LOS ANGELES -- A new study suggests the ebb and flow of North American industry since the dawn of the Industrial Age can be tracked through lead traces found in a 450-foot ice core drilled in Greenland three years ago.
The core contains a high-resolution record of how much lead settled from the atmosphere onto Greenland between 1750 and 1998. The study says the source of the lead appears to have been factories in the United States and Canada.
Lead emissions began to spike in 1870 and had increased 300 percent just 20 years later, said Joseph McConnell, an associate research professor at the Desert Research Institute in Reno, Nev.
The 1890 pollution levels were higher than previously thought, suggesting intense levels of both industrial activity and pollution, said McConnell, co-author of the study expected to appear in an upcoming issue of the journal Geophysical Research Letters.
Lead levels plummeted during the Depression, then climbed during the industrial boom that followed World War II, according to the study. The period marked the beginning of the widespread use of lead as a gasoline additive.
In the early 1970s, when leaded gasoline began to be phased out and stricter pollution controls were clamped on smokestack emissions, lead levels in Greenland dropped. They fell more than 75 percent by 1985, from what had been peak levels a little more than a decade earlier.
North American lead emissions are near zero today, but lead levels in Greenland remain about three times greater than those seen in ice samples dating to 1870. McConnell said that suggests a source outside North America.
Lead has been detected in Greenland ice samples before. A 1994 study suggested Greenland ice cores contained 2,000-year-old traces of lead pollution attributable to smelting activity by the ancient Greeks and Romans.
The new study offers a higher resolution look and includes about 25 samples for each year covered. Scientists were able to separate out certain spikes in lead levels attributable to volcanic eruptions in nearby Iceland.