Critical period of sensitivity to petroleum toxicity in the chicken embryo

Microliter amounts of South Louisiana crude oil (SLCO) or Prudhoe Bay crude oil (PBCO) were applied to the shell of fertile leghorn chicken eggs on day 8, 8.5 or 9 of incubation. Percent mortality and prevalence of grossly visible lesions were evaluated 96 h after treatment. The 96-h LD50s of SLCO at 8, 8.5 and 9 d of incubation were 2.6, 4.3 and 34.3 μl, respectively. Five μl PBCO caused nearly 100% mortality in 8 and 8.5-d-old embryos, while 12 μl caused 32% mortality in 9-d-old embryos. Liver necrosis, edema and increases in body weight and in the ratio of body weight to crown-rump length were found in embryos treated on day 8, 8.5 or 9 of incubation with either SLCO or PBCO. The 16-fold decrease in sensitivity of the embryo from day 8 to day 9 of incubation suggests that the chorioallantoic membrane may be important in the toxic action of petroleum oil.