NEW YORK (AP) _ For the first time, scientists say they have pinpointed many of the industrial polluters responsible for the dioxin that is ending up in the Arctic.

To perform the study, scientists at New York City's Queens College modified a computer program originally designed to track fallout in the event of a nuclear accident.

They found that 35 municipal waste incinerators, cement kilns and steel plants in the eastern and central United States account for one-third of the dioxin reaching Nunavut Territory in the Canadian Arctic.

For example, during the one-year study a single municipal waste incinerator in Harrisburg, Pa., accounted for nearly 5 percent of the dioxin reaching Broughton Island, just north of the Arctic Circle on Baffin Bay.

Another waste incinerator in Ames, Iowa, contributed about 5 percent of the dioxin reaching Chesterfield Inlet on Canada's Hudson Bay, 2,000 miles away.

``I think the study demonstrates that we should revise our concept of neighbors,'' said Greg Block, director of the North American Commission for Environmental Cooperation. The organization funded the study.

Dioxin is of particular concern in the Arctic because it is an extremely long-lived pollutant that tends to build up in the fat of animals and people. Native people in the Arctic consume a diet high in fish and sea mammals, so on average their bodies carry about twice as much dioxin as a person living in southern Canada or the United States.

Dioxin has been shown to cause cancer, brain damage and reproductive abnormalities in animals, but the degree of its threat to humans remains unclear.

``We are increasingly worried about this situation,'' said Sheila Watt-Cloutier, the Canadian president of the Inuit Circumpolar Conference. ``The environment is actually our supermarket.''

The computer program used in the study, developed by the National Oceanic and Atmospheric Administration, simulates the weather across North America on an hour-by-hour basis.

Researchers entered into the program detailed information about releases from more that 40,000 dioxin sources, then followed individual ``puffs'' of contaminated air. Once the air had reached the Arctic, they estimated the dioxin fallout.

The study showed that most of the dioxin reaching the eastern part of the Canadian Arctic comes from the eastern United States. Dioxin released in the Midwest tends to end up farther west.

Dioxin is made whenever chlorine and carbon are burned together, so it is produced in a wide variety of situations, from steel manufacturing to trash burning.