More than 120 nations will formally sign a pact on Tuesday to outlaw or minimise the use of the "dirty dozen" toxic chemicals blamed for causing fatal diseases and birth defects among humans and animals. The chemicals, used in pesticides, in fire retardants in homes and in paints or plastics, have been found to trigger disastrous side-effects including cancers. Traces of the 12 so-called Persistent Organic Pollutants (POPs), swept around the globe by air or ocean currents, have been found even in the breast milk of Inuit women in the Arctic and have been blamed for turning polar bears into hermaphrodites.