Plastics debris characteristics in Cikapundung River

River plays the important role for transporting plastics from land to the ocean. Cikapundung river is one of tributary rivers which contributes significantly to Citarum River. The Cikapundung river transports the riverine plastic debris from the area of Bandung City and Bandung District to Citarum River that finally flows to the North Java Sea through its estuary at Muara Gembong-Bekasi. The aim of the study is to monitor plastic debris characteristic of in Cikapundung. It is important to understand the characteristic of plastic debris from the settlement area which potentially contaminates the sea. Monitoring was conducted in April to June 2021 by using net sampler 2x1x3 meters. The sampler was set at two transversal sites across the river in 15-30 minutes each. The observations were conducted three times (morning, noon, and afternoon) of each sampling day. Collected plastics were estimated the weight and the volume, and were separated, enumerated and classified afterwards. The top three common plastic types both in weight and number founded in Cikapundung river including plastic bags, clear plastic bags and sachet. The majority of commonly encountered plastics were clear plastic bags, plastic with aluminum, sachets (plastic packing), plastic bags, and plastic cups. It reflects the dominance of domestic source wastes rather than industrial plastic debris.


Introduction
Citarum River receives tributaries from more than 100 different sources [1].The Cikapundung River is one among them.A popular tourism attraction in the highlands, Lembang, is traversed by the 28 km long Cikapundung River.The river eventually reaches the Citarum River in Southern Bandung after uniting with the Cigede River.Recently, the function of Cikapundung River turns into the discharge place of domestic and industrial wastewater.There are normal to find significant volumes of waste beside the river because it is used for both domestic and non-domestic purposes.In 2013, WHO's claim that the Citarum River is the world's most contaminated river supports this as well.The 20 most polluted rivers in the world, the most of which are in Asia, are accountable for about two-thirds of the plastic debris that ends up in the ocean.[2].
According to earlier research, food and beverage-related items such bottle caps, straws, bottles, bags, and polystyrene fragments account of large marine debris (40-80%) with diameter size is >20 mm that is made of plastic [3].Plastics are a popular material because they are affordable, durable, long-lasting, lightweight, simple to produce, and can be used for a range of temperatures [4].Even though the specific 1260 (2023) 012030 IOP Publishing doi:10.1088/1755-1315/1260/1/012030 2 number of plastics entering the aquatic environment is not yet known, it is increasing every time because the most of plastics are not biodegradable.Its impacts aquatic life in a number of methods, including plastic attachment and consumption by fish and other aquatic organism.[5].
In recent decades, risks of flooding have increased in urbanized areas like Bandung.Which is paired with large debris accumulations in Cikapundung River.River water quality is deteriorating due to the discharge of untreated industrial and domestic waste.The aims of this study are to identify and quantify of plastic debris characteristics in Cikapundung River.

Time and location
This study focuses on the downstream of Cikapundung River before entering the main Citarum river.A tributary of the Citarum River Basin, the Cikapundung River is highly polluted by plastics and other rubbish because of inadequate debris clearance [6].Sampling of plastic debris was conducted in April to October 2021.Sampling location is in downstream of Cikapundung River (Bojongsoag, Bandung Regency) (Figure 1).
Sampling was done once a month for six months, allowing for the dry and rainy periods' seasonal changes.The Meteorological, Climatological, and Geophysical Agency's data will be used to determine the seasonal change in Bandung City's annual rainfall rate.

Plastic debris monitoring
Similar to Widyarsana et al's study [7], a similar method was used to collect plastic debris from riverine areas, with a variety of modifications.The procedure includes monitoring the floating debris, setting up a sampler, collecting, drying it in the air, and taking measurements.By using a sampler net with dimensions of 2 x 1 x 3 meters and a mesh size of 1-inch, plastic waste was collected and will be installed from the bridge above the river (Figure 2a,c).The net sampler has buoys and ballast so that when it is set up in the water, its frame will stand up straight.The sampler was set up in each site location at one or two locations in the river (near the river bank side and close to the centre) in the morning, at noon, and in the afternoon for 30 minutes each.
The bulk volume of each piece of wet trash collected was measured using measuring boxes (Figure 2b).A volume measurement box that was 58 x 38 x 39 cm in size was used to measure the wet volume of each trash item that was collected.It was filled to capacity without being compacted, and at that time the waste's original height was determined.After gathering, the debris was sorted out on the field (separation, identification, counting, and weighting of plastic debris).

