Plant extract as gas adsorbent to reduce smoke toxicants of cigarette

Cigarette smoke contains thousands of chemicals including many known toxicants and annually leads to millions of deaths worldwide. To reduce the harms of cigarette, plant extracts were applied to adsorb smoke toxicants of cigarette. Results showed that platycladus orientalis leaf extract and mulberry fruit extract particles lled into cigarette cellulose acetate lter can signicantly reduce 15 major cigarette smoke toxicants emission including hydrogen cyanide (HCN), benzo[α] pyrene (B[a]P), formaldehyde, crotonaldehyde, 2-butanone, P-hydroquinone, M-dihydroxybenzene, catechol, phenol, M-P-cresol, O-cresol, N'-nitrosonornicotine (NNN), 4-methylnitrosamino-l-3-pyridyl- butanone (NNK), (R,S)-N-nitrosoanatabine (NAT) and (R,S)-N-nitrosoanabasine (NAB) by 11.90% to 60.42% (P<0.01). Platycladus orientalis leaf extract particles added in the outer cigarette lter also can adsorb other 125 kinds of chemicals most of which are harmful. Our results also indicated that plant extract has extensive gas adsorption characteristics and different plant extracts displayed different adsorption capacity to different toxicants. The adsorption capacities of ve randomly selected plant extracts are all signicantly higher than that of activated carbon(cid:0)P<0.01). These ndings suggest that plant extracts are excellent cigarette smoke adsorbents.


Introduction
Smoking is common worldwide. Cigarette smoke contains more than 4,500 chemicals including many known toxicants (Sobus et al., 2014;Ryu et al., 2020). These toxicants are responsible for a variety of cancers and other diseases. Tobacco smoking is the key cause of lung cancer (Jassemet al., 2009;Jung et al., 2016), and a major cause of cancers of the oral cavity, larynx, oropharynx, hypopharynx, oesophagus, stomach, liver, pancreas, bladder, ureter, kidney and cervix, and myeloid leukaemia (Hecht et al., 2003;Wittel et al., 2012;Jethwa et al., 2017;Chunxia et al., 2019;Khan et al., 2020;Nocini et al., 2020). Tobacco-speci c N-nitrosamines (TSNAs) are a group of carcinogens and they cause cancers of the lung, esophagus, pancreas, and oral cavity by DNA adduct formation. The most carcinogenic TSNAs in laboratory animals are 4-(methylnitrosamino)-1-(3-pyridyl)-1butanone (NNK) and N'-nitrosonornicotine (NNN) (Hecht et al., 1999;Ramírez et al., 2014). NNK has been proved to be related to lung and head and neck cancer (Xue et al., 2014;Doukas et al., 2020). NNN is one of potent carcinogenic TSNAs and it induces several malignancies including lung, esophageal, and pancreatic cancers in laboratory animals (Selvin et al., 2018). Benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is one among the principal constituents of tobacco smoke that plays a key role in lung and breast carcinogenesis (Kasala et al., 2015;Guo et al., 2015). Hydrogen cyanide (HCN) is volatile and highly toxic with acute and chronic effects on humans (Tran et al., 2020). HCN of smoke inhibits the enzyme systems necessary for oxidative metabolism and oxygen transport at the cellular level (Silverstein et al., 1992). Unsaturated oxidative formaldehyde is a noxious aldehyde in cigarette smoke that causes edematous acute lung injury (Cui et al., 2016) and exposure to formaldehyde has been linked to asthma, especially in children (McGwin et al., 2011). Smoking not only directly causes health harm to smokers, but also poses a health threat to non-smokers through secondhand smoke exposure (Xisca et al., 2017;Kelvin et al., 2020).
Based on the report of WHO, annually about 7 million deaths were attributable to smoking (GBD 2015Tobacco Collaborators, 2017. The Framework Convention for Tobacco Control(FCTC) opened for signature from 2003 in Geneva has became the the most widely embraced treaty in United Nations with 168 signatories today(https://fctc.who.int). Although the daily smoking rate has declined, the overall number of smokers remains a rapid increase worldwide and was more than 1 billion in 2019(Marissa et al., 2021).
For nicotine is addictive, smoking cessation is still di cult to most smokers despite ongoing legislative actions and public health efforts targeted at tobacco avoidance (Mark et al., 2014;Nicola et al., 2019;Judith et al., 2019;Federico et al., 2020). Although in recent years electronic cigarettes (e-cigarettes) and vape devices have rapidly become the new tobacco products used by youth, most smokers are still the faithful consumers of traditional cigarettes (Walley et al., 2019;Cherian et al., 2020). This compels us to adopt more measures to reduce the smoking harms of traditional cigarette. Here, we applied a kind of material-plant extract as gas adsorbent to cigarette harm reduction.

Adsorbents preparation
In this experiment, we randomly selected ve kinds of plant extracts-platycladus orientalis leaf extract(10:1, water extraction), mulberry fruit extract (10:1, water extraction), blueberry fruit extract (10:1, water extraction), pine needle extract (10:1, water extraction) and ginkgo leaf extract (10:1, water extraction) as experimental materials (Xi'an Senran Bioengineering Co., Ltd). The powder of these plant extracts was squeezed into particles with 1 mm diameter and used as adsorbents. The activated carbon of antigas mask was broken into particles with 1 mm diameter and used as control adsorbents.

