This news from Toronto: Taking aim at the world’s most toxic chemical pollutants, delegates from more than 100 nations begin negotiations today on the first global treaty banning or reducing the use of the so-called dirty dozen. They include pesticides, such as DDT, as well as industrial products, such as PCBs. At weeklong talks in Montreal sponsored by the U.N. environmental program, delegates will start crafting a legally binding treaty to be in place by the year 2001 that would curb emissions of 12 of the most dangerous human-made substances. Greenpeace, another group actively campaigning for a global ban, warned chemical industry lobbyists would be on hand during the talks to play down the risks posed by the pollutants. Dozens of NGOs are sending representatives to the talks, hoping to use the occasion to intensify pressure for tough action.