Perchlorate Found in Texas Milk

BRITT E. ERICKSON Environmental Science & Technology 25sep03

Also see
Perchlorate Mystery Surfaces in Texas: 30,000 square miles in western Texas

When perchlorate turned up in lettuce grown in California and Arizona last spring because irrigation water had been contaminated with rocket fuel, farmers worried that the problem could be more widespread. Researchers at Texas Tech University have now confirmed some of those fears, reporting that milk purchased randomly from supermarkets in Lubbock, Texas, contains perchlorate at levels of concern. Although the source of perchlorate contamination in western Texas is unknown, the findings, which are reported in research posted to ES&T’s Research ASAP website on September 19, suggest that perchlorate is more prevalent in the environment and food supply than was previously thought.

The Texas Tech study was limited to seven milk samples, but “what amazed us was that all seven of them had perchlorate,” says Purnendu “Sandy” Dasgupta, one of the study’s corresponding authors. Perchlorate levels in the milk ranged from 1.7 to 6.4 micrograms per liter (µg/L). The U.S. EPA has not yet set a maximum level for perchlorate in drinking water and is currently waiting for the National Academies’ Institute of Medicine to review the issue (Environ. Sci. Technol. 2003, 37, 166A–167A). Meanwhile, the state of California has set its maximum level for perchlorate in drinking water at 4 µg/L.

“These are fairly low levels that we are talking about. Until a relatively sensitive ion chromatography technique was developed, you couldn’t detect perchlorate at these levels,” Dasgupta says. Now that researchers have satisfactory analytical methods for perchlorate, they are beginning to find more of it. “It’s going to be something like DDT. Everywhere you look, it is going to be there,” Dasgupta predicts.

Although most of the attention surrounding perchlorate has centered on contamination from rocket fuel, natural sources of it appear to be fairly common. “Here in west Texas, there are contaminated wells that are so far away from any possible source of munitions or munitions manufacturing that it certainly cannot be that,” Dasgupta says. Some evidence shows that it is generated atmospherically through the reaction of chloride aerosols with ultraviolet radiation, ozone, or lightning, he says.

Regardless of whether perchlorate is anthropogenic or naturally generated, it is beginning to show up in the food supply. Researchers speculate that crops like alfalfa, which is fed to dairy cows, may be one route for contaminating milk. Once thought to be essentially safe because of its low reactivity, perchlorate is now considered a cumulative toxin because it interferes with the transport of iodide, which is critical for proper thyroid function. As a result, researchers are calling for more studies to look at the general occurrence of perchlorate in drinking water and in food crops, so that regulatory agencies such as EPA and the U.S. Department of Agriculture can set allowable perchlorate limits based on good science.

source: http://pubs.acs.org/subscribe/journals/esthag-w/2003/sep/science/be_texasmilk.html 3oct03