she says, “Because the perchlorate is frequently present in such small amounts, it’s hard to isolate enough of it to study [the source] directly and try to figure out if it’s natural or manmade.” Orris and Jackson predict, however, that the extent of low-level perchlorate occurrence, especially in Western aquifers and likely beyond Texas, has been underestimated and is more widespread than previously thought. “Nobody was looking for it before,” Jackson says, but now that detection limits are at the sub-parts-per-billion range, “more people are going to find it.” —KRIS CHRISTEN
Perchlorate found in milk in Texas
RHONDA SAUNDERS
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 this issue of ES&T (pp 4979–4981), suggest that perchlorate is more prevalent in the environment and food supply than
Better analytical methods are finding perchlorate contamination in new places.
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 draft level for perchlorate in drinking water at 2–6 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
News Briefs Chemical rule will work The controversial chemical legislation under development in the European Union (Environ. Sci. Technol. 2003, 37, 241A–242A) will work, finds a report prepared for the European Commission, because the law’s provisions would have identified the risks posed by several particularly hazardous substances before significant environmental damage occurred. If four chemicals— nonylphenol, short-chain chlorinated paraffins, tributyltin, and tetrachloroethylene—whose uses were or are in the process of being prohibited or restricted under existing legislation had been subjected to the requirements called for under the new legislation, information on the substances’ properties would have been available more quickly, the study says. The Impact of the New Chemicals Policy on Health and the Environment can be accessed at http://europa.eu.int/comm/environment/ chemicals/whitepaper.htm.
Politically distorted science The Bush Administration has “repeatedly suppressed, distorted, or obstructed science to suit political and ideological goals,” charges a report from a prominent Democrat in the U.S. House of Representatives. The report asserts that Bush’s actions have gone well beyond typical shifts in policy occurring with a change in political party in the White House. It details 29 actions, such as the Administration’s replacement of 15 of the 18-member National Center for Environmental Health at the U.S. Centers for Disease Control and Prevention. The report, prepared by the Democratic staff of the House Government Reform Committee and released by Rep. Henry Waxman (D-Calif.), can be found at www.politicsandscience.org.
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rence points to a natural mineral source, either in the subsurface water where it’s dissolved and then transported to the aquifer, in the saturated zone, or possibly even an upwelling from deeper layers, Jackson says. Researchers have found perchlorate in the low-parts-per-billion range in some naturally occurring evaporite materials in scattered locations in the Western hemisphere, says Greta Orris, a research geologist with the U.S. Geological Survey. It’s possible that the perchlorate in Texas could be coming from such a source, “but we don’t know enough yet at this point,” she notes. Also,
Environmental▼News 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. —BRITT E. ERICKSON
Newly developed bacterial biosensors may offer a cheap and simple way to detect arsenic contamination in potable water, according to research in the October 15 issue of ES&T (pp 4743–4750). The sensors could help people living in areas like Bangladesh and Vietnam, where arsenic contamination is endemic and a way is needed to quickly determine if water is safe to drink. Although the health of millions of people is threatened by high arsenic concentrations in the groundwater they drink, the chemical field test kits currently used to detect arsenic are unreliable (Environ. Sci. Technol. 2003, 37, 35A–38A). Jan Roelof van der Meer and colleagues at the Swiss Federal Institute for Environmental Science and Technology (EAWAG), the Swiss Federal Institute of Technology, the German Collection of Microorganisms and Cell Cultures, and the University of Kentucky set out to address this issue by constructing three different biosensors based on nonpathogenic, genetically engineered E. coli. The sensors could potentially be used for routine field applications, the researchers claim. In the presence of arsenic, the genetically engineered bacteria in the sensors produce a “reporter” protein—bacterial luciferase, -galactosidase, or green fluorescent protein—that can be detected through bioluminescence or colorimetry. The -galactosidase biosensor is the simplest of the three because it directly gives a visible
JAN ROELOF VAN DER MEER, EAWAG
Biosensors for quickly detecting arsenic in drinking water
Arsenic contamination in water can be detected by paper strip tests with immobilized sensor bacteria. Upon detection of arsenic, the bacteria produce a blue color whose intensity correlates with the sample’s arsenic concentration.
color response and does not require sophisticated detection. For this sensor, bacterial cells immobilized on paper strips can be dipped in the water sample and visually read after about 30 minutes, making the system especially suitable for semiquantitative field tests. The luciferase sensor, in which the bacteria are placed in microtiter plates, requires a luminometer for detection but is more quantitative than the paper strip system. “Practice has to show which method people in the field prefer,” van der Meer says, and he stresses that field-portable luminometers are available.
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The biosensors are living organisms, and continued incubation with the sample leads to an increasing response, so that the output values need to be compared to a simultaneously run standard series, van der Meer says. This also means that the biosensors can be disturbed by toxic compounds; however, corrections can be made by spiking the samples with a known amount of arsenic, he adds. The sensors were constructed to give optimal results in the important concentration range for arsenic between 8 and 80 micrograms per liter. The paper strip sensors can be stored for two months without loss of activity, and frozen cell batches for the luciferase system can be stored for several years, van der Meer says. The luciferase biosensor is now being field-tested in Vietnam by EAWAG chemist Michael Berg and the Research Center for Environmental Technology and Sustainable Development in Hanoi. Berg says that the biosensors have promise as fast screening devices for large amounts of samples. “I could envision a system where water samples are screened for high arsenic concentrations on a community level and positive samples subsequently sent to the laboratory for more sophisticated chemical analysis,” Berg says. Another use for the method could be for local quality control in hospitals and water treatment, van der Meer suggests. The material costs for the paper strip biosensors are less than 10 cents per strip, according to van der Meer. EAWAG has applied for a patent for the new system. “The arsenic biosensors have an excellent potential for routine field
