Polychlorinated biphenyls (PCBs) have been produced commercially since be fore 1930. They proved to be highly versatile mixtures and their uses continued to expand during the early 1970's even after the unanticipated world-wide en vironmental contamination had been discovered (Jensen et aI., 1969; Koeman et aI., 1969). Over 600,000 metric-tons were produced and/or used in the U. S. during this time and it is estimated that worldwide production totaled about 1,200,000 metric-tons (Table 1). With low acute toxicities (Fishbein, 1974), these mixtures were considered gen erally biologically...