The cities litter toll on oceans

Jun 3, 2021Know how0 comments

Plastic pollution of the marine environment is currently one of the most growing concerns. Large amounts of floating plastic are observed in the main oceanic gyres. The presence of plastic has been detected on shorelines of all continents, among which cigarette butts are the most frequent litter encountered during shore clean-up operations. As we know now, this is just the tip of the iceberg. Many macro-plastics degrade into micro-plastics and depending on their density, drift over large distances or sink.

Today in Europe, 75% of the population lives in cities and the increase in the urban population represents a global trend1. Cities are turning into centers of activity and recreation; social habits change; the population takes over public spaces. Waste increases – and with it, incivilities (littering, dirt, etc.). Waste that escapes collection diffuses into the environment. In particular, cities are held responsible, as the main source of input, for the issue of cigarette butt release into the waterbodies 2.
Various studies have been done to estimate the quantities of plastics entering the oceans globally. A study by Boucher et al. estimates that yearly 3% of all produced plastic is leaking into the environment3. More specifically, a recent study conducted by the University of the Côte d’Azur investigates the cigarette butts’ leakage and suggests an average release rate of 6% for the entire world. These simulations -global models- help to size the problem and identify the root causes in order to define and implement the corrective actions.

Generally, modelling the plastic leakage consists of three main steps: (i) estimating the mass of plastic ending up as waste, (ii) quantifying the fraction of mismanaged waste, and (iii) estimating the release from the mismanaged waste fraction3 2. The models run based on a set of default assumptions such as mismanaged waste- , littering- , and release rate, etc. A great challenge for estimating the mentioned rates has been cited by all model developers. Fundamentally, because these rates are hardly measured in the field and relative data are very limited.

During a case study in the city of Geneva, Cortexia tried to characterize and measure, in the field, the litter leakage from the urban area into the environment. This would help to compare the measured results with the global models’ assumptions. This project completes the previous work of the company on the environmental impact of urban cleaning and the solutions to reduce cigarette butt littering. The study aims to answer which, and how much litter is released from cities?
Cigarette butts, small pieces of plastics, and papers are the most littered items found in cities 4. Cortexia assumes that street litter, which is not collected by urban cleaning, leaks into the city’s water runoff system. Therefore, quantities of litter, which escape the mechanical cleaning process, as well as the quantities of litter found in the water runoff system were measured for calculation of a release rate. Then the result was compared to the assumptions used in release models.


Street sweepers are widely used to clean the roads from trash, dust and to avoid the growth of weed. Does this mean that after the cleaning the road is free of litter?

The monitoring of urban cleanliness, using for instance the Clean City Index, confirms that the cleanliness level after mechanical cleaning is very high. The quality of cleanliness after the work of the machines is not disputable. Nevertheless, a more detailed observation shows that if all litter is removed, this is not the case for cigarette butts. We have got used to it and no longer see the cigarette butts remaining on the road’s cracks, between paving stones, and in tree grates even after a street sweeper or manual cleaning cleans a passage.

"Petit Voyou" campaign in the city of Geneva, where the city cleaning department monitored cigarette butts daily using Cortexia’s system.
On average 16% of cigarette butts remained on the ground even after cleaning the road at “Rue de la Servette” in Geneva.
"Petit Voyou" campaign in the city of Geneva, where the city cleaning department monitored cigarette butts daily using Cortexia’s system.
Cigarette butts accumulate in poorly accessible places for cleaning.
We have characterized the “cleaning efficiency” of mechanical cleaning on our reference street, which has a standard coating and does not impose any difficulties on the cleaning process. We have counted the number of litter on the street and pavement, before and after cleaning. As mentioned before, the only remaining litters are the cigarette butts. On average, 16% of the cigarette butts remained permanently on the ground after the passage of the sweeper in the studied street. This value confirms the assumption in L. Pourchier’s model –“15% cigarette butts left on the ground without collection option in high-income countries” 2.
The amount of littered trash in an urban area, which is exposed to be leaked, depends on the littering rate, efficiency of mechanical cleaning, and frequency of cleaning. As we have seen, right after the mechanical cleaning, the road stays in the cleanest state (16% of remaining cigarette butts in the case of our refence street). Afterward, the trash keeps accumulating due to the act of littering until the next cleaning session (state of 100 percent dirt). On average, between each two consecutive cleaning sessions, an amount equal to 58% of total littered trash during this duration is temporarily exposed to be leaked to the natural environment.

No matter how efficient the cleaning process is, there is always a portion of the total littered trash that will be exposed to leakage, temporarily! This fact highlights the importance of anti-littering measures and reduction of littering rate in a city.


The assumption we made in our previous Clean City Lab papers5 6 is that part of the litter, which is permanently on the street, leaks to the natural environment through the city drainage system. Therefore, to monitor the amount and composition of trash leakage via drainage system of the city, Cortexia designed a mesh strainer to place at the entrance of the drains. These meshes act like a filter, trapping the trash before it enters the urban water collection system.

