Plastic Pollution Research inIndonesia: State of Science and FutureResearch Directions to ReduceImpactsPaul Vriend1,2*, H. Hidayat2, J. van Leeuwen3, M. R. Cordova4, N. P. Purba5, A. J. Löhr6,I. Faizal 5, N. S. Ningsih6, K. Agustina7, S. Husrin8, D. D. Suryono8, I. Hantoro6,9,B. Widianarko9, P. Lestari 10,11, B. Vermeulen1 and Tim van Emmerik1

1Hydrology and Quantitative Water Management Group, Wageningen University and Research, Wageningen, Netherlands,2Research Center for Limnology, Indonesian Institute of Sciences (LIPI), Bogor, Indonesia, 3Wageningen University,Environmental Policy Group, Hollandseweg 1, Wageningen, Netherlands, 4Research Center for Oceanography, IndonesianInstitute of Sciences (LIPI), Jl. Pasir Putih 1 Ancol, Jakarta, Indonesia, 5Department of Marine Science, Faculty of Fishery andMarine Science, Universitas Padjadjaran, Bandung, Indonesia, 6Oceanography Research Group, Faculty of Earth Sciences andTechnology, Bandung Institute of Technology, Bandung, Indonesia, 7The National Plastic Action Partnership, World ResourcesInstitute (WRI) Indonesia, Jakarta, Indonesia, 8Marine Research Centre, Research Agency, and Human Resource Development,Ministry of Marine Affairs and Fisheries, Jakarta, Indonesia, 9Department of Food Technology, Faculty of Agricultural Technology,Soegijapranata Catholic University, Semarang, Indonesia, 10Department of Environmental Engineering, Faculty of Civil Planningand Geo Engineering, Sepuluh Nopember Institute of Technology, Surabaya, Indonesia, 11Department of Agricultural andBiosystems Engineering, Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia

Several studies have suggested Indonesia to be among the top plastic polluting countriesglobally. Data on the presence and amounts of plastic pollution are required to help designeffective plastic reduction and mitigation strategies. Research quantifying plastic pollution inIndonesia has picked up in recent years. However, a lack of central coordination in thisresearch has led to research output with different goals, methods, and data formats. In thisstudy we present a meta-analysis of studies published on plastic pollution in Indonesia touncover gaps and biases in current research, and to use these insights to suggest ways toimprove future research to fill these gaps. Research gaps and biases identified include a clearpreference for marine research, and a bias toward certain environmental compartments withinthe marine, riverine, and terrestrial systems that have easy to apply methods. Units ofmeasurement used to express results vary greatly between studies, making it difficult tocompare data effectively. Nevertheless, we identify polypropylene (PP) and polyethylenevariants (PE, HDPE, LDPE) to be among the most frequently found polymers in bothmacro- and microplastic pollution in Indonesia, though polymer identification is lacking in alarge part of the studies. Plastic research is mostly done on Java (59% of the studies). Werecommend research methods used to quantify plastic pollution to be harmonized. Moreover,we recommend a shift in focus of research toward the riverine and terrestrial environments anda shift of focus of environmental compartments analyzed within these systems, an increase inspatial coverage of research across Indonesia, and lastly, a larger focus on polymercharacterization. With these changes we envision future research which can aid with thedesign of more effective and targeted reduction and mitigation strategies.

Keywords: macroplastic, microplastic, indonesia, litter, marine, river, pollution, review

Edited by:Anabela Cachada,

University of Porto, Portugal

Reviewed by:Veerasingam S,

Qatar University, QatarKai Zhang,

City University of Hong Kong, China

*Correspondence:Paul Vriend

Paul.vriend@wur.nl

Specialty section:This article was submitted toToxicology, Pollution and the

Environment,a section of the journal

Frontiers in Environmental Science

Received: 09 April 2021Accepted: 17 May 2021Published: 08 June 2021

Citation:Vriend P, Hidayat H, van Leeuwen J,

Cordova MR, Purba NP, Löhr AJ,Faizal I, Ningsih NS, Agustina K,

Husrin S, Suryono DD, Hantoro I,Widianarko B, Lestari P, Vermeulen B

and van Emmerik T (2021) PlasticPollution Research in Indonesia: State

of Science and Future ResearchDirections to Reduce Impacts.Front. Environ. Sci. 9:692907.

doi: 10.3389/fenvs.2021.692907

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929071

REVIEWpublished: 08 June 2021

doi: 10.3389/fenvs.2021.692907

INTRODUCTION

Plastic pollution has been a topic of rising environmental concernin recent years. Model estimates show that between 0.8 and 30million metric tonnes of plastic waste enter the aquaticenvironment annually around the globe (Borrelle et al., 2020;Lau et al., 2020; Meijer et al., 2021). The majority of plasticpollution is generated on land and transported through rivers tothe marine environment (Pawar et al., 2016; Schmidt et al., 2017;Lebreton and Andrady, 2019). Plastic pollution can have adverseeffects in all three of these systems, which include mortality offauna through ingestion or entanglement, reduction oflivelihoods of those dependent on ecosystem health (e.g.fishing and tourism), contamination of seafood withmicroplastics with implications for food safety and humanhealth, property damage, and an increased risk of floods inurban areas (Gall and Thompson, 2015; Koelmans et al., 2017;Conchubhair et al., 2019; Hantoro et al., 2019; Honingh et al.,2020; van Emmerik and Schwarz, 2020).

Indonesia is estimated to be among one of the top emittingcountries of plastic pollution in the world (Meijer et al., 2021).This is supported by a comparative study of previously publishedfield observations, which ranked drains in Jakarta (IndonesiaCapital City) among the highest polluting rivers globally (vanCalcar and van Emmerik, 2019). Plastic pollution found in theIndonesian Seas not only comes from inland, but also fromseveral countries surrounding it. The ocean currents transportthis plastic pollution to the inner seas (Purba et al., 2021). Highplastic emission rates are hypothesized to be caused byIndonesia’s high population densities in coastal areas incombination with improper waste management andinsufficient service coverage (Lebreton and Andrady, 2019;Lestari and Trihadiningrum, 2019). Indonesia is located withinthe Coral Triangle, a hotspot for global marine biodiversity whichis highly susceptible to the negative effects of plastic pollution(Tomascik et al., 1997; Spalding et al., 2001; Lasut et al., 2018).Reducing plastic emissions in Indonesia will therefore have alarge impact on both reduction of global plastic emissions to theoceans, and on protecting global biodiversity. The Indonesiangovernment has committed to reduce plastic pollution. To thisend, it has set a target to improve solid waste management(Presidential Decree No 97/2017) as well as the goal to reducemarine plastic debris by 70% in 2025. This commitment isfollowed up by the establishment of the national action planfor marine debris management 2018–2025 (Presidential DecreeNo. 83/2018).

Reliable and frequent data on plastic pollution and its effectson fauna and ecosystems are required for the development andassessment of policy measures aimed to reduce plastic emissionsto the oceans (Conchubhair et al., 2019; Owens and Kamil, 2020;Vriend et al., 2020). Moreover, data on exposure and toxicity areneeded to assess microplastics’ human health risks from exposureto, for example, contaminated seafood (Hantoro et al., 2019).Plastic pollution has been extensively studied in Indonesia (e.g.Uneputty and Evans, 1997; Rochman et al., 2015; Cordova andWahyudi, 2016; Syakti et al., 2017; van Emmerik et al., 2019).However, observations are scattered across the country and vary

widely in the methods that are used. To gather reliable andfrequent data, a nationally coordinated monitoring strategy isrequired which, in turn, will form the basis for prioritizing anddesigning effective plastic pollution reduction and mitigationstrategies. An overview of the current knowledge and researchgaps and biases is needed to determine what types of monitoringdata is missing to inform such strategies. These overviews havepreviously been made on a global scale for plastic pollution infreshwater environments (Blettler et al., 2018), for specificcountries (e.g. Chowdhury et al., 2020), and for specificenvironmental systems in Indonesia (Purba et al., 2019).However, such an overview for plastic pollution across allenvironments in Indonesia does not yet exist.

This review study provides an overview of the current state ofknowledge on plastic pollution in Indonesia and provides insightsinto current research biases and knowledge gaps. We then usethese data to suggest ways forward for plastic research inIndonesia to overcome these gaps. This overview was gatheredthrough a review of current literature on plastic pollution inIndonesia, and through performing a meta-analysis of the 83identified peer-reviewed articles published between 1986 and2020. The goal of this study is to provide insights on what typesof research questions should be answered to fill research gaps,with the aim of having a clear picture for effective policymeasures to be implemented and their efficacy to bemonitored.

METHODOLOGY

Literature ReviewThe literature search was performed using a snowball method.First, a literature search was performed in the Google Scholar andResearchGate databases, using different combinations of thefollowing keywords: plastic, macroplastic, microplastic, litter,marine, river, Indonesia, debris, and waste. Studies thatquantified environmental plastic pollution in Indonesia wereselected. Studies that considered plastic pollution that couldnot directly be linked to a specific location were excludedfrom further analysis (e.g. plastic pollution in consumablesand policy studies). Second, selected articles were scanned forreferences to other studies concerning plastic pollution inIndonesia. These studies were then also added to the review.Lastly, a group Indonesian researchers specialized in plasticpollution was asked to identify any literature missing in thereview. These studies were also added to the literature review.The literature search was concluded on October 1, 2020. Studiespublished after this date have therefore not been included in thesubsequent analysis. The corresponding author of this paper readall identified literature (n � 83, Supplementary Materials), andthe following information was extracted to a unique dataset:

(1) The environmental system which was studied for plasticpollution (e.g. terrestrial, riverine, marine, atmosphere).

