Environmental ▼News Perchlorate mystery surfaces in Texas esearchers from Texas Tech University (TTU) have uncovered the largest area of contiguous perchlorate contamination in the United States, which exceeds 30,000 square miles in western Texas. Although concentrations are at low levels—the bulk of them in the 4 parts-per-billion (ppb) detection rangethe big question now is, Where is the perchlorate coming from? It all started when the Texas Commission on Environmental Quality (TCEQ) was conducting routine sampling under the U.S. EPA’s Unregulated Contaminant Monitoring Rule, according to Steve Walden, a TCEQ special projects manager. After detecting trace levels of perchlorate in drinking water wells supplying the Midland, Texas, area and in an elevated water storage tank in the city of Levelland, roughly 100 miles north of Midland, TCEQ continued taking samples. Surprisingly, the agency found perchlorate almost everywhere it looked. TCEQ turned to TTU for help, and the study area was expanded to nine counties around the sites where perchlorate was found in an attempt to establish a contamination perimeter. Of the 217 public drinking wells the TTU researchers tested, 73% had detectable perchlorate concentrations of more than 0.5 ppb and 35% had concentrations equal to or above 4 ppb. California’s draft drinking water standard is currently set in a range of 2–6 ppb. The highest level found was 58.8 ppb, according to Andrew Jackson, an environmental engineer at TTU, who presented the findings in late July at a perchlorate symposium in Sacramento, Calif. Finding no limit to the contami-
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nation, the TTU researchers expanded their study to 54 counties, an area of roughly 60,000 square miles, which is bigger than some states. “In the northern part of the Panhandle [in northern Texas], we’re finding much reduced occurrence, but in the bottom two-thirds, it’s fairly consistent,” Jackson says. The findings could have huge implications for the state, depending on whether • Levelland
• Midland
EPA chooses to regulate perchlorate in drinking water in the low-parts-perbillion range. EPA recommended a preliminary drinking water limit of 1 ppb in 2002 (Environ. Sci. Technol. 2002, 36, 125A), but the risk assessment on which this draft limit is based is currently under review by the National Academy of Sciences (Environ. Sci. Technol. 2003, 37, 166A–167A). Drinking water in western Texas is typically culled from a mix of surface and groundwater sources, the latter coming from the High Plains aquifer system. Here, the underground Ogallala aquifer is the main water source, and it is where most of the perchlorate was detected. “It’s a massive water resource for
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the state,” Walden says, adding that regardless of EPA’s decision, people will have to continue using these water supplies because no other options exist. Until now, most perchlorate contamination has been associated with point sources. “They usually have a tight, controlled plume produced off some industrial site that used to manufacture or handle perchlorate,” Jackson says. An occurrence survey of national drinking water supplies published in 2002 by the American Water Works Association’s Research Foundation confirms this. In Texas, however, no plumelike pattern is discernible, according to Jackson. Moreover, perchlorate’s occurrence is random. For example, the TTU researchers have found some wells yielding relatively high perchlorate concentrations immediately adjacent to wells with little or no detectable perchlorate. The four scenarios considered to be most plausible for generating the widespread contamination are agricultural use of fertilizers containing perchlorate, in situ generation of perchlorate by an electrochemical reaction, a natural source, or some combination of these three. For example, TTU researchers believe that the high perchlorate concentrations initially detected in Levelland’s water storage tank were generated by the unit’s cathodic protection system through mechanisms confirmed in laboratory experiments. “A lot of oil wells, pipelines, and water wells have active systems on them,” Jackson says, but the parameters necessary for perchlorate formation have only been observed with this one tank. More likely, the patchy occur© 2003 American Chemical Society
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,
