Microplastic distribution in Surface Water and Sediments of Way Belau River, Lampung, Indonesia

Microplastic research in Lampung water body is becoming concern because of its strategic location towards the Sunda Strait. The Way Belau River in surface water and sediments are one of the places to identify the potential for microplastic deposition, and to estimate the distribution of microplastics from upstream to downstream. In the surface water, the abundance of microplastics are found about 36.76 ± 21,81 particles/500 ml, and in the sediments of the Way Belau River, it showed the abundance of microplastics are about 21.03 ± 11.92 particles/100 g of dry sediment. The dominant microplastic morphologies are fragments and fibers with a size range of 20-250 µm. The results of identification of polymer types using Raman spectroscopy showed the presence of polyethylene and polypropylene plastic types.


Introduction
Microplastics are plastic particles with a diameter of less than 5 mm [1].Microplastics can be categorized into primary microplastic and secondary microplastic [2].Primary microplastic has the origin size less than 5 mm from the production source, but the secondary microplastic can come from degradation of larger plastic due to physical, chemical or biological process [2].Microplastic can potentially have several impact to organisms that unintentionally consuming it, such as reduction in growth rate, an increase in mortality, and reduced food consumption [3].
Previous research about microplastic mostly focus on marine and freshwater environment because it can be sources for microplastic distribution [4].The distribution and accumulation of microplastic can be caused by the speed of river flow and the anthropogenic activites around the river [5].The abundance of microplastics in Indonesia is assumed to be very high considering that Indonesia is the second largest contributor of plastic waste to the sea [6] From some previous research conducted in Indonesia, abundance of microplastic were found in Ciwalengke River, West Java [7], Banten Bay [8], and Jakarta Bay [9].It can be seen that the research about microplastic were mostly conducted in Java Island, Indonesia, not much microplastic in other area of Indonesia [10].
Lampung province which is located near Java island, and separated by Sunda straits potentially has microplastic distribution in the water body.Way Belau River is one of the rivers that cross the city of Bandar Lampung.The Way Belau River has a high potential for microplastic abundance caused by the land use around the watershed and also waste disposal sites that thrown to the river.Moreover, the Way Belau River is used by residents to bathing and washing activities that potentially release microfiber [11].Therefore, it is necessary to identify the distribution microplastics in surface water and sediments in the Way Belau River to represents the condition of microplastic status in the water body.

Methods
To analyse the distribution of microplastic, it begin with sampling, pre-processing, visual identification, polymer identification, and data analysis.

Sampling
The sampling process was conducted on August 16, 20, and 22, 2021, from 7:00 to 9:00 AM.Sampling was conducted in five different sampling station from upstream to downstream.The map of sampling location can be seen in Figure 1.

Figure 1. Map of sampling location
The sampling site were chosen based on anthropogenic activities around the river.The samplig site condition can be seen in Table 1.[12].Every 500 ml of water sample at each station was taken using composite sampling method which was applied by taking water samples in the morning and afternoon, composite sampling was carried out at all five stations.Considering the complex river flow velocity distribution, this treatment was carried out as a form of water sample representation on that day.Sampling was carried out for three days (two days on weekdays, one day on weekend).The type of tool/container for taking water samples is a horizontal water sampler with a 500 ml glass bottle volume.
To maintain the quality of the water sample, several quality controls were carried out: 1.The selection of glass bottles is intended to reduce the possibility of other microplastics (outside the sample) being released into the water sample.2. The sample is then stored in a cool box with a temperature of 4 °C.3. The exposure time of water to the sampler container is 1 minute, which is intended to increase the level of representation and limit the volume of the sample taken to avoid fouling and reduce the amount of minerals and organic matter trapped.4. Water samples are taken at the surface of the river.

Sediment samples
The number of samples was taken based on five stations over three days.Each sampling station is carried out compositely, i.e. three points of capture with distance intervals horizontal 1 m with total sediment amounting to 1 kg [13].Composite sediment is carried out to provide sufficient samples replication to reduce sampling bias and explain natural variability along the flow.The total number of 30 samples were then analyzed.
Sampling for rocky river conditions of sediments was taken using a shovel [14].The collected sediment is placed in a container glass 1 L. Sediment samples that have been taken are then preserved on temperature 4 ºC in cool box [15].

.Sample preparation
A wet sediment sample of one kg is dried in the oven at temperature 90 ºC for 48 hours until the sediment sample is dry [16].Dried sediment samples were taken as much as 100 g and then given a saturated NaCl solution (300 g NaCl / 1 liter of aquades) as much as 300 ml on beaker 500 ml.The sediment and NaCl solution are stirred using the stirring rod.The sample then covered with aluminum foil to avoid contamination from outside, and let stand for 24 hours so that a perfect supernatant is obtained [17].
For both water sample and the sediment were then filtered using Whatman GF/C filter paper (Glass microfiber filter 1.2 mm) [18].The filter is then placed on a petri dish and dried for 30 minutes at a temperature of 105 ºC [7].

Visual identification.
Filter paper is visually identified and further identified using a light microscope with an objective lens magnification of 10× (total magnification of 100×).The abundance of microplastics is calculated by total of the number of microplastic particles obtained per weight of dry sediment [19].Microplastics are further identified based on the shape and color of microplastics.

