Littered cigarette butt as a well-known hazardous waste: A comprehensive systematic review

Journal of Hazardous Materials 383 (2020) 121242

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Review

Littered cigarette butt as a well-known hazardous waste: A comprehensive systematic review Javad Torkashvanda,b,c, Mahdi Farzadkiaa,b, Hamid Reza Sobhid, Ali Esrafilia,b,

T

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a

Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran Department of Environmental Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran c Student Research Committee, Faculty of Public Health Branch, Iran University of Medical Sciences, Tehran, Iran d Department of Chemistry, Payame Noor University, Tehran, Iran b

ARTICLE INFO

ABSTRACT

Editor: R Teresa

Most of cigarettes used in the world have filters. Following smoking, the cigarette butts (CBs) are often littered as wastes in the environment. CBs generally contain several toxic substances that are trapped in the cigarette filter. Filters are made of non-biodegradable materials and remain in the environment for a long time. Within this study, it is attempted to systematically review the articles on CBs and find out the answers to the problems associated with the factors including quantity, distribution, origin and toxicity of CBs in the environment. It is estimated that approximately 5.5 trillion cigarettes are being produced annually in the world and the CB wastes would reach 1.2 million tons and increase by 50% until 2025. CBs contain thousands of dangerous chemicals such as arsenic, benzene, hydrogen cyanide, PAHs, pyridine, heavy metals and so forth. It is also believed that eachCB can pollute 1000 liters of water. Given the inadequacy of mechanical equipment as well as the cost of collecting these wastes, there should be a special focus on these items as follows: producing cigarettes with degradable filters, reducing the rate of smoking in the world, reducing the toxic and chemical substances in the process of plant growth, processing and production of cigarettes, training people to discard CBs properly, putting legal and financial pressures on cigarettes production, and the last but not least, providing effective solutions for collecting CBs.

Keywords: Cigarette butt Debris Litter Solid waste Environmental impact

1. Introduction Nowadays, in different societies, cigarette consumption has been observed among many people even in youngsters (Green et al., 2014). This amount has reached several hundred billion cigarettes per year in some countries (Marah and Novotny, 2011). Trillions of cigarettes are produced annually in the world to meet the above consumption; (Marah and Novotny, 2011; Aeslina and Mohajerani, 2012). As a result, billions of cigarette butts (CBs) are being thrown away in the world on a daily basis. Therefore, these CBs are regarded as one of the largest wastes in the streets, urban roads, and public places (Green et al., 2014; Novotny and Zhao, 1999; Ariza and Leatherman, 2011; Becherucci et al., 2017; Haseler et al., 2018; Dobaradaran et al., 2017; Cutter et al., 1991; Chevalier et al., 2018; Lee and Lee, 2015; Moerman and Potts, 2011). In spite of the small size, CBs are considered as environmental hazards for the aquatic organisms, insects, infants, domestic and wild animals and due to the fact that a high number of these wastes containing a great number of dangerous chemicals such as nicotine, heavy

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metals, PAHs, PAC, and ethylphenol are littered (Green et al., 2014; Moerman and Potts, 2011; Dieng et al., 2013; Novotny et al., 2011; Dieng et al., 2014; Parker and Rayburn, 2017). Additionally, owing to the preparation of cigarettes filters from non-biodegradable materials (Ariza and Leatherman, 2011; Ariza et al., 2008), CBs remain in the environment for a long time (Green et al., 2014; Novotny and Zhao, 1999). Meanwhile, collecting the CBs of small size is very difficult and expensive. For example, in a city scale, collecting them could cost up to multi-million dollars (Marah and Novotny, 2011; Patel et al., 2013; Rath et al., 2012). Meanwhile, due to high rate of cigarette production and consumption, dispersion of the resulting wastes (Green et al., 2014; Marah and Novotny, 2011), the cost of collecting cigarettes (Patel et al., 2013; Rath et al., 2012), as well as the presence of toxic and chemical substances in the CBs (Dobaradaran et al., 2017; Moriwaki et al., 2009; Slaughter et al., 2011; Dieng et al., 2011) remaining in the environment for a long time (Ariza and Leatherman, 2011; Ariza et al., 2008), a special attention needs to be paid in this regard.

Corresponding author at: Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran. E-mail address: [email protected] (A. Esrafili).

https://doi.org/10.1016/j.jhazmat.2019.121242 Received 31 July 2019; Received in revised form 9 September 2019; Accepted 14 September 2019 Available online 19 September 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.

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Table 1 Search protocols and the number of articles found on the databases. Search protocol

Source

Article

A: (I) Study on the CBs as a waste, (II) Time limit for search was not considered, (III) the keywords "cigarette butt" OR "cigarette filter" OR "cigarette waste" OR "cigarette litter" OR "cigarette debris" had to appear in the title- abstract-keyword, (IV)the keywords "solid waste" OR "municipal solid waste” OR waste OR litter OR debris OR MSW OR MSWM had to appear in the title- abstract-keyword. B: (I) Study on the CBs as a waste, (II) Time limit for search was not considered, (III) the keywords "cigarette butt" had to appear in the title

Scopus PubMed Web of science

164 38 61

Scopus PubMed Web of science

118 25 26

_

Herein, a systematic scientific-based review was conducted to determine the quantity of CBs in different parts of the world and their dispersion, as well as raising awareness about the type and amount of contaminants measured in these wastes. This study was initially aimed at examining and comparing the results of the studies with the solid waste perspective in order to obtain information about the followings: the amounts of CBs in the world, the recognition of their distribution, the ratio of these wastes to other wastes, the identification of contaminants presence in the CBs, the toxicity of CBs for creatures, and the factors affecting the amount of CBs toxicity.

the effects of CBs on humans and organisms Having considered these characteristics, this study was mainly focused on 53 papers from three databases (Fig. 1).

2. Methods

3.1. Smoking rates and status of CB as a waste

2.1. Literature search

Cigarette consumption is a common phenomenon among people in different societies. It is reported that on average 16 cigarettes are consumed by 20% of the above15-year-old population per day (Green et al., 2014). This volume of consumption is responded by producing a large amount of cigarettes per year. According to the estimation by the US Department of Agriculture in 2014, 5.5 trillion cigarettes were produced annually in the world and this trend is expected to rise (Aeslina and Mohajerani, 2012). In 2007, 1.35 trillion cigarettes were produced in the United States alone, while in the same year 360 billion cigarettes were consumed in this country (Marah and Novotny, 2011). This amount of cigarette production and consumption in the world results in a significant number of CBs (Green et al., 2014). CBs could be easily seen anywhere in the streets, urban areas, and seacoasts (Novotny and Zhao, 1999). The widespread dispersion of these wastes in the environment is an important issue originating from their small size. This phenomenon is based on the fact that an important part of the produced CBs by smokers is not properly disposed and often littered in public and urban areas (Green et al., 2014; Ariza and Leatherman, 2011; Becherucci et al., 2017; Haseler et al., 2018; Cutter et al., 1991; Ariza et al., 2008). This has led to the introduction of the CBs as the most important wastes found in urban, public, coastal, and marine areas (Chevalier et al., 2018; Lee and Lee, 2015; Moerman and Potts, 2011). The amount of disposedCBs is directly relative to the amount of cigarette production and consumption. Reports show that 5.5 trillion cigarettes were produced in the world annually (Aeslina and

3. Literature review This study covers the specific researches on CBs between 2005 and 2019. Within the studies on CBs, the amounts of pollutants found in CBs were considered and tabulated in Table 2. Then, the research results were categorized as described below.

This systematic study by identification of keywords and definition of two search protocols was carried out. Having gone through a number of three scientific databases over 2019, this review was conducted with the aim of studying CBs as solid wastes. The results and strategies used are presented in Table 1. 2.2. Screening and selection of criteria Having finished the literature search, the titles and abstracts of all the related articles found were studied by our group. The search was followed by a screening process to identify the relevant documents. After that, the following parameters were considered: (i) Title and abstract: papers with a title and/or abstract lacking relation to CBs were excluded; (ii) Abstract: each paper's abstract was thoroughly read once more so as to further select papers addressing CBs; (iii) Content: the full paper was fully read to identify the studies that includedthe quantity of CBs and/or CB pollutants; (iv) Related documents: relevant documents referenced on the initially selected papers were searched and read. Then, all studies on CBs including the topics below were selected and fully considered. _ CB quantity _ toxic compounds in CBs _ the effects of CBs on the environment

Fig. 1. Screening process to make a short list for this study.

