Toxicity of various combinations of X-rays, caffeine, and mercury in mouse embryos

Preimplantation mouse embryos in vitro were exposed to various doses of X-rays (0.25-2 Gy) and to different concentrations of two chemicals: caffeine (0.5-2 mM) and mercury (0.5-5 microM). X-irradiation was given first, followed immediately by exposure to the chemicals. The effects of the agents, applied either singly or in combination of two or of three, were studied using morphological, proliferative and cytogenetic endpoints (formation of blastocysts, hatching, trophoblast outgrowth, formation of inner cell mass, cell numbers, micro-nucleus frequency). The term 'enhancement in risk' was used whenever the effects observed after combined exposure (two or three agents) significantly exceeded the sum of the effects due to the component individual agents. The enhancement in risk observed after exposure to the three agents could be explained by the interactions already detected at the level of a combined exposure to only two agents. There was no increase in risk specific for the presence of all three agents.