To the Inuits of northern Canada, it is the one of the scariest poisons imaginable: an invisible toxin that has infiltrated the cells of arctic creatures from plankton to people and turned ordinary whales into floating hazardous waste dumps.
To governments in central Africa, it is a chemical safety net, a primary defense against a worsening malaria epidemic that kills 5,000 children each day in countries south of the equator.
On Monday, officials from as many as 120 nations will begin to try to reconcile these starkly contrasting views of DDT, the infamous insecticide long banned in the United States but still widely used in many parts of the developing world.
Armed with new evidence about the pesticide's global spread, negotiators will gather in Montreal to start work on an unprecedented United Nations treaty to phase out DDT and 11 other toxic compounds that have been linked to cancers, birth defects and ecological disruption.
The 12 chemicals, called "persistent organic pollutants," also include dioxins, PCBs and other industrial compounds known for their ability to travel long distances and concentrate in animal tissues. Largely unknown before World War II, many substances on the dirty-dozen list are present in trace levels in virtually every person on Earth.
Some of the worst cases of contamination are found in the Arctic, where high levels of DDTs, dioxins and PCBs are found in humans and marine creatures thousands of miles from the nearest industrial centers. Levels of the toxins have remained steady for more than a decade, even though production of most of them has been banned in Western countries for a quarter-century.
"This is a global problem and therefore requires a global solution," Rafe Pomerance, the State Department's deputy assistant secretary for the environment, told a recent Washington news conference. "Many of these problems we cannot solve alone. They exist and are created outside our borders."
Governments at the Montreal meeting will frame the proposed accord this week in anticipation of signing the treaty in 2000. But negotiations are complicated by national interests and concerns over other kinds of public health threats -- particularly malaria.
The Clinton administration, which strongly supports a ban, is reluctant to be viewed as bullying governments into halting DDT use at a time when malaria deaths are rising. Other countries see the pesticide as a crucial weapon against encephalitis and related insect-borne illnesses with lethal effects that are far more direct.
"Our position is we'd optimally like to see a phaseout," said one administration official who will participate in this week's talks.
Malaria remains a major health problem in more than 90 countries and kills as many as 2.7 million people each year, especially in sub-Saharan Africa. DDT remains the pesticide of choice for developing countries because it is relatively cheap and is less acutely toxic than many alternatives. The World Health Organization continues to endorse DDT as a "most valuable tool" for controlling malaria, although it also has begun issuing warnings about the spread of pesticide through the food chain.
But environmental groups, citing evidence of long-term ecological damage, are calling for an expedited phaseout of all 12 compounds -- along with economic and technical assistance to help developing countries find replacements. The World Wildlife Fund, in a report earlier this year, said persistent organic pollutants pose a particular health threat to whales and dolphins, who typically store large amounts of man-made chemicals in their body fat. The report suggested toxin contamination may have been an indirect cause of several well-publicized die-offs of marine mammals in recent years.
"DDT is clearly impacting the environment in some serious ways," said Cliff Curtis, WWF's global toxics campaign director. "We see alternatives [to DDT] that already exist and possibilities for other solutions in the near term. All that's required is political will."
The 12 chemicals targeted for phaseout were selected because of their wide distribution -- most, like DDT, are commonly found in animals around the world -- and because of a high potential for damage to health and ecosystems. In addition to DDT and PCBs, the list includes the industrial compound hexachlorobenzene, dioxins and furans, and seven pesticides. All are banned for commercial use in the United States.
Typically, the chemicals usually enter humans through contaminated foods. Because they are not easily broken down or excreted, the compounds remain in the body for months or years, stored in organs such as the liver, or in fat. In ecosystems, they tend to concentrate or "bioaccumulate" in animals at the top of the food chain, in the bodies of large meat-eaters such as marine mammals, polar bears, raptors and people.
At high levels, the chemicals are known to damage the central nervous system and suppress the body's ability to fight off diseases. Many of them are also known endocrine disruptors, which can cause deformities in sex organs as well as long-term disruption of reproductive systems.
"A lot of these effects occur at much lower concentrations than it takes to kill the organism," said Robert Hale, an organic environmental chemist at the Virginia Institute of Marine Science. At his laboratory in the Chesapeake Bay town of Gloucester Point, Hale examines fish and amphibians collected around the country for traces of DDT and PCBs -- and finds them everywhere.
"One of the scariest things," Hale said, "is that we still know so little about them."
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