Suspect Salads: EWG tests confirm research
EWG’s study was the first to test produce from grocery store shelves. Although the findings are unsettling, they were not unexpected: Previous research on perchlorate uptake by vegetation clearly indicates the potential for widespread contamination of lettuce and other crops.
The first known tests of field-grown vegetables were conducted in 1997 by Lucky Farms of San Bernardino, Calif., after the grower learned that its wells had been polluted with perchlorate from a former Lockheed Martin rocket-testing facility. This plume of Lockheed rocket fuel has polluted dozens of drinking water sources in San Bernardino County, and the five wells on Lucky Farms property have concentrations of perchlorate ranging from 20 to 130 ppb, averaging 40.1 ppb. 
Lucky Farms tested eight samples of otherwise unidentified “leafy vegetables” and “vegetable matter.” Four samples of "leafy vegetables" averaged 4,490 micrograms of perchlorate per kilogram (ug/kg, which is essentially equivalent to ppb), with a maximum concentration of 6,900 ug/kg. Perchlorate levels in the “vegetable matter” were lower, averaging 213 ug/kg with a high of 420 ug/kg. Overall, the vegetables were found to have an average of more than 2,600 micrograms per kilogram — thousands of times higher than the 1 ppb EPA considers to be safe in a liter of water. 
Because we don’t know which wells were used to irrigate which Lucky Farms samples, it is difficult to calculate exactly how much each of the tested vegetables concentrated perchlorate, but using average figures for the amount of perchlorate found in the wells and the vegetables, EWG analysis shows that the vegetables concentrated perchlorate by a factor of 65x. This means that perchlorate levels in the vegetables were on average 65 times higher than the levels in the water. This information came from documents that were subpoenaed in a lawsuit against Lockheed Martin by 800 San Bernardino-area residents who say drinking perchlorate-contaminated water caused a variety of illnesses, including thyroid cancer. 
Tribes Raised Concerns Earlier
However, as long ago as 1998, Native American tribes, who are among the major producers of Colorado River lettuce, were raising serious questions posed by the recently discovered contamination of the Colorado River. At a public forum in Henderson, Nev., the environmental manager for the Yuma, Ariz., Quechan tribe stated:
“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.” 
The tribes urged the government to conduct a study of crops grown with Colorado River water and examine their perchlorate concentration. At an “eco-summit” convened by the EPA in April 1999, this type of “market basket” study was given top priority.  The attendees included the Air Force, major perchlorate manufacturers and users (including Lockheed Martin) and five Indian tribes who produce winter vegetables irrigated by the Colorado River. Unfortunately, although the Department of Defense pledged $650,000 to fund this and other studies, and EPA, USDA and the Food and Drug Administration developed an extensive protocol for the study, and neither this nor any other “real world” study was ever conducted. Defense Department representatives later stated that they had postponed the study indefinitely because it was too expensive. 
The Defense Department did fund a set of studies on hydroponically-grown greenhouse lettuce seedlings. The first study, conducted in 1999 by the EPA’s National Exposure Research Lab, found that “perchlorate was accumulated in the leaves to significant levels” — factors of 100x or more.  This extraordinarily high rate of bioaccumulation would mean that lettuce grown in water with even low levels of perchlorate could deliver large doses of the toxin to consumers — doses far higher than the EPA’s provisional drinking water standard.
Yet the EPA discounted the results of the 1999 study because the water used was contaminated with concentrations of perchlorate much higher than are typically found in water supplies, the lettuce seedlings were harvested before maturity, and the seedlings were grown in greenhouses rather than typical field conditions. A second, longer greenhouse study was later conducted, but aside from a brief summary that indicates an “accumulation of perchlorate into the green tissue,” results have never been made public.  In October 2002, at a perchlorate conference in Ontario, Calif., when a Department of Defense spokesperson was asked publicly when the data would be released, he replied: “Someone walked away with the data.” EPA officials have since indicated that they plan to release the results within the next few months. 
Perchlorate in Other Plants and in Fertilizer
Additional studies have also pointed to the potential for crop uptake of perchlorate when contaminated fertilizer or irrigation water is used. Several lab studies, for example, have found that a variety of non-crop plants can concentrate perchlorate, with a wide range of concentration factors — from 7.5x to 25x in one study, from 0 to 330x another, and from 30 to 10,000 in yet another. [1, 25-27] Additional studies examining the potential of different kinds of plants to bioremediate contaminated areas also found perchlorate accumulation in vegetation, with some species taking up 95 percent of the perchlorate in the irrigation water. [29-31] All of these studies have found that perchlorate tends to accumulate in the leaves of plants rather than the stems or roots, an important finding for the safety of vegetable crops.
