COMPARISON OF THE TOXICITY OF SEVERAL POLYCHLORINATED DIBENZO-PARA-DIOXINS AND 2,3,7,8-TETRACHLORODIBENZOFURAN IN EMBRYOS OF THE JAPANESE MEDAKA (ORYZIAS-LATIPES)

Nine polychlorinated dibenzo-p-dioxins (PCDDs) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) were tested in the Japanese medaka embryo bioassay. Individual embryos were exposed to varying nominal concentrations of a PCDD or 2,3,7,8-TCDF under static conditions. The LC50 with 95% confidence intervals for survival to 3 days post-hatch were as follows: 2,3,7,8-TCDD, 13 (10-17) nanograms (ng)/liter (L) (parts per trillion); 2,3,7,8-TCDF, 16 (12-22) ng/L; 1,2,3,7,8-PeCDD, 27 (23-31) ng/L and 1,2,3,4,7,8-HCDD, 2900 (718-11717) ng/L. Both 1,2,7,8-TCDD and 2,3,7-TriCDD caused a concentration dependent increase in visible lesions from 50 to 50000 ng/L. In the 1,2,7,8-TCDD exposed embryos, lethality was observed only at the highest concentration tested (50000 ng/L). For 2,3,7-TriCDD, there was no concentration related increase in lethality from 50 to 50000 ng/L. At 50000 ng/L, 1,3,6,8-TCDD, 2,8-DCDD and 2,3-DCDD did not cause any visible toxicity. The octachlorodibenzo-p-dioxin congener did not cause any visible toxicity at 10000 ng/L. The toxic PCDDs and 2,3,7,8-TCDF caused the same sequela of lesions in the developing Japanese medaka, suggesting that they may act through a common mechanism. These results demonstrate that 2,3,7,8-TCDF and PCDDs with the four lateral positions chlorine substituted and at least one other position non-substituted are toxic to the Japanese medaka embryo. The structure activity relationship observed here is similar to that observed in guinea pigs, mice and trout eleutheroembryos. © 1990.