Organic pollutants tracked down to US parking lots

日期:2019-03-01 02:05:06 作者:贾蠕芭 阅读:

By Jeff Hecht Chemical detectives have tracked down the main source of a troublesome family of organic pollutants. Their “fingerprinting” of polycyclic aromatic hydrocarbons (PAHs) shows that surface sealers based on coal tar are responsible for most of the noxious substances by far. PAHs have accumulated rapidly over the past 40 years in many US stream and lake beds, and many are toxic or carcinogenic. Suspected culprits had included used motor oil and the burning of wood, coal and oil. Current US guidelines consider certain PAHs dangerous to organisms that live at the bottom of streams and lakes if there is more than 22.8 milligrams of the chemical per kilogram of sediment. Many urban and suburban lakes have higher levels; worse still, other kinds of PAH are air pollutants. Yet controlling that pollution has been difficult. “There are so many small sources that people had thrown up their hands,” says Peter Van Metre of the US Geological Survey (USGS) Texas Water Quality Center in Austin. Then Austin water-quality officials suggested that coal-tar roadway sealer might have caused local PAH problems. The thick tarry sealers are widely used in the US to coat blacktop driveways, parking lots and paved portions of playground. Most sold outside of the western US are based on coal tar and contain about 50 grams of PAH per kilogram of dry weight, although some sealers are based on heavy petroleum compounds such as asphalt and contain only 50 milligrams of PAH per kilogram. Van Metre and colleagues had earlier showed that dust from coal-tar-sealed parking lots was laden with PAHs. Now he and USGS colleague Barbara Mahler say they have nailed the case. They took sediment samples from 40 lakes across the US and compared the chemical fingerprints of the PAHs they contained – the ratios of different PAH compounds – with those of possible sources. Dust grains from the break-up of coal-tar parking lot sealant were by far the biggest source. In eight of the nine lakes with PAH levels above the 22.8-milligrams-per-kilogram guideline, the concentration of the coal-tar component alone exceeds the guideline. In some, it approaches 60 milligrams per kilogram. In areas where coal-tar sealers are widely used, Van Metre says, “they were the primary drivers” in the increase of PAH levels over the past decade. Even before the new results, Austin had banned coal-tar sealers after linking them to high PAH levels. Six Minnesota communities have banned or restricted coal-tar sealers because they have contaminated sediments in storm-water ponds so much that disposal cost up to hundreds of thousands of dollars per pond, says Judy Crane of the Minnesota Pollution Control Agency. In North Carolina there have been similar reports. Journal reference: Science of the Total Environment, DOI: 10.1016/j.scitotenv.2010.08.014 More on these topics: