Objective:To make an assessment on the genotoxicity caused by black carbon ( BC ) and ozonized black carbon (O3-BC).Methods: In this study, 74 healthy male ICR mice [weighed (28 ± 1.5) g] were randomly divided into 7 groups, including one phosphate buffer solution ( PBS) control group and six particles exposed groups by intratracheal instillation with either BC or O 3-BC at the doses of 50, 100, 200 μg/mouse, respectively.There were 12 mice in the groups of 200μg/mouse and 10 mice in others.The mice were sacrificed 24 h after four intratrachealinstillations .The activities of catalase ( CAT) in serum and the levels of malondialdehyde ( MDA) in lung tissue homogenate were measured . As the DNA damage mark , 8-hydroxyguanosine ( 8-OHdG ) in urine and serum were quantified with ELISA method.Micronucleus test was used for potential genotoxicity of BC and O 3-BC.Hematoxylin and eosin staining was used to stain lung paraffin section .Results:The mice were in good condition during instillation , and the liver coefficient of the test groups was significantly lower than that of the control group (P<0.05).The activities of CAT in serum significantly increased in the 100 μg/mouse and 200μg/mouse groups after being exposed to these two kinds of particles .The micronucleus rate in allthe BC and O3-BC exposed groups increased ( P <0.05), but there was no statistically significant difference among the groups in the levels of 8-OHdG in serum and urine and MDA in lung tissue homogenate .In-flammatory response was found in the lung tissue under the microscope after exposure to BC and O 3-BC. Conclusion:Intratracheal instillation of BC and O 3-BC induced increasing of oxidative stress and genetic damage in mice .But there was no significant difference between these two particles in toxicity .Whether the genotoxicity of O 3-BC is higher than that of BC or not is uncertain .Further research is needed .

Background Blue light, as an occupational hazard, is widely present in welding and related work environments. However, China's occupational health standard system has not yet established any limit for blue light exposure in welding work environments. Objective To study and propose blue light exposure limits in welding operation environments, and provide a reference for evaluation of blue light hazard and maximum allowable exposure time in welding operations. Methods A function between retinal irradiance and welding arc radiance was introduced by studying arc light and blue light radiation generated in welding operation environments, analyzing the incoherent light radiation protection guidelines issued by the International Commission on Non-Ionizing Radiation Protection (ICNIRP), and combined with factors such as the size of arc light in welding operations, the distance between the welder's eyes and the arc light, and the diameter of the human eye pupil, as well as the geometric optics principle of human eye imaging and the conservation of energy. Then, the radiance limit (100 W·m⁻²·Sr⁻¹) issued by ICNIRP was input into the above function to calculate the blue light irradiance exposure limit in the welding operation environments. Results The blue light irradiance exposure limit in the welding operation environments (\begin{document}$ {E}_{{\rm{B}}}^{{\rm{EL}}} $\end{document}) was 3 W·m⁻². Considering the high repeatability of welding operations, the exposure limit for blue light radiant exposure (\begin{document}$ {H}_{{\rm{B}}}^{{\rm{EL}}} $\end{document}) was 60 J·m⁻². According to the definitions of radiant exposure and irradiance, the maximum allowable exposure time within one working day was calculated according to the formula \begin{document}$ {t}_{\mathrm{m}\mathrm{a}\mathrm{x}}={H}_{{\rm{B}}}^{{\rm{EL}}}{/E}_{{\rm{B}}} $\end{document}, in which \begin{document}$ {E}_{{\rm{B}}} $\end{document} was the measured blue light irradiance in a welding environment. Conclusion Exposure limits of radiant exposure for blue light are proposed to provide important references for evaluating the hazards and maximum allowable exposure time of blue light in welding operations, and for future development of occupational exposure limit standards for blue light in China.