April 28, 2003

Suspect Salads: Dietary analysis

EWG’s Lettuce Tests and Dietary Analysis

During the weeks of January 20 and February 10, 2003, EWG purchased 22 samples of lettuce from the shelves of seven different grocery stores in Northern California and sent them to be analyzed for perchlorate by scientists at Texas Tech University, which has emerged as a major center for perchlorate-related research. The samples included pre-packaged and head lettuces, adult and baby greens, organic and conventional lettuces, from several different distributors.

Four samples were found to contain perchlorate at levels that ranged from 30 to 121 ppb and averaged 70 ppb. [Note: ppb = nanograms per gram (ng/g) lettuce wet weight.] There was no relationship between the results and the type or brand of lettuce tested. Because the detection limit for perchlorate in lettuce is relatively high (30 to 40 ppb in lettuce, compared to 1 to 4 ppb in water), it is possible that some of the other samples tested also contained perchlorate at concentrations lower than the detection limit.

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 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. [1] Based on an average adult body weight of 70 kilograms, and not counting exposures from food, EPA calculated that a safe level for perchlorate in drinking water is 1 ppb, or 1 microgram of perchlorate per liter of water.

Provisional Standard 10x Too High

The provisional RfD indicates the latest and best assessment of a chemical’s safe consumption level. A final, enforceable drinking water standard could be higher or lower than the proposed RfD. Sen. Barbara Boxer, D-CA, has introduced legislation requiring EPA to set an enforceable drinking water standard by July 1, 2004, but the agency says it can’t meet that deadline. To provide the margin of safety needed to protect the most sensitive populations, EWG has urged the EPA to set a safety standard of 0.1 ppb, or one-tenth the provisional RfD. [2]

EWG analysis shows that a one-cup (two-ounce) serving of the contaminated lettuce samples would contain, on average, 4 micrograms of perchlorate. This is four times what the EPA says is safe to drink in a liter of water. The most contaminated sample contained 7 micrograms of perchlorate per one-cup serving. But women’s eating habits vary greatly — some eat very little lettuce; others may eat a large salad twice a day. Women’s body weights also vary. These variances have important implications for risk analysis because they show that some women can have much higher exposures to perchlorate than others.

To better assess the health risks of perchlorate in lettuce, EWG analyzed USDA’s 1994-1996 Continuing Survey of Food Intakes by Individuals database, which monitors the food consumption of thousands of ordinary Americans. [7] The database contained information on 2,453 women of childbearing age (15 to 44) who measured their lettuce consumption over two days. One-fourth of the women ate lettuce on a given day, with 2 ounces the typical serving. But some ate up to 10 times as much in a given day. No differences were found in lettuce consumption by women who were pregnant or breastfeeding, compared to others of child-bearing age.

Using this consumption data and adjusting for body weight, EWG calculated the percentage of women who would exceed EPA’s provisional RfD under different scenarios. If the lettuce eaten contained the average amount of perchlorate found in the contaminated samples, 57 percent of the women would get a dose higher than the RfD, and 37 percent would get at least twice as much. If the woman with the highest lettuce consumption in the USDA database ate lettuce with the highest amount of perchlorate in our samples, she would get a dose that is 44 times the provisional RfD, based on her body weight.

One-fourth of women in the USDA database ate lettuce on a given day and 18 percent of the winter lettuce samples tested had measurable levels of perchlorate. From those values, EWG estimates that more than 2.8 million American women of childbearing age eat perchlorate-contaminated lettuce daily during the winter months. Approximately 1.6 million of these women get a daily dose of perchlorate greater than the EPA’s proposed reference dose, and more than 1 million of them get a daily dose at least twice the RfD.

Health Risks for Children and Adults

Women of child-bearing age are the most important population to consider when assessing the risks of perchlorate consumption because the developing fetus is 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. [2]

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. [1] Numerous studies on laboratory animals have shown that perchlorate affects the developing fetus at much lower levels than it affects exposed adults. [8,9] 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. [10]

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. [11] 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. [12] 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. [13]