Authors: Nematollah Jaafarzadeh, Neda Reshadatian, Touran Feyzi Kamareh, Mohamad Sabaghan, Rozhan Feizi, Sahand Jorfi
Categories: Article, Chemistry, Environmental sciences, Plastic waste, Solid waste, Urban pollution
Source: Scientific Reports
Microplastic is one of the most important environmental challenges of recent decades. Although the abundance of microplastics in water sources and water bodies such as the marine were investigated in many studies, knowing the sources of microplastics requires more studies. In this study, litter was investigated as one of the challenges of urban management and the sources of primary microplastic and secondary microplastic in the urban environment. For this purpose, Clean Environment Index and Cigarette Butt Pollution Index, were used to interpret the density of litter and estimate the abundance of microplastic resources in Khuzestan province, Iran. The results showed that the density of litter in the studied cities was 0.0001–0.6502 items/m^2^. The calculated clean environment index and cigarette butt pollution index were 0.211–35.05 and 0.112–12.897, respectively. The density of primary microplastic and secondary microplastic sources in the studied cities was 47,207–62,767 µg/m^2^ (average = 52782) and 2127–3140 µg/m^2^ (average = 2570), respectively. The abundance of primary microplastic due to littering in the studied cities was estimated at 150 g/year. Reducing the ratio of littering waste in the urban environment and increasing the efficiency of the urban cleaning service is necessary to manage the most dispersed source of microplastics in the urban environment.
Keywords: Solid waste, Urban pollution, Plastic waste
**Subject ** Environmental sciences, Chemistry
Characteristics such as resistance, flexibility, durability, lightness, and low price have led to the widespread use of plastics^1^. Wide use of plastic in industry and production of various goods and its use in applications such as packaging has created a big business in the world^2^. In this situation, dependence on plastic has increased in recent decades by various plastic products or its significant proportion in the of various products^3^. However, the widespread use of plastic has further challenges, the most important of which is the production of a significant volume of plastic waste^4^. Every year, millions of tons of municipal solid waste are produced in the world, in which plastic waste has a significant proportion^1,5^. For example, the proportion of plastic waste in Iran is reported to be 9%, and according to the average waste production per capita of 640 gr/day, Iran’s plastic waste production is estimated at 4900 tons/day^1^. The requirements of plastic waste management are effective in the fate of them in waste management routes according to the source of this type of waste that can include industries, health care centers, packaging and transportation, commercial centers, and residential sources^1,6^.
Litter is one of the important types of municipal solid waste, which is caused by the behavior of citizens in improper disposal of waste^7–9^. Throwing waste in the environment instead of properly disposing of it in trash cans or waste storage containers leads to the formation of litter in cities and public areas, in which plastic has a significant ratio to its composition^10^. The wastes that contribute the most to the composition of litter include cigarette butts, paper, and plastic^11^. This composition has been reported in many studied cities. For example, in the most populous coastal city of Argentina, the composition of litter including cigarette butts (33%), plastic (22%), and paper (31%)^12^. Also, it has been reported that the composition of litter in Behbahan, Iran has 16% plastic waste^13^. The durability of litter in the urban environment and public areas due to low efficiency of the urban cleaning services have caused them to be known as a scattered source of plastic waste^14,15^.
Plastic waste is the main source of microplastics in the environment^16^. Although the degradation of plastic into microplastics is a main way of creating microplastics, which are known as secondary microplastics^17^, some types of waste also contain or consist of very small plastics that decomposition of them in the environment lead to the release of primary microplastics^18^. For example, the degradation of plastic bags or disposable plastic containers will lead to the production of secondary microplastics, while the decomposition of cigarette filter, which is made of entanglement of very fine fibers, will lead to the release of primary microplastics^19,20^. The aim of this study was to investigate the density and composition of litter in Iranian cities in Khuzestan province to estimate the potential of microplastic release in the urban environment. Because the hypothesis is that the density of litter, especially littered cigarette butts, is significant in Iranian cities due to behavioral factors and low efficiency of the urban cleaning service. So, litter durability leading to the release of microplastics into the environment. Also, investigation of the share of primary microplastic and secondary microplastic sources in the composition of litter was considered in this study.
As shown in Fig. 1, this study was conducted in Khuzestan province in southwestern Iran. The studied cities included Behbahan, Ahvaz, Khorramshahr, Dezfol, Izeh, and Shosh, which were numbered C1-C6 respectively. Ahvaz was selected because it was the largest city in the studied province and the capital of the province. Other studied cities were selected based on the same geographical distribution of studied locations in the whole province. The per capita production of municipal solid waste in this province is reported to be 440 g/day on average^1^. The composition of municipal solid waste in the province includes 60.92% organic waste, 8.38 plastic waste, and 30.7% other types of solid wastes^1^. The urban cleaning system in all studied cities included the use of brooms by sweepers during low traffic hours, often at night. In all studied urban environments, in addition to streets and sidewalks, there was at least one low-level access point, including tree pit, shrub borders, and runoff channels.
