Macro Waste and Microplastics on Moyo and Medang Islands, Nusa Tenggara Barat, Indonesia

Abstract

Indonesia is an archipelagic country with many small islands. However, studies on the distribution of plastic waste in coastal areas of small islands are still minimal compared to larger islands. This study aims to identify the types, quantities, and distribution of plastic waste (both macro and microplastics) on the coasts of Moyo Island and Medang Island, West Nusa Tenggara Province, Indonesia. Samples were collected at high and low tide through visual observation using transects for macro waste and by collecting coastal sediments for microplastics. Subsequently, sediments were analysed in the laboratory for microplastic identification using fragment, film, fibre, and granule classifications. The results showed that on Moyo Island, 273 macro waste items (8727 g) were recorded at high tide and 277 items (9539 g) at low tide, dominated by hard plastics (125 items), soft plastics (80 items), and rubber (15 items, 3375 g). Meanwhile, on Medang Island, 146 items were found at high tide and 205 items at low tide, with rubber contributing the highest weight (1115 g). Microplastic concentrations were also quite high, with 866 particles/kg at high tide and 689 particles/kg at low tide on Moyo Island, while on Medang Island, 807 particles/kg and 659 particles/kg were recorded, respectively. The most abundant types were films (401 particles/kg at Moyo, 251 particles/kg at high tide) and fragments (201–252 particles/kg), while granules were more prevalent at low tide (213 particles/kg at Moyo, 134 particles/kg at Medang).

1. Introduction

Plastic waste is one of the most significant environmental issues worldwide today. Over the past few decades, the production of plastic has continued to increase, reaching more than 390 million tons annually. Unfortunately, only about 9% of plastic waste is recycled. The rest is carelessly discarded and pollutes the environment, particularly in water areas [1,2,3,4]. Plastic waste that is not managed correctly can enter rivers and then be carried to the sea, where it can harm coastal ecosystems and affect marine life. It is estimated that approximately 8 million tons of plastic pollute the oceans annually [1,2,3,5].

The Southeast Asian region, including Indonesia, is one of the most significant contributors of plastic waste to the ocean. This is due to an inadequate waste management system [3,6,7]. This condition is further exacerbated by the dynamics of currents in Indonesia, which cause Indonesian waters to become a hotspot for waste accumulation. During the west monsoon, waste carried by the current moves eastward, while during the east monsoon, waste carried by the current moves westward [8].

Plastic that enters the sea undergoes natural processes, such as exposure to sunlight and being carried by currents, which cause the plastic to break down into small pieces measuring less than 5 mm, known as microplastics [9,10,11]. These microplastics can originate from various sources, such as damaged plastic packaging, fishing nets, or ingredients in cosmetic products, including microbeads [12,13,14]. In addition, microplastics can also be carried by river currents from land to sea, then spread further due to ocean currents, tides, and their physical properties [9,15,16,17].

The amount of microplastics in coastal areas is estimated to reach 7000–35,000 tons per year [1,10,18,19]. Microplastic particles can float on the surface, remain suspended in the water, or sink to the seabed, depending on their density. Microplastics that are heavier than seawater will settle and accumulate on the seabed, becoming a long-term problem because they are difficult to decompose [20,21,22,23].

Several studies have shown that microplastics have been found in various coastal and marine areas of Indonesia. Their presence is not only on large, densely populated islands but also on small islands with few or no inhabitants, such as in the Banda Sea, Nusa Tenggara, Sumatra Barat, and Karimunjawa. Microplastics not only exist floating/hovering in the water column but also settle with sediments on the coast and the seabed [24,25,26]. In addition, global research shows that small islands in the Pacific, Atlantic, and Caribbean Oceans also experience similar problems, where plastic accumulation is strongly influenced by human activities, tourism, and ocean current dynamics [27,28]. Thus, studies on small islands are crucial to provide a comprehensive picture of the contribution of local and regional sources to plastic pollution.

Moyo Island and Medang Island are small islands located in the Province of Nusa Tenggara Barat, Indonesia. The population on these two islands is relatively small, but they have the potential for marine tourism due to the natural beauty of the sea and their rich biodiversity. This condition has the potential to produce waste, especially plastic waste. Not far from these two islands is Satonda Island (uninhabited), which has a lake in the middle of the island and makes it a tourist spot. The presence of large plastic waste (microplastics) found around this island can be an early indicator that the waste was carried by the current and stranded on nearby islands such as Moyo and Medang Islands [29,30]. Therefore, research on the presence of plastic waste on Moyo Island and Medang Island is crucial. The results of this study are expected to provide scientific data that is useful for environmental management efforts and the preservation of Indonesia’s marine tourism areas in a sustainable manner.

