ACORA1
12-27-2001, 05:20 PM
Stream bed bugs eat gasoline pollutants.(organisms breaking down unhealthful pollutants)(Brief Article)
Author/s: C. Wu
Issue: June 12, 1999
Microbes dwelling in the muck at the bottom of a stream can digest certain pollutants before they well up into the water, a new study finds.
Scientists have determined that microbes in sediment can dispose of methyl tertiarybutyl ether (MTBE) and tertiarybutyl alcohol (TBA). The two compounds are commonly added to gasoline to reduce vehicle emissions of carbon monoxide, an air pollutant. However, MTBE and TBA contaminate drinking water supplies in various ways, and the Environmental Protection Agency has classified MTBE as a possible human carcinogen.
The new finding should help environmental engineers more accurately assess the threat posed to streams by MTBE, says James E. Landmeyer. He, Paul M. Bradley, and Francis H. Chapelle, all of the U.S. Geological Survey in Columbia, S.C., report their findings in the June 1 ENVIRONMENTAL SCIENCE AND TECHNOLOGY.
"There has been considerable concern that this compound doesn't degrade," says Robert C. Borden of North Carolina State University in Raleigh. "If [the finding] turns out to be true, that would be very encouraging."
The USGS scientists looked at two sites in South Carolina where gasoline that contains MTBE had leaked from underground storage tanks. The researchers took sediment from nearby streambeds to their lab for testing.
They added radioactively labeled MTBE and TBA to the samples and traced the breakdown of the compounds into carbon dioxide. Over about 3 months, organisms--probably bacteria--in the sediment degraded up to 73 percent of the MTBE and 84 percent of the TBA. In contrast, if the scientists removed oxygen or heated the sediment to kill all the microbes, the pollutants remained intact.
Other groups have found bacteria that feed on MTBE in special environments, such as sewage sludge. "This study is the first to show that it happens in a natural system," Landmeyer says.
MTBE also enters the environment through gasoline spills and evaporation at the pump. The evaporated pollutant returns to Earth in rainwater, which soaks into the ground and eventually seeps up through streambeds.
"Bacteria in the groundwater don't have the correct digestive systems to degrade MTBE," Landmeyer notes, nor do they have access to oxygen. "But once MTBE reaches the stream, the bacteria just gobble it up." To microbes used to feeding on decaying leaves and such, MTBE "is just another organic compound to chew on," he says.
The evidence is convincing, but it's only part of the picture, comments Robert M. Cowan of Rutgers University in New Brunswick, N.J. A study of this duration, says Cowan, prompts a question: Is the rate of degradation fast enough to destroy pollutants as they flow through sediments in streams? "They haven't taken it to that point yet," he remarks.
The results, though encouraging, don't mean that people can rest easy about MTBE, Landmeyer cautions. Water in underground wells and rain that falls directly onto a stream won't benefit from this microbial filter.
COPYRIGHT 1999 Science Service, Inc.
COPYRIGHT 2000 Gale Group
:usa: :usa:
Author/s: C. Wu
Issue: June 12, 1999
Microbes dwelling in the muck at the bottom of a stream can digest certain pollutants before they well up into the water, a new study finds.
Scientists have determined that microbes in sediment can dispose of methyl tertiarybutyl ether (MTBE) and tertiarybutyl alcohol (TBA). The two compounds are commonly added to gasoline to reduce vehicle emissions of carbon monoxide, an air pollutant. However, MTBE and TBA contaminate drinking water supplies in various ways, and the Environmental Protection Agency has classified MTBE as a possible human carcinogen.
The new finding should help environmental engineers more accurately assess the threat posed to streams by MTBE, says James E. Landmeyer. He, Paul M. Bradley, and Francis H. Chapelle, all of the U.S. Geological Survey in Columbia, S.C., report their findings in the June 1 ENVIRONMENTAL SCIENCE AND TECHNOLOGY.
"There has been considerable concern that this compound doesn't degrade," says Robert C. Borden of North Carolina State University in Raleigh. "If [the finding] turns out to be true, that would be very encouraging."
The USGS scientists looked at two sites in South Carolina where gasoline that contains MTBE had leaked from underground storage tanks. The researchers took sediment from nearby streambeds to their lab for testing.
They added radioactively labeled MTBE and TBA to the samples and traced the breakdown of the compounds into carbon dioxide. Over about 3 months, organisms--probably bacteria--in the sediment degraded up to 73 percent of the MTBE and 84 percent of the TBA. In contrast, if the scientists removed oxygen or heated the sediment to kill all the microbes, the pollutants remained intact.
Other groups have found bacteria that feed on MTBE in special environments, such as sewage sludge. "This study is the first to show that it happens in a natural system," Landmeyer says.
MTBE also enters the environment through gasoline spills and evaporation at the pump. The evaporated pollutant returns to Earth in rainwater, which soaks into the ground and eventually seeps up through streambeds.
"Bacteria in the groundwater don't have the correct digestive systems to degrade MTBE," Landmeyer notes, nor do they have access to oxygen. "But once MTBE reaches the stream, the bacteria just gobble it up." To microbes used to feeding on decaying leaves and such, MTBE "is just another organic compound to chew on," he says.
The evidence is convincing, but it's only part of the picture, comments Robert M. Cowan of Rutgers University in New Brunswick, N.J. A study of this duration, says Cowan, prompts a question: Is the rate of degradation fast enough to destroy pollutants as they flow through sediments in streams? "They haven't taken it to that point yet," he remarks.
The results, though encouraging, don't mean that people can rest easy about MTBE, Landmeyer cautions. Water in underground wells and rain that falls directly onto a stream won't benefit from this microbial filter.
COPYRIGHT 1999 Science Service, Inc.
COPYRIGHT 2000 Gale Group
:usa: :usa: