Assessment of microplastic on tropical tidal lake waters in Medan (study cases-Siombak lake)

Siombak Lake is an artificial lake in Medan City. We investigated microplastic pollution in tropical tidal lake waters in the current research. Grab samples of water and sediments were taken by Indonesian standards. Organic digestion and density separation were used in the preparation of the sample. The categorization of the polymer was determined by Raman Spectrophotometry, and the quantity and shape, were determined by microscopy. The result indicated that the sediment and water in Siombak Lake were polluted with microplastic. Both water and sediments are dominated by fragment shapes. The concentration of microplastic in sediments water ranging from 91 to 126 particles for 100 ml water and 262 to 398 particles for one gram of dry sediment. Microplastic contains polyethylene, polypropylene, and polystyrene, and data analysis shows a strong correlation between the amount of microplastic in water and sediment.


Introduction
Activities related to water tourism have the potential to produce significant amounts of litter, such as the plastic trash that is frequently seen in tourist regions.Plastic garbage is one of the non-organic wastes that produce in massive quantities, according to several research on waste management in marine tourism regions like lakes.Plastic litter makes up 21% of the total solid waste in the Lake Toba Area [1] and 24,8% of the total waste in the Lake Singkarak tourist region [2].
Chemicals could be released during the process of breaking down large plastics into small pieces like mesoplastic or microplastic, which is a problem that affects worldwide today.When heated or as a result of specific physical processes, many types of plastic can potentially release dangerous chemicals.Plastic can slowly decompose naturally or as a result of external intervention.Plastics with a size of less than 5 mm are referred to as microplastics.Plastic with this very small size has even more potential to have an impact on the environment.Microplastics can reduce the ability to eat marine animals when ingested because microplastics can accumulate in the digestive systems of marine animals.
Lake can keep water for longer than rivers and have relatively lower flow rates, more microplastics can settle there [3].Tides is one factor that affects the movement of microplastics in marine ecosystems [4].Siomak Lake is one of the artificial lakes in Medan City which is in the Medan Marelan District which is close to the sea coast.Lake Siombak has an area of 41.44 ha with a long coastline reaching 2.83 km, The water for this lake comes from the Balmerah river and is controlled by the tides [5].Tidal Lake is rare [5].At high tide, this lake has a maximum depth of 5 m, while at low tide, it can have a maximum depth of 4 m [6].Sungai Balmerah is One of the rivers that flows TPA Terjun.The purposes of Lake Siombak are flood management, fishing, and tourism.A residential, agricultural, aquaculture, and animal husbandry zone surrounds the lake.The residents who live close to Siombak Lake use it as a supply of water for their fish ponds.Due to the number of fishing spots and near to Medan City's, Lake Siombak is one of the city's prospective water tourism destinations.
Several lakes in Indonesia, including Lake Singkarak [7] in West Sumatra and Lake Towuti in South Sulawesi [8], have been the subject of research on microplastics in lakes.This study intends to characterize the types and concentrations of microplastics in the sediments and water of Lake Siombak, one of the city of Medan's primary tidal lakes.

Method
The investigation was done at the Lake Siombak tourist attraction in Medan City's Jl.Ps.Nippon Medan Marelan District.Purposive sampling, a sampling strategy with a specified goal and consideration of the circumstances of the research region, is used to identify the sample point.S1A1 stands for the Badera River, S2A2 for the middle of Lake Siombak, A3S3 for the lake's outlet, A4S4 for the lake's tourism area, and A5S5 for drainage.Sampling was repeated twice at each location.The sampling locations are as follows: Surface water sampling is defined by SNI 6989.57:2008.The method used is the instantaneous collection.A water sampler was used to collect river water, and an ekman grab was used to collect the sediments.Water is taken in mid down of the lake's depth, and sediment is collected between 0 and 10 cm below the sediment's surface.At 40C, water and sediment are kept.An adaptation of a National Oceanic and Atmospheric Administration (NOAA) procedure was used to prepare the water and sediment samples.
A light microscope (XSP-12) and Raman microscopes (The LabRAM HR Evolution Horiba) used to measure the morphology of microplastics.Based on shape features, such as films, pieces, pellets, forms, and fibers, microplastics are divided.Polyethylene, Polypropylene, and Polystyrene were the three types of microplastics that were examined.With the hypothesis that there is a relationship between the abundance of microplastics in water and sediments, the abundance will be analysed by the Pearson Correlation test using SPPS with an alpha value of 95%.