2. Materials and Methods

Sampling was conducted in April 2023 at two locations: Moyo and Medang Island, Nusa Tenggara Barat Province (Figure 1). Access to both places is generally via a tourist boat from Sumbawa Island. Plastic sampling was carried out during the full moon phase. Additionally, sampling was conducted twice at each location, at both high and low tides. The research location was selected using a random purposive sampling method, which involves the deliberate selection of locations based on research objectives and the potential for marine debris [1,27]. The area studied was in the northern part of the island, known for its large amount of waste.

Macro waste data collection was conducted in open areas surrounding small docks on each island. The method used was a 100 m line transect, divided into five transects of 20 m each. Each transect measures 5 × 5 m and is further divided into 25 sub-transects measuring 1 × 1 m (Figure 2). Five sub-transects were randomly selected for sampling (the upper and lower shorelines of the beach). Macro waste (size > 2.5 cm to 100 cm) was identified in the field based on type classification, counted, and weighed [30].

Marine debris is identified directly in the field based on its type or classification. Every kind of debris is recorded and weighed to determine its respective weight. Furthermore, the data is used to calculate the density of marine debris by applying the equations (Equations (1)–(3)) of total density and density based on weight [31].

$$\left(\%\right)={\displaystyle \frac{x}{{\sum }_i^n=x_i}}\times 100\%$$

(1)

$$Density\left(area\right)={\displaystyle \frac{amountofwaste}{area\left(m^2\right)}}$$

(2)

$$Density\left(area-weigh\right)={\displaystyle \frac{weighofwastetype}{area\left(m^2\right)}}$$

(3)

• $x$ = Weight of waste (type);
• $i$ = Represents each category of marine debris;
• $n$ = Total number of marine debris categories observed;
• $\sum x$ = Total weight of waste (transect);
• $x_i$ = Total weight of waste type.

Microplastic samples found in sediment were taken using the integrated sampling method, namely mixing samples from several points taken simultaneously with a uniform volume [32]. The total sediment collected was 1000 g per location. The samples were then analyzed to identify microplastic content using laboratory procedures.

The microplastic analysis process involves several stages. The first stage: drying. The sample is dried in an oven at 40–50 °C for 48 h [33]. The second stage: grinding. The dried sample is ground using a mortar [34]. The third stage: volume reduction using a 0.45 µm sieve to separate macro particles [31]. The fourth stage: separation. Functions to increase density to separate microplastics (lighter) from sediment (heavier) and remove attached organic matter (H₂O₂ oxidation). The dry sediment (50 g) is mixed with 150 mL of saturated NaCl solution, added with 0.05 M Fe (II) solution (20 mL) and 30% H₂O₂ (20 mL), stirred for two minutes, then left to stand until the suspension is clear [35]. The fifth stage: filtration. The suspension is filtered using a 0.45 µm Millipore filter paper—the sixth stage: drying and observation. Filter paper is placed in a Petri dish and allowed to dry for further analysis.

The microplastic particles obtained were visually analysed using a microscope and classified into four categories: films, fibres, fragments, and pellets [36,37]. The abundance of microplastics in seawater was compared between high and low tide conditions using a one-way ANOVA statistical test. To identify the type of plastic polymer, Fourier Transform Infrared (FTIR) analysis was carried out, and the spectrum results were compared with references from previous studies [10,18,37,38,39,40].

Microplastic abundance was calculated using Equation (4) [29,35,41]:

$$abundanceofmicroplastics={\displaystyle \frac{Amount}{DrySediment\left(\mathrm{k}\mathrm{g}\right)}}$$

(4)

3. Results

3.1. Macro-Waste

Macro-waste sampling results showed significant variations in the quantity and specific gravity of waste found in the waters of Moyo and Medang Islands during high and low tide (

Table 1. Results of macro waste sampling on Moyo and Medang Islands.

Location	Type of Waste	High Tide		Low Tide
		Amount of Waste (Item)	Waste Weight (g)	Amount of Waste (Item)	Waste Weight (g)
Moyo Island	Hard plastic (pipe, plastic bottle, food container)	125	1043	145	1376
	Soft Plastic (plastic bag, food label, straw)	80	840	62	528
	Plastic strap	0	0	0	0
	Metal	4	68	1	14
	Glass	11	657	12	1508
	Rubber	15	3375	30	3960
	Cloth	2	589	0	0
	Wood	3	1080	4	1432
	Foam	8	619	8	49
	Paper	0	0	0	0
	Fishing Gear	19	109	3	13
	Others	6	348	12	659
	TOTAL	273	8727	277	9539
Medang Island	Hard plastic (pipe, plastic bottle, food container)	86	885	122	1266
	Soft Plastic (plastic bag, food label, straw)	60	701	83	498
	Plastic strap	0	0	0	0
	Metal	0	0	1	14
	Glass	7	108	14	1308
	Rubber	6	1115	21	4060
	Cloth	1	102	0	0
	Wood	6	1594	3	3
	Foam	1	129	5	58
	Paper	0	0	0	0
	Fishing Gear	7	105	3	11
	Others	0	0	7	666
	TOTAL	174	4740	259	7884