(2) The compartment in the system that was studied forplastic pollution (e.g. floating plastic, in the watercolumn, beached plastic, plastic in biota).

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929072

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

(3) The location of the study (coordinates).(4) The size of plastic that was studied (e.g. microplastic,

macroplastic, or both).(5) The year the study was published.(6) The institutions the authors were affiliated to.(7) The top three most frequently found plastic polymer

types and/or shapes that were reported in the study.(8) The units in which the data were reported.

Meta-AnalysisThe dataset created through the literature review was used forseveral analyses, including a spatial analysis of research locations,an analysis of research output over time, an analysis of units ofmeasurement in which the data were reported, and an analysis ofmost frequently found polymers and shapes.

The majority of the literature identified during the review used asize classification that deviated from more recent definitions. Forexample, van Emmerik and Schwarz (2020) define four size classes ofplastic pollution, these being macro- (>50mm), meso- (5–50mm),micro-(0.1 µm–5mm), and nanoplastic (<0.1 µm). Most literatureidentified during the review aggregate nano- andmicroplastic and callthis size range microplastic (<5mm), and aggregate meso- andmacroplastic and call this size range macroplastic (>5mm). Toavoid confusion during the analysis it was decided to use thesame terminology as used in the identified literature.

The spatial analysis of research locations was performed byimporting the logged coordinates into ESRI ArcMap (ArcMapversion 10.7.1), plotting the latitude and longitude data, andaggregating the point data to Indonesia’s administrative sub-regions.The shapefiles on sub-regions of Indonesia were retrieved fromDIVA-GIS (n.d.). Point data within a specific regionwere then aggregated andsummed to determine the total amount of studies per region. Pointdata in the open sea were aggregated to their closest landmass.

For each study, where possible, the top three most frequentlyfound shapes, and polymers were noted. The number of studies inwhich each shape and polymer were present in the top three wasthen counted to determine those most frequently found items inplastic pollution in Indonesia.

RESULTS AND DISCUSSION

Research per Size Category andEnvironmental SystemA total of 83 studies were considered for the meta-analysis(Table 1). The majority of studies on plastic pollution inIndonesia quantify macroplastic pollution (40), a smallergroup quantified microplastics (37), and a handful of studiesquantified both (6). This is in contrast with the findings on globalplastic research by Blettler et al. (2018), who found thatmicroplastic is most frequently studied on a globally. Wesuspect that the lower number of microplastic studies is due tothe limited availability of research equipment and suitedlaboratories in Indonesia, as well as the absence of astandardized protocol for monitoring microplastics (Michidaet al., 2019). Plastic pollution is most frequently studied in themarine environment, with 68 papers studying marine plastic,

compared to 10 studies in the riverine and three in the terrestrialenvironments. No studies on atmospheric plastic pollution wereidentified during the literature search.

Within environmental systems, there is a bias to study specificsub-compartments (Table 2). For example, plastics on the beachand floating plastic are most frequently studied for the marineenvironment (29 and 15 out of 77 studies respectively), while thewater column (9 out of 77), seafloor sediment (9 out of 77) biota(7 out of 77), and mangroves (4 out of 77) receive less attention. Asimilar bias can be identified in riverine plastic research, wheremost research so far has been done on floating plastics (5 out of15) and plastics in the water column (4 out of 15), while researchon other compartments such as the riverbank (2 out of 15),riverbed (2 out of 15), or in biota (2 out of 15) are lagging behind.

The observed bias can be attributed to the type of researchmethod available for each system compartment. Some methodsused to quantify plastics in aquatic environments are cheaper andeasier to apply than others, leading to a preference of application.For example, method to quantify riverine macroplastic on theriver surface or the riverbanks can be easily applied without anyheavy and/or expensive equipment (e.g. González-Fernández andHanke, 2017; van Emmerik et al., 2018; Vriend et al., 2020;Cordova et al., 2021), and are therefore most frequentlyapplied in river systems. Similarly, the analysis of beachedplastic and floating plastic in the marine environments can bedone by visual observation, and therefore do not require any largeequipment (e.g. OSPAR Commission, 2010). The limited numberof research dealing with microplastic measurement andidentification so far can also be attributed to the fact thatresearch institutions in Indonesia are still building theircapacity to perform proper microplastic analyses. However,some progress on the development of standard methods formicroplastics analysis has already taken place (e.g. Hantoroet al., 2020).

