Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) in the embryos and newly hatched larvae of the Japanese medaka (Oryzias latipes)

Studies were undertaken to evaluate the toxicities of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and five PCB congeners using the Japanese medaka embryo-larval assays. The embryos and newly hatched larvae exposed to TCDD and two non-ortho PCB congeners; 77 and 126, showed a similar type and sequence of lesions. The toxic effects in the cardiovascular system were the first to appear. The typical lesions observed were multifocal hemorrhages, pericardial and yolk sac edema, craniofacial malformation, and inhibition of swim bladder inflation (SBI). The TEFs for PCB 126 and PCB 77 based on the LC50 values calculated from nominal water concentrations were 0.032 and 0.000014, respectively. These values are different from those reported for rainbow trout species, and similar to those for mammalian species. One mono-ortho PCB congener, 105, and two di-ortho PCB congeners, 138 and 153, did not cause any toxic effects on the embryos exposed up to 2000 ng/ml. However, all three PCB congeners (105, 138 and 153) caused an inhibition of swim bladder inflation in the newly hatched larvae. The inhibition of swim bladder inflation was the most sensitive end point measured, and it is suggested that the inhibition of SBI may be mediated by an unknown mechanism with/without an AhR activation.