Milk from cows raised in some parts of California may expose infants and children to more of a toxic rocket fuel chemical than is considered safe by the U.S. Environmental Protection Agency (EPA) and the State of Massachusetts, according to unreleased tests by state agriculture officials and independent laboratory tests commissioned by Environmental Working Group (EWG).
In the first study to look for perchlorate in California supermarket milk, EWG found perchlorate in almost every sample tested - 31 out of 32 samples purchased from grocery stores in Los Angeles and Orange counties. Through a state Public Records Act request, EWG also obtained results of tests for perchlorate in milk by the California Department of Food and Agriculture (CDFA), which the agency has not made public or provided to state health officials. CDFA's tests found perchlorate in all 32 samples of milk collected from unspecified sources in Alameda, Sacramento, and San Joaquin counties — but the agency kept this information quiet even as health officials were deciding how much perchlorate is safe for Californians to consume.
EWG's computer-assisted analysis of federal dietary data shows that by drinking milk contaminated with the levels ‡1 of perchlorate found in the two studies, 7 percent of women of childbearing age would get a daily dose of rocket fuel larger than the level currently considered safe by the EPA. But children are by far more at risk: Half of all children 1 to 5 would exceed EPA's provisional daily safe dose just by drinking milk, and more than a third would get twice that dose. One-third of children 6 to 11 would get a larger dose than EPA says is safe, with one-fifth consuming twice as much. These risk estimates assume zero perchlorate exposure from other sources, such as contaminated tap water and foods.
Perchlorate, the explosive component of solid rocket and missile fuel, can affect the thyroid gland's ability to make essential hormones. For fetuses, infants and children, disruptions in thyroid hormone levels can cause lowered IQ, mental retardation, loss of hearing and speech, and motor skill deficits. Currently there are no enforceable perchlorate safety standards at the state or federal level, but based on research showing health effects in laboratory animals at very low levels, EWG believes a national safety standard should be no higher than one-tenth the EPA's current safe dose.
Perchlorate contaminates more than 350 drinking water sources in California alone. Nationally, perchlorate contamination of drinking water has been confirmed by testing in 22 states. Among contaminated sources is the Colorado River, which not only provides drinking water for Los Angeles, Phoenix, Las Vegas and other cities, but also irrigates 1.4 million acres of farmland in California and Arizona. Many crop and feed plants, including lettuce, cucumbers, tomatoes and alfalfa, concentrate perchlorate in their tissues when grown with contaminated water. This perchlorate, in turn, can be passed along in cows' (or human's) milk.
In March, California health officials adopted a public health goal for perchlorate of 6 parts per billion (ppb) in a liter of drinking water. (A public health goal is the level used to set an enforceable state drinking water standard, expected later this year.) But the EPA's most recent provisional daily safe dose (RfD, for reference dose) is 1 ppb - the same level as a final risk assessment released last month by Massachusetts state scientists. Using the California health goal as a benchmark, only about 1 percent of children under 12 would get an unsafe dose of perchlorate by drinking milk. But both the EPA and Massachusetts have criticized the California goal as too weak, in light of the available data on health effects at very low levels.
The average perchlorate level in milk tested by the state, 5.8 ppb, is essentially the same as the maximum safe level of the just-adopted public health goal. The average level found in the EWG tests was lower, at 1.3 ppb, but could still present health risks, particularly for small children, who drink large amounts of milk relative to their size.
What's more, EWG's dietary risk analysis does not include additional perchlorate exposure through drinking water or foods other than milk. Our findings are not a call for California mothers to stop drinking milk or stop giving it to their children. But they do show that the public health goal is inadequate, and the state must set a tougher final drinking water standard that fully protects public health. Mothers should not be forced to wonder if milk — for many people the very symbol of a healthy diet — is affecting their child's growth and development.
- California agriculture officials must immediately release complete results and details of their tests for perchlorate in milk and other foods.
- California health officials must review the state's recently-announced perchlorate public health goal and tighten it to reflect exposure from milk and other foods as well as drinking water.
- The National Academy of Science's pending review of the EPA's perchlorate risk assessment must also account for exposure from food as well as water.