2

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Table 2 The reported CB quantity in various studies. Country

Report

Reference

Australia

Annual litter of 24 to 32 billion CBs 10 to 15 percent of the litter collected in the country are CBs cigarette smoking comprised 1 to 11 percent of the debris on some of the country's beach Average density 2.7 CBs per square meter in the city of Berlin The share of 31% of CBs and cigarette filters in the total number of coastal debris 23 percent of New Jersey's debris are CBs 12 percent of total sea debris was CBs, with a mean number of 58 per 500 meters In two campuses, San Diego State University (SDSU) and University of California San Diego (UCSD), with 63 volunteers in one hour23885, and with 17 volunteers in one hour 6525CBs were collected. The average for each volunteer in the two universities was about 380 The share of 9% of CBs and smoking filters in the total number of beach debris The most abundant debris on the coast of the Balearic Islands wasCB: maximum 68 number per meter The CBs collected on the coast of Catalan in different seasons was reported to be 2.2, 2.5 and 3.5 number per square meter A survey of 56 points from the Mediterranean coast in Spain showed that CB and smoking filter accounted for 45.6 percent of total coastal debris, with an average of 0.023 items per square meter Average 150 CB per km of roads per month 5 percent of the marine debris and most of the beachdebris consisted of CBs In the study of three beaches in Brazil, it was found that CB are the second most abundant debris on these coasts, equivalent to 26.7% in the winter of 2015 and 22% in the summer of 2017. 33 percent of the total debris from a coastal city with a mean density of 14 per square meter was CBs. The largest observed marine debris with an average of 1008 number was CBs At 8 coastal sites, the largest number of debris was CB with an abundance of 4496, accounting for 29.7% of debris. The weight of this number was 1708 ± 712 grams estimated. CBs are the most litter in Malaysia. In an investigation on the Malaysian coast, 13,193 litter observed, the most frequent of which was CBs On average, 4.94 CB were reported per meter of studied sandy beaches. In 2016 and 2017, at 10,490 square meters of coast, 1545 and 3007 CB were collected, respectively, with the highest number of coastal debris. In the 132,895 square meter area on Thailand's 11 beaches has 101,000 CB, an average of 2.26 number per square meter. with a maximum of 13.3 and a minimum of 0.25 CB per square meter.

(Micevska et al., 2006) (Micevska et al., 2006) (Taffs and Cullen, 2005) (Green et al., 2014) (Haseler et al., 2018) (Cutter et al., 1991) (Ribic, 1998) (Sawdey et al., 2011)

Germany United States

Lithuania Spain

Japan Brazil Argentina Bulgaria Malaysia Morocco Cyprus Thailand

(Haseler et al., 2018) (Martinez-Ribes et al., 2007) (Ariza et al., 2008) (Asensio-Montesinos et al., 2019) (Moriwaki et al., 2009) (Oigman-Pszczol and Creed, 2007) (da Silva et al., 2018) (Pon and Becherucci, 2012) (Simeonova et al., 2017) (Simeonova and Chuturkova, 2019) (Yi and Kannan, 2016) (Maziane et al., 2018) (Loizidou et al., 2018) (Kungskulniti et al., 2018)

Many researchers have considered CBs and plastics as two well-known wastes found in different areas such as coastal areas (Ariza and Leatherman, 2011; Becherucci et al., 2017; Moriwaki et al., 2009).

Mohajerani, 2012; Novotny and Zhao, 1999), of which 83% were filtered cigarettes (Novotny and Zhao, 1999) In a further related study, the number of littered CBs all over the world was around 75–97% of the cigarette consumed in 1995 (Micevska et al., 2006). According to the two separate reports, the ratio of littered CBs to the cigarette consumption was about 76% (Patel et al., 2013) and 84% (Lee and Lee, 2015), indicating the effect of smoker’s behavior on the amount of these litters. CBs are known as a common waste in cities (1,291,824), coasts (Ariza and Leatherman, 2011; Haseler et al., 2018; Dobaradaran et al., 2017; Ariza et al., 2008; Martinez-Ribes et al., 2007; Oigman-Pszczol and Creed, 2007; Taffs and Cullen, 2005), roads (Moriwaki et al., 2009; Rath et al., 2012), public places such as universities (Sawdey et al., 2011), and even aquatic and sea environments (Becherucci et al., 2017; Ribic, 1998; Simeonova et al., 2017; Smith et al., 2014; Yi and Kannan, 2016). Therefore, CB is one of the most common and epidemical wastes (Pon and Becherucci, 2012) and contributes to the largest number of wastes in the world (Micevska et al., 2006). The estimated rate for the CBs in the world was at least 4.5 trillion per year (Novotny and Zhao, 1999; Micevska et al., 2006; Pon and Becherucci, 2012; Register, 2000). It was understood that the weight of these wastes in the world would reach 1.2 million tons per year and, according to various parameters such as the world population growth, the rate of CB wastes would increase by 50%in 2025. In addition, the measured amounts of CBs released by a different clean-up programs indicates that the CBs contribution to all collected trashes is quite high. For example, in 1997, during the waste collection program from 5000 sites in 90 countries, 19.1% of the wastes collected were CBs while this rate was 12% in 1990 (Novotny and Zhao, 1999). Elsewhere in the United States, in 2009, of the total 51.2 billion collected debris from roadside, 38% was attributed to tobacco wastes (Rath et al., 2012). Additionally, 21% of the wastes collected by the international coastal cleanup campaign in 2009 were CBs, which is twice as high as any other wastes (Moerman and Potts, 2011). Also, a total number of 2,043,470 CBs were collected in 2013 during the international cleanup, which was the highest level reported for any wastes (Parker and Rayburn, 2017).

3.2. Temporal and spatial variation of littered CB Although CBs are known as the most common waste and debris found in the urban areas, some reports indicate that they include 22–46% of the visible wastes (Green et al., 2014), but their distribution is not the same in all parts of the city and in different landuse. For example, in a study conducted in Berlin, it was observed that as a result of changing landuse, the highest mean concentration of CBs was 5.2 CBs per square meter while the lowest site mean concentration was 0.29. Also, within this study it was reported that the highest concentration was 48.8 CBs per square meter in near a train station entrance (Green et al., 2014). In another study cited in San Diego, it was investigated that in the places with a higher probability of CBs and in the places with a low probability, an average of 38.1 (11–77) and 4.8 (0–25) CBs were observed respectively, while only in 6 regions the number of CBs was reported to be zero (Marah and Novotny, 2011). In urban areas, there are meaningful correlations between the rates of CB littering on the one hand, and the parameters including the population density, the availability of cigarette sales on the other hand (Araújo and Costa, 2019).Studies have shown that certain locations in cities have a greater potential for the existence of CBs, some of which are as follows: the areas around shopping malls and cigarette consumption in restaurants, bars, grocery stores, gas stations, cafés, liquor stores, convenience stores, and traffic signals (Green et al., 2014). In a study carried out in San Francisco, it was shown that the largest number of CB wastes was found to be around the venues (Marah and Novotny, 2011). Also, the difference in the level of CB wastes found in these places (i.e., the venues) and the corresponding level found in other parts of the city is very significant (up to 8 times). It was reported that the application of GIS system is a useful tool for understanding and distinguishing the density of CBs in urban and public areas (Marah and 3