"Petit Voyou" campaign in the city of Geneva, where the city cleaning department monitored cigarette butts daily using Cortexia’s system.
Entrance to the city’s storm water drain.
"Petit Voyou" campaign in the city of Geneva, where the city cleaning department monitored cigarette butts daily using Cortexia’s system.
Sample of the designed mesh filter- to be placed at the entrance of storm water drains
"Petit Voyou" campaign in the city of Geneva, where the city cleaning department monitored cigarette butts daily using Cortexia’s system.
Entrance to the city’s storm water drain-emplacement of the designed mesh filter
Different parameters such as meteorological data (temperature, precipitation, wind), volumetric amount of water used for cleaning, and the position of the drains’ gate (in calm or crowded location) were monitored during the experiment. The experiment took place in Geneva on the same pilot street with a monitoring period of 7 months.
"Petit Voyou" campaign in the city of Geneva, where the city cleaning department monitored cigarette butts daily using Cortexia’s system.

General overview of a street and location of the 2 monitored drain’s entrances- the left side of the street is in line with commercial shops.

Entrance to the city’s storm water
of the designed mesh filter

The “harvest” over this period shows that cigarette butts and packaging plastics are the most frequently leaked wastes from the streets, at a rate of respectively 6,2 and 1,8 items per drain per day. To give an order of magnitude, there are 90 drains in this street and 20’000 in the entire city. If the leakage rate would be representative for the whole city, this means that according to the study, 61.000 (daily) and approximately 22 million (yearly) cigarette butts are leaking from Geneva’s streets to the waterbodies via the city drainage system.

Number of litter per day collected in the left and right drainage systems.

Cigarette butts and packaging plastics are the most frequently collected litters by the mesh filters!

The commonly cited release rate in the literature address the fraction of mismanaged waste that reaches the ocean7,3. Mismanaged waste, according to Jambeck et al. 7 , is “the material that is either littered or inadequately-disposed. Inadequately disposed waste is not formally managed and includes disposal in dumps or open, uncontrolled landfills, where it is not fully contained.” In this study, Cortexia only investigated the release rate associated with littering. It is worth mentioning that in a developed country such as Switzerland, where no municipal waste is allowed to be dumped or landfilled, the chances for inadequately disposing of cigarette waste is so low. Therefore, we consider the amount of inadequately-disposed cigarette butts to be zero.
Passways from cigarette waste generation to release to the waterbodies (© Julien Boucher et al.3).
Knowing the number of cigarette butts that permanently stay on the street (permanently littered CBs), as well as the number of cigarette butts that leak into the drainage system of the city (Leakage), the cigarette butts’ release rate from the streets was calculated. The result of this case study in the city of Geneva suggests a 2% release rate for cigarette butts.
The first and most commonly used release rate for plastics is the generic rate of 25% within 50 km of the coast, which was published by Jambeck et al.7 in 2015. However, recently, Boucher et al. 3 suggested a release rate matrix calibrating this generic rate for each country according to its distance to the shore and the catchment run-off. Considering the adjustments suggested by Boucher et al. 3, the plastic release rate for Switzerland will be 6%. Moreover, Pourchier 2 suggests a 5.5% release rate specifically for cigarette butts and for the entire of Europe. In comparison to the literature, Cortexia’s case study in Geneva suggests a smaller release rate for cigarette butts.


The simulation models are very powerful tools to make anti-littering campaigns around the world more efficient by targeting main root causes and hotspots. A brand new platform called PLASTEAX provides a good database on plastic waste management and a great opportunity to model plastic leakage across a value chain 8. Among many different types of plastic, cigarette butts are the most encountered litter in nearshore areas and L. Pourchier has recently developed a global model to simulate the input of cigarette butts into the oceans 2.

Within the Geneva Clean City lab, we have performed some experiments to confirm if the cities, as predicted by the models, bear an important contribution to the plastic pollution of the marine environment. The followings highlight the results of this study and the conclusions:
  • By equipping the stormwater drains with filters, we have indeed confirmed that street litter is carried to the natural watercourses. Cigarette butts (almost 75 %) and packaging plastics (25%) are the most frequently litter taking this path. 2% of the cigarette butts present on the streets will end in the city drainage system.
  • A clean city will release less waste into the natural environment.Therefore, the cleanliness of a city contributes not only to the well-being of its inhabitants, but also to its ecological footprint streets.5 This reinforces the importance of efficient urban cleaning.
  • The amount of litter that is released into the environment ultimately depends on the amount of litter permanently present on the road. Between two sweepings, it depends on the behavior of users. According to the old adage “Prevention is better than cure”, measures that reduce littering, such as those described in our previous article streets 6 are the most effective for a sustainable city.
1 JRC. [Online] European Commission. [Cited: April 14, 2021.]

2 . Pourchier, Lionnel. Fate of cigarette butts in marine environments. 2020. Master thesis

3 The marine plastic footprint. Boucher, J., Billard, G., Simeone, E. and Sousa, J. Gland, Switzerland : s.n., 2020.

4 [Online]



7 Plastic waste inputs from land into the ocean. J. R. Jambeck, R. Geyer, C. Wilcox, T. R. Siegler, M. Perryman, A. Andrady, R. Narayan, K. Lavender Law. s.l. : Science, 2015, Vol. 347. DOI: 10.1126/science.1260352

8 PLASTEAXA. [Online] :