Type
Based on study, Clear plastic bags, plastic with aluminum, sachetes (plastic packing), plastic bags, and plastic cups are types of plastics that are frequently encountered in large amounts (Figure 3).The highest number of type is clear plastic bag.Additionally, van Calcar and van Emmerik's study in 2019 [8] on global riverine plastic debris discovered a lot of plastic bags.Other plastic debris which found are straws, styrofoam, thick plastic packaging, plastic bottles, and cigarrete butts.Difference type of plastic found will affect the fragmentation, buoyancy and terms of retention because they are made from different polymers, sizes, shapes, and density [9].

Weight and number
The results of six months of observations show significantly high in August, both on weight and number of items.At midday and in the afternoon, there appears to be a higher amount of plastic waste.(Figure 4 and 5).
According to weight or item measurements, the highest number of plastic debris in August appears to have come from the area of Bandung City.Cikapundung River, which flows through a district and other local activities including Bandung's traditional market and also influenced by the season.Based on Meteorological, Climatological, and Geophysical Agency (BMKG) data at (http://dataonline.bmkg.go.id), in the day and a days before research there is high precipitation in Bandung which causes the debris to be carried away by the river flow.Besides that, behaviour of people who throw their waste including plastic debris directly into river and the unavailability of facilities for disposing of waste in the area.The size and weight of the plastic will affect the fragmentation process from macroplastic to microplastic [10].

Volume and density
Volume, which includes both plastic and non-plastic debris, is the total amount of debris or material dredged out of a river.From six months observation, there were no significant differences between the distribution patterns of the number of plastic debris in the Cikapundung River and the number of plastic debris.High amounts and weight resulting a high volume of plastic debris.The overall amount of debris was also higher in August at noon, reaching up to around 333 liter (333,918 cm 3 ) per area of the framed sampler (2 m 2 ).In comparison, the least amount in September morning observation was only about 4,3 cm3 per framed sampler (Figure 6).The largest amount of debris was collected during the observation in August at midday.Density is the weight of plastic debris measured in kilograms compared to the measured volume of waste (kg/m 3 ) (Figure 7).Results of this study indicate that it is true that the total of plastic debris produced in Indonesia is reaching an unsustainable level of growth.For instance, according to data from the World Bank 2021, our cities and municipalities produce over 7.8 million tons of plastic debris yearly, of which more than half is inadequately managed.As seen by the government's preventive targets, preventing plastic pollution in Indonesia requires a comprehensive strategy.It is important to promote the reduction of the amount of plastic debris produced and its recovery and recycling, which has many other social, economic, and environmental benefits.Other actions that can be taken include implementing an efficient system for waste collection and improving the sanitary nature of landfills..There are already several communities that are aware of the waste problem in the Cikapundung river.A community was created to raise awareness of the environment, especially rivers, by making an appeal and a call to action for people to clean up their surroundings and make arrangements along the river.The social movements raised environmental awareness among the general people, particularly with regard to the issue of trash in the rivers [11].

Conclusion
Clear plastic bags, plastic with aluminium, sachets (plastic packing), plastic bags, and plastic cups are the majority of the plastics that were commonly found.More than 400 kg of plastic trash were released per hour, especially during the rainy season.

Figure 3 .
Figure 3. Type of plastic debris that were found in observation.

Figure 4 .
Figure 4. Weight of plastic debris that were found in observation.

Figure 5 .
Figure 5.The quantity of plastic debris found during observation.