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Until recently, perchlorate contamination of water supplies has been considered a local or regional problem. But new findings from the Environmental Working Group have made perchlorate contamination a national issue of concern.

New research has shown that lettuce grown in the fall and winter months in Southern California or Arizona may contain higher levels of toxic rocket fuel byproduct, perchlorate, than is considered safe by the U.S. Environmental Protection Agency, according to independent laboratory tests commissioned by Environmental Working Group (EWG). The EWG says that simply by eating lettuce, 1.6 million American women of childbearing age were being exposed daily during the winter months to more perchlorate than the EPA's recommended safe dose.

EWG’s complete report, titled “Suspect Salads,” is available at http://www.ewg.org/reports/suspectsalads/es.php.

According to reports in the Baltimore Sun, the lettuce samples contained substantial quantities of perchlorate. One, which was a prepackaged variety of organic mixed baby greens, had a level of perchlorate contamination considered 20 times higher than the amount California currently considers safe for drinking water. The others had perchlorate rates five times higher than California's safety level.

Perchlorate is a contaminant that exists in the environment as a part of other compounds such as ammonium, potassium, or sodium perchlorate. Ammonium perchlorate is manufactured as an oxygen-adding component in solid fuel propellant for rockets, missiles, and fireworks.

In the first-ever tests of perchlorate in supermarket produce, 18 percent of lettuce samples contained detectable levels of perchlorate, and an average serving of contaminated lettuce contained 4 times more perchlorate than the EPA says is safe in drinking water. The source of the perchlorate, according to the EWG, is most likely the Colorado River, whose perchlorate-contaminated water irrigates more than 1.4 million acres in California and Arizona.

EWG’s tests on retail produce confirm previous research on greenhouse-grown lettuce seedlings and field-grown lettuce, kale and spinach.

"Our findings and the earlier tests show that toxic rocket fuel is not just a regional problem in areas where drinking water is contaminated, but a national concern for everyone who eats winter lettuce," said Renee Sharp, a senior analyst in EWG's California office and co-author of the report. "To protect people from perchlorate not just in water but food, safety standards will have to be much tougher than what's currently proposed."

Perchlorate, the explosive component of 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, but the EPA’s currently recommended safe dose is equal to 1 part per billion (ppb) in drinking water. EWG’s review of the latest studies argues that a national safety standard should be no higher 0.1 ppb — one-tenth the EPA’s currently recommended level.

Perchlorate contaminates more than 500 drinking water sources in 20 states, serving well over 20 million people. Among major contaminated sources is the Colorado River, which not only provides drinking water for Los Angeles, Phoenix, Las Vegas and other cities, but also irrigates 70 percent of the nation’s lettuce grown from October to March. Of the 15 leading lettuce-growing counties in the U.S., 10 have known or suspected sources of perchlorate pollution.

The report is being released as lawmakers in Washington and Sacramento are urging tougher perchlorate regulations.