Fig. 1 Location of Khuzestan province and studied cities, C1: Behbahan, C2: Ahvaz, C3: Khorramshahr, C4: Dezfol, C5: Izeh, C6: Shosh^23^.
Data on the density and composition of litter in the studied cities were collected using visual survey in the urban environment. For this purpose, ten locations were evaluated in each of the studied cities, which included four locations from each of commercial and residential land-uses, and two locations from recreational land-use^21^. In the evaluation of the studied urban environments, all types of litter were counted in five main categories, including cigarette butts, paper, plastic, masks, and other litter^22^. At each assessment in all the studied locations, the counted litter were collected and transported to the laboratory for weighing. All the studied locations were evaluated on working days and in the last hours of the day before sunset^10,22^.
The density and composition data for each of the studied locations were interpreted using two indexes, Clean Environment Index (CEI) and Cigarette Butt Pollution Index (CBPI). CEI was calculated by applying the number of all types of litter counted in the studied locations in formula 1 ^11^. Based on the calculation results, the studied locations were classified into five statuses, including very clean, clean, moderate, dirty, and extremely dirty^21^. CBPI was calculated by applying the number of counted cigarette butt in the studied locations in formula 2 ^24^. Based on the calculation results, the studied locations were classified into six statuses, including very low pollution, low pollution, pollution, significant pollution, high pollution, and sever pollution^24–26^.
Quantitative data of litter in the studied cities are shown in Table 1. The results showed that cigarette butts had the highest density in the studied locations. On average, 0.211 butt/m^2^ was observed in all the studied locations. Also, the paper had significant density in the observed locations. On average, 0.057 paper/m^2^ was counted in all the studied locations. However, the density of litter in different land-uses was not the same. The density of litter in residential, recreational, and commercial land-uses in the studied cities was on average 0.103, 0.744, and 0.009 item/m^2^, respectively. Also, the density of litter was different in the studied cities. The highest density of litter was observed in Dezfol (C4) and the lowest density was observed in Behbahan (C1). The average density of litter in the studied locations of C1, C2, C3, C4, C5, and C6 was 0.767, 0.923, 0.871, 0.978, 0.791, and 0.815 item/m^2^, respectively. The difference in the composition of litter in the studied cities is shown in Fig. 2. On average, in the studied cities, cigarette butts consist 62% of the composition of litter, while the ratio of plastic, paper, sanitary, and other types of litter in the studied cities was 13.8%, 17.1%, 5.83%, and 1.1%, respectively. The results showed that the composition of litter in the studied land-uses was not the same, so that in the commercial land-use of all studied cities, on average, the ratio of cigarette butts, plastic, and paper was 59.59%, 14.3%, and 18%, respectively. But, in the recreational land-use of all studied cities, on average, the ratio of cigarette butts, plastic, and paper was 27.98%, 8.41%, and 16.14%, respectively.
Fig. 2 Composition of litter in studied cities.
Several factors are effective in the density of littering in the urban environment, which were the cause of the observed differences in the studied cities. The behavior of citizens is one of the effective factors in the density of littering in the urban environment^27^. The lack of citizens’ awareness of the negative consequences of littering, including the leak of pollutants and the negative effect on the urban economy, causes littering to be a common behavior among most citizens^28^. Access to waste disposal equipment such as trash bins or waste storage containers in the urban environment is one of the effective factors in the density of litter^29^. However, the density of litter in the studied locations despite the presence of trash bins in short distances, indicating the low impact of this factor in the observed results. The durability of the litter in the urban environment, which is affected by the structural conditions such as the surface material, the frequency of low-level access points, and the efficiency of the cleaning service, is effective in the density^30^. In this situation and due to the density of different types of litter, there was a diverse status of pollution in the studied locations. The results of CEI calculation for the evaluated locations in all studied cities are shown in Fig. 3. The results showed that the lowest CEI was 0.176 and the highest CEI was 35.05. Accordingly, 12 locations were in very clean status, 21 locations were in clean status, 3 locations were in moderate status, 4 locations were in dirty status, and 20 locations were in extremely dirty status. The average CEI was different in each of the studied cities, so that it was 10.697, 12.824, 11.712, 13.750, 9.021, and 11.551 in C1, C2, C3, C4, C5, and C6, respectively. Also, the average CEI in the studied residential, recreational, and commercial land-uses was 3.91, 0.304, and 24.92, respectively.
