Exploring marine surface microplastic around Pasaran Island, Lampung Province

Microplastics have been challenging issues as an emerging pollutant in the marine environment. The objective aims to assess the surface microplastic abundance and morphology around Pasaran Island, Lampung Province. Sampling was done by using plankton net in four sampling stations, which were selected purposively and sampled using the composite method in the morning and evening. The microplastics would be analyzed by visual inspection for the morphology (shape, size, and colors) and polymers. The microplastic abundance around Pasar Island was identified as 67,25±24.8 items/L. The highest finding was located in the fourth station, which was the nearest area of fishing activities. However, there was no significant difference spatially and temporally. The dominant size distribution was 401-1000 (40%) mm, while blue (33%) and black (28%) were the most commonly found colors. The microplastic shape was observed in fiber (72%), followed by fragment (20%). The Raman test was done to identify its polymer, using a blue fragment sample detected as polypropylene.


Introduction
Waste production has risen over time [1].Waste is not only attributed to land but also the presence could be found in bodies of water such as oceans, rivers, and others [2].Marine debris is the solid waste from human activities intentionally or unintentionally left in the environment [3,4].One type of waste found in the ocean is plastic.Plastic pollution is more than 5 trillion plastic weighing over 250.000 tons floating on the ocean [5].Plastic degrades into smaller particles, or less than 5 mm is called microplastics.Accumulation of microplastics in large quantities in seawater can threaten the marine biota [2,6,7].Due to the small size, microplastic could be harmful to organism and increase plastic availability for digestion by marine living organism [8].The microplastic exposure in organism can enter to human food chain and cause potential health hazard [9].Indonesia is the world's second-largest contributor of plastic pollutants to the ocean after China, amounting to 0.48 to 1.29 million metric tons of plastic per year.These quantities increase continuously each year with society's increasing use of plastic, which is directly proportional to the increase in microplastics [10].In the previous study, the coastal environment around Java Island had a relatively higher abundance of microplastic than other coastal [11,12].However, the microplastic research was more spread on Java Island (49%) than other Indoensia islands [11].The sources of microplastics in Indonesia led to domestic waste, tourism, and fishing activities as the primary sources [13].Those activities were found in Lampung Province as a part of Minapolitan.Geographically, Lampung Province has a total land area of 35,288.35km 2 , including 132 islands.The authority of ocean waters is approximately 24.820 km 2 .This province has immense potential to be a marine and fisheries resource [14] and tourism activities which impacted economic growth [15].Pasaran Island is a strategic position in Lampung Province related to the business opportunities from fishery activities as a promising sector [16].Close to that site, the estuary of Way Belau River exists in which the river also has been contaminated by microplastic with an average of 73.53±43.6 items/L [17].However, the area is potentially contaminated with microplastics.As a center for fish processing in Bandar Lampung, it is essential to know the abundance of microplastics in its waters.The main economic activity of the community of Pasaran Island is the fisheries sector.In addition to being a center for fish processing, The freshwater of Way Belau River flows into an estuary near Pasaran Island.The area is also a settlement area, tourist destination, and fishery acivities [18].Various activities in this area will result to different potential levels of microplastic abundance.With the growth tourism, frequent activities, and other potential causes, the identification of abundance of microplastics spatially and temporally around Pasaran Island becomes a study to conduct.This work provides a morphological description according to its type, size, and colour.In order to do further analysis, polymer study also would be identified to obtain better understanding of the microplastic in Pasaran Island.

Sampling location
This research was conducted from August to December 2021.Sampling was carried out from August 16 th to August 22 nd , 2021 at 07.00 and 16.00 (UTC+7).The sampling was located around Pasaran Island-Teluk Betung.This study included 4 stations and was repeated twice.The four sampling points represent the conditions of community activities around the waters of Pasaran Island.Those area are estuary (the bonderline between Way Belau River and the Ocean), mangrove ecosystem, domestic area, and fishery activites.The sampling site and its dominant activities are shown in Table 1 and specifically illustrated in Figure 1.

Sampling collection and sample preparation
The microplastic sampling was conducted on the surface using a nylon plankton net (mesh size: 5 µm, net mouth: 30 cm, length 100 cm).The collected water samples were then transferred into glass jars, each containing one liter of water.Afterwards, the sample was put into a cool box and transported into laboratory to be further analyzed.
One liter of water from each sampling station was separated into two samples for duplication.Subsequently, 250 mL of H2O2 (Hydrogen Peroxide) was added to each liter of water sample to remove organic pollutant [19].A total of 6 g of NaCl (Natrium Chloride) was added per 20 mL of water sample, and the samples were covered with aluminum foil and remained to settle for 24 hours [20].The added solution was for separating particle based on their density [21].The water samples were sieved and filtered using filter paper (whatmann GF/C 1,2 µm).After that, the filter paper was dried in an oven at 105°C for 30-45 minutes to ease the identification.The dried filter containing suspected microplastic were transferred to petri dishes to be analyzed microplastic abundance and visual sorting step.

