لخّصلي

To the general public, dioxin is the archetype of toxic chemicals, a substance that in minute amounts causes cancer and birth defects. Raised to a high level of visibility by the use of Agent Orange in Vietnam, it continues to generate environmental issues that capture public attention: Times Beach, Seveso, Love Canal, herbicide spraying in the United States, waste incineration, and chlorine-bleached paper.
Public fear has engendered a counterreaction. Some have claimed that dioxin causes no harm to humans other than chloracne, a disfiguring skin disease. Others have compared the public attitude toward dioxin with witchhunts. Dioxin, they say, is a prime example of "chemophobia," the irrational fear of chemicals. The counterreaction made front-page news in 1991. U.S. Assistant Surgeon General Vernon Houk claimed that the evacuation of Times Beach, Missouri, had been a mistake. Administrator William Reilly of the U.S. Environmental Protection Agency ordered a reevaluation of the toxicity of dioxin. He stated that "I don't want to prejudge the issue, but we are seeing new information on dioxin that suggests a lower risk assessment for dioxin should be applied.
In our opinion, the public fears are largely justified. The current scientific evidence argues not only that dioxin is a potent carcinogen, but also that the noncancer health and environmental hazards of dioxin may be more serious than previously believed. Indeed, dioxin appears to act like an extremely persistent synthetic hormone, perturbing important physiological signaling systems. Such toxic mimicry leads to a host of biological changes, especially altered cell development, differentiation, and regulation. Perhaps the most troubling consequence is the possibility of reproductive and developmental effects at the levels of dioxin and dioxinlike compounds now present in the bodies of the average person. This phenomenon has already been observed in wildlife, especially fish eating birds from the Great Lakes. These findings suggest that the environment is already overburdened with these dangerous compounds.
The pendulum of official opinion may be swinging back. Contradicting Houk, U.S. Assistant General Barry Johnson testified in June, 1992, that the evacuation of Times Beach was not a mistake. The USEPA's reevaluation, although still incomplete at this writing, is currently indicating that the "danger from dioxin may be broader and more serious than previously thought. " In this overview, we will discuss the technical basis for this dramatic turnaround and its logical implication: a policy directed toward exposure reduction and pollution prevention.