Microplastic morphologies
Microplastic morphology consists of the shape and type of microplastic polymer.The current classification of microplastic forms is still very varied, so this research refers to the classification of the research [9].The results of the analysis of the shape of microplastics using a light microscope (XSP-12) showed that fragments, films, fibers and pellets were found in Lake Siombak where fragments were the most prevalent form in the water, accounting for 75%, followed by films at 14%, and fiber at 11%.In sediments, fragments represent most of the microplastic in terms of percentage (74%), with films following in second at 11% and fiber in third at 15%.
In the form of pellets, they are only found in the inlet, namely from the Sei Badera River and drainage.Most of the microplastics in the sediments and water of the tidal Lake Siombak is fragments.Sharp edges, uneven forms, and thickness are characteristics of fragments [9] and [10].Several investigations have demonstrated the presence of microplastics in various lakes, including the Yangtze Estuary lake containing 39% [11], Lake Bolsena dan Lake Chiusi [4], Singkarak Lake [7] and Lake Towuti in South Sulawesi [8].The amount of microplastics present in Lake Siombak's water and sediments is as follows: Danau siombak is one lake that has the potential to attract tourists, At the moment, tourism-related activities have grown in the area around the lake, and on the other side of the lake, there are many other community activities, including residential areas.Secondary microplastics, or those formed by major plastic fragmentation, are produced by tourism and community activities.Waste from food packaging, plastic bags, wraps, and bottles all include microplastics in the form of fragments and films [7].The formation of secondary microplastics is accelerated by heat reactions, photodegradation, and current waves from water dynamics [8].2012) in research [12], the density of polymers can affect the distribution of microplastics in waters.The results of the spectral wave peak analysis on the microplastic samples at the inlet from drainage were 1528.84cm-1, 1452.08 cm-1, 1341.77cm-1, 747.49cm-1, and 680.71 cm-1, and for samples in lake sediments, they were 1581.27cm-1, 1527.84 cm-1, 1428.73 cm-1, 1363.21cm-1, and 746.40 cm-1.The existence of methylene chains in common alkanes (1452.08 cm-1 and 1428.73 cm-1) and an aromatic chain (1528.84cm-1 and 1581.27cm-1) is indicated by several spectral wave peaks.Polystyrene (PS) is the only type of plastic polymer with an aromatic carbon chain; polyethylene (PE) and polypropylene (PP) only contain regular alkane carbon chains.The spectral peaks at 747.49 cm-1 and 746.40 cm-1 suggest the methylene group (CH2) has the potential for the presence of polyethylene (PE), whereas the peaks at 1341.77 cm-1 and 1363.21cm-1 show the methyl group (CH3) is potentially polypropylene (PP).The results of this investigation show that PS, PE, and PS are present in the sediment and water samples from Lake Siombak.Due to their lower density, PE and PP have a propensity to float and stay to the water's surface for a long period of time [12].

Abundance of Microplastic
The analysis of all samples showed that Lake Siombak was polluted with microplastics at each site chosen for sampling.The average concentration of microplastics in water is 90-126 particles/100 ml, while the average concentration in dry sediment is 278-397 particles/g.

