In an effort to reduce pollution and environmental toxins, San Francisco could become the first city in the nation to favor "green" products in purchases from window cleaner to electricity to playground equipment. The philosophy, known as the "precautionary principle," is a response to the growing incidence of disease some health experts attribute to pollution and environmental toxins. For instance, a 2004 report from the Breast Cancer Fund found that scientific evidence shows some 85,000 synthetic chemicals are contributing to breast cancer by altering hormone or gene function."We are seeing alarming increases in asthma, in cancer and chronic illness, but we don't why. We do know that many of the products we buy contain hazardous ingredients that are perfectly legal," said Debbie Raphael, toxics reduction program manager for The City. The precautionary principle has been guiding environmental policy in a number of European countries, but is just gaining attention in the United States, where cities in Oregon, New Mexico and a handful of other states are looking at creating similar plans.