Effects of tris(2-chloroethyl) phosphate exposure on chicken embryos in a shell-less incubation system

Tris(2-chloroethyl) phosphate (TCEP) is an organophosphate flame retardant that used in textiles, industrial materials, and furniture to delay the spread of fire after ignition. TCEP has been detected in the tissues and eggs of fish and birds. However, there are no studies regarding the effects of TCEP on avian embryos. In the present study, we investigated the developmental toxicity of TCEP exposure on chicken embryos in a shell-less incubation system, which enables in situ observation. Chicken embryos were treated with graded doses of TCEP (50, 250, and 500 nmol/g egg) on incubation day 0. The survival rate, morphological biometrics, heart rate, and length and branch number of extraembryonic blood vessels were measured on incubation days 3-9. Survival rates were reduced from incubation day 3 and were significantly decreased until day 9. Body length, head + bill length and eye diameter were significantly reduced by TCEP exposure. Regarding skeletal effects, spine length was decreased in a dose-dependent manner on day 9. Body weight on day 9 significantly reduced in all TCEP treatment groups. These results suggest that TCEP exposure to >50 nmol/g egg retards development in chicken embryos. TCEP exposure to 500 nmol/g egg significantly increased heart weight to body weight ratio in the embryos. More than 250 nmol/g egg of TCEP significantly reduced the heart rate of embryos in the early developmental stage. The formation of extraembryonic blood vessels and the number of erythrocytes were significantly reduced even with 50 nmol/g egg of TCEP. These findings suggest that TCEP exposure specifically affects the cardiovascular system in chicken embryos, which leads to developmental delay. The results of this study also demonstrate that the shell-less incubation system can be used to continuously monitor the effects of chemicals on developing avian embryos.