Figure 4. Abundance of Mps
Microplastics were identified in high concentrations in the middle part of Lake Siombak, reaching 92 particles/100 ml of water and 262 particles/g of sediment.Siombak Lake serves as a location for fishing and other aquatic life.The concentration of microplastics in tourist-oriented locations is as high as 126 particles/100 ml and 366 particles/g of sediment.In comparison to fishing sites, tourist areas have a higher concentration of microplastics.Several studies that indicate how much plastic waste is produced in tourist regions, such as Merek on Lake Toba Brand, which is estimated to account for 21% of all waste produced [1] and the Lake Singkarak tourist area contributes 24.8% of plastic waste [2].In addition, the data also shows that the inlet channel from Lake Siombak which originates from the Sei Balmera River and the drainage already contains microplastics with an amount of 94 particles/100 ml and 398 particles/g of sediment where the Sei Balmera River which passes through TPATerjung as the main TPA for waste management in Medan City and 91 particles/100 ml and 279 particles/g in the sediment for the source of the drainage.At the Lake Siombak outlet, there were 362 particles/g of sediment and 103 particles/100 mL.Fish Ponds and locals near Lake Siombak frequently use the water from the lake's outlet as a source of water.
The results of the data analysis show that there are greater concentrations of microplastics in sediment than there are in water.This is so because water's hydrodynamic characteristics have an impact on microplastic particles [12], Strong currents and waves with irregular directions allow microplastic particles to spread inconsistently [8].Beside that, Danau Siombak is affected by tides so retention time (Rt) considered short, it is only 11 to 25 hours [5].According to the Pearson correlation analysis test results, there is a significant relationship between the amount of microplastics in water and sediment, which is 0.026, and the Pearson correlation value, which is 0.694 and qualifies into the strong correlation.The correlation between the number of microplastics in water and sediments is significant, and it means that the greater number of microplastics there are in the water, the more there are in the sediments.According to [13], microplastics that have been distributed in the water will settle and be swept away by currents, causing them to mix with sediment and increasing the speed at which microplastics accumulate in sediments.

Conclusion
Microplastic contamination has been found in Lake Siombak, with concentrations in the water ranging from 91 to 126 particles for 100 ml water and 262 to 398 particles for one gram of dry sediment, with fragments, which are typical of secondary microplastics, dominated found.Lake Siombak contains microplastics from of polyethylene, polypropylene, and polystyrene.An integrated plastic management strategy is required in Lake Siombak, as supply of water for fisheries and aquaculture, to reduce the effects of microplastic contamination on the biota.

4 Figure 3 .
Figure3.Characteristic of microplastic shape in water and sediment Siombak Lake Some selected point on sample was analysed by Raman to find the chemical compositions.The polimer type of microplastic was identify such polypropylene (PP), polyethylene (PE) and polystiren (PS).According to Hildago-Ruz et al (2012) in research[12], the density of polymers can affect the distribution of microplastics in waters.The results of the spectral wave peak analysis on the microplastic samples at the inlet from drainage were 1528.84cm-1, 1452.08 cm-1, 1341.77cm-1, 747.49cm-1, and 680.71 cm-1, and for samples in lake sediments, they were 1581.27cm-1, 1527.84 cm-1, 1428.73 cm-1, 1363.21cm-1, and 746.40 cm-1.The existence of methylene chains in common alkanes (1452.08 cm-1 and 1428.73 cm-1) and an aromatic chain (1528.84cm-1 and 1581.27cm-1) is indicated by several spectral wave peaks.Polystyrene (PS) is the only type of plastic polymer with an aromatic carbon chain; polyethylene (PE) and polypropylene (PP) only contain regular alkane carbon chains.The spectral peaks at 747.49 cm-1 and 746.40 cm-1 suggest the methylene group (CH2) has the potential for the presence of polyethylene (PE), whereas the peaks at 1341.77 cm-1 and 1363.21cm-1 show the methyl group (CH3) is potentially polypropylene (PP).The results of this investigation show that PS, PE, and PS are present in the sediment and water samples from Lake Siombak.Due to their lower density, PE and PP have a propensity to float and stay to the water's surface for a long period of time[12].