Greenland snow shows lead-lowering success.

Snowflakes falling on central Greenland have grown cleaner over the past two decades because of antipollution measures adopted in the United States and other nations, conclude French and Soviet scientists who have conducted extremely sensitive measurements of heavy metals in Greenland snow.

Between 1967 and 1989, lead levels dropped by more than 85 percent while concentrations of cadmium and zinc declined by 60 percent, report Claude F. Boutron of Grenoble (France) University and his colleagues. They describe their findings in the Sept. 12 NATURE.

The group's analyses are part of a European project to collect climate information by drilling through the thick glacial cap that covers much of Greenland (see story, p.168). To ensure the purest possible samples, Boutron and his co-workers collected their snow from a site several kilometers away from the main drilling camp, which sits on the summit of the Greenland ice sheet.

"These are very difficult measurements. That's the reason why this is the first time such a profile has been made," Boutron told SCIENCE NEWS.

Because stray dirt or dust can contaminate samples, the researchers dressed in special "clean-room" clothing and wore shoulder-length polyethylene gloves while in the field. They used an all-plastic drill, cleaned in ultrapure nitric acid, to core a 10.7-meter-deep hole. After transporting the frozen snow core to France, the scientist removed samples from its center to obtain the cleanest snow for spectrometry measurements.

Previous work in Greenland showed that lead levels in the snow rose dramatically during the 1950s and 1960s, when the use of lead additives in gasoline increased. The subsequent lead decrease detected by Boutron's group reflects widespread efforts taken by many countries in the 1970s to curb lead additives in gasoline, the researchers say. In the United States, for instance, use of lead additives has declined by 90 percent since the late 1960s.

Cadmium and zinc pollution comes from many different sources, primarily fossil fuel burning, metal production, iron and steel manufacturing and garbage incineration. The snow analyses indicate that efforts to reduce cadmium and zinc pollution from these sources have significantly decreased atmospheric levels of the two metals in the Northern Hemisphere, the researchers conclude.