone disruptors.) The severity of these precursor lesions have been shown to be related to high doses of perchlorate and therefore the EPA considers the chemical to be a probable carcinogen. (EPA 1998.)

In 1996, about 800 residents of Redlands, Calif., in San Bernardino County near a now-closed Lockheed Martin plant, filed lawsuits against the company. They claim that the water they have been drinking for decades, today known to be contaminated with perchlorate and other toxins associated with the aerospace industry, has caused cancer and other health problems. Three of the plaintiffs have already died of leukemia and other cancers. Trial is set for 2002.