June 22, 2004

Rocket Fuel in Cows' Milk - Perchlorate: Perchlorate Accumulation

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." [26]

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." [1] 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." [1] 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." [1]

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. [11] 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. [7] It is known to concentrate in several other food and feed crops such as wheat, soybeans*, strawberries, blackberries, alfalfa and Bermuda grass. [7] [*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
1 Alfalfa 2900 wet 5.5 (water) field TX [6]
2 Bermuda grass 1300 dry 11 (water) field TX [6]
3 Blackberry 593,000 NA 497 (soil) wild TX [6]
4 Cantaloupe 1645 wet 81 (water) garden KS [7]
5 Chile 128 wet ND (water) garden NM [7]
6 Cucumber 766 wet 81 (water) garden KS [7]
7 Lettuce 121 wet NA farm NA [4]
8 Okra 2 wet ND (water) garden TX [7]
9 Soybean* 7485 dry 100 (water) lab TX [6]
10 Squash 99 wet ND (water) garden NM [7]
11 Strawberries 1300 NA 467 (water) lab TX [6]
12 Sunflower 31 wet 5 (water) wild TX [7]
13 Tomato 221 wet 81 (water) garden KS [7]
14 Wheat 1400 dry 6 (water) field TX [6]

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. [4]

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. [12]

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.