Fig. 3 Calculated CEI for studied cities.
As shown in Fig. 4, different CBPI was calculated in the studied locations of different cities. The results showed that the lowest CBPI was 0.112 and the highest CBPI was 12.897. Accordingly, 18 locations were in very low pollution status, 17 locations were in low pollution status, 4 locations were in pollution status, 5 locations were in significant pollution status, 9 locations were in high pollution status, and 7 locations were in sever pollution status. The average CBPI was different in each of the studied cities, so that it was 3.50, 4.07, 3.60, 4.50, 3.35, and 3.89 in C1, C2, C3, C4, C5, and C6, respectively. Also, the average CBPI in the studied residential, recreational, and commercial land-uses was 1.17, 0.301, and 8.23, respectively. Although the observed density is the basis for the calculation of CEI and CBPI^22,24^, but the most important effective factor in the calculated these indexes was the pollutant leakage potential and climatic and environmental conditions^11^. In the CEI, a coefficient of 2 was defined for waste that is a source of pollutant leakage such as toxins and heavy metals. Also, wastes that are likely to be infected, such as facial tissue and face masks, have a coefficient of 2 ^22^. In the CEI, a coefficient of 1.5 defined for plastic waste due to the concern of the emission of microplastics into the urban environment^8^. Therefore, the difference in calculated CEI in the studied cities was due to the difference in the density of litter and the difference in the composition of litter in the studied locations^11^. In this situation, the effective factors in the density of each type of litter in the urban environment and the coefficient defined for each type of litter according to its pollution potential, were effective in the observed results^21^.
Fig. 4 Calculated CBPI for studied cities.
Considering that CBPI is a specific index for interpreting the pollution status caused by littered cigarette butts^26^, the environmental factors that lead to more durability of cigarette butts in the urban environment increase the index and was effective the observed difference of CBPI in the studied locations^31^. For example, the number of low-access points in the location is one of the reasons for the increase in CBPI^24^. Also, climate conditions such as humidity, which is more in places like gardens due to irrigation, led to an increase in CBPI compared to commercial and residential land-uses^32^. Considering that the structure of the cigarette filter consists of interwoven fibers of cellulose acetate bonded with plasticizer^24^, its decomposition will lead to the dispersion of microplastics in the environment. Because the cigarette filter, which forms the main part of the cigarette butt, contains Y-shaped fibers of cellulose acetate^22^, which are separated in the environment under the influence of physical factors and climatic conditions, and each fiber will be in the environment as a microplastic. Therefore, littered cigarette butts can be a source of microplastics in the urban environment and in public areas such as roads and coasts^20,33^. Also, the presence of various types of plastic in the composition of litter in the studied locations is consider as a source of microplastics^33,34^. The results of estimating the abundance of microplastics in the environment of the studied cities are shown in Table 2. The results showed that the abundance of primary microplastics in the studied locations was 6.74 µg/m^2^ to 1855 µg/m^2^. On average, 95% of estimated microplastic was related to primary microplastics caused by the decomposition of littered cigarette butts, and 5% was related to the degradation of littered plastic items in the environment of the studied cities. These results were estimated based on the weight of the analyzed litter in this study and assuming a degradation/decomposition ratio of 1.2%, 1.5%, and 1.8% in commercial, residential, and recreational land-uses. This assumption was based on the durability of different types of litter in the studied land-uses due to the different efficiency of the urban cleaning service. Factors leading to temporal variation and spatial variation in the quantity of litters^35^, make it difficult to accurately estimate the abundance of secondary microplastics in the urban environment of the studied province. But the estimation of primary microplastic caused by littered cigarette butts can be estimated according to the consumption of filtered cigarettes and its littering ratio by considering the durability. Considering the annual consumption of 65 billion filtered cigarettes in Iran^36^, proportional to the ratio of the population of the studied province in the country and considering the 85% for littering ratio (The ratio of cigarette butts littering in different studies was reported as 74% to more than 90%)^37^, the annual number of littered cigarette butts was estimated at 1105 million. Therefore, the primary microplastic source caused by littered cigarette butts in the studied province was estimated at 331 ton/year based on the average weight of each cigarette butt equal to 0.3 g.
