But I wouldn't see any problem spending a few days in Belgium and eating meals without knowing whether they were prepared from contaminated chicken or eggs. Dioxins form most readily between 300 degrees Celsius and 700 degrees Celsius, says Mr. Dorn. The rate of formation of dangerous dioxins at lower temperatures is much slower, Mr. Dorn says, while at temperatures above 1000 degrees Celsius dioxins become unstable and degraded. Dioxins were first identified by U.S. researchers in the early 1970s, and about the same time Dutch scientists discovered dioxins in emissions from municipal incinerators. Authorities in most developed countries now maintain tough safety standards and elaborate monitoring programs on waste incineration, but it's a thorny problem because burning waste throws together thousands of chemicals indiscriminately that become a volatile brew if mixed with chlorine atoms.
Dioxins also can come from natural sources, however.
One contamination case in the U.S. a few years ago resulted from the use of clay as a binder in chicken feed. American regulators eventually traced the contaminated clay to a quarry in the state of Arkansas and established that the source of dioxins was prehistoric. Such vigilance has paid off. C.T. Howlett Jr., executive director of the Chlorine Chemistry Council, an industry group, says dioxin levels in the environment have declined steadily over the past 25 years as a result of compliance with regulatory requirements imposed on industry and waste-incineration users. In cases of potentially large-scale contamination, scientists and regulators have to scramble to keep up.