- The U.S. Food and Drug Administration and U.S. Department of Agriculture must move quickly to conduct a definitive study of perchlorate contamination in the American food supply, and make all results public. FDA should use its findings to promptly establish national safety standards for perchlorate in food.
- Irrigation water sources - not just drinking water sources - must be tested for perchlorate.
- Milk producers, other farmers and landowners must be fully compensated for lost profits and property values.
‡1 - EWG employed a probability-based model to estimate the percentage of individuals in the USDA's CSFII database that would exceed the EPA's reference dose, based on their body weight and milk consumption patterns, if they drank milk contaminated with perchlorate at the levels found in EWG's and CDFA's samples. The perchlorate concentrations of individual EWG and CDFA samples (not average concentrations) were used in the analysis. A perchlorate concentration of zero was assumed for those samples where perchlorate was not detected.
Milk Consumption Not Safe?
Infants and children may consume more perchlorate in milk than the EPA considers safe
Drinking milk from cows raised in some parts of California may expose infants and children to more of a toxic rocket fuel chemical than is currently considered safe by the U.S. Environmental Protection Agency (EPA) and the State of Massachusetts, according to unreleased tests by state agriculture officials and independent laboratory tests commissioned by Environmental Working Group (EWG).
In the first study to look for perchlorate in California supermarket milk, EWG found perchlorate in almost every sample tested - 31 out of 32 samples purchased from groceries in Los Angeles and Orange counties. EWG also filed a state Public Records Act request to obtain results of tests for perchlorate in milk by the California Department of Food and Agriculture (CDFA), which the agency has neither released publicly nor provided to state health officials. CDFA's tests found perchlorate in all 32 samples of milk collected from unspecified sources in Alameda, Sacramento, and San Joaquin counties. ‡1
EWG's computer-assisted analysis of federal dietary data shows that by drinking milk contaminated with the average levels ‡2 of perchlorate found in the two studies, 7 percent of women of childbearing age would get a daily dose of rocket fuel larger than the level currently considered safe by the EPA. But children are by far more at risk: Half of all children 1 to 5 would exceed EPA's safe dose just by drinking milk, and more than a third would get twice that dose. One-third of children 6 to 11 would get a larger dose than EPA says is safe, with one-fifth consuming twice as much.
Last month, California health officials adopted a public health goal for perchlorate of 6 parts per billion (ppb) in a liter of drinking water. (A public health goal, or PHG, is the level used to set an enforceable state drinking water standard, expected later this year.) But the EPA's provisional daily safe dose (RfD, for reference dose) is equivalent to 1 ppb - the same level as a risk assessment released last month by Massachusetts state scientists. [1, 2] Using the California health goal as a benchmark, only about 1 percent of children under 12 would get an unsafe dose of perchlorate by drinking milk.
The average perchlorate level in milk tested by the state, 5.8 ppb, was essentially the same as the maximum safe level for drinking water under the state's new PHG. The average level found in the EWG tests was lower, at 1.3 ppb, but could still present health risks, particularly for small children, who drink large amounts of milk relative to their size.
But both the EPA and Massachusetts have criticized the California goal as too weak in light of the available data on health effects at very low levels. According to the report from the Massachusetts Department of Environmental Protection, "the currently available data support a lower value in order to be sufficiently protective of sensitive individuals, including pregnant women and infants."  The report said that an even lower standard would be supported by the toxicity data, but that detection methodologies are not yet good enough to reliably detect perchlorate below 1 ppb.
What's more, EWG's dietary risk analysis does not include additional perchlorate exposure through drinking water or foods other than milk. In 2003, EWG and the Riverside Press-Enterprise found perchlorate contamination, at levels exceeding the EPA's provisional reference dose for drinking water, in samples of Southern California lettuce grown with contaminated water. [4, 5] EWG's study found that if women ate lettuce with perchlorate concentrations at the average level found in our contaminated samples, 57 percent would get a dose greater than the EPA's daily safe dose. These findings have since been confirmed by tests on lettuce and other foods conducted by the U.S. Army Corps of Engineers and academic researchers in Arizona and Texas. [6, 7, 8] Therefore, for many Californians, perchlorate exposure can't be assessed by looking at milk, or any other commodity, in isolation.
