Banned toxic chemicals that can cause cancer are sneaking into food more often and at higher levels than anyone suspected. Tests on over 20,000 food samples in Belgium in the wake of a massive food scandal in 1999 have revealed that up to four per cent of the samples contain high level of polychlorinated biphenyls (PCBs) from a different source, says Luc Hens of the Free University of Brussels ( New Scientist , June 26, p4).