Moreover, recent greenhouse experiments at Texas Tech University have also demonstrated that not only lettuce plants, but other crop plants such as cucumbers, alfalfa and soybeans* can quickly take up and concentrate perchlorate to high levels when grown with contaminated water.  These findings, as well as another study which found perchlorate in blackberries growing in a contaminated area in Texas, are particularly important. They indicate that although lettuce has been of greatest concern with regards to perchlorate contamination of food plants, the problem is potentially much larger.  [*Perchlorate was found in several parts of the soybean plant, but not in the soybean seeds themselves.]
The recent experiments on crop plants have also yielded several important insights: Nitrogen levels in the soil affected the rate of perchlorate uptake but not the final concentration; plants grown for in sand dosed with perchlorate during both the first and fourth week of growth continued to take up perchlorate during all eight weeks of the experiment; and perchlorate concentrations in vegetation were found to decrease with washing.  Further research at Texas Tech is under way to examine how multiple generations of rodents exposed to perchlorate-contaminated food may be affected — including survival and reproduction, thyroid structure and thyroid hormone levels — but no data are yet available. 
Studies of perchlorate accumulation are not just limited to controlled laboratory experiments. Researchers have found high levels of perchlorate in plants and animals living in contaminated areas such as the Alleghany Ballistics Laboratory in West Virginia, the Long Horn Army Ammunition Plant in Texas, the McGregor Naval Weapons Industrial Reserve plant in Texas — not far from President Bush’s ranch — and the Lake Mead Recreation Site in Nevada. Species with documented perchlorate concentration include blackberries, salt cedar, crabgrass, goldenrod, crickets, as well as fish, mice, rats, raccoons, birds and frogs. [27, 32-35] These field studies have found concentration factors in vegetation ranging from 1.5x to 80x. 
High levels of perchlorate have also been found in the leaves of field-grown tobacco plants where Chilean saltpeter, which is used as a nitrogen source and is naturally high in perchlorate, had been added to the soil. [1, 36] The concentration factors in this study exceeded 40x. Chilean saltpeter is preferred by farmers for growing tobacco in many regions, and EPA researchers have found perchlorate in six of seven brands of cigarettes, cigars and chewing tobacco tested. [36, 37] Citrus farmers, at least in some regions of the country, are also known to prefer Chilean saltpeter fertilizer, but so far no studies have been conducted on citrus juice. [1, 32]
Overall, however, contaminated fertilizer is not considered to be a major source for perchlorate in the environment or in food crops. Chilean fertilizer, the only known source of perchlorate in fertilizer, currently makes up only 0.1 percent of the U.S. fertilizer market.  Furthermore, the company that distributes Chilean saltpeter has made processing modifications to decrease the concentration of perchlorate in the final product sold. After much study, there is now “a consensus among researchers from the EPA, the fertilizer industry, and other federal and state laboratories that currently used fertilizers are negligible contributors to environmental perchlorate contamination.”  The studies that have been done on perchlorate uptake from fertilizer are significant, however, because they provide more evidence that plants can take up and concentrate perchlorate — wherever it might be coming from.
EPA: “No Question That Plants Absorb Perchlorate”
In its 2002 report documenting the provisional RfD of 1 ppb in drinking water, EPA reviewed the numerous studies on plant uptake of perchlorate and concluded: “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 knowing that the Colorado River is a major source of irrigation water, despite the clear evidence that plants take up and concentrate perchlorate, and despite the lack of data on how much perchlorate might be in U.S. or imported produce, the EPA concluded that “the available information . . . suggests that foods do not contribute to the body burden.” 
The California EPA’s Office of Environmental Health Hazard Assessment (OEHHA), which is working towards a state drinking water standard for perchlorate, did consider perchlorate exposure through food in its March 2002 proposed public health goal (PHG).  OEHHA assumed that 60 percent of perchlorate exposure was coming from water and 40 percent was coming from food. Yet under intense pressure from the chemical and defense industries, the state’s scientists retreated: In a revised PHG draft released in January 2003, OEHHA assumes that only 20 percent of a pregnant woman’s perchlorate exposure comes from food. 
Although EWG’s tests of grocery store lettuce do not constitute a definitive study and further research is needed, the results clearly show that food is an important exposure pathway for perchlorate. All future drinking water standards must adequately reflect this fact.