Perchlorate, the explosive main ingredient of solid rocket and missile fuel, can affect the thyroid gland's ability to take up the essential nutrient iodide and make thyroid hormones. These hormones regulate metabolism in adults and play important roles in the development of organ systems in fetuses, infants and children. Small disruptions in thyroid hormones in utero or during early development can cause lowered IQ; larger disruptions can cause mental retardation, loss of hearing and speech, or deficits in motor skills.  EWG's analysis of the latest scientific studies, showing harmful health effects from very low doses, argues that a national perchlorate safety standard should be no higher than one-tenth the EPA's currently recommended level of 1 ppb. 
There are no enforceable safety standards for perchlorate in drinking water at either the state or federal level. Attempts at setting them have been highly contentious and drawn out for more than a decade. Last year, in what was widely seen as another stalling tactic, the Bush Administration directed the National Academy of Sciences to review the EPA's 2002 study, and results are expected later this year. But evidence that at least two members of the review panel have financial ties to perchlorate polluters has raised what Sens. Barbara Boxer and Dianne Feinstein, in a letter to the NAS, call "serious issues about NAS review of conflict of interest, bias, and balance for this panel."  In June 2004, one of the two NAS panel members with ties to Lockheed was forced to resign.
During the weeks of December 8, 2003 and January 12, 2004, EWG and Physicians for Social Responsibility purchased 32 containers of milk from stores in Irvine, Pacific Palisades, Santa Fe Springs, Whittier and three different locations in Los Angeles. The samples included low-fat and whole milk from four well-known brands. Scientists at Texas Tech University, a leading center of perchlorate-related research, conducted the analyses. All but one sample contained measurable amounts of perchlorate, with the samples averaging 1.3 ppb.
Our study was the first to look for perchlorate in California milk. But in 2003, Texas Tech researchers were the first to find that milk could be contaminated. In that study, researchers found perchlorate in 7 out of 7 samples of whole milk purchased from local supermarkets, with levels as high as 6.3 ppb. The milk was purchased from grocery stores in Lubbock, where some water supplies are known to be contaminated with low levels of perchlorate. The samples represented six different brands of milk - essentially all of the brands of milk available in the area.  They also found perchlorate in a single sample of human breast milk taken from a woman living near Lubbock. The scientists were extremely thorough in validating their results: Each sample was tested three different times tested by two different laboratories, using two different methods. With these findings, plus the EWG and CDFA studies, there is no question that perchlorate is being passed from contaminated water into the U.S. food supply.
31 out of 32 samples of milk EWG tested had detectable perchlorate
|Brand||City Purchased||Fat Content||Perchlorate level (ppb)|
|1||Brand D||Los Angeles||whole||3.62|
|2||Brand A||Los Angeles||2 percent||2.66|
|3||Brand C||Santa Fe Springs||whole||2.06|
|4||Brand A||Los Angeles||whole||1.92|
|5||Brand D||Santa Fe Springs||whole||1.89|
|6||Brand A||Los Angeles||2 percent||1.87|
|7||Brand B||Pacific Palisades||2 percent||1.85|
|8||Brand C||Santa Fe Springs||whole||1.63|
|9||Brand B||Los Angeles||2 percent||1.59|
|10||Brand A||Whittier||2 percent||1.56|
|11||Brand C||Santa Fe Springs||whole||1.45|
|12||Brand C||Santa Fe Springs||"reduced fat"||1.38|
|13||Brand D||Los Angeles||whole||1.32|
|14||Brand C||Santa Fe Springs||"reduced fat"||1.31|
|17||Brand C||Santa Fe Springs||"reduced fat"||1.04|
|18||Brand C||Santa Fe Springs||whole||1.01|
|19||Brand B||Pacific Palisades||2 percent||0.98|
|22||Brand A||Los Angeles||whole||0.78|
|25||Brand B||Los Angeles||whole||0.72|
|26||Brand A||Whittier||2 percent||0.69|
|27||Brand B||Irvine||2 percent||0.68|
|28||Brand B||Irvine||2 percent||0.66|
|29||Brand A||Los Angeles||2 percent||0.65|
|32||Brand B||Los Angeles||2 percent||ND|
|Average perchlorate concentration in all EWG milk samples: 1.3 ppb|
After we completed analysis of our samples, EWG heard reports that the California Department of Food and Agriculture (CDFA) had also tested milk for perchlorate, but had not shared its findings with health officials. EWG requested CDFA's findings under the state Public Records Act. The state records showed CDFA collected samples of milk in Alameda, Sacramento, and San Joaquin counties, and found perchlorate in every one of them - in concentrations that were often higher than EWG's samples. The perchlorate levels in the CDFA samples ranged from 1.5 ppb to 10.6 ppb. The average level found, 5.8 ppb, is essentially the same concentration the state has said should be the limit for drinking water. 
