Environmental▼News moved from heavy-traffic areas, with lead levels at 64 parts per billion (ppb) in the sweepings and 86 ppb in runoff. Roger Bannerman, an environmental specialist at the Wisconsin Department of Natural Resources, has been studying street sweeping for decades and says that the lead levels found in Muhammad’s study seem high and were probably the result of residual pollution. He also said that bacterial runoff was greater than allowable Wisconsin standards for swimming (400 bacteria/100 mL). However, Bannerman says it’s not clear whether street sweepers are really effective at mitigating water pollution. “We recently tested one of the best [street sweepers] out there, and it’s hard to see how it improves water quality,” he explains. Part of
the problem is deciding when to measure pollution in runoff—during the first five minutes of a storm, or by sampling over multiple time events. Another problem, he adds, is trying to compare treated and untreated streets since there are so many variables in the environment. In Madison, Wis., for instance, he notes that more than one-third of the municipality’s roads were too broken up and filled with potholes to allow for mechanized street sweeping. Also, the effectiveness of equipment can be highly variable, with some models merely moving the dirt around, while others send out jets of air that blow the dust into the vehicles’ catchments. And the machines are expensive, with newer models approaching $200,000.
Still, Bannerman holds out hope that future sweeper models will do a better job of tackling water pollution. “The latest model on the market is like a carpet sweeper and sends out a jet of water,” he says. “Who knows? Maybe 10 years from now, we’ll see it being promoted as a way to clean things up.” Although the U.S. EPA does not have an official position on street sweepers, Eric Strassler, a policy analyst with the Office of Water, says that as long as a city is already sweeping streets, they might as well get a good model that can scrub away pollutants as well. But he adds, “Any vendor who says that if you buy these gadgets that they will place you in water compliance is selling you a ‘pig in a poke’.” —PAUL D. THACKER
New results from a U.S. Geological Survey (USGS) sampling of the nation’s streams, aquifers, and water basins reveal that the water has been degraded in regions with large farm facilities and urban expansion, leaving water basins there contaminated with mixtures of pesticides, nutrients, volatile organic chemicals, metals, and degradation products. Outside of these areas, the nation’s streams are generally suitable for drinking water, irrigation, and recreational uses. The prevalence of chemical mixtures is one of the highlights of the 10-year study, says Robert Hirsch, USGS chief hydrologist. Regulatory criteria currently target individual chemicals but don’t take into account exposure to mixtures or seasonal variations in concentrations, he adds. “Many would agree that there is certainly more work needed to understand the consequence of how mixtures” affect health and the environment, Hirsch says. The sampling results show belowregulatory threshold levels of at least one pesticide in 95% of the total streams sampled. Chemical mixtures were even more prevalent: 25% of the streams sampled
USDA
Urban and farm runoff still a national problem
Nonpoint source runoff from large agricultural and animal farms is a major source of nutrients and pesticides in U.S. water, according to the U.S. Geological Survey.
showed low levels of at least 10 chemicals. Nearly all of the streams in urban areas contained insecticides commonly used on lawns, such as diazinon and malathion. Streams in agricultural areas contained herbicides, especially atrazine, alachlor, and cyanazine. These results are explained in a series of reports from USGS’s National Water Quality Assessment (NAWQA) program. The NAWQA results provide a unique look at 51
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water basins in the United States by providing data that have been collected by using a national study design and consistent methodology. Samplers monitor for contaminants such as pesticides, nutrients, metals, and vehicle fuel oxygenates, including methyl tert-butyl ether (MTBE). The report notes some improvements. For example, a switch in the irrigation method on some of the agricultural land in the Yakima River Basin in Washington reduced sediment runoff into the streams, resulting in DDT levels dropping by half since the 1980s, according to the report. The second round of sampling has begun, but USGS will study only 42 river basins this go-round, mainly because of a reduced budget, says Hirsch. Congress has provided flat funding for NAWQA; after adjusting for inflation, NAWQA has sustained a 33% cut over 8 years. NAWQA’s original study design was 60 “units”, which were reduced to 51 in 2000. But 42 water units are the lowest number NAWQA can sample and still provide a national look at water quality, Hirsch says. Copies of the reports are available at http://pubs.water.usgs.gov/ nawqasum. —CATHERINE M. COONEY
