Association between metal exposure from e-cigarette components and toxicity endpoints: A literature review.

Electronic cigarette is often promoted and perceived as an 'healthy' alternative compared to conventional cigarettes. However, growing body of evidence indicate the possible adverse health effect associated with e-cigarette. Here we reviewed the literature with a focus on metal exposure in relation to e-cigarette use and related toxicity endpoints. Twenty-nine studies were identified for full text screening after applying the screening criteria of which 5 in vitro studies and 11 epidemiological studies were included for data extraction. Cr, Cu, Ni, Sn are the most found metal in all studies. In vitro, metal from e-cigarette (liquid or aerosols) induced cytotoxicity, oxidative stress, genotoxicity and pro-inflammatory responses. It was observed that the presence of nicotine can influence metal-induced in vitro toxicity. Based on epidemiological studies, the metal burden in e-cigarette users showed to be elevated in different populations (including e.g. NHANES). However, most often such studies were limited by the missing user characteristics, and information of other potential sources of metal exposure. In general, metals from e-cigarette use can be associated with toxicity endpoints but to uncover the metal related hazard of e-cigarette in users, more detailed data on metals in vapors and e-liquids; user habits and user demographics are needed.

Improving the collection efficiency of the liquid impinger for ultrafine particles and viral aerosols by applying granular bed filtration.

Liquid impingers are utilized to collect bioaerosols for many advantages, such as avoiding dehydration of biological agents. However, many previous studies have reported that the liquid impingers are surprisingly inefficient for the collection of ultrafine bioaerosols, with collection efficiencies <30%. In the present work, we have successfully improved the collection efficiency of the liquid impinger (AGI30) to as high as 99% for particles in the size range of 20-400 nm with the aid of packed glass beads. We also systematically investigated the effects of influential factors on the collection efficiency. These factors include the volume of the sampling liquid (0, 20 and 30 mL), depth (0, 7 and 10 cm) of packed glass beads and sampling flow rate (4, 6 and 8 liter per min, lpm). According to our experimental results, increasing the depth of packed glass beads and the volume of sampling liquid can enhance the collection efficiency. Also, decreasing the sampling flow rate can increase the collection efficiency and reduce the loss of sampling liquid. For the sampling of viable MS2 phages, the collection efficiency of AGI30 sampler with packed glass beads is much higher than that without packed glass beads. Conclusively, this study validates that the granular bed filtration can enhance the collection efficiency of liquid impingers for submicron and ultrafine particles and viral aerosols.