Every milk sample CDFA tested had detectable perchlorate ‡1
|County||Perchlorate level (ppb)||County||Perchlorate level (ppb)|
|Average perchlorate concentration in all CDFA milk samples: 5.8 ppb|
Almost as disturbing as the concentrations of perchlorate found by CDFA is the fact that the agency kept the data secret. The state Office of Environmental Health Hazard Assessment, which was in charge of studies to set the recent public health goal, was not even informed that CDFA was doing a study. At a time when state officials up to and including Gov. Arnold Schwarzenegger were working to reach a final decision on a public health goal, and under intense lobbying by perchlorate polluters, CDFA apparently didn't think finding rocket fuel in supermarket milk was important enough to tell anyone. 
The documents received EWG from CDFA leave many questions about the state's testing program. They show that the samples were analyzed in April 2004 by the California Animal Health and Food Safety Laboratory at UC Davis. But they do not include information about how the study originated, how the samples were collected, what analytical method was used or whether the agency planned more tests.
EWG requested details that would put the results in context, but CDFA refused to supply them. The agency's chief lawyer replied to our request with a one-sentence statement: "These [documents] are our public records." Sources within the agency say the samples EWG obtained documentation of may be part of a much larger sampling project, but CDFA has released no additional information to the public or to state health officials.
Although we can't be sure of the source of the perchlorate found in any of CDFA's or EWG's samples, the chemical clearly is coming either from contaminated food or drinking water provided to livestock. Testing of public water supply wells around the state has turned up more than 350 drinking water sources in ten counties, with many sources still untested.  Although there has been little testing of agricultural wells, given the extent of perchlorate pollution it is virtually certain that at least some California dairy cows are drinking contaminated water.
But a more significant source of the perchlorate in milk is likely to be alfalfa grown with contaminated water. Scientists have found that alfalfa concentrates perchlorate to levels up to 950 times higher than found in the water it was irrigated with.  In 2002, California's Imperial County alone harvested more than 1.4 million tons of alfalfa for livestock feed - virtually all of it grown with water from the Colorado River.  This water is tainted with perchlorate from a now-closed manufacturing plant near Las Vegas, once owned by the Department of Defense and is now owned by defense contractor Kerr-McGee. 
EWG's and CDFA's findings of perchlorate in milk, and the agency's attempt to keep them quiet, call into question how rigorously the agency is upholding the state Food and Agriculture Code. A primary legislative charge in California's law regulating commercial livestock feed is to "to ensure in every way possible a clean and wholesome supply of meat, milk, and eggs for the benefit of the consumer."  CDFA claims that its inspection, sampling, testing, education, and "voluntary quality assurance" programs are "leading the nation in ensuring a safe and wholesome supply of commercial feed to the benefit of both the agricultural community and the consumer."  Ensuring that feed is uncontaminated is particularly important since, according to CDFA, California produces more livestock feed than any other state, and Imperial County is the state's leading feed producer. 
Although there are no safety standards for perchlorate in food, EPA has been working for more than a decade toward establishing a safe drinking water standard. In 2002, EPA proposed a reference dose (RfD) for perchlorate of 0.00003 milligrams per kilogram of body weight per day, which is the dose at which no adverse effect would be expected.  To assess the health risks of perchlorate in milk, EWG analyzed USDA's 1994-1996 Continuing Survey of Food Intakes by Individuals database, which monitors the food consumption of thousands of ordinary Americans.  The database contained information on more than 14,000 children (ages 1 to 11) and over 4,000 women of childbearing age (ages 15-44) whose milk consumption was measured over two days. (The database also includes information on other milk products such as cheese, yogurt and ice cream, but we only considered fluid milk consumption in our analysis.)
