Content of toxic components of cigarette, cigarette smoke vs cigarette butts: A comprehensive systematic review Farshid Soleimani a , Sina Dobaradaran a,b,c, ⁎ , Gabriel E. De-la-Torre d , Torsten C. Schmidt c,e , Reza Saeedi f,g a Systems Environmental Health and Energy Research Center, The Persian Gulf Biomedical Sciences Research Institute, Bushehr University of Medical Sciences, Bushehr, Iran b Department of Environmental Health Engineering, Faculty of Health and Nutrition, Bushehr University of Medical Sciences, Bushehr, Iran c Instrumental Analytical Chemistry and Centre for Water and Environmental Research (ZWU), Faculty of Chemistry, University of Duisburg-Essen, Universit¨atsstr. 5, Essen, Germany d Universidad San Ignacio de Loyola, Av. La Fontana 501, Lima 12 Lima, Peru e Centre for Water and Environmental Research, University of Duisburg-Essen, Universitätsstr. 5, Essen 45141, Germany f Workplace Health Promotion Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran g Department of Health, Safety and Environment, School of Public Health and Safety, Shahid Beheshti University of Medical Sciences, Tehran, Iran HIGHLIGHTS • Cigarette butts (CBs), main and side- stream smoke (MS and SS) contents were reviewed. • PAHs and aromatic hydrocarbons were the most commonly chemical reported in studies. • For all chemical classes (except metals), MS was the most studied component. • Benzo[a]pyrene has been reported more frequently compared to other chemicals. • Secondhand and thirdhand smoke can re- tain chemicals and pose health concerns. GRAPHICAL ABSTRACT ABSTRACT ARTICLE INFO Article history: Received 16 October 2021 Received in revised form 20 December 2021 Accepted 20 December 2021 Available online 25 December 2021 Editor: Anastasia Paschalidou The commercially sold cigarettes contain more than 7000 chemicals, and their combustion produces potential toxicants in mainstream smoke (MS), sidestream smoke (SS), secondhand smoke (SHS), thirdhand smoke (THS), and discarded ciga- rette butts (CBs). We conducted a systematic review of published literature to compare the toxicants produced in each of these phases of tobacco combustion (MS, SS, and CBs). The initial search included 12,301 articles, but after screening and final restrictions considering the aims of this review, 159 published studies were selected for inclusion. Additionally, SHS and THS are briefly discussed here. Overall, polycyclic aromatic hydrocarbons (PAHs) and other aromatic hydrocarbons have been represented in more studies than other compounds. However, metals and nitrosamines were detected in higher concentrations than other components in SS. The concentrations of most PAHs and other aromatic hydrocarbons in MS and SS are higher compared to concentrations found in CBs. Also, the concentrations of all the studied carbonyl compounds, aldehydes and ketones in SS and MS were higher than in CBs. The mean levels of alcohols and phenols in SS were higher than those reported for both MS and CBs. Tobacco toxicants are inhaled by smokers and transmitted to the environment through SS, SHS, THS, and discarded CBs. However, further studies are necessary to assess adverse effects of toxicants found in CBs and THS not only on human health, but also on the environment and ecosystems. The results of this review provide updated information on the chemical contents of MS, SS, SHS, THS, and CBs. It adds to the growing understanding that smoking creates major health problems for smokers and passive smokers, but also that it generates environmental haz- ards with consequences to the ecosystems and human health through discarded CBs, SHS, and THS exposure. Keywords: Cigarette butts Mainstream smoke Secondhand smoke Sidestream smoke Thirdhand smoke Tobacco toxicants Science of the Total Environment 813 (2022) 152667 ⁎ Corresponding author at: Systems Environmental Health and Energy Research Center, Boostan 19 Alley, Imam Khomeini Street, Bushehr, Iran. E-mail address: s.dobaradaran@bpums.ac.ir (S. Dobaradaran). http://dx.doi.org/10.1016/j.scitotenv.2021.152667 0048-9697/© 2021 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv