at least 120 countries have agreed to become signatories to a un treaty banning or restricting the use of 12 toxic chemicals known as persistent organic pollutants ( pop s). The treaty, known as the Stockholm Convention on Persistent Organic Pollutants, was signed on May 23, 2001, and will become legally binding once it has been ratified by at least 50 countries. The treaty was finalised in Johannesburg in December 2000 (see