Visual identification
First observation was done by identifying the microplastic abundance.The microplastic was observed visually using a microscope with a 10x magnification.This identification would obtain the information of each item in the dried filter of microplastic as suspected microplastic at first.Every suspected plastic microplastic was validated as plastic with testing by hot needle [22].The verification of the plastic was shown if the microplastic was shrank and destructed immediately after contacted to hot needle.This was done for some samples randomly.According to Environmental Research Institute, some steps could be followed by dividing the filter into grid pattern.Then, the examination of the microplastic could be started within filtration perimeter.It was observed from the left to the right side and moving down one row to continue reading from right to the left [20].The particle of microplastic was observed and accounted individually to gain the number of items.After that, the abundance calculated using equation (1).

Microplastics Abundance =
ℎ     (1) After identifying the microplastic abundance, visual sorting was performed for charaterizing morphology of microplastic [6].The concern of microplastic identification was sorted by the shapes (fiber, fragment, film, and granule), colours (such as red, blue, black, brown, green, transparent etc.), and sizes (50µm -5 mm).The morphological description would give information of their fate in the environment such as their residence time in the ocean and determinant for living organism expsore [23].

Polymer identification
Some samples would employ raman spectroscopy to determine their polymer type.The laser type was Nd:Y AG DPSS (Diode-Pump-Solid-State).The particles were subjected to a 785 nm laser for 30 seconds with integration time of 20s and co-addition three times.The sample spectra would be matched to sprectrum reference and the fittes match was then chosen according to matching peak wavenumber positions [24].Technically raman analysed was used because of the efficeny of its use to quantify microplastic numbers instead of FTIR (Fourier Transform Infra Red) imaging [25].The polymer identification aims to elaborate the potential source of microplastic and gives better knowledge of microplastic characteristics.

Statistical analysis
The sampling location was divided into several sites and time sampling in order to describe the abundace gap spatially and temporally.Statistical analysis was conducted by Kruskal-Wallis test to explore the differences.Signifincat difference is set of p-value lesser than 0.05.

Microplastic abundance
Microplastics are present at all four sites, with an average concentration of about 82.75±24,8 items/L.The highest microplastic presence was detected on the first sampling day, with an average of 82.76±29 items/L, while the most abundant microplastics were specifically found close to the fishery area, with 93.4±23.6 items/L.Compared to the study on Sumatera Island, the concentration was relatively lower than that in Bintan Regency (122.8±67.8items/L) [26].In addition, the microplastics were observed to be higher than those of Bali Island (<1 item/L), Sulawesi Island (<55 items/L), ENT (<28 items/L), and some sampling locations in Java, such as the northern coastal waters of Surabaya and Muara Kamal and Marunda (area with microplastics<103.8 items/L) [11].Since the previous study showed that microplastic in the Way Belau River has been accounted for approximately 73.53±43.6 items/L, the abundance in station-1 was potentially contributed from the river instead of activities around the Pasaran Island.The particles in the station 2 and 3 were relatively lower because the possibility of the mangrove around station-1 captured the microplastic.Mangroves have capability to reduce microplastic flowing to ocean and play important role in migration and precipitation of microplastic entering the ocean.The influence of mangrove could be associated to its density [27].Further research regarding the contribution of mangrove in the sites is needed.In addition, the abundance in station 4 was relatively increasing caused frequent fishery activities.
The figure 1 shows the comparison of the field survey results among time-location sampling stations.The abundance of microplastics in the marine environment of Pasaran Island may be influenced by anthropogenic activities, particularly the uncontrolled plastic management or another activities using plastic products.In addition, weather and oceanographic conditions, such as tides, may also affect microplastic distribution in the marine environment.Tides can transport particles from the sea to the land and vice versa, distributing and depositing them [28].Based on tides data from Panjang Harbour, in the 16 th August 2021 tend to have highest fluctuation because the tide condition was lower (water level 98.6 cm) than other time in August (water level >100 cm).It can affect slack water conditions where the waters were unstressed and calm [29].

