Magazine article Science News , Vol. 146, No. 13
Dioxins and furans are chlorinated pollutants that can form during any of several combustion and industrial activities. Together with polychlorinated biphenyls (PCBs), these related families of chemicals possess a similar ability to bind with a protein in the body -- the ah receptor -- and then enter cells to turn genes on or off inappropriately.
However, not all family members exhibit this toxic activity. For convenience, authors of EPA's new three-volume tome Estimating Exposure to Dioxin-Like Compounds (SN: 9/17/94, p.181) have tended to broadly term as "dioxin" all those compounds that do: 7 of the 75 dioxins, 10 of 135 furans, and 11 of 209 PCBs. To account for their respective potencies, each was assigned a toxic equivalency (TEQ), which relates its potential for harm to 2,3,7,8-TCDD, the most toxic of the dioxins.
Though data are very limited, the report notes, what is known suggests that annual dioxin deposition rates of about 1 nanogram TEQ per square meter of land are typical for remote regions of the United States. Rates two to six times that are common in urban areas. High-concentration "hot spots" may occur near industrial emitters of these compounds.
Overall, EPA officials estimate that incineration generates about 90 percent of the dioxin in air. Among these sources, hospital-waste incinerators may be the largest polluters. The reason, EPA suspects, is that there are so many of them (more than 6,000 nationally), they use fairly unsophisticated pollution controls, and they burn chlorine-rich wastes.
Though municipal-waste incinerators are the next biggest culprit, EPA says that new, mandated controls "should substantially reduce [their] emissions in the near future." Other sources include incinerator ash, diesel vehicles, manufacturing of chlorinated chemicals, wood burning, and papermaking.
However, notes William Farland, director of EPA's office of health and environmental assessment in Washington, D. …