Cigarette sample preparation
The total length of test cigarette(ZiYun, Hongyunhonghe Group, China) was 84 mm and the cellulose acetate lter length was 25 mm. The diameter of test cigarette was 7.8 mm. These plant extract particles were lled into the front 15 mm cellulose acetate lter of test cigarette with 1.5 mg/mm (Fig.1). These cigarettes with cellulose acetate lter including plant extract particles were used as experimental cigarettes. These cigarettes with blank cellulose acetate lter were used as control cigarettes.

Outer cigarette lter preparation
The outer cigarette lter had a plastic shell embodying two cellulose acetate lters(the length is 1cm and the diameter was 7mm).There was a cavity between these two cellulose acetate lters.50mg adsorbent particles were lled into the cavity (Fig.2).

Quantitative and qualitative analysis of hazard constituents in mainstream smoke
The test smoking of cigarette was carried out by a 20-port Borgwaldt RM200 rotary smoking machine (Borgwaldt, Germany). The HCN), B[a]P, formaldehyde, crotonaldehyde, 2-butanone, P-hydroquinone, Mdihydroxybenzene, catechol, phenol M-P-cresol, O-cresol, N'-nitrosonornicotine (NNN), 4-methylnitrosamino-l-3pyridyl-butanone (NNK), (R,S)-N-nitrosoanatabine (NAT) and (R,S)-N-nitrosoanabasine (NAB) emission level in mainstream cigarette smoke of cigarette were determined by commercial test according to the Chinese standard of cigarettes as described as Cai et al (2019)(4 replicates). In this experiment, using platycladus orientalis leaf extract particles as adsorbent in the outer cigarette lter (Fig.2), changes of chemical composition of adsorbent before and after smoking were determined through gas chromatography and tandem mass spectrometry method as described as Shen et al(2016)(2 replicates).
2.5. The adsorption capacity comparison between the activated carbon and ve kinds of plant extracts In experiment, ve kinds of plant extracts and activated carbon particles were used as adsorbents in the outer cigarette lter, the adsorbent weight changes of before and after one cigarette smoking were recorded as the adsorption capacity of one cigarette(3 replicates).

Statistical analysis
The difference of 15 major cigarette smoke toxicants emission and the difference of adsorption capacity were assessed using the ANOVA program of SPSS 22.0 for Windows (IBM SPSS Inc., New York, USA) . The signi cance level was set at 1% (P< 0.01) in all tests.
Based on above quantitative analysis results, 15 major toxicants in the mainstream cigarette smoke were signi cantly reduce by 11.90% to 61.50% (P<0.01). Different plant extracts displayed different adsorption capacity to different toxicants. The same plant extract showed different adsorption preference to different toxicants.

The absorptive effects on other smoke chemicals of cigarette
Platycladus orientalis leaf extract adsorbent particles added in the outer cigarette lter also showed absorptive effect to other 125 kinds of chemicals (Table 1) most of which are harmful. For example, methanethiol is a highly toxic chemical and can cause metabolic acidosis, seizures, myocardial infarction, coma and death (Maddry et al., 2020). Furan, a human carcinogen, is found in heat treated foods and tobacco smoke (Grill et al., 2015). Phenols or phenolic compounds(p-Cresol, 2-ethyl-Phenol, 2-methyl-Phenol, 2-methoxy-Phenol, 2,3dimethyl-Phenol, 2,4-dimethyl-Phenol and 2,4,6-trimethyl-Phenol) in tobacco smoke are cardiovascular toxins, act as tumor co-promoters and show genotoxic activity (Vaughan et al., 2008). This indicated that plant extract has extensive gas adsorption characteristics.

The adsorption capacity comparison between the activated carbon and plant extracts
Due to the large speci c surface area, rich porous structure, and high adsorption capacity, activated carbon adsorbents are widely used in gas puri cation (Zhang et al., 2015). In this experiment, we also compared the adsorption capacity to cigarette smoke between the activated carbon and plant extracts. Result indicated that the adsorption capacities of ve plant extracts platycladus orientalis leaf extract, mulberry fruit extract , blueberry fruit extract, pine needle extract and ginkgo leaf extract are all signi cantly higher than that of activated carbon P<0.01 (Table 2).

Implications
Most plant extracts(such as grape seed extract, hawthorn leaf extract, cyclocarya paliurus leaf extract, rosemary extract, folium artemisiae argyi extract, ginkgo leaf extract, persimmon leaf extract, sea buckthorn extract, kudzuvine root extract, buckwheat extract,etc) are nontoxic, harmless, cheap and have wide raw material sources. They can be applied to tobacco industry simply and conveniently( Fig. 1-2). This provides a new choice for the smokers di cult in quitting smoking. We can use plant extracts as adsorbent to reduce harms of cigarette smoking.
In recent years, with rapid development of industry, the problem of air pollution arises. The air pollution derives from different resource including industrial waste gas(Cong, 2018), automobile exhaust(Guarnieri et al., 2014), indoor air pollutants(Zhao et al., 2020), etc. The air pollutants include many toxic chemicals such as formaldehyde and phenols. In our experiment, plant extracts displayed excellent adsorption capacity to these toxicants and the adsorption capacities of ve plant extracts are all signi cantly higher than that of activated carbon. This implied that we can use plant extracts as new type of adsorbents to replace activated carbon in air cleaner and anti-gas mask.

Declaration of competing interest
The authors declare that they have no known competing nancial interests or personal relationships that could have appeared to in uence the work reported in this paper.

Figure 2
Platycladus orientalis leaf extract was used as adsorbent in outer lter to reduce harms of cigarette smoking( Plant extract particles were lled into the outer lter; Cigarette was insert into lters; Smoking; Plant extract particles adsorb the harmful gas and turn black. ).