Using the USDA consumption data and adjusting for body weight, we used a probability-based model to calculate the percentage of individuals who would exceed EPA's provisional RfD if they drank milk with perchlorate concentrations found in EWG's and CDFA's studies. Our analysis showed that 51 percent of children aged 1 to 5 would get a perchlorate dose higher than the rfd, as would 35 percent of children aged 6 to 11 just by drinking milk. Thirty-five percent of children aged 1 to 5 and 20 percent of children aged 6 to 11 - would get a dose twice as high as the EPA thinks is safe. And 7 percent of women of childbearing age (15-44) would exceed EPA's RfD just by drinking milk.
|Population of Concern||Percent of individuals exceeding EPA's proposed reference dose|
|Analysis using EWG data only||Analysis using EWG and CDFA data||Analysis using CDFA data only|
|Infants and young children
|Women of childbearing age
It is clear from the USDA data that children are the most at risk for perchlorate in milk. Children not only tend to drink milk more often than adults, they also drink milk in greater quantities. For example, according to the USDA database, about 85 percent of children aged 1 to 5 drank milk on a given day, compared to only about 45 percent of women aged 15 to 44. And of those who drank milk, children between the ages of 1 and 2 drank an average of 1.8 cups of milk per day, while women in their twenties drank just a half-cup per day. EWG's analysis shows how much more likely kids are to exceed the EPA's proposed safety standard for perchlorate.
Milk appears to be a less significant exposure route for adults - unsurprising since adults typically drink much less milk in proportion to their body weight than kids. Yet, according to EWG analysis, 7 percent of women of childbearing age (15-44) would still exceed the EPA's proposed safe perchlorate level just by drinking milk. These calculations used milk concentrations from both EWG and CDFA's study. The percentages of individuals found to exceed EPA's reference dose are somewhat different if the calculations use only EWG's or CDFA's data. But no matter which subset of data is used in the calculations, it is clear that California milk is an important perchlorate exposure route for many children and some adults.
Again, none of our calculations account for water consumption or food consumption other than milk. With more than 350 drinking water sources in California contaminated with perchlorate, and the contaminated lower Colorado River irrigating 1.4 million acres of some of the nation's most productive farmland, it is very likely that many people are being exposed to perchlorate via multiple pathways.  EWG's 2003 study of winter lettuce found that if women ate lettuce with perchlorate at the average level found in our contaminated samples, 57 percent would get a dose greater than the EPA's rfd. 
Our findings have broad implications not just for the safety of the U.S. food supply, but also for current efforts to set perchlorate safety standards. Perchlorate has now been found to be taken up and concentrated by many foods besides lettuce and milk. Perchlorate exposure clearly is not just a risk for people in areas where the water is contaminated, but for anyone who consumes food produced with contaminated water.
‡1 - CDFA documents number their samples from 1 to 34, but numbers 19 and 23 are missing.
‡2 - EWG employed a probability-based model to estimate the percentage of individuals in the USDA's CSFII database that would exceed the EPA's reference dose, based on their body weight and milk consumption patterns, if they drank milk contaminated with perchlorate at the levels found in EWG's and CDFA's samples. The perchlorate concentrations of individual EWG and CDFA samples (not average concentrations) were used in the analysis. A perchlorate concentration of zero was assumed for those samples where perchlorate was not detected.
Women of child-bearing age and infants are the most important population to consider when assessing the risks of perchlorate consumption because the developing fetus and infant are much more susceptible to injury from perchlorate exposure than adults. Perchlorate interferes with normal thyroid function by blocking iodide uptake, a necessary building block of thyroid hormones, and can lead to hypothyroidism. In adults, hypothyroidism is associated with a variety of adverse symptoms such as 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.  Numerous studies on laboratory animals have shown that perchlorate affects the developing fetus at much lower levels than it affects exposed adults. [19, 20] Unlike adults, infants and fetuses do not have large stores of thyroid hormones, which would enable them to buffer changes in iodide availability and thyroid hormone levels in the body. 