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Novotny, 2011). In a study done on 14 Moroccan sailors, Maziane and his colleagues reported that CB consisted of 32% and 14.1% of debris in urban and rural areas, respectively (Maziane et al., 2018). Meanwhile, Montesinos and his colleagues studied on 56 Mediterranean coastal sites in Spain and found out that the CB abundance was greatly varied according to beach typology, from 1028 units at 19 natural sites (0.025 items/m2), 1148 at 17 village sites (0.020) to 2431 at 20 urban sites (0.023). This is equivalent to an average content per 100 m long beach sector of 54 CBs at natural coastal sites, 67 at village sites and 121 at urban sites (Asensio-Montesinos et al., 2019). The number of CBs disposed in some areas, especially in touristic areas varies in different seasons, but there is no report on the significant correlation between the number of CBs and the change in the season (Green et al., 2014; Ariza et al., 2008). However, in another study performed on the coasts, CB wastes were up by 46% in the tourism season (i.e., summer) which was twice as large as other seasons (Martinez-Ribes et al., 2007). In a further related study, it was reported that CB wastes disposed in the summer time were more than those of the autumn (Simeonova et al., 2017). In a study on the debris found in the Black Sea and Bulgarian coastal sites, it was reported that the largest observed litter was CB (4496 number), accounting for 29.7% of the total debris. These researchers reported a significant difference in the number of littered CB in different seasons. For example, for respective summer, autumn, winter and spring, a total number of 2637, 1072, 454 and 333 CB was seen in the studied area (Simeonova and Chuturkova, 2019). In addition, the extent of consumption and the presence of people in public areas are also effective in the density of this type of wastes. As reported elsewhere, the level of CBs found on the public beaches was reported to be higher than that of other places (Taffs and Cullen, 2005). Meanwhile, the number of disposed CBs at different times of a week may also vary. As reported by a researcher in Brazil, during the week, the amount of CBs per square meter of the studied area was doubled during the holidays (Oigman-Pszczol and Creed, 2007).

Slaughter et al., 2011). In addition, the presence of these wastes in public environments can cause complications in infants, pets, and birds because they may eat them (Novotny et al., 2011). The presence of toxic contaminants in CB has prompted some researchers to control and confirm their effect on these creatures (Dieng et al., 2013, 2014; Dieng et al., 2011). 3.4. Contaminants within CBs The existence of CB wastes in different areas increases the environmental risks and the transmission of contaminants into the environment (Moerman and Potts, 2011). It is stated that 75% of chemicals of cigarette smoke are in gas phase and the rest are in the tar phase (Aeslina and Mohajerani, 2012). Some of the chemicals found in the cigarette smoke are: hydrogen cyanide, nitrates, ammonia, acetaldehyde, formaldehyde, benzene, phenol, pyridine, carbon monoxide, Polycyclic aromatic hydrocarbons (PAHs), N-nitrosamines, aromatic amines, heavy metals such as arsenic, chromium, nickel and cadmium (Aeslina and Mohajerani, 2012; Lee and Lee, 2015; Micevska et al., 2006) due to trapping of these pollutants in the filter (Dieng et al., 2013). In addition,CB is one of the main causes of contamination in coastal areas and has the potential for diffusing some contaminants, especially heavy metals, into the sea environments (Dobaradaran et al., 2017). This is called an environmental problem and a threat to aquatic species due to its entry into water resources (Patel et al., 2013). Since CB contains tar, cadmium, lead, and arsenic, it can be a serious hazard to the wildlife organisms and aquatic creatures (Pon and Becherucci, 2012). 3.4.1. Heavy metals in CBs Heavy metals are one of the most important pollutants found in CBs (Aeslina and Mohajerani, 2012; Dobaradaran et al., 2017; Lee and Lee, 2015; Moerman and Potts, 2011; Moriwaki et al., 2009). These pollutants, if leaked into the aquatic environment, can be the source of contamination in the marine environment and can enter the food chain as well (Dobaradaran et al., 2017). The amount of heavy metals such as cadmium, arsenic, nickel, copper, lead, and zinc is reported from several micro grams per gram to several hundred grams per gram in CBs (Chevalier et al., 2018). Heavy metals trapped ontoCBs can be removed by leaching into the environment (Aeslina and Mohajerani, 2012). In a study, the leak of heavy metals potential from CB with an average of 150butt/km/month in road areas was expressed as 0.02–1.7 mg/km/ month. For example, the leak of cadmium, copper, lead, chromium, and arsenic was reported to be 0.02, 1.7, 0.59, 0.15 and 0.81 mg/km/ month, respectively (Moriwaki et al., 2009). The percentages of different heavy metals leaking from CBs are shown in Fig. 2.

3.3. Nature of CB CB is made up of a cigarette filter and the remaining tobacco containing chemicals and environmental contaminants (Green et al., 2014; Chevalier et al., 2018; Moerman and Potts, 2011; Dieng et al., 2013; Parker and Rayburn, 2017). The major compound used in cigarette filters is cellulose acetate which is a biodegradable resistant material (Ariza and Leatherman, 2011; Dieng et al., 2013; Ariza et al., 2008) and will remain in the environment under normal conditions for 18 months (Green et al., 2014; Novotny and Zhao, 1999). Although it is non-biodegradable, it can be turned into smaller particles under ultraviolet (UV) rays, lasting from 10 to 15 years (Marah and Novotny, 2011; Dieng et al., 2013). Cellulose acetate fibers, each roughly 20 mm size, are subjected to titanium dioxide (a delustrant) and over 15,000 of them are packed firmly together with triacetin (glycerol triacetate) as a binding agent, to produce a single filter (Slaughter et al., 2011). It is well-known that cellulose acetate is made via acetylation (ca., the addition of acetic anhydride and acetic acid). Once the procedure elapsed, plasticizers are added (such as polyethylene glycol). Cellulose is easily biodegraded by the cellulase enzyme, but because of the chemical modification of the polymer it has a limited potential for the biodegradation. Moreover, the decomposition of conventional cigarettes is hindered by the high level of fiber's compactness and the inclusion of plasticizers (Araújo and Costa, 2019). These conditions have made CBs as a good candidate for causing toxic problems in the environment (Ariza and Leatherman, 2011). Although the content of contaminants in each CB is not a significant problem for the environment due to its small size, a large number of CBs and their dispersion have the potential for exacerbating local pollution (Moerman and Potts, 2011). The effect of CB contaminants on aquatic species has been investigated and confirmed elsewhere (Lee and Lee, 2015; Parker and Rayburn, 2017;

3.4.2. Organic pollutants within CBs CBs have the potential for PAH release, which can have carcinogenic impacts on living organisms in the environment (Dieng et al., 2013; Moriwaki et al., 2009). In the study on the CBs in a roadway, it was reported that the average potential emission of PAHs in the littered CBs was 0.032 mg/km/month, while the amount of each PAH examined in a CB was around 0.0065 to 0.0078 mg/kg and the total PAHs were determined to be 0.039 mg/kg (Moriwaki et al., 2009). Under these conditions, the emissions of these pollutants are affected by variables such as precipitation and wind (Moriwaki et al., 2009). Different proportion of PAHs can be found in CBs. In a separate study, it was shown that the highest levels of PAH in a CB was phenanthrene with the level of 20% and the lowest level of PAHs was for dibenzoanthracene and anthracene with less than 2% of the total PAHs in CBs (Fig. 3). Meanwhile, CBs contain polycyclic aromatic compounds (PACs) having toxic effects on organisms (Green et al., 2014), but the most toxic substance found in CBs is nicotine. Nicotine leaches from CB to aquatic ecosystems and is easily absorbed by the skin, lung alveoli, small intestine, and bladder, and can contribute to heart disease and 4

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Fig. 2. The rate of leakage of various heavy metals from the CB (%) (Moerman and Potts, 2011).

affect the central nervous system. The nicotine leakage occurs very quickly from CBs to the aquatic environment, and this is true in both cases of the precipitation on CBs and the submergence of CBs in aquatic environments. In a study performed in Berlin, it was found out that when the cigarette was soaked in the stagnant water, nicotine quickly began to leach[7.3 mg/g (equivalent to 2.5 mg/l) leakage occurred over 1,440 min],half of which occurred as early as 26 min while by the 651 min,90% of the leakage had taken place.In a precipitation test, for a 21.6 mm precipitation layer an equivalent of 3.8 mg/g nicotine leakage occurred, almost half of which leached from the layer with 1.6 mm of precipitation (Green et al., 2014). The study revealed that a quick leakage of nicotine into the water was adapted to the first-order reaction and depended on the amount of nicotine remaining in CB. In the meantime, the rate of nicotine leakage to water resources was also dependent on other conditions such as soil and bed filtration properties (Green et al., 2014). The level of nicotine and other pollutants leakage also depends on the behavior of smokers according to the characteristics of the littered CBs, such as the weight and the proportion of the remaining tobacco on the filter. Based on these results, each cigarette can pollute 1000 liters of water (Green et al., 2014). In another study, the level of nicotine leakage was reported at 3.8 mg/l. However, the exact emission of this pollutant through precipitation to the environment and the exposure of the organisms with it is not clear, but the harmfulness of this contaminant is clear (Moriwaki et al., 2009).

