Preliminary results of a 3 month toxicity study on rats with 2,3,7,8,-Tetrabromodibenzo-p-dioxin (2,3,7,8-TBDD)

2,3,7,8-Tetrabromodibenzo-p-dioxin (2,3,7,8-TBDD) was administered by gavage daily to 10 rats of both sexes in doses of 0-0.01-0.1-1-3-10 μg/kg body weight on 90 consecutive days. 7 out of 10 males and 5 out of 10 females of the highest dose died within 35 days. The remaining 3 males and 5 females were killed in extremis. In the dose-group 3 μg/kg 5 males and 5 females died during the study. The mean body weight of the dose-groups 1 μg/kg and higher was reduced by treatment with 2,3,7,8-TBDD. Poor health conditions and signs of icterus indicated by yellowish discoloration of the urine were recognized in the dose-groups 3 and 10 μg/kg. Clinical chemistry after 12 weeks indicated an increase of plasma alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase in males and females of the highest surviving dose (3 μg/kg). Additionally the total bilirubin in males and females of this dose-group was increased. Thyroxine (T4) was reduced beginning at a dose of 0.1 μg/kg, triiodothyronine (T3) was increased at 1 and 3 μg/kg. Relative thymus weights were reduced in animals of the dose-groups 1, 3 and 10 μg/kg. In the groups 0.01 and 0.1 μg/kg no treatment-related signs of toxicity were seen. After 0.1 μg/kg the only effect was the reduction of Thyroxine. From comparison with a similar study (Kociba et al., 1976) it is concluded that 2,3,7,8-TBDD may be less toxic than 2,3,7,8-Tetra chloro dibenzo-p-dioxin by a factor of approximately 3–10, whereas the quality of reactions seems to be comparable between the two compounds. Further evaluations (blood biochemistry, hematology, pathology, histopathology, kinetics of enzyme induction, 2,3,7,8-TBDD content of liver and adipose tissue) are in progress.