Greenpeace yesterday called for a global halt to the production of persistent organic pollutants (POPs) — synthetic chemicals that damage the environment, pollute the food chain, and can even be found in breast milk. In a new report, the group said POPs were spreading over thousands of miles and killing striped dolphins, polar bears, and gray seals. In other toxic news, research published in New Scientist magazine suggests that exposure to toxic chemicals in the womb could cause lower sex drives in females. Zoologists at Michigan State University found that female rats exposed to PCBs in the womb were reluctant to mate as adults.