from CBs into the environment in conventional wastewater treatment processes and they cannot be eliminated from the aquatic environments (Chevalier et al., 2018). The results of a study showed that heavy metals can be found in CBs and non-smoked filters in both dissolved and nanoparticle form. As shown in Table 3, the nanoparticle form is more likely for all metals than the dissolved form (Chevalier et al., 2018) 3.5. The origin and elements of contaminants in CBs It is already evident that CBs are deadly for aquatic life (Dieng et al., 2013). Due to the presence of contaminants such as those mentioned earlier, it should be noted that the origin of these contaminants in CBs comes from the different stages of tobacco cultivation, processing and manufacturing of cigarettes, and tobacco consumption. These toxic substances are added naturally to cigarettes during cultivation or production process (Dieng et al., 2013). Some toxins such as nicotine naturally exist in tobacco leaves and other toxic substances such as heavy metals are adsorbed by tobacco from soil and fertilizers during plant growth. Some of the toxic substances present in cigarettes, which can be the origin of contamination in the CBs, result from the materials previously added to the plant such as fungicides, herbicides, insecticides, and pesticides during the growth process (Moerman and Potts, 2011; Dieng et al., 2014; Micevska et al., 2006). In addition, the steps of leaf treatment and adding brightening agents on the wrapping paper increase the level of contaminants such as heavy metals in cigarettes (Moerman and Potts, 2011). Finally, level of toxicity in CBs depends on other factors such as type of plant, and part of the plant used in producing. Meanwhile, smoking behavior and the way a cigarette is consumed can also affect the content of chemicals in CBs and the characteristics of the filter such as porosity (Dieng et al., 2013).

3.4.3. Nanoparticles in CBs One of the most important polluting emissions from CBs is nanoparticles. Organic particles in CBs are measured in the range of 70 to 400 nm (with an average of 202 nm), which can absorb other contaminants and transfer them to living organisms. Nanoparticles can leak

Fig. 3. The proportion of PAHs present in the CBs (%) (Moriwaki et al., 2009). 5

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Table 3 The metals and their corresponding ratios of particle to dissolved form in CBs (10). Metals

Cr

Al

Mn

Fe

Co

Ni

Cu

Cd

Zn

Pb

As

Particle-to-dissolved ratio

> 90

> 80

> 60

> 65

> 65

> 60

> 60

> 70

> 50

> 65

> 50

3.6. Toxicity of CBs

Meanwhile; in a study by Loizides and colleagues, they found out that despite collecting 1545 and 3007 CBs in the cleanup at 9 sites of the Blue Flag Beaches in Cyprus in respective years of 2016 and 2017, the CBs were still present on the beaches even after the cleanup (Loizidou et al., 2018).

Given the high amount of littered CB, the presence of highly toxic and polluting substances in CB should be seriously taken into account. The toxicity of this litter has been confirmed for fish and some aquatic organisms such as bacteria (Dobaradaran et al., 2017); the toxicity of cigarettes has well been documented in several researches (Table 4). The researchers claimed to have observed the following events: 100% Aedes aegypti died in the first stage of larvae caused by a toxin from a CB in 100 ml of water for 24 h (Dieng et al., 2013), CB cessation for Aedes albopictus in the larval stage, and its effect on the decomposing of the Aedes aegypti (Dieng et al., 2014), the toxicity of CB on Aedes albopictus (Dieng et al., 2011), the potential of fish deaths due to the presence of substances in the CB (86), the presence of insecticidal properties for the larval period of Aedes aegypti (Dieng et al., 2013) and the toxicity of CB for Dafina and Water flea Daphnia Magna (Dieng et al., 2013). Also, in a study by Rebischung and co-workers, three types of CB were analyzed in terms of Hazard properties (HP 4 (irritant – skin irritation and eye damage), HP 5 (specific target organ toxicity/aspiration toxicity), HP 6 (acute toxicity), HP 7 (carcinogenic), HP 8 (corrosive), HP 10 (toxic for reproduction), HP 11 (mutagenic) and HP 13 (sensitizing))and they reported that nicotine was the main responsible in CB hazard with regard to HP 6 (acute toxicity) according to the European regulations (Rebischung et al., 2018).

3.9. Methods of CB control and recycling Considering a number of problematic issues posed by CBs such ashigh cost of cleaning, unsightly views, increasing risk of fire and safety, some researchers came up with some tips for controlling littered CBs. The researchers claimed that smoke-free policies would increase the amount of CBs, their environmental risks, and cleaning costs (Sawdey et al., 2011). Therefore, several legal measures such as raising cigarette tax, production of cigarette filters using degradable material, raising awareness about the importance of CBs and prevention of cigarette smoking, and development of non-governmental organizations (NGOs) can be effective (Novotny and Zhao, 1999). Raising an awareness among individuals is an important point for reducing littered CBs, because individual behaviors play a key role in the production of these wastes (Ariza and Leatherman, 2011). It is also suggested that portable ashtrays should be used to reduce the amount of CBs in coastal areas. In a further related study, it was found out that CBs consisted of 50% of the debris found in most portable ashtrays placed on the coast. The numbers of required portable ashtrays are estimated by calculating the numbers of CBs littered and their proportion to the total number of CBs at the coastline (Widmer and Reis, 2010). Owing to the toxicity of CB and its numerous contaminants, Landfill and Incineration methods are not recommended for CB management and recycling can be an appropriate choice in this regard (Torkashvand and Farzadkia, 2019). So far, 10 types of CB recycling have been reported on. However, different CB recycling methods were set in three categories: a) reuse of chemicals trapped in the cigarette filter after their extraction, b) recycling of cellulose acetate, and c) reuse of CB with no further component separation (Torkashvand and Farzadkia, 2019).

3.7. Other hazards of CBs In addition to the role of CB in causing toxic effects and the transfer of contaminants to aquatic environments, this waste has a direct poisoning effect on infants, domestic/wild animals due to its ingestion. Eating of CB can cause complications of vomiting and neurotoxicity. For example, ingestion 40–60 mg of nicotine in children is fatal (14). For younger children, 1–2 mg nicotine may be toxic and cause nausea and vomiting resulting in nerve symptoms. Higher dosages can inflict nerve symptoms and in the case of domestic animals, 9.2 mg/kg of nicotine is fatal, but clinical symptoms are observed at 1 mg/kg (Novotny et al., 2011). CBs have also been seen in birds’ nest, which can lead to the transmission of the pollutants in the bird. For example, in a study, CBs were found in 12% of thrush nests (Igic et al., 2009). In addition, there is a risk of fire due to the disposal of CBs when they are not completely put out (Pon and Becherucci, 2012). In a survey conducted in New Zealand, a large proportion of smokers littered CBs, most of which were kindled (Patel et al., 2013).

