Suspect Salads: Nationwide implications
Localized Contamination, Nationwide Implications
Until now, contamination of drinking water supplies with perchlorate has been considered largely a regional concern — most serious in California, Arizona and Nevada, with hot spots in dozens of other states. But finding rocket fuel in grocery store lettuce means consumers across America are unknowingly getting doses of perchlorate equal to the levels in some drinking water supplies. Lettuce is the second-most consumed vegetable in the U.S. The average American consumed 33 pounds of lettuce in 2000, and the Imperial-Yuma crop accounted for 40 percent of year-round production. 
Decades of neglect at the now-abandoned perchlorate manufacturing facility near Las Vegas, formerly operated by Kerr-McGee of Oklahoma City, have polluted Lake Mead and the Colorado River with perchlorate at levels that typically range between 4 and 16 ppb.  But concentrations vary widely, depending on rainfall, the time of year, and how well the Kerr McGee facility's treatment system is working. From 1997 to 2000, for instance, the average perchlorate level in Lake Mead was 9 ppb, but reached 24 ppb in November 2000, and was measuring 14 ppb in January 2003.  Although perchlorate levels in the river tend to decrease farther from the Kerr-McGee site, testing near irrigation intakes near Yuma — more than 250 miles downstream — have found perchlorate concentrations ranging from 3 to 6 ppb. 
Water from the Colorado River irrigates more than 1.4 million acres of cropland in California and Arizona.  It is unlikely that lettuce is the only crop that takes up and concentrates perchlorate, but lettuce is of particular concern because its cultivation uses so much water, the edible portions have a high water content, and so much of the nation’s lettuce is grown with contaminated water. In 2001, almost 70,000 acres in Yuma County and more than 22,000 acres in Imperial County were planted with lettuce. [17,18] At the peak of production last winter, 374 truck loads of lettuce were shipped each day from Yuma and Imperial Counties. 
Because we purchased lettuce from grocery stores rather than picking it from specific fields, for most of the 22 samples little is known about where the crops were grown. However, given the perishability of lettuce (about a week) and the time of year the samples were purchased (January and February), it is highly likely that most if not all of the samples were grown in Yuma or Imperial County. Eighty-eight percent of the winter lettuce eaten in the U.S. (i.e., grown from December to March) is grown in these two counties. 
Lettuce Concentrates the Perchlorate in Water
If the irrigation water was contaminated with 3 to 6 ppb of perchlorate, as measured near irrigation gates in Yuma County, the levels detected in the samples would mean the lettuce concentrated the chemical by a factor of 5x to 40x. More research is urgently needed to answer this and other questions about the prevalence of perchlorate in the American food supply.
Unfortunately, the Colorado River is not the only source of agricultural water that is polluted with perchlorate. Looking only at commercially harvested lettuce, USDA data show that perchlorate contamination of water or soil is known or suspected in 10 of the 15 leading lettuce-producing counties in the U.S.  (Table B.) For example, in late 2002, a perchlorate plume from an abandoned highway flare factory was discovered in the San Martin area of Santa Clara County, Calif., contaminating almost 300 public and private wells.  Santa Clara is the 15th-ranking lettuce-producing county in the nation, with more than 1,200 acres commercially harvested in 1997. All but two of the top lettuce-producing counties are in California, where perchlorate contamination has been most widely documented.
Table B. Perchlorate contamination of water or soil is a known or suspected problem in 10 of the 15 top lettuce-growing counties in the U.S.
(a) Known perchlorate contamination
(b) Known perchlorate user, contamination status unknown
(c) Suspected perchlorate handler, contamination status unknown.
Source: , ,  Download this table in PDF format
The EPA says there are sites of known perchlorate use in more than 40 states — but the exact number of states is unknown, as some military locations are confidential  — and has stated that sampling is expected to confirm contamination at every site where perchlorate is or has been produced, handled or used.  So far, nationwide sampling has been spotty and in some states not a single sample has been taken, including many locations where perchlorate contamination is likely.  It is therefore possible that there are other regionally or nationally important farming regions unknowingly relying on perchlorate- contaminated water.