Physicochemical Property And Cytotoxicity Structure-activity Relationship Studies Of Secondary Ultrafine Particles Forming From SO₂ Reaction On CeO₂ Ultrafine Particles

Purpose: Secondary fine particulate matters are found as the major components in PM2.5 in megacities of China,the toxic components in PM2.5 that contribution adverse health effects is still unclear due to the complex composition of the fine particulate matters.To study the structure-activity relationship between properties of Secondary inorganic fine particle and cytotoxicity,we used cerium dioxide ultrafine particles（CeO₂ UFPs）as secondary fine particulate matters model to investigate its heterogeneous reaction with sulfur dioxide（SO₂）under various simulated atmospheric conditions,such as various humidity（RH）,ultraviolet（UV）irradiation and nitric dioxide（NO₂）existence,which formed secondary inorganic ultrafine particles,i.e.,CeO₂ SFPMs.Method:（1）The chemical property of CeO₂ UFPs and CeO₂ SFPMs were detected using DL-Dithiothreitol（DTT）.The Sulfur K-edge X-ray absorption near-edge structure（XANES）spectral data were collected at beamLine 4B7 A of the Beijing Synchrotron Radiation Facility in order to analyse Sulfur valence state.（2）Cytotoxicity: The cell viability of CeO₂ UFPs and CeO₂ SFPMs was measured by CCK-8 assay.（3）Determination of the Inflammatory cytokines levels in the supernatant by ELISA,The levels of reactive oxygen species detected by Fluorescent probe DCFH-DA.（4）JC-1 was used to detect the change of mitochondrial membrane potential（MMP）.（5）The apoptosis rate of RAW264.7macrophage cells and 16 HBE bronchial epithelial cells were observed using Annexin V/PI staining,ELISA are also used in DNA damage.Results: The chemical properties strength results of CeO₂ UFPs and CeO₂ SFPMs show as follows: CeO₂ < CeO₂+SO₂ <CeO₂+SO₂+RH < CeO₂+SO₂+RH+UV < CeO₂+SO₂+RH+NO₂ < Ce O₂+SO₂+RH+O3.In addition,The oxidation performance of 2 ppm SO₂ CeO₂ SFPMs is less than 30 ppm SO₂CeO₂ SFPMs.The data showed that SO₂ could be oxidized to sulfate,S heterocyclic and sulfoxide after interaction with CeO₂ UFPs under the simulated atmospheric conditions.After exposed different time,The cytotoxicity presents the following rule: CeO₂ <CeO₂+SO₂ < Ce O₂+SO₂+RH < Ce O₂+SO₂+RH+UV < CeO₂+SO₂+RH+NO₂ <CeO₂+SO₂+RH+O3.The resules of inflammatory cytokines,ROS,mitochondrial membrane potential,cell apoptosis and DNA damage also confirmed the above results.Conclusion: S element exists in its oxidation state after surface heterogeneous reaction,The stronger oxidation reduction properties caused more significant cytotoxic effect.The cytotoxicity was shown as follows: CeO₂ < CeO₂+SO₂ < CeO₂+SO₂+RH <CeO₂+SO₂+RH+UV < Ce O₂+SO₂+RH+NO₂ < CeO₂+SO₂+RH+O3.Especially,CeO₂+SO₂+RH+UV,CeO₂+SO₂+RH+NO₂ and CeO₂+SO₂+RH+O3 have the strongest toxicity.It is suggested that SO₂ and UV,NO₂ O3 combined action strengthening the surface heterogeneous reaction of SO₂ to form sulfate,Sulfate component on SFPMs is one of the sources of cytotoxicity.