4. Discussion The results of this review indicates that CB is the most debris found in the world. Due to the amount of pollutants in this waste, CB can be regarded as a hazardous waste that is widely prevalent in the urban environment. Littered CB is one of the most challenging parts of municipal waste that cannot be easily managed due to its several features. The most important challenges posed by CB can be seen in Fig. 4. The predominant form of cigarette produced in the world, which is an equivalent of several million tons annually, is filtered cigarette resulting in the production of waste called CB. CB is composed of cigarette filter and tobacco, which is often littered by smokers. CB quantity is directly linked to the production and consumption of cigarettes in the world. The behavior of smokers is very effective in the amount of CB wastes as these people litter the CBs. According to a several reported studies, a large part of CBs is disposed by smokers which constitutes a considerable amount of urban and environmental wastes. Evaluating the behavior and attitude of smokers in a study demonstrated that 74% of respondents often litter CBs (Rath et al., 2012). Even in the places equipped with trash bins, the smokers litter their CBs on the ground. Moreover, a similar-related study showed that in spite of the existence of trash bins placed within a radius of 24 m, an average of 5.5 CBs were

3.8. Costs and problems associated with CB collection Given a high number of CBs, their small size and widespread dispersion, the collection of them is definitely costly. In fact, CBs as a common litter increases cleanup costs (Patel et al., 2013). An economic estimate showed that the cost of cleaning up and collecting littered CBs in streets and parks in San Francisco was 0.5–6 million dollar annually (Rath et al., 2012). In 2009, in the same place, another study revealed that a total of 6,098,969 US dollars were spent for cleaning CBs (Marah and Novotny, 2011). Some studies demonstrated that the use of mechanical cleaning equipments for CBs was inefficient (4.4% at the beginning of July and 14.4% in mid-August) (Ariza et al., 2008). It should also be noted that the application of these devices in places like coastal areas can affect the nest of animals such as birds and turtles (Ariza and Leatherman, 2011). 6

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Table 4 Data released on the toxicity of tobacco. The objective of CB study Evaluation of CB for Vector control

remarks Ae. Aegypti

Ae. Aegypti

Aedes albopictus

aegypti vulnerability to butts during its development. • Ae. showed insecticidal activities against larvae. • CBs effect was seen most during the early developmental phases and in • This the presence of increased amounts of cigarette remnants. great presence of CBs, mortality was high even for the late • Indevelopmental stages. deposition occurred at higher rates in the microcosms containing CBs. • Egg after exposure to CBs results in reduced life span. • survival CBs acted both as an attractive signal to gravid A. aegypti females • Clearly, and as a life-shortening factor for survivors. females derived from survivors exposed to CBs were fertile. However, • All parental fecundity tended to be greater than that of their daughters. have detrimental effects on the population dynamics of Ae. albopictus. • CBs CB microcosms tended to cause more egg deposition as • The decomposition progressed. mortality rates of young larvae (1 st and 2nd instars) were extremely • The high in the microcosms with cigarette remains compared to control larvae

reference (Dieng et al., 2013)

(Dieng et al., 2014)

(Dieng et al., 2011)

mortality, especially as decay advanced.

developmental stages (3rd and 4th instars, pupae) were unaffected • Late by CBs, but increased amounts of CBs prevented development completion of most young larvae.

release large amounts of labile substances, some of which act as egg • CBs hatching inhibitors by depleting bacterial populations. of the newly hatched larvae in CB microcosms died, where as their • most counterparts present in control microcosms showed almost 100% Toxicity of CB on organisms

medakaembryos(Oryzias latipes)

survival.

embryo exposed to CB at 0.2 pc/l appeared to be larger and had • The higher eye density than the control, while the one at 5 pc/l appeared to be

(Lee and Lee, 2015)

smaller and had lower eye density.

leachates significantly increased the heart rate and accelerated • CB embryonic development at low concentrations (0.2–2 pc/L), and lowered

Ceriodaphnia cf. dubia and Vibrio fischeri

• • • • • • • •

marine topsmelt (Atherinops affinis) and the freshwater fathead minnow (Pimephales promelas)

• • • • • • • •

the heart rate and suppressed development at high concentrations (5–10 pc/L). CB leachates at 2–5 pc/l induced anxiety-like behavior in exposed hatchlings. A strong dose-dependent effect of the CB leachates on medaka development. Acute toxicity of 19 CB types to Ceriodaphnia cf. dubia (48-hr EC50 (immobilization)) and Vibrio fischeri (30-min EC50 (bioluminescence)) was determined. Organic compounds caused the majority of toxicity in the CB leachates. Of the 14 organic compounds identified, nicotine and ethylphenol were suspected to be the main causative toxicants. Toxicity data for cigarette butts for one species could not predict or model the toxicity of cigarette butts to the other species. Brand affected the toxicity. Toxicity of CB is caused by or is strongly associated with polar and nonpolar organic compounds. Toxicity was also suspected to be caused by volatile, oxidizable, or sublatable compounds, for example, chlorine, surfactants, and heavy metals, particularly divalent metals. Increase in toxicity (decreased EC50 values) with increased tar content within CB. chemicals in CB leachate can be acutely toxic to aquatic organisms Leachates from CB with remnant tobacco were significantly moretoxic to fish than the CB alone, but even unsmoked filters exhibited a small level of toxicity. The LC50 for leachate from smoked CB (smoked filter + tobacco) was approximately one CB/l for the marine topsmelt (Atherinopsaffinis) and the freshwater fathead minnow (Pimephalespromelas). Leachate from smoked cigarette filters (notobacco), was less toxic, with LC50 values of 1.8 and 4.3cigarette butts/l, respectively for both fish species. Toxicity of CB leachate increased from unsmoked cigarette filters (no tobacco) to smoked cigarette filters (no tobacco) to smoked cigarette butts (smoked filter + tobacco). Toxicity of cigarette butts to fish and some other representative marine organisms such as daphnids and marine bacteria. Different reactions in various species to CB toxicity may be due to their different susceptibility to CB toxic substances such as nicotine or due to their metabolic complexities. Unsmoked filter has toxic effect due to: 1. Pesticides, potentially remaining in unsmoked cigarettes, may contribute to the toxicity of cigarette leachate. 2. Chemical additives in cigarette production process. 3. using triacetin (glycerol triacetate) as a binding agent to create filter and alkali metal salts of organic acids (eg, sodium acetate) in order to maintain burning while the cigarette is being smoked.

7

(Micevska et al., 2006)

(Slaughter et al., 2011)

(continued on next page)

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Table 4 (continued) The objective of CB study

remarks Xenopus laevis embryos

96-h LC50 for thetwo clutches of embryos exposed to CB was • The 0.68–1.65 CBs/L EC50 for the two clutches of embryos exposed to CB • The96-h was0.34–1.21 CBs/L. Teratogenic Index (TI) for the two clutches was1.36–1.95 CBs/L. The • The Minimum Concentration to Inhibit Growth(MCIG) for CB was calculated

reference (Parker and Rayburn, 2017)

to be 0.25 and 0.5 CBs/L.

was a sharp direct negative correlation between embryolength and • There CB leachate concentration. Lowest and NoObservable Effects Concentrations (LOEC, NOEC) for • The Mortality wereconsistent with 0.5 CBs/L for the LOEC and 0.25 CBs/L for theNOEC.

Allium cepa(roots)

malformations for CB were loose gut coiling, • Dominant facialmalformations, notochord malformations, and stunting CB in the environment can have cytotoxic, genotoxic, and • Littered mutagenic effects on plants. exposed to CB leachate presented low relative growth index, high • plants inhibition index, large number of abnormal cells, and high abnormality

(Montalvão et al., 2019)

frequency at metaphase/ anaphase.

chemicals in the BC leachate had aneugenic and clastogenic effect on • The the genetic material of the tested plants, either when they acted Chemicals in CB

Heavy metals

individually, synergistically, or additively.

may serve as a means for transport of metals in the marine • CBs environment and notable metals may enter the coastline areas by CB litter annually.

