SCIENCE NEWS Water pollution point sources still significant in urban areas Twenty-three years after Congress passed the Clean Water Act, point sources remain an important contributor of nitrogen and phosphorus pollution in some streams and rivers, according to nationwide studies by U.S. Geological Survey (USGS) scientists. These studies provide detailed estimates of point and nonpoint source pollution. "Streams in urban areas, particularly in the Northeast, may still be heavily impacted by point source pollution," says Larry Puckett (USGS, Reston,VA). Results were reported at the American Geophysical Union meeting in December. In a recently completed analysis of 600,000 miles of streams and rivers and 850 major water reservoirs in the lower 48 states—the largest of its kind to date—USGS scientist Richard Alexander reports that point sources contribute more than half of the nitrate and phosphorus around many urban centers. In addition, Alexander's group found that point sources of phosphorus dominate river pollution downstream of large reservoirs because the reservoirs trap nonpoint
source phosphorus typically bonded to soil particles from farm runoff. Nevertheless, as expected, nonpoint sources are the dominant contributor of these two nutrients in most stretches of rivers and streams. According to the USGS watershed-based analysis, nonpoint sources were responsible for >90% of the nitrogen load in more than half of the 86 rivers and streams studied, and were responsible for >90% of the phosphorus in one-third of the rivers and streams. Computer modeling results were similar, indicating that for more than 80% of the river and stream miles modeled, nonpoint sources were the dominant contributor. The USGS studies used a geographical information system (GIS) as part of their approach to estimate point and nonpoint source pollution. They tapped a variety of databases for the analyses, including county and municipal surveys of wastewater discharge; census statistics on fertilizer sales, crop acreage, and farm animal populations; atmospheric deposition val-
ues from the National Trends Network; USGS monitoring stations; land use inventories; and estimates of nutrient runoff from animal manure. The watershed-based approach employs a budget analysis that essentially subtracts calculated point source pollution from total amounts in rivers and streams to estimate nonpoint source values. The computer modeling approach uses a nextgeneration GIS model, which, Alexander says, is unique in being able to estimate errors in predictions of pollutant concentration in each of the 62,000 river reaches in the model. For example, the model's estimates of phosphorus levels match observing station data within a factor of two. The USGS analyses indicate that the relative amounts of nonpoint and point sources nutrient loading to U.S. waters vary significantly by location. These findings show, argues Puckett, "that we can't have a blanket policy for water. We need management plans tailored for watersheds." —ALAN NEWMAN
New home radon monitor developed Los Alamos National Laboratory (LANL) researchers have applied for a patent on a home detector that continuously monitors for radon gas. This new monitor, should be straightforward to manufacture and affordable, claim LANL developers. "There is nothing in a home smoke detector that is more complicated than what we have developed," says co-developer Richard Bolton. EPA, having identified radon as a high-risk indoor air pollutant that causes lung cancer, has mounted an ad campaign to get home owners to test for the radioactive gas. Current commercial radon test kits are expensive and potentially misleading. The kits use a charcoal canister to trap the gas; the canister must be sent to a laboratory for analysis, and
each canister yields only a single measurement. LANL's monitor can detect single atoms and, with the proper electronics, trigger an alarm when a threshold value is exceeded. The prototype consists of nested chambers made from camp cooking gear. A filter in an inlet allows only gas molecules into the inner section. A small, charged pin in the center sets up an electric field, which indirectly detects radon. As radon (and its product isotopes) decay, they emit alpha particles, which in turn ionize air molecules. LANL scientists discovered that the positively charged molecular ions had a lifetime of a few seconds and thus could be detected. In actual operation, it is the free electrons that are measured by the detector's electrometer.
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Prototype of a home radon monitor developed at Los Alamos National Laboratory
According to Bolton, other sources of ionizing radiation, such as cosmic rays, do not confuse the detector. "We've used better electronics and a better understanding of the materials to cut back on other sources of current that could mask radon's signature." —ALAN NEWMAN
