ASSESSING THE CANCER RISK FROM ENVIRONMENTAL PCBS

A new approach to assessing the cancer risk from environmental polychl orinated biphenyls (PCBs) considers both toxicity and environmental pr ocesses to make distinctions among environmental mixtures. New toxicit y information from a 1996 cancer study of four commercial mixtures str engthens the case that all PCB mixtures can cause cancer, although dif ferent mixtures have different potencies. Environmental processes alte r PCB mixtures through partitioning, chemical transformation, and pref erential bioaccumulation; these processes can increase or decrease tox icity considerably. Bioaccumulated PCBs are of greatest concern becaus e they appear to be more toxic than commercial PCBs and more persisten t in the body. The new approach uses toxicity studies of commercial mi xtures to develop a range of cancer potency estimates and then conside rs the effect of environmental processes to choose appropriate values for representative classes of environmental mixtures. Guidance is give n for assessing risks from different exposure pathways, less-than-life time and early-life exposures, and mixtures containing dioxin-like com pounds.