Research Output Over TimeSimilar to findings by Blettler et al. (2018), Indonesian plasticpollution research has been dominated by marine plasticresearch. Plastic pollution in the Indonesian marineenvironment was observed and reported starting from 1986(Willoughby, 1986), with a total of six papers that flaggedplastic pollution on Indonesia beaches being published in theperiod between 1986 and 2013. These studies were qualitative innature and did not quantify the plastics which were observed.Papers that quantified plastic pollution started to bepublished around the year 2013 (Figure 1). Since 2013, 77papers on plastic pollution were published in peer reviewedjournals, of which 67 were focused on the marineenvironment. Studies on plastic pollution in the riverineenvironment started being published in 2018, with 18studies quantifying riverine plastic pollution. Theterrestrial environment is the least studied system, withonly four studies having been identified, all of which werepublished since 2019.

The focus on plastic pollution in the marine environment canbe explained the impacts it may have on the tourism sector and onthe possible human health risks posed by contaminated sea food.

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929073

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

Marine plastic pollution can negatively impact revenue frombeach tourism (Jang et al., 2014; Petten et al., 2020).Furthermore, microplastic is considered a novel contaminantexpected to pose food safety risks due to consumption of coastalseafood, i.e. bivalves, shellfish and fish (Hantoro et al., 2019).Accordingly, several studies have found microplasticscontamination in commercial edible fishes and bivalves inIndonesia (Rochman et al., 2015; Khoironi et al., 2018; Hastutiet al., 2019; Cordova et al., 2020).

To better understand potential sources of plastic pollution,more research is needed to determine the type and sources ofpollution in the riverine and terrestrial systems of Indonesia.Rivers are widely regarded as the largest sources of marineplastics (Li et al., 2016; van Emmerik and Schwarz, 2020).Plastic pollution is in turn produced through the consumptionand improper disposal of waste on land, and is transported tothe oceans by rivers (Schmidt et al., 2017; Lebreton andAndrady, 2019; Lestari and Trihadiningrum. 2019). Here,plastic pollution is dispersed over a large volume of water,which causes the plastic pollution to be more diluted in theocean compared to plastic pollution in the riverine andterrestrial environments. Quantifying plastic pollutionearlier in its journey from land to sea allows for thequantification of more plastic while using fewer resources.We, therefore, underscore the importance of the shift towards

the monitoring of plastic pollution in the riverine andterrestrial environments.

Units of Measurement in Plastic ResearchWhile all research considered in this study quantifies plasticpollution in some capacity, the units of measurements inwhich they report their findings differ greatly. Such differencescreate difficulties when comparing data from multiple studiessince some units are not compatible with each other. Studies onmacroplastic pollution in Indonesia generally use two types ofunits to express their results in. They either express results initems per area, volume or sample, or in a mass per area, volume orsample (Table 3). While some studies report in both types of units(e.g. van Emmerik et al., 2018; Cordova and Nurhati, 2019;Cordova et al., 2021), a large part only reports in one type.

The usage of different units in macroplastic research leads totwo challenges when trying to compare data from differentstudies. First, data expressed in items per sampling unitcannot be directly converted into data expressed in mass (e.g.kg) per sampling unit. Previous studies on floating macroplasticpollution in rivers have tried to solve this issue using a conversionrate based on the average mass of macroplastics in rivers (Castro-Jiménez et al., 2019). However, this increases uncertainty in theresults due to the variability in plastic pollution characteristicsbetween different locations. A second problem relates to thesampling unit used. When ignoring the fact that data areexpressed in either items or kg, a range of sampling units isused, including macroplastic per volume, per area, and persample (Table 3). These differences stem from the use ofdifferent methods to quantify plastic pollution acrossenvironmental compartments (e.g. a sample of water isexpressed in volume while a beach sample is taken in a certainarea).

Similarly, data presented in microplastic research are difficultto compare because a wide range of sampling units are used.While most microplastic research expresses their results in termsof particles per sampling unit (Table 3), the sampling units rangefrom particles per volume, mass, and mass of tissue. Again, thesedifferences are caused by the methods that are utilized for eachenvironmental compartment: volumetric samples are mostlytaken in the water column (e.g. Cordova and Hernawan,2018), tissue samples are taken from biota (e.g. Rahmawatiand Patria, 2019), and samples based on area and/or depth aretaken from riverbanks, beaches, and from sediment at the bottomof the waterbody (e.g. Syakti et al., 2018). While these units allow

TABLE 1 | Overview of studies included in the meta-analysis sorted by environmental system and size class of plastic considered. Note, we only considered the categoriesmicroplastic (<5 mm) and macroplastic (>5 mm). Numbers are in bold to demarcate that they are totals of the numbers above.

Environmental system Number of studies Macroplastic Microplastic Macro- and microplastic

Terrestrial 3 3 0 0Riverine 10 5 5 0Marine 68 30 32 6Atmosphere 0 0 0 0Riverine + marine 1 1 0 0Terrestrial + riverine + marine