The results of this study can be generalized to other regions due to the similar behavior of citizens in other cities of Iran, as well as the similar status regarding cigarette butts in most cities of the world. Because in other studies, a similar status in the density of litter, especially in cigarette butts was reported. In recent years, studies on the sources of microplastic emission and its abundance in the environment have increased^37,38^, which shows the importance of this pollutant. The entrance of primary microplastics and secondary microplastics from solid wastes into water sources is one of the reported ways about the emission of microplastics in the environment^39^. This route has caused microplastics to be transferred to humans’ body through drinking contaminated water, even bottled water^40,41^. For example, it has been reported that annually 0.22–1.2 × 10^6^ microplastics enter the human body from drinking water^42^. This is due to the transfer of plastic waste as a source of microplastics to the water body. For example, face masks are one of the wastes that are known to be of microplastic origin, and as a result of the covid-19 pandemic, their accumulation in the water body was reported^43^. In addition, the direct transfer of cigarette butts to the water body by the runoff flow or pollution leakage from it due to its durability in the environment and the transfer of pollutants to the water body was reported^44^. In addition, microplastics can be seen in the food chain and have health consequences for humans^42^. Although the health effects caused by microplastics can depend on factors such as sensitivity and intensity of exposure, evidence of the negative effects of this pollutant on tissues and the nervous system has been reported^42,45^. Also, one of the effects of microplastic is the transfer of pathogens to the body because the surface of microplastic can provide a substrate for the growth of microorganisms^46^. Some of the complications caused by exposure to microplastics include cytotoxicity, oxidative stress, neurotoxicity, disruption of the energy homeostasis and metabolism, and cancer^45^. Therefore, it is necessary to control the sources of microplastic emission to reduce the health and environmental consequences caused by them. The management of littered wastes is one of the solutions for the release of microplastics in the urban environment, which was estimated in the results of this study. The first stage of litter management is to change the behavior of citizens with the aim of reducing littering ratio^21^. Correct disposal of waste by citizens prevents litter dispersion in the environment and degradation of plastic waste and decomposition of cigarette butts^10^. Increasing awareness using the media or putting informative messages about the consequences of cigarette butts on the pockets is a strategy to reduce littering^21,47^. However, increasing waste disposal equipment such as trash bins and especial containers such as ballot bin for cigarette butt can lead to the reduction of littering ratio^48^. Also, increasing the efficiency of the urban cleaning service will reduce the durability of litter in the urban environment and will reduce the possibility of microplastics emission^13^. There were strengths and limitations in this study. The strength of this study was the evaluation of all types of litter in different cities of a province. Interpreting the environment status using CEI and CBPI simultaneously was another strength of this study. Although the investigation of spatial variations was one of the strengths of this study, one of the limitations of this study was the lack of evaluation of temporal variations. Therefore, it is suggested to evaluate the temporal variation in different seasons and holidays for future studies. In addition, the evaluation of pollutants such as heavy metals caused by litter, especially cigarette butts, can be considered in future studies. Also, evaluating the impact of behavior change methods on reducing litter density as a source of microplastics was another limitation. Therefore, pilot programs or interventions in this issue including public awareness campaigns, penalties for littering, or ballot bin can be considered in future studies.
The density of litter in the urban environment of one of Iran’s provinces was studied and the emission of microplastics due to their decomposition was estimated. The results of the study of 60 locations in 6 cities of Khuzestan province showed that the density of litter was in the range of 0.0001 items/m^2^ – 0.650 items/m^2^. On average, the composition of littered waste in the studied cities included cigarette butts (62%), plastic waste (13.8%), paper (17.1%), and other types of waste (5.9%). Calculated CEI in the range of 0.176–35.05 showed that 40% of the studied locations were in a dirty status or worse. Also, the calculated CBPI in the range of 0.112–12.897 showed that 41.6% of the studied locations were in a polluted status or worse. The emission of primary microplastic and secondary microplastic was estimated at 659 µg/m^2^ and 31 µg/m^2^, respectively. littered plastic waste and littered cigarette butts were identified as an emission source of secondary microplastic and as an emission source primary microplastic in the urban environment. In this situation, it is necessary to reduce the ratio of littering by change the behavior of citizens. Also, increasing proper waste disposal equipment and increasing the efficiency of urban cleaning service will reduce the dispersion and durability of litter, which can be effective in reducing the emission of microplastics in the urban environment.
This research project has been financially supported by Behbahan Faculty of Medical Sciences, Behbahan, Iran under grant number 98088 and ethical IR.BHN.REC.1399.044.
Nematollah Jaafarzadeh: Conceptualization, Methodology, Investigation, Formal analysis, Writing–original draft. Neda Reshadatian, Touran Feyzi Kamareh, Mohamad Sabaghan: Methodology, Writing–review & editing. Rozhan Feizi, Sahand Jorfi : Methodology, Writing–review & editing, Supervision. All authors reviewed the manuscript.
The datasets generated and analyzed during the current study were available from the corresponding author on reasonable request.
The authors declare no competing interests.
Rozhan Feizi, Email: rozhanfeizi@gmail.com.
Sahand Jorfi, Email: Sahand369@yahoo.com.
The datasets generated and analyzed during the current study were available from the corresponding author on reasonable request.