Some problems of biological effects under the combined action of nitrogen oxides, their metabolites and radiation

The progress of power engineering envisages the intensive construction of nuclear-energy plants, where an organic or nuclear fuel is used. Nowadays the concept of nuclear-energy plant with the coolant based on dissociating N2O4 is being developed. A great deal of radioactive and chemical products escapes into surroundings as the result of the power plants being in service. Their action on organisms is performed simultaneously, that could have an essential effect on the quantitative and qualitative regularities of response. The estimation of the combined effect of nitrogen oxides, sodium nitrite and nitrate and radiation has been carried out on the base of the investigation into methemoglobin formation, genetic effects and the pathomorphological changes in lungs. The formation of methemoglobin has been studied on rats in 1, 3, 7 and 15 days after the single total irradiation of 300 and 700 R doses at the gamma-installation (UGU-420) using a radioactive 60Co. Methemoglobin was determined in the interval of 15-180 min after NaNO2 administration in the dosage of 7.0 mg per 100 g body weight. The irradiation essentially affects the process of methemoglobin formation and its reduction. The methemoglobin content in the blood of radiation exposed animals exceeds the value, that could be expected to obtain by summing up its concentration under the separate effects of nitrite and irradiation. The genetic effects of sodium nitrite and nitrate and X-radiation have been studied on the Drosophila. The one-day flies were exposed to the radiation dose of 1500 R in the medium with the sodium nitrite or nitrate contents of 0.1 or 1.0 g/l, respectively. The combined action estimated through the frequency of the dominant lethal mutation, recessive coupled with a lethal mutation sex, viability and fecundity definitely differs from the expected summing values of the separate effect indices of radiation and toxic factors. The morpho- and functional changes in the rat lungs (the irradiation in the range of 300-700 R; sodium nitrite - 7.0 mg/100g body weight; nitrogen oxides - 60 mg/m3), the peculiarity of remote after-effects, the average lifetime under the 'given experimental conditions are determined, mainly by a radiation dose. It is rather complicated to estimate the specific contribution of each factor. The maximum manifestation of changes takes place under the joint action. Thus, according to the majority of indices, the joint action effect of the studied factors under the given experimental condition is more than additive. (author)