TOXICITY OF 2,4,4'-TRICHLOROBIPHENYL IN RATS FOLLOWING 90-DAY DIETARYEXPOSURE

The toxicity of 2,4,4'trichlorobiphenyl (PCB 28) was investigated in r ats after a 90-d dietary exposure. Groups of 10 male and 10 female wea nling Sprague-Dawley rats were administered PCB 28 in the diet al 0, 0 .05, 0.50, 5.0, or 50.0 ppm for 13 wk. Growth rate and food consumptio n were not affected by treatment, and no clinical signs of toxicity we re observed. Mottled liver was noted in both control and PCB-treated m ales, but was found with increased incidence in the highest treatment group. Increased urinary ascorbic acid and hepatic microsomal ethoxyre sorufin O-deethylase activity were observed in the 50.0 ppm group of b oth sexes. The vitamin A content in liver, lung, and kidney was not si gnificantly affected by treatment. Analysis of brain biogenic amines s howed a decreased dopamine concentration in the substantia nigra regio n of female rats receiving 0.5 ppm PCB 28 and higher doses. Female rat s appeared to be more sensitive than males to the neurochemical effect s of PCB 28. Dose-dependent histologic changes were observed in the th yroid and liver, with biologically significant changes occurring at 5. 0 ppm and above. Based on these data, the no-observable-adverse-effect level (NOAEL) for this PCB congener was considered to be 0.5 ppm in d iet or 36 mu g/kg body weight/d.