Moreover, recent research has shown how remarkably sensitive the developing fetus can be to small disturbances in thyroid hormone level. 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 women in this group had thyroid hormone levels considered to be in the normal range.  This is important because it means that perchlorate does not have to alter women's thyroid hormone levels dramatically to have critical effects.
There is also evidence to suggest that perchlorate can have effects even at low doses. An epidemiological study of newborns in Arizona, for example, found that babies born to mothers who drank contaminated Colorado River water during pregnancy had significantly different thyroid hormone levels than infants of mothers who drank uncontaminated water.  An epidemiological study of thousands of California infants born in 1996 had similar findings, with significant differences in infant thyroid hormone levels of infants whose mothers drank water contaminated with perchlorate levels at just 1 to 2 ppb. 
Regulators are faced with a wide array of scientific decisions when developing risk assessments for a given chemical: Should they use a "weight of the evidence" approach that considers multiple studies, or base the assessment on a single "critical" study? What should they choose for the value of the "uncertainty factors" which account for remaining scientific uncertainties and variability within the population? How appropriate is each given human or animal study for the purpose of risk assessment? The three regulatory bodies that have so far published risk assessments for perchlorate — the US Environmental Protection Agency (EPA), California EPA (Cal-EPA), and the Massachusetts Department of Environmental Protection (MADEP) — have all come up with somewhat different answers to these recurring questions. But all three have agreed that perchlorate poses a health risk to the population at low doses.
Cal-EPA's Office of Environmental Health Hazard Assessment (OEHHA) relied on a single human study, known as the Greer study, to derive a perchlorate PHG of 6 ppb.  The Greer study involved dosing a small number of healthy adults (7 to 10 per dose group) with perchlorate for two weeks and examining how the toxin affected iodide uptake by the thyroid.  Although the study provided some valuable information, it also "has a number of inherent limitations" that make it difficult to extrapolate the results "to long-term exposures of infants and other susceptible people to perchlorate," as the MADEP noted in a recent report. 
Because of these limitations, both Massachusetts and the EPA chose to use a "weight of the evidence" approach in their toxicological risk assessments, looking not only at the Greer study but also the many animal studies that showed perchlorate-related effects on the developing fetus and nursing neonates. [1, 3] Looking at these earlier life stages is critical since studies dating back to the 1950s have clearly shown that perchlorate affects young animals at much lower doses than it does adults. But notably, after reviewing the process by which OEHHA arrived at its PHG, MADEP concluded that "the Greer study results themselves support a lower interim guidance value for sensitive individuals than adopted by CA EPA." 
Aside from its choice of studies to include, California also differed considerably from Massachusetts and the EPA in how it accounted for scientific uncertainty in its perchlorate risk assessment. While OEHHA used a single uncertainty factor of 10 (or just 3 for its calculations for infants) to account for differences between children and adults, variability between individual sensitivities within the general population and remaining scientific data gaps, both Massachusetts and EPA determined that a much higher uncertainty factor (UF) was needed to adequately protect sensitive populations. [1, 2, 12] In fact, when MADEP evaluated the California PHG it concluded that, using Cal-EPA's approach, a total "UF of at least 30 is clearly justified and values from 100 - 300 can be supported," resulting in a PHG "from approximately 1 ppb to the sub-ppb range."  The EPA's proposed and Massachusetts' final perchlorate reference doses are both equivalent to 1 ppb in drinking water. The MADEP, however, has stated that although it chose a "guidance level" of 1 ppb, a lower level "can be supported on the basis of the toxicity data" and noted that a driving factor in their decision was that current testing methodologies can not reliably detect perchlorate below 1 ppb. 
The EPA's RfD has been highly contentious, no doubt because the Department of Defense, perchlorate manufacturers, and major defense contractors face liable for millions of dollars in clean-up costs. Perchlorate contamination has now been detected at eight DOD sites around the country so far, and most have not even been tested. The National Academy of Sciences (NAS) has been called into review the EPA's proposed standard, but the objectivity of this body is in question: As California Sens. Barbara Boxer and Dianne Feinstein charged in a recent letter to NAS president Bruce Alberts, at least two members of the review panel have documented financial ties to polluters, raising "serious issues about NAS review of conflict of interest, bias and balance."  The NAS review was originally scheduled to be released in August of 2004, but has now been delayed until at least December, if not later.