). At high tide, a total of 273 items of waste were found, weighing 8727 g. The most common types of waste were hard plastic (125 items) and soft plastic (80 items), weighing 1043 g and 840 g, respectively. Next came fishing gear (19 items), rubber (15 items), and glass (11 items). Meanwhile, foam, metal, wood, and cloth were found with fewer than 10 items. Although rubber waste was not abundant, it had the highest weight (3375 g), followed by organic waste (1080 g) and plastic (both hard and soft). At low tide, the total amount of waste found was similar to that at high tide (277 items), but increased (9539 g). Hard plastic, rubber, and glass waste increased not only in quantity but also in weight, while soft plastic, metal, cloth, and fishing gear decreased in quantity and weight.

The types of waste found on Medang Island were not significantly different from those on Moyo Island. Plastic waste was also found, but the amount was still lower than the amount of plastic waste on Moyo Island during high tide (146 items). Other types of waste were found in amounts of less than 10 items. Likewise, in terms of waste weight, rubber waste still ranked first (1115 g), followed by foam, glass, fishing gear, and cloth, each weighing under 130 g. Metal waste was not found, but at low tide, it was found, although only one item weighing 14 g. Likewise, plastic, glass, rubber, and foam also experienced an increase in quantity (205, 14, 21, and 5 items, respectively). In terms of weight, rubber, glass, and hard plastic waste continued to increase in weight (4060, 1308, and 1266) while other types of waste experienced a decrease in weight.

Interestingly, based on field observations, the macro-waste found wasn’t exclusively from Indonesia. Glass jars were found on Moyo Island, while plastic water bottles were found on Medang Island. Both types of waste were labelled in a foreign language, not in Indonesian (Figure 3).

Based on Table 1, plastic macro-waste is the most predominant type of waste on both islands. This amount increases during low tide. Therefore, further research will focus on the presence of microplastic waste in the sediment, particularly in intertidal areas.

3.2. Microplastics on Moyo Island and Medang Island

Based on

Table 2. Microplastics on Moyo Island and Medang Island.

Location	Condition	Microplastic Abundance (Particles/kg)				Total (Particles/kg)
		Fragment	Film	Fiber	Granule
Moyo Island	High Tide	201	401	84	180	866
	Low Tide	150	259	67	213	689
Medang Island	High Tide	252	251	85	87	807
	Low Tide	236	212	76	134	659

, the total abundance of microplastic waste on Moyo Island at high tide (866 particles/kg) is higher than on Medang Island (807 particles/kg). However, at low tide, the amount of microplastic decreases. On both islands, the types of microplastic abundance found are the same: fragments, films, fibres, and granules (Figure 4). On Moyo Island, the film type is more abundant in the sediment at high tide and decreases by 35% at low tide. Although the number of fragments and fibres found at high tide is lower than that of film, at low tide they decrease by 25% and 20%, respectively. Conversely, the abundance of granules increases at low tide (32%) compared to high tide.

Furthermore,

Table 3. FTIR identification of microplastics on Moyo and Medang Islands.

Wavenumber (cm−1)	Functional Group/Vibration Mode	Polymer Indication
2912; 2845	C–H stretching (–CH2 asymmetric & symmetric)	Polyethylene (PE)
1465	CH2 bending/scissoring vibration	Polyethylene (PE)
720	CH2 rocking vibration (long chain)	Polyethylene (PE)
2917	C–H stretching (–CH3/–CH2)	Polypropylene (PP)/PE
1435	CH2 bending	Polypropylene (PP)
1078; 1007	C–C stretching/skeletal vibration	Polypropylene (PP)
855	C–H rocking (isotactic PP)	Polypropylene (PP)
710	CH2 rocking (PE overlap)	Polyethylene (PE)

and Figure 5 present the FTIR results from Moyo and Medang Islands for Polyethene (PE) and Polypropylene (PP). Polyethene (PE): The absorption peaks at wavenumbers 2912, 2845, 1465, and 720 cm⁻¹ are in good agreement with the standard spectra reported by Jung et al. [42]. This confirms the dominance of PE in the Moyo Island samples. Polypropylene (PP): Additional peaks at 1078; 1007, and 855 cm⁻¹ seen in the Medang Island samples are characteristic of PP. Jung [42] also reported that PP frequently co-occurs with PE in marine microplastic samples. These results indicate that PE and PP are the most dominant polymers in marine microplastics, making the findings from Moyo and Medang Islands consistent with global patterns.