Microplastic morphology (shape, colour, and size)
The morphology characteristics of observed microplastics are depicted in Figure 3, and the examples of some detected microplastics from samples showed in Figure 4.There were four types of microplastics, namely fibers, fragments, films, and granules.Fibers were the most dominant shape in the marine surface water around Pasaran Island.A total of 12 samples were identified as 72% of fiber type, followed by fragments (20%), film (7%), and granules (1%).The fibers were constantly found higher near the estuary and fishery activities.The condition was similar to previous studies conducted in the NE Atlantic Ocean, Mariana Trench, Pacific Ocean, and Monterey Bay California where the fiber was dominant in the marine environment [30].The observed microplastic in Pasaran Island by the previous study reported that sandfish cultured (Holothuria scabra) was detected to fiber type followed by sphere and fragment [31].
Since the sampling was on the surface, the polymer type of fiber potentially had lower specific gravity than seawater specific gravity (1.025) because they were found floating [30].The polymer with low polymer (specific gravity< 1.025) was a form of LDPE (low-density polyethylene), PE (polyethylene), HDPE (high-density polyethylene), PP (polypropylene), and PS (polystyrene) [30,32].The fibers from different sources such as washing clothes, ropes and fishing gear, fiber-reinforced ships are a common type of microplastic in the waters.This form has higher buoyancy and lower suspension speed than other types even though with similar density and volume [33].Its characteristic can impact microplastics distribution in the ocean.Eight colors of blue, red, black, green, transparent, yellow, brown, and purple were detected on the marine surface around Pasaran Island.The proportion of blue, black, and red colors was commonly observed, and the microplastics average accounting for 33%, 28%, and 26% of the total, respectively, while the least commonly found was transparent for only one percent.Almost all samples were observed microplastics with blue color, and it was relatively higher in station-1 than that of other sites.
The high frequency of blue microplastics were suspected to coming from fish farming activities in the surrounding area and the use of fishing nets during fishing.Black and dark colors (red, green, brown, and purple) may indicate the amount of contaminants absorbed by microplastics or other human activities [6].Yellow and transparent colors may indicate that the microplastics have been in the ocean and oxidized [21].The color of observed microplastic can be seen as their original colors or other colors from degradation results, such as photodegradation processes [34].Additionally, transparent plastic is considered to have been exposed to UV and occurred photodegradation over an extended period time [35].Blue and transparent microplastics are a potential threat for tiny ocean organisms such as planktivorous fish since the microplastics resemble plankton as their primary food [36].Microplastics ingested by marine organisms can physically hinder their digestion process and can risk death [37].The dominant size of microplastics found in the samples was 401-1000 µm with an average proportion of 40%, followed by microplastics with sizes ranging from 1001-2000 µm.The large microplastic was the slightest presence of 24%, ranged 2001-4500 µm.The largest size had the lowest abundance.The microplastics size was relatively constant distributed in all four locations.Over time, plastics will undergo fragmentation and generate microplastics with increasingly smaller sizes [38].Other causes of plastic fragmentation into various sizes are ultraviolet radiation, seawater waves, and the hydrolytic properties of seawater [39].

Polymer identification
Raman identification of two samples was made to identify further for the polymer of observed microplastics.The known polymer gives the information of the possibility of the microplastic sources.The blue fragment was chosen to be identify because there was a limitation in the raman test to identify fiber as the highest abundance in the sites.The fiber was relatively found in tiny size and it had diffiulties to check by instrument availability.The differences in peak points may be due to impurities in the microplastics.A combination of polymer and dye overshadow the polymer spectrum [40].The Raman shift peaks in the graph can indicate the type of polymer that is compared to the reference.The result based on Figure 5 shows that the tested microplastics are Polypropylene (PP).Polypropylene can come from bottle caps, straws, and various household plastic waste originating from daily activities of the community as well as plastic waste carried by currents [41] since the specific gravity is relatively low (0.9-0.92) and can be floating [30].
Figure 5 .Raman test result of microplastic samples

Spatial and temporal distribution
Sampling in four stations and three times a week was done to understand the microplastics distribution around Pulau Pasaran.The statistical test using Kruskall Wallis (p-value<0.05)reveals no significant difference in spatial and temporal distribution.This might be caused by the short periods of sampling time and oceanography characteristics.Distribution of microplastics in the ocean can be influenced by the hydrodynamic process (coastal currents, tides, seasonal variability of water currents drift and river outflow act), polymer density, biofouling, aggregation, and topography [29,30].How well the disperse leads to the abundance of microplastics.According to the previous study, the current in Lampung Bay ranged 0.017-0.168m/s (average of 0.0472 m/s).The tidal wave of Lampung Bay was categorized as a mixed tidal wave [42].Furthermore, the condition in the estuary, river and bay area usually has backforth condition in which the movement pattern can be fluctuative The sea water level can be higher than estuary making tidal current moves to estuary called flood.On the contrary, the condition of sea water level is lower than estuary making tidal current going to sea, called ebb [43].The back-forth condition can possibly impact the movement of microplastic itself, but the further research of their distribution is needed.

Conclusion
The microplastic abundance around Pasaran Island, Lampung Province, was about 67.25±24.8items/L.According to different time and site sampling, there was no significant difference in microplastic abundance.It was potentially caused by the short period of time-space sampling and oceanographic characteristics that tended to be calm.The type of fiber was dominantly found near Pasaran Island, followed by fragment.The study has shown that the dominant size of microplastic was 400-1000 mm with colors of blue and black.The microplastic was also further identified its polymer using raman test where the chosen microplastic of fragment was identified as polypropylene.

Table 1 .
Coordinate location