A dozen notoriously toxic chemicals have been outlawed, or restricted around the world under a landmark United Nations treaty signed in Stockholm in May. It is a rare piece of good news for the global environment. The accord will ban, phase out or severely cut back a range of industrial chemicals and pesticides that linger in soil and water for decades. These pollutants pass up the food chain and accumulate in the body's fatty tissues. They are a suspected source of allergies, birth defects, cancer and damage to the immune system and reproductive organs.