Toxicity Of Heavy Metals In Air Particulate Matter Toward Human Lung Epithelial Cells (A549)

Particulate matter?PM?pollution is one of the main atmospheric environmental problems in China,which has attracted growing attention from the perspective of public health.PM is a mixture containing many components,among which heavy metals are recognized as a kind of important toxic components in PM due to their no-degradability and high bioaccumulation.Because multiple heavy metals often coexist in PM,metal-metal interactions are critical to the final observed effect.However,very little is known about the major toxic metals in PM and their corresponding contributions.Therefore,the present study attempted to investigate the toxicity and combined effects of PM contained metals on human lung epithelial cells?A549?,and explore the most reasonable mixture model for heavy metals by comparing the differences between the observed and the predicted effects.Our results will provide a reference for subsequent studies on the health effects and risks of PM and its components.The main research results are as follows:?1?Major toxic heavy metals in PMA549 cell viability was measured after exposure to increased PM?a standard ambient particulate matter sample,SRM 1648a?concentrations,and the calculated critical toxic concentration of PM?EC50?was 107.90 ppm.At this concentration,the cell viability of A549 cells increased by 12.3%after the removal of Chelex-labile metals,and the contribution of heavy metal components to the toxicity of PM was estimated to 22.9±11.5%.Eleven heavy metals,Zn,Cr,Mn,Fe,Ni,Cu,As,Se,Sr,Cd and Pb,were chosen for further exposure because of their high toxicities or high levels.Among these tested elements,Zn,Cr,Mn,Fe,Cu and Pb were identified as the most important elements in PM causing cytotoxicity,and the order of their EC₅₀s was as follows:Fe>Cr>Mn>Zn?Cu>Pb.?2?Mixture toxicity of heavy metals in PMWe next studied the combinational toxicity of these six heavy metals?Zn,Cr,Mn,Fe,Cu and Pb?in a permutation.Generally,the presence of Fe significantly reduced cell death caused by other metals or mixtures,and the absence of Fe resulted in a marked increase in cell death relative to that of the hexanary mixture,suggesting that Fe might serve as an“antagonistic agent”to metal toxicity in PM.In contrast,Mn was found to induce greater toxicity when co-exposed with other metals,and led to a decrease in cell death after removal,indicative of a synergistic effect.Besides,the varied effects of other metals?Zn,Cu,Pb and Cr?on different metal mixtures might be explained by their interactions?e.g.,similar or dissimilar membrane transporters and intracellular targets?.?3?Metal mixture toxicity predictionThe joint effects of six heavy metals on A549 cells were modeled and predicted using four mathematical models:concentration addition model?CA?,independent action model?IA?,integrated addition model?IAM?,and integrated addition and interaction model?IAI?,respectively.For the former three models,most of the predicted effects were dispersed from the observed value,while the IAI model exhibited the least variation?r²=0.875?after a linear regression analysis.These results demonstrated again that there were considerable interactions among the six heavy metals.Although the IAI model performed well in this study,its applications need to be further evaluated for more complex metal compositions,cell lines and toxic endpoints.Our results emphasize the potential contribution of heavy metals to PM toxicity and their interactions,and promote the application of toxicity prediction models to metal components in PM.