The issue of perchlorate contamination of crops was first raised in 1998, when Native American tribes, who are among the major producers of Colorado River lettuce, saw the serious ramifications of the recently discovered contamination of the Colorado River. As the environmental manager for the Yuma, Ariz., Quechan tribe stated in a public forum:
"Irrigation is a way of life for our people. We have 13,000 acres dedicated to the production of lettuce. We produce annually eight heads of lettuce for every man, woman and child [in the U.S.]. That food is produced from Colorado River water and 23 million people derive their water supply from the lower Colorado River in three states and two countries. That's how big this problem is." 
Four years later, EPA reviewed the numerous studies that had been conducted on plant uptake of perchlorate and, in its report documenting the RfD of 1 ppb in drinking water, said: "There can be no question that at least some vascular plants absorb perchlorate from their local environments."  This is important because the agency's policy in setting drinking water standards is that, once an RfD is established, "any burden posed by exposure routes other than potable water necessarily requires that the contaminant's concentration in a water supply be lowered by an equivalent amount."  In other words, if food is found to contain perchlorate, the drinking water safety standard must be set lower to account for this additional exposure. Yet, despite significant evidence to the contrary, the EPA concluded that "the available information . . . suggests that foods do not contribute to the body burden." 
Two years later, there is an armload of research indicating how far off base EPA was with this conclusion. Perchlorate has now been found in grocery store-bought lettuce and milk from California and Texas. [4, 11] It has been found in the breast milk of a woman whose tap water had no detectable perchlorate in it at the time.  Perchlorate has been found in cucumbers, cantaloupes, tomatoes, squash, chiles, and okra grown in gardens irrigated with contaminated water in Kansas, New Mexico and Texas, at levels up to 1,645 ppb.  It is known to concentrate in several other food and feed crops such as wheat, soybeans*, strawberries, blackberries, alfalfa and Bermuda grass.  [*Note: perchlorate was found in several parts of the soybean plant, including the seed coat, but not in the soybean seeds themselves.]
Perchlorate accumulates in at least 14 food and feed crops
|Plant type||Max perchlorate level detected (ppb)||Wet or dry weight||Perchlorate level in water or soil (ppb)||Location grown||State grown||Ref|
|2||Bermuda grass||1300||dry||11 (water)||field||TX|||
NA = data not available
ND = not detected
*Perchlorate was found in the soybean seed coat and leaf, but not in the seed itself
What's more, the concentration factors found in these studies are high — typically 10x to 300x, but over 1,000x in some cases. [1, 6, 27, 28, 29] This is important, as it follows that even low levels of perchlorate in irrigation water can translate into considerable perchlorate concentrations in crops - and substantial exposures to the population via food consumption. Based on our tests of grocery store lettuce, EWG calculated that more than 1.6 million women each day are likely exceeding the EPA's reference dose for perchlorate just from eating winter lettuce. 
When Cal-EPA's Office of Environmental Health Hazard Assessment (OEHHA) calculated the public health goal for perchlorate, the agency assumed that 60 percent of perchlorate exposure was coming from water and 40 percent was coming from food. Although this ratio was a significant improvement over a previous draft that assumed only 20 percent of exposure would come from food, is it highly questionable whether even the revised ratio sufficiently reflects the significant potential for perchlorate exposure through food. 
Although a comprehensive study of perchlorate in the food supply still has not been conducted, EWG's and others' tests clearly show that food is an important exposure pathway for perchlorate. All future drinking water standards must adequately reflect this fact.
Principal author: Renee Sharp
Editor: Bill Walker
Design and graphics: T.C. Greenleaf
Photo: Water Resources Archives, UC Berkeley
Thanks to Physicians for Social Responsibility, Los Angeles, for sample collection; the Institute for Environmental and Human Health, Texas Tech University, for laboratory analysis; and Richard Wiles of EWG for editorial contributions.
This project was made possible by the support of the Sacramento Natural Foods Coop and other members of the National Cooperative Grocers Association, and the California Wellness Foundation. The author and editors are soley responsible for the report and any errors.