On the horizon

Nuclear waste: new casing needed

Need to store some high-level radioactive waste for, say, 250,000 years? Probably not. But those who do should think twice about encasing it in zircon-based ceramics.

A research team from Oxford University in Cambridge, England, and the Pacific Northwest National Laboratory in Richland, Wash., found that radiation from plutonium degrades zircon-based ceramics far faster than previously estimated – in 1,400 years, rather than the 250,000 years that waste-management experts had suggested. Zircon has been touted as a useful material for immobilizing plutonium for storage in underground nuclear-waste dumps. (Plutonium used in nuclear reactors must be isolated for 250,000 years to ensure it becomes harmless, scientists say.) The results appear in the current issue of the journal Nature.

Forest fires pump more mercury into the air than previously believed, according to a study from scientists at the University of Michigan. The results also suggest that wildfires would pump less mercury into the air if fires were allowed to burn in their natural cycles, rather than suppressing them for long periods.

Mercury naturally accumulates on leaves and pine needles. As they fall and decompose, the mercury binds to organic material in the soil. Abir Biswas, a University of Michigan graduate student, and other researchers began making soil and air measurements near Jackson Hole, Wyo., over a two-year period following a series of fires near a research station there. The team collected samples from burned and unburned areas. By comparing the mercury levels found in samples in burned areas to samples in unburned areas, they could estimate the amount of mercury that fires released into the air.

Mercury emissions varied by type of tree as well as a by fire's severity. The team estimated that fires set intentionally to reduce fire hazards make up 25 percent of the mercury found in the nation's air. Moreover, when fires are suppressed and an area finally burns, as in the Yellowstone fire in 1988, the fires burn hotter and release more mercury than if managers had let fires burn naturally as they occur. Those fires happen more often but are less severe. Results appear in the current issue of the journal Global Biogeochemical Cycles.

Dust from northern Chad appears to be the Amazon rain forest's version of Scotts Miracle-Gro.

Scientists in Britain, Brazil, Israel, and the United States have found that some 40 million tons of dust head west from the Sahara over the Atlantic to Brazil's Amazon basin each year, far more than previous estimates. Without this dust, the forest soil would likely have no replacement for the minerals from local weathered rocks. Those minerals wash out during the rainy season, which typically runs from April to September.

Scientists have long known that African dust benefits the Amazon basin. But the team was surprised to find that slightly more than half of the dust comes from one small location northeast of Lake Chad. The highest deposit rates come between November and March.

The team used NASA's Terra and Aqua satellites to track the dust plumes. Its results appear in a recent issue of the journal Environmental Research Letters.