Nicotine

represent potential point sources for environmental contamination. • CB filters—made of cellulose acetate—may behave like other • Cigarette plastics in transporting metals in the marine environments. metals and chemicals in CB leachate may be acutely toxic to marine • heavy species. from littered CBs in the marine environment may increase the • metals potential for acute harm to local species and may enter the food chain. cigarette butt may contaminate an amount of 1000 l water • one contain a mixture of substances with toxic effects to organisms, most • CB notably heavy metals, polycyclic aromatic compounds, ethyl phenol, and

(Dobaradaran et al., 2017)

(Green et al., 2014)

nicotine.

is easily absorbed through the skin, lung alveoli, small intestine, • Nicotine and urinary bladder. It passes easily through the placenta to the fetus. PAHs

Strong teratogenic and genotoxic effects have been observed.

smoked CBs may potentially release 21 tons of ΣPAHs to the • Freshly environment each year which is mainly due to emission of naphthalene (4.9 ton).

smoked CBs may potentially release 1.6, 1.6, 1.3, 1.3, 1.1, 1.04, • Freshly and 0.8 tons of indeno(1,2,3-cd) pyrene, dibenz(ah)anthracene, benzo(a)

•

(Dobaradaran et al., 2019)

pyrene, benz(a)anthracene, benzo(b)fluoranthene, chrysene, and benzo (k)fluoranthene respectively to the environment each year. there is a possible risk that remaining PAHs in CBs, especially the higher molecular weight ones, may be transported in the environment by CBs and via this path eventually reach water bodies.

observed per hour (Patel et al., 2013). In another study conducted in a coastal area, it was found out a large number of smokers continuously littered CBs (Widmer and Reis, 2010). However, the smokers have often take CB pollutant for granted and they care less about it than other pollutants (Araújo and Costa, 2019). Since a major proportion of the CBs are discarded unconsciously, these wastes can end up in the seas and oceans and ultimately form an important part of the marine pollution (Novotny and Zhao, 1999; Becherucci et al., 2017). It should also be noted that the existence of CBs compared to the other litters is significant in terms of number and ranked first (see Table 5). However, the potential for the emission of pollutants from this litter is of particular importance. Although, CB is one of the most important wastes in terms of number and typically has the highest waste rate on the German coasts and is also the second important waste in the Lithuanian coast (Haseler et al., 2018), it usually constitutes a smaller fraction of the debris in terms of volume. For example, in a study conducted in New Jersey, it was reported that CBs included 23% of urban wastes in terms of number while only 0.5% of the space occupied by total wastes belonged to CBs. Generally, CBs have the highest number, but plastic and paper wastes have the highest rate in terms of

the occupied space (Cutter et al., 1991). In a study conducted in Japan, it was found out that the CBs were responsible for 22% to 24% of road wastes in terms of weight, and this was identical with the rate of plastic and paper wastes (Moriwaki et al., 2009). Distribution of CBs varies from country to country and this applies to different cities as well. Therefore, CBs can be seen everywhere ranging from public places, cigarette sales and smoking centers. In addition, seasonal variations and different days of a week are also related to the amounts of CB. For example, during the holiday especially in summer time more CBs are littered in the tourism areas. CBs can be transmitted through water resources into aquatic environments globally and can cause toxicities in different organisms (Araújo and Costa, 2019). Also, the leakage of toxic substances from littered CBs into the aquatic environment is significant and takes place very fast (Green et al., 2014), which can make this litter more important than other wastes. there are numerous toxic pollutants in CBs like PAHs and heavy metals causing major problems in the environment. The presence of copper, zinc, nickel, chromium, cadmium, titanium, iron, manganese, arsenic, aluminum and bromine had already been confirmed in CBs. 8

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Fig. 4. Challenges associated with hazard of cigarette butt.

However, the amount of each of these metals varies (Dobaradaran et al., 2017; Moerman and Potts, 2011). Changes in the level of heavy metals can be due to tobacco planting and growth processes and the use of substances such as insecticides and pesticides during the plant growth stages. Also, the process of cigarette production can affect the amount of contaminants including heavy metals (Dobaradaran et al., 2017). In a study by Dobaradaran and co-workers performed in the northern coasts of the Persian Gulf, they found out that the average number of CBs per square meter was about 10, indicating that the concentrations of Hg and Pb in CBs were 2.5–86.32 and 650-8,360 ng/ g, respectively. They also found that littered CBs are major sources of prolonged heavy metal contaminations (i.e., Hg and Pb in coastal area) (Dobaradaran et al., 2018). Additionally, the rate of leakage of metals from CBs is also different. For example, more than 50% of iron and strontium leak from CBs compared to the value for titanium which was less than 1% (Moerman and Potts, 2011). The rate of leakage of heavy metals from CBs can also be considered under varying chemical conditions of the environment. In a related study, it was revealed that at pH 4, 5 and 6, no significant difference was observed regarding the heavy metal leaks from the CBs into the solution (Lee and Lee, 2015). In addition, the chemical properties of various heavy metals also affect their leakage from CB. In a further related study, it was reported that the amount of heavy metal leaked from CBs into the solution, is heavily dependent on the kind (type) of heavy metal (Moerman and Potts, 2011). Also in this study, it was demonstrated that with an increase in the soaking time of CB, the concentrations of leaked metals such as barium, iron, manganese, strontium and boron increased, while these changes were almost negligible for the metals such as nickel, lead, titanium and zinc. In addition, by increasing the soaking time, the concentration of leaked aluminum, chromium, cadmium, and copper decreased (Moerman and Potts, 2011). Based on these findings, it is stated that iron, manganese, and

strontium are the most important metals that leak from CBs over the first 24 h, and estimated that about 9.3 to 38.1 kg of each of these mentioned metals would be released annually from CBs worldwide (Lee and Lee, 2015). If CBs are used for reuse purposes such as clay bricks production, they can be heavily heated, and as a result, heavy metals leach much less since they are fully oxidized (Aeslina and Mohajerani, 2012). In a study, it was stated that strontium with a leakage of about 59% from a given CB had a potential release of 19.7 kg/year in the world, while for other metals such as aluminum, barium, cadmium, chromium, lead, nickel, iron and magnesium a leakage rate of 1.2, 21, 14, 1, 59, 12, 11 and 23% and a global emission potential of 9.26, 8.76, 0.120, 0.254, 1.2, 0.288, 38.1 and 33.8 kg/year for CB were observed, respectively (Moerman and Potts, 2011). In addition to heavy metals, the organic compounds in CB play a key role in the toxicity of this kind of particular waste. In a study, 14 organic substances were detected in the CB including nicotine and ethylene phenol with the most toxic effects (Micevska et al., 2006). Also, toxic effects of organic compounds in CBs is higher than that of heavy metals, and nicotine is of high importance amongst them. Nicotine has the potential to damage liver in fish and can cause planarians affect in mammals (Green et al., 2014).The effects of nicotine on the respiratory and reproductive systems are well-known, but the effect of this poison once combined with other pollutants in CB such as heavy metal has not been fully understood yet (Lee and Lee, 2015). In addition to the nicotine leakage from CB to the environment and the likelihood of contamination of water resources, the results of a study showed that nicotine of CB could be absorbed by the plants and could cause “plant-derived commodities” contamination (Selmar et al., 2018). PAHs, as one of the most important pollutants in CB, can contaminate resources and cause disease in organisms. An important point about these pollutants is their release from CB, which could indicate the importance of proper CB disposal. In a yet study by Dobaradaran and co-workers, it was shown that the level of PAHs in freshly smoked CBs was higher than that of the CBs littered in streets and rivers indicating the rapid emission of these pollutants from the CB(42). The different concentration of PAHs observed in three types of CBs are shown in Table 6. The data clearly shows that Naphthalene has the highest and Phenanthrene the lowest proportion of PAHs in the freshly smoked CB. Additionally, as can be clearly seen, the rate of emission of each PAH differs by changing the type of CB. In addition to that, assessing the release of 210Po from littered CB revealed that CBs could be point sources of prolonged radionuclide contamination as well. It was shown the 210Po activity was 8.0 mBqg − 1 (Desideri et al., 2019). The study concluded that although a little amount of 210Po is trapped within the cigarette filter while smoking, a

Table 5 The ratio of CB to other debris in terms of number, weight and volume. Location

Criterion

Ratio of CB to total debris

Reference

Road way Beach Beach Beach Beach Road way City City

Weight Number Weight Number Number Number Volume Number

23% 25% 0.8% 52% 59% 68% 0.5% 23%

(Moriwaki et al., 2009) (Maziane et al., 2018) (Maziane et al., 2018) (Martinez-Ribes et al., 2007) (Loizidou et al., 2018) (Moriwaki et al., 2009) (Cutter et al., 1991) (Cutter et al., 1991)

