Living routes to toxic routs

Federal scientists and university engineers have taken different approaches to quashing the potentially carcinogenic pollutant perchlorate. The chemical is in jet fuels, explosives, and some fertilizers (SN: 10/16/99, p. 245: http://www.sciencenews.org/sn_arc99/10_16_99/fob3.htm).

Government researchers say they’ve treed the pollutant. In contrast, the engineers have cleaned tainted water by running it through a community of perchlorate-chomping microbes. The treatments exemplify the range of approaches being explored to cope with this pollutant, which disrupts thyroid hormones.

Last fall, the federal government ruled that by 2001, community water suppliers must begin monitoring perchlorate. Utilities are now investigating how they might deal with this toxic mineral salt if it shows up in drinking-water sources.

A paper in the July 10 Science of the Total Environment suggests planting salt cedar (Tamarix ramosissima)—or tamarisk—along affected waterways.

These shrubby trees mine salt from the water about them. Among the salts they sop up is perchlorate, finds Edward T. Urbansky’s team at the Environmental Protection Agency’s research lab in Cincinnati. Stalks of the plant submerged in the Las Vegas Wash, a stream near Las Vegas, picked up 300 micrograms of perchlorate per gram of tissue. Even dry twigs growing well above the water acquired 5 mg/g.

Ironically, the federal government considers salt cedar—an invasive Asian native—to be a nuisance plant warranting removal. However, having had more than a century to put down U.S. roots throughout the arid West, where perchlorate contamination is common, “salt cedar must now be regarded as a major part of [that] ecosystem,” Urbansky and his colleagues say. Instead of targeting the plant for removal, they suggest it be explored as a trap for the toxic agent.

In the July 15 Environmental Science & Technology, Joel P. Miller and Bruce E. Logan offer a high-tech alternative. These engineers at Pennsylvania State University in State College describe a 5-month laboratory test with their new bioreactor—a 10-centimeter-high cylinder packed with glass beads supporting perchlorate-degrading bacteria. Although water passing through the reactor spends just 1 minute in contact with the microbes, they eliminated roughly 40 percent of the perchlorate—despite the pollutant’s high starting concentration of 740 mg/liter in the experiment.

Miller and Logan suspect that bigger reactors, offering longer contact between the microbes and the tainted water, might remove an even greater share of the pollutant.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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