More than 120 countries are slated to meet in December in South Africa for a final meeting to draft a global treaty restricting the production of 12 persistent organic pollutants (POPs). At high doses, POPs — which include pesticides, many industrial pollutants, and PCBs — are deadly toxic, and at low exposures, they have caused cancer in and damaged the reproductive, nervous, and immune systems of lab animals. Scientists are also concerned about the ability of POPs to travel great distances from their sources — all the way to the Arctic, for example. The treaty would likely exempt some countries from some restrictions until replacement chemicals are found, especially for DDT, which is used widely in Africa to control malaria. Enviros criticize the treaty talks for focusing on only 12 POPs when there may be tens of thousands in production. Joe Thorton, a scientist at the Columbia Earth Institute and formerly of Greenpeace, said, "We know nothing about most of the chemicals produced, and right now they are considered harmless until proven dangerous. We are being killed by our own ignorance."