Polymer identification
Raman identification is carried out at the ITB Physical Chemistry Laboratory, with the following implementation procedures: 1. Microplastic samples are taken using tweezers 2. Microplastics are taken and then placed on the preparation glass and flanked using other prepared glass 3.After that, the prepared glass is glued together using duct tape 4.After the microplastic sample is prepared, the microplastic sample is sent to ITB Physical Chemistry Laboratory.
The microplastic particles are then tested to determine the polymer from the microplastic sample.Microplastics were tested by Raman with a light shot with a wavelength of 785 nm for 30 seconds.The type of microplastic polymer is identified by the sample spectrum compared to the reference spectrum of the most suitable polymer plastic where matching is viewed based on the position of the peak wave number [19].

Data analysis
The results of microplastics abundance at each research location station will be analyzed using Kruskal Wallis statistical analysis to identify if there were any differences between sampling location.
After that, the results then will be described descriptively and displayed in the form of tables and figures.

Figure 2. Abundance of microplastic in surface water from each sampling station
The smallest abundance of microplastics was found at station 1 with 16.50 particles/500ml, and the largest abundance of microplastics was found at station 5 with 67.33 particles/500ml.This can be related to station 1 which is assumed to have maintained water quality [20] and there is a dam right before the sampling point, the presence of the dam makes the water velocity decrease which facilitates the deposition of microplastic particles in sediment [21], so that microplastic particles on the surface of the water tend to be less.Meanwhile, station 5 is the end point of the Way Belau River flow which is connected to the sea on Pasaran Island, where all water flows and all its contents flow into it, so that microplastics accumulate from previous stations and there are indications of microplastic accumulation carried from the sea.This finding is in line with previous research which states that downstream or estuary parts of rivers are complex environments where tidal movements cause plastic waste to accumulate both from rivers and seas [22], [23].Furthermore, downstream rivers are also identified as the main location for evaluating the release of microplastics from rivers to the sea [24].Population density also has a relationship with microplastic abundance [25], considering many residents who live along Way Belau River.This explains how the trend of increasing microplastic abundance from upstream to downstream stations.

Microplastic in sediments
The average abundance of microplastics in sediments in the Way Belau River is 21.03±11.92particles/100 g of dry sediment, with the dominant shape was fragment (48%) and red color.The highest abundance of microplastics was found at station 5 downstream on holidays with a total of 48±21.21particles/100 g of dry sediment and the least abundance of microplastics was found at station 1 on weekday 2 at 10±0.70 particles/100 g of dry sediment.The amount of microplastic abundance in sediments in the Way Belau River flow varies greatly at each point where the station has an average microplastic abundance in the sediment of 21.03±11.92particles/100 g of dry sediment.Compared to previous studies, the abundance of microplastics in sediments in the Way Belau River flow was higher compared to the abundance of microplastics in sediments in the Batang Arau River, Padang [26], Citarum River, Indonesia [27] and Ciwalengke River, Indonesia [7].However, in the Thames River, England [19] and in the Sei Sikambing River Medan [28], the abundance of microplastics in the sediments is higher than the abundance of microplastics in the sediments in the Way Belau River.A comparison of microplastic abundances can be seen in Table 2.The amount of microplastics in the Way Belau River can be attributed to the composition of Bandar Lampung's waste, namely the composition of plastic waste as much as 28% which is the second largest composition of waste after the composition of food waste which is as much as 30% [29].With the amount of plastic waste composition, the composition of plastic waste in Bandar Lampung city is high compared to big cities in Indonesia.The large composition of plastic waste in Bandar Lampung has the potential to increase the abundance of microplastics in sediments in the Way Belau River.However it is need to be further identified because the comparison will be reliable when the sampling protocols were identical [30].

Microplastic comparison in water and sediments samples
The abuncance of microplastic were increasing from upstream to downstream from both in water and sediments samples.However, microplastic distribution in water were shown to be higher compared to sediments samples (Figure 3).The factors of microplastic deposition can be caused by anthropogenic activities, hydrodynamic conditions, and also physical characteristics of microplastics [31].

Figure 3. Comparison of microplastic abundance in water and sediments
From the statistical analysis, it also found that there were significantly different abundance between sampling station both in water and sediments samples (p-value 0.00 < 0.05).Different sampling station showed that various anthropogenic activities can influence the microplastic distribution.

Microplastic polymer type
Microplastic particles were observed with raman spectroscopy.In water samples, yellow fragmenttype microplastics with a length of 1940 μm are indicated as polypropylene.In sediments sample, blue fragment was tested and showed that the microplastic was also identified as polypropylene.But in the other sediment samples on the observed green fragments shows the type of microplastic found is polyethylene (Figure 4).Polypropylene can be sourced from beverage bottles, food boxes, flower pots, storage containers folders, buckets, carpets, furniture, storage boxes, and other types of plastic [32].But for polyethylene microplastics can come from plastic waste bottles, drums, pipes, wire insulation, packaging layers and other types of plastic [33].

Conclusion
Microplastic were found both in surface water and sediments of Way Belau River, Lampung Province.The abundance of microplastic in surface water are about 36.76 ± 21,812 particles/500 ml, and in the sediments are about 21.03 ± 11.92 particles/100 g of dry sediment.The distribution of microplastic in the Way Belau River can be influence by anthropogenic activity around the river such industry, market, and resident area.

Figure 4 .
(a) Spectrum of polypropylene sample (b) Spectrum of polyethylene sample

Table 1 .
Sampling location

Table 2 .
Comparison of microplastic abundance in sediments