Progress on toxicity of co-exposure to ambient fine particulate matter and e-cigarettes

Ambient fine particulate matter (PM_2.5) is particulate matter with an aerodynamic diameter less than 2.5 μm, and has an extremely wide range of sources. It affects the environmental quality in many cities and regions around the world, and associates with lots of negative effects on public health. E-cigarettes, a group of products that atomize e-liquid by an atomizer and then deliver nicotine and/or other substances to the respiratory system, have been introduced as smoking cessation products or replacement of tobacco cigarettes in recent years. The usage rate of e-cigarettes has grown rapidly all over the world. When these two pollutants coexist in the same atmosphere, they would induce certain adverse health effects not only on the e-cigarette users, but also on the people around them. Besides causing cardiopulmonary toxicity, the co-existing pollutants may associate with higher risks of developmental toxicity and carcinogenicity. In addition, the combined exposure may be related with the occurrence of depression. Therefore, there is an urgent need to conduct studies on the toxic potential of the combined exposure to PM_2.5 and e-cigarettes, which is also important for the evaluation and control of the atmospheric compound pollution associated health risk. This paper reviewed the current situation of PM_2.5 pollution and e-cigarettes use, introduced the epidemiological studies of PM_2.5 and e-cigarette combined exposure, their toxic effects in vivo and in vitro, and possible mechanisms, aiming to provide a reference for subsequent toxicity studies.