9

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cigarettes with different brands and manufacturers would eventually turn into CBs with different levels of toxicity. An investigation on the toxicity of 19 types of artificially smoked cigarettes in two different species showed that the change in the brand can affect the toxicity and also the tested animal species react differently to the toxicity (Micevska et al., 2006). This study indicated that tar and nicotine were variable in different brands, and with an increase in the level these mentioned components the EC50 decreased for both species (Micevska et al., 2006). The toxicity level for a CB containing a cigarette filter and left-over tobacco is higher than that of tobacco-free CBs and unsmoked cigarette filters (Dobaradaran et al., 2017). One reason for this is the absorption of heavy metals on nanoparticles due to smoking. Thus, the level of effects of metals on the environment and health increases (Chevalier et al., 2018). In another study, it was confirmed that cigarette smoking led to a 100% fatality in minnow during 96 h of exposure to 8 liters of cigarette smoking where more than 16 non-smoking cigarettes were used. In a similar study, it was found out that the concentration level of 0.5–2 per liter of CB was sufficient to kill all D magnas after 48 h (Lee and Lee, 2015). Another study on the LC50 values for the two fishes (Atherinops affinis and Pimephales promelas) subjected to two following types of CB, stated that the respective values were 1.8 and 4.3 for smoked cigarette filters (no tobacco) per liter, as well as 5.1 and 13.5 for unsmoked cigarette filters (no tobacco) per liter (Slaughter et al., 2011). These cases confirm the impact of CB type on toxicity as well as the sensitivity of different species. In addition, electrical CBs and even unused cigarette filters have also toxic effects. A different research was centered on the presence of some heavy metals and chemicals in steam and nanoparticles of electrical cigarettes, but there is almost little information about electric CBs as a waste. In a related investigation, littered electrical CBs was categorized as hazardous waste due to its lead leakage (Parker and Rayburn, 2017). The study on the impacts of three different types of cigarettes known as regular, menthol and electrical on the frog embryo indicated that regular CB was very toxic, while menthol CB was highly teratogenic and the least toxic effect was observed for electrical CB. Meanwhile, for both menthol and regular CBs a minimal level of complications was seen (∼1 per liter) whilst the corresponding value for electrical CB was 8. Additionally, the values of LC50 reported for an electric CB and the other two were 17.9 and 1 litter per liter, respectively (Parker and Rayburn, 2017). The presence of CB in the environment can also have toxic effects on plants and cause abnormality in them. This was confirmed in a study by Montalvão et al. in which the CB-exposed Allium cepa developed a wide variety of abnormalities such as diagonal metaphase/anaphase, metaphase/ anaphase presenting chromosome fragments, binucleated cells, displaced nucleus, chromosome bridges, micronuclei, necrotic cells, stick metaphase, chromosome adherence, notched nucleus, among other cell disturbances (Montalvão et al., 2019). Meanwhile, the impact of CB on the growth and development of Lolium perenne (perennial ryegrass) and Trifolium repens (white clover) revealed that shoot length and germination success were significantly reduced by CB exposure. In a further related study, although total grass biomass was not substantially affected, the root biomass and root/shoot ratio were less in the clover when exposed to CB. Additionally, it was indicated that cigarette filters led to an increase in both chlorophyll-a in clover shoots and chlorophyll-b in grass shoots. Accordingly, the chlorophyll a/b ratio was increased in the clover exposed to CB, whilst it was decreased in grass (Green et al., 2019). Although the toxicity of CBs and cigarette filters on the aquatic organisms has well been established, it is not possible to quantify the toxicity of CB for other organisms based on the toxicity of a particular species. Here comes a challenge by raising this question as follows: Is there any model describing the toxicity of CB and could be applied to other organisms? (Micevska et al., 2006).

Table 6 PAHs concentration levels (μg g−1) of different type of CB (adapted from 42). PAHs

Naphthalene Acenaphthylene Acenaphthene Fluorene Anthracene Phenanthrene Fluoranthene Pyrene Benz_a_anthracene Chrysene Benzo_b_fluoranthene Benzo_k_fluoranthene Benzo_a_pyrene ndeno_123cd_pyrene Benzo_ghi_perylene Dibenz_a_h_anthracene Total

FCBa

CCB

RCB

mean

%

mean

%

mean

%

5.76 1.11 1.66 1.57 1.17 0.48 1.13 1.03 1.51 1.23 1.31 0.95 1.28 1.83 0.74 1.83 24.6

23.4 4.51 6.75 6.38 4.76 1.95 4.6 4.11 6.14 5 5.33 3.86 5.21 7.44 3.01 7.44

2.9 1 1.31 1.45 1.7 0.46 1.1 0.98 1.51 1.23 1.3 0.95 1.28 1.82 1.72 1.65 20.4

14.2 4.89 6.41 7.09 5.72 2.25 5.38 4.79 7.38 6.01 6.36 4.65 6.26 8.9 3.52 8.07

0.82 0.81 0.62 0.87 1.1 0.49 1.12 1.01 1.7 1.37 1.45 1.07 1.43 2.05 0.8 1.98 18.7

4.38 4.33 3.31 4.65 5.88 2.62 5.98 5.43 9.08 7.32 7.75 5.72 7.64 10.95 4.27 10.5

a FCB: freshly smoked CB, CCB: CB collected from city street, and RCB: CB collected from river.

large amount of CBs in the environment can be a major concern (Desideri et al., 2019). All together, the presence of these mentioned toxins has made CB as a well-known hazardous waste, which has attracted the interest of researchers. For example, the results of a study conducted by Cardoso and colleagues shows that an exposure to the CB-contaminated water, even at low levels, led to a change in the defense response of the female mice to two main potential predators (cats and snakes), indicating the potent neurotoxic damage inflicted by CB (Cardoso et al., 2018). In a similar related study, Booth and co-workers also examined the effect of CB on three species of tidepool snails. They showed that the CB leachate (5 CBs per liter soaked for 2 h) killed all the species studied after 8 days. This implies that CB leachate is highly toxic, but its toxicity was different by varying species (Booth et al., 2015). To this end, the CB toxicity study on the soil snails conducted by Gill et al. showed no mortality occurred during a 32-day toxicity study in which six effluent concentrations ranging from 0 to 4 CB/L(0-0.92 CB/Kg of soil) were used. However, in the first weeks of testing the snails were selected to preferably rest in the 0-CB habitat and avoided the 4-butt habitat (Gill et al., 2018). In the study focusing on the CB toxicity for C. cf. Dubia and V. fischeri, it was found out that CB was highly toxic at the concentrations of 8.9 and 25.9 mg/L, indicating that the major contributor was organic pollutants (Micevska et al., 2006). An investigation on the exposure of medaka embryos (oryzias latipes) to smoked cigarette filters and unsmoked cigarette filters showed that the low concentrations of these wastes (0.2–2 filters per liter) increased heart rate, accelerated development and made a number of behavioral changes; Whilst high concentrations of these wastes (5–10 filters per liter) decreased heart rate, suppressed development, and increased mortality. Additionally, at a concentration level of 0.2 smoked CB per liter, the eyes became larger and denser; Contrarily, at the concentration of 5 filters per liter the eyes size got smaller and their density decreased. The minimum concentration of complications was 0.2 per liter for CBs, while in the non-used cigarette filter, up to 20 filters per liter caused no complications (Lee and Lee, 2015). Differences in the toxicity of cigarettes and cigarette filters arise from the differences in the measured organisms, the type of cigarette smoked by a machine or smoker, the type of cigarettes and its brand. The results showed that the difference in the brand of cigarettes is not relative to the corresponding observed toxicity (Lee and Lee, 2015). The 10

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Moreover, cigarettes and CBs can cause variety of diseases and complications in children and domestic animals. There are various reports on the explanation of this phenomenon in the literature. For example, in 1983, in Italy, four cases of ingestion of CBs by children were reported. Also, in the United States, in 1988, 51 cases of ingestion of CBs by children aged 5 months to 2.5 years were reported. In Greece, in 1995, 15 cases of ingestion of CBs by Children aged 2–4 years and while in Japan between 2001 and 2006, 276 cases of CB ingestions were reported (Novotny et al., 2011). Additionally, there are also numerous reports on the cigarette ingestions by domestic animals (Novotny et al., 2011). Therefore, the presence of this littered waste in public places can increase the risk of ingesting among children and domestic animals. In addition, the CB features outlined in this review makes it difficult to manage it as waste. Having considered wide dispersing and toxicity of CB, it is highly essential to find a suitable way to finalize CB disposal as landfill and incineration cannot be easily used in this regard. Meanwhile, the problems such as changes in the quality of the final products, the generation of wastewater, and gas pollutants emission during the recycling methods, remain to be resolved yet (Torkashvand and Farzadkia, 2019). Given a high number of CBs, toxicity and types of chemicals within them, and the inefficiency of mechanical equipment for collecting these litters, as well as the cost of collecting, there should be a special focus on the following items: the production of cigarettes with degradable filters, reducing smoking in the world, reducing toxic and chemical agents in tobacco growth and processing for cigarette producing, educating people to apply appropriate CB disposal, putting legal and financial pressures to produce fewer cigarettes.

