By Janet Raloff
New computer models come out so frequently that the one you just bought seems obsolete the moment you get it home. This quick obsolescence encourages frequent purchases and creates a large, constant flow of computer systems into landfills. A new study demonstrates that this waste stream could be shedding lead into the environment.
The picture tubes in televisions and computer monitors employ lead-impregnated glass. This heavy metal shields viewers from most of the X rays generated when electrons collide with light-emitting phosphors to produce images. In color sets, the unit’s face panel is fused to the funnel-shaped body in a process using extra lead. The fused glass is called frit.
Though anecdotal reports have hinted that picture tubes’ glass might leach the metal, no one knew how much, notes Timothy G. Townsend of the University of Florida in Gainesville. To fill that data gap, his team tested 36 picture tubes produced between 1984 and 1998. The units came from 15 manufacturers and had been marketed under 21 brand names.
The researchers disassembled the units and took samples from different portions of the tubes’ glass. Then, they crushed the glass into fine and coarse particles, shook 100 grams of each sample in a beaker of acidic water for several hours, and measured how much lead had leached into the water.
Federal law limits concentrations of lead in water to 5 milligrams per liter (mg/l). While lead leaching from crushed glass of black-and-white TV tubes and monitors never reached that limit, lead from all 30 color units exceeded that concentration, Townsend and his colleagues report in the Oct. 15 Environmental Science and Technology. Some glass tainted water with more than 200 mg/l of lead. When that glass was crushed to pieces less than 5 millimeters in diameter, it had the largest surface area and leached the most—often tainting water with 400 mg/l lead.
The researchers also discovered why color units leach so much lead: It’s their frit, which is 70 percent lead by weight. From now on, the researchers conclude, color picture tubes “should be considered hazardous waste” and kept out of landfills and municipal-waste incinerators.