4. Discussion

Based on macro-waste sampling results, the presence of plastic waste (hard and soft plastic) dominates on both islands, both at high and low tide. This indicates high consumption of hard plastic products such as bottles, jerry cans, and packaging containers (hard plastic). Soft plastics were also found in high quantities, suspected to originate from plastic bags, food wrappers, and other flexible materials. The dominance of these two types of plastic confirms that the main contributors to pollution are residents, boat operations, fishermen, and tourists [1,43].

The presence of hard plastic, rubber, and glass waste increases during low tide on Moyo and Medang Islands. This is due to the tidal currents in these areas. When the sea tide is high, the waste on the beach floats on the surface of the water, but when the sea tide is low, heavy waste (hard plastic, rubber, metal, and glass) is trapped on the beach. Meanwhile, light waste is carried by the tidal current to the sea. This light plastic waste has the potential to move to other places. This condition indicates that seawater conditions during high and low tide greatly affect the presence of waste [5]. Although the amount is lower than hard plastic, this type still shows a consistent presence in the coastal environment. Soft plastics such as plastic bags and food packaging tend to be easily carried by ocean currents and stranded on the coast. The increase in the number and sustainability of this type in two conditions (high and low tide) shows that soft plastic has high persistence in the marine ecosystem [44,45]. Therefore, handling marine waste requires broader collaboration between regions and countries to reduce the rate of entry of foreign waste into Indonesia’s coastal areas.

Other types of waste, such as plastic rope, metal, glass, cloth, wood, foam, paper, and fishing gear, were recorded in relatively small quantities. However, some, such as rubber, metal, and glass, contributed significantly to the total weight of waste, even though the number of items was insignificant [1]. This indicates that types of waste with small volumes but large weights tend to remain in place even at low tide. This fact demonstrates that waste management in coastal areas requires considering not only the number of items but also their weight and potential environmental impact. It is essential to consider the mass parameter of waste, not just the amount, in coastal pollution mitigation efforts [31,46].

Over time, macroplastics that are intentionally discarded and trapped on the beach will decompose into microplastics. These microplastics are carried to the beach by tidal currents. They can then be taken back to the sea due to their light weight, but some are trapped in the sediment, as is the case on Moyo and Medang Islands. The number of granule-type microplastics increases in the sediment (Table 1) during low tide. This data indicates that tides play a significant role in the distribution of microplastics, as they transport light particles such as films and fragments from the sea to the coast [31,47]. Tidal currents play a role not only in macroplastics but also in microplastics. This is evidenced by the presence of microplastics in various forms, including fragments, films, fibres, and granules.

Variations in the abundance of these microplastic types are closely related to their physicochemical properties, particularly their density. Film and fragment microplastics, which originate from the degradation of plastic bags, food wrappers, and hard plastic products, generally have a low density (<1 g/cm³), so they tend to float and be carried by ocean currents to the intertidal zone [48,49]. In contrast, granules and fibres often have a higher density, making them more likely to settle on the seabed or coastal substrate [50]. Therefore, granules are more dominant at low tide on Moyo Island and Medang Island, when ocean currents recede and heavy particles settle. Fibres from synthetic textiles also tend to be trapped in the sediment due to their thin and flexible nature [20]. Overall, these results demonstrate that fragments and fibres are essential types of microplastics to consider, as they can persist for long periods in the environment and potentially enter the marine food chain. The predominance of film on Moyo Island also indicates that single-use plastic remains a serious problem in the region. This pattern of findings is consistent with other studies reporting that fragments and fibres tend to dominate in tropical and coastal marine areas [42].

Location factors also influence microplastic composition. Moyo Island, which is relatively larger than Medang Island and has a potentially larger population and greater tourism potential (often visited by international tourists), tends to experience higher microplastic accumulation than the more remote Medang Island. Seasonal ocean currents in the West Nusa Tenggara region also play a significant role in distributing microplastics from the source to accumulation sites [51]. Furthermore, the use of plastics in fishing activities, such as nets and buoys, contributes to an increase in microplastics, including fibre and fragments, in the surrounding waters [44,52]. Therefore, coastal protection and plastic waste management are crucial in minimizing long-term impacts on marine ecosystems.

5. Conclusions

Plastic waste remains the most common type of waste found not only on large islands but also on smaller ones. Conversely, high-density waste such as rubber, although the amount of high-density waste (e.g., rubber) is relatively small compared to lightweight plastics, its contribution to the total coastal waste load remains substantial due to its much higher weight per unit volume. Therefore, in terms of total mass, high-density waste accounts for a significant portion of the waste accumulation in coastal areas. The density of the material strongly influences the distribution of microplastic types. Light, buoyant films and fragments tend to be found more frequently at high tide, while denser granules and fibres tend to accumulate on the coast at low tide. Macro waste and microplastic abundance were higher on Moyo Island than on the more remote Medang Island. Waste management requires more than just counting the amount of waste; it also requires considering the weight and characteristics of the material, as well as the dynamics of seawater, especially tides.