Therefore, it is urgently suggested that as well as increasing the efficiency of cigarette filters for the trapping harmful compounds in cigarette smoke, a number of new researches should be performed to efficiently collect and manage hazardous CB wastes to ultimately prevent the release of toxic compounds into the environment. It can be concluded that studies on CB research have mainly centered on its quantity and toxicity so far. It seems that the researches on lowering CB toxicity and also less production of CB have yet to be taken fully into account. Finally, it is suggested that a surveillance system on a local/regional/global basis should be founded so that the access to the valid and reliable data concerning CB would be easier. Acknowledgement The authors gratefully acknowledge the financial support provided by Iran University of Medical Sciences, Tehran, Iran. References Aeslina, A., Mohajerani, A., 2012. Leachability of heavy metals from fired clay bricks incorporated with cigarette butts. In: 2012 IEEE Symposium on Business. Engineering and Industrial Applications, IEEE. pp. 872–877. Araújo, M.C.B., Costa, M.F., 2019. A critical review of the issue of cigarette butt pollution in coastal environments. Environ. Res. 172, 137–149. Ariza, E., Leatherman, S.P., 2011. No-smoking policies and their outcomes on US beaches. J. Coast. Res. 28, 143–147. Ariza, E., Jiménez, J.A., Sardá, R., 2008. Seasonal evolution of beach waste and litter during the bathing season on the Catalan coast. Waste Manag. 28, 2604–2613. Asensio-Montesinos, F., Anfuso, G., Williams, A., 2019. Beach litter distribution along the western Mediterranean coast of Spain. Mar. Pollut. Bull. 141, 119–126. Becherucci, M.E., Rosenthal, A.F., Pon, J.P.S., 2017. Marine debris in beaches of the Southwestern Atlantic: an assessment of their abundance and mass at different spatial scales in northern coastal Argentina. Mar. Pollut. Bull. 119, 299–306. Booth, D.J., Gribben, P., Parkinson, K., 2015. Impact of cigarette butt leachate on tidepool snails. Mar. Pollut. Bull. 95, 362–364. Cardoso, L.S., Estrela, F.N., Chagas, T.Q., da Silva, W.A.M., de Oliveira Costa, D.R., Pereira, I., Vaz, B.G., de Lima Rodrigues, A.S., Malafaia, G., 2018. The exposure to water with cigarette residue changes the anti-predator response in female Swiss albino mice. Environ. Sci. Pollut. Res. 25, 8592–8607. Chevalier, Q., El Hadri, H., Petitjean, P., Bouhnik-Le Coz, M., Reynaud, S., Grassl, B., Gigault, J., 2018. Nano-litter from cigarette butts: environmental implications and urgent consideration. Chemosphere 194, 125–130. Cutter, S.L., Tiefenbacher, J., Birnbaum, S., Wiley, J., Solecki, W.D., 1991. Throwaway societies: a field survey of the quantity, nature and distribution of litter in New Jersey. Appl. Geogr. 11, 125–141. da Silva, M.L., Castro, R.O., Sales, A.S., de Araújo, F.V., 2018. Marine debris on beaches of Arraial do Cabo, RJ, Brazil: An important coastal tourist destination. Mar. Pollut. Bull. 130, 153–158. Desideri, D., Meli, M.A., Roselli, C., 2019. Leaching tests to assess the release of 210Po from discarded cigarette butts. Microchem. J. 145, 42–46. Dieng, H., Saifur, R.G., Ahmad, A.H., Rawi, C.S.M., Boots, M., Satho, T., Zuharah, W.F., Fadzly, N., Althbyani, A., Miake, F., 2011. Discarded cigarette butts attract females and kill the progeny of Aedes albopictus. J. Am. Mosq. Control Assoc. 27, 263–272. Dieng, H., Rajasaygar, S., Ahmad, A.H., Ahmad, H., Rawi, C.S.M., Zuharah, W.F., Satho, T., Miake, F., Fukumitsu, Y., Saad, A.R., 2013. Turning cigarette butt waste into an alternative control tool against an insecticide-resistant mosquito vector. Acta Trop. 128, 584–590. Dieng, H., Rajasaygar, S., Ahmad, A.H., Rawi, C.S.M., Ahmad, H., Satho, T., Miake, F., Zuharah, W.F., Fukumitsu, Y., Saad, A.R., 2014. Indirect effects of cigarette butt waste on the dengue vector Aedes aegypti (Diptera: Culicidae). Acta Trop. 130, 123–130. Dobaradaran, S., Nabipour, I., Saeedi, R., Ostovar, A., Khorsand, M., Khajeahmadi, N., Hayati, R., Keshtkar, M., 2017. Association of metals (Cd, Fe, As, Ni, Cu, Zn and Mn) with cigarette butts in northern part of the Persian Gulf. Tob. Control 26, 461–463. Dobaradaran, S., Schmidt, T.C., Nabipour, I., Ostovar, A., Raeisi, A., Saeedi, R., Khorsand, M., Khajeahmadi, N., Keshtkar, M., 2018. Cigarette butts abundance and association of mercury and lead along the Persian Gulf beach: an initial investigation. Environ. Sci. Pollut. Res. 25, 5465–5473. Dobaradaran, S., Schmidt, T.C., Lorenzo-Parodi, N., Jochmann, M.A., Nabipour, I., Raeisi, A., Stojanović, N., Mahmoodi, M., 2019. Cigarette butts: An overlooked source of PAHs in the environment? Environ. Pollut. 249, 932–939. Gill, H., Rogers, K., Rehman, B., Moynihan, J., Bergey, E.A., 2018. 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5. Conclusions This systematic review has mainly centered on CBs as being wellknown wastes in human societies due to the presence of several chemicals and toxic substances within them. Despite the importance and wide distribution of these wastes in various urban areas and their transfer to the environment, few researches have been done on the contaminants present in the CBs and how they are transported and their impact on the environment. Most CBs are littered by smokers and are not directly entered the municipal solid waste management system. High rate of leakage of hazardous compounds into the environment as well as high durability in the environment has highlighted CBs as being the most widespread hazardous waste in the world. Generally, the small size of CB undermines its importance, but the large number of this dispersal in the world and its increasing trend indicates the importance of this waste as a hazardous waste. The confirmed existence of toxic and carcinogenic compounds in CB and their severe impacts on several organisms have to be taken seriously and the solutions should be offered for controlling this waste. Due to the design of cigarette filter to trap harmful substances in cigarette smoke, it is expected that high-quality cigarettes will be able to trap larger volumes of smoke pollutions, which will ultimately lead to more polluted CB entering the environment. Considering the urgent need for high performance cigarette filters to further trap the pollution, it should be focused on the introduction of new methods to reduce the amount of contaminants present in cigarette smoke as much as possible. Additionally, modifying or changing the stages of tobacco cultivation and processing in the production of cigarettes can also reduce the amount of pollutions in CBs, which requires further research to be done in the tobacco industry. On the other hand; cellulose acetate used in the production of the cigarette filter has made CB to be known as hazardous and durable waste, therefore further studies should be done to produce more degradable cigarette filters. Whilst, the rapid leakage of the contaminants presents in CB such as nicotine and some heavy metals into the environment (especially in the humid conditions) justifies the manufacturing of highly absorbent filters. 11

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