About the threshold concentration of nickel oxide nanoparticles in long-term inhalation exposure of rats

Introduction. Nickel oxide nanoparticles are of interest for toxicological science, not only as engineered nanoparticles, producing for industrial and scientific needs, but also as spontaneous pollutants of the atmosphere and the working area in industrial processes related to metallurgy and welding. Materials and methods. Rats were exposed to nickel-oxide aerosol at a concentration of 2.4 ± 0.4 µg/m3 in a “nose only” inhalation setup for 4 hours at a time, 5 times a week, during an overall period of 2 weeks to 6 months. Results. Of the several dozen examined parameters, only a few statistically significant manifestations associated with the reaction of the deep airways to inhaled nanoparticles were noted. However, in the biochemical and morphometric parameters of the lungs, even at the longest periods of exposure, the intergroup differences were insignificant. At the same time, even from the first weeks of the exposure period, genotoxic and allergic indices shifts are detected. Conclusion. For most of the evaluated effects, this level of exposure to nickel oxide nanoparticles may be considered as close to LOAEL, or even to NOAEL. However, according to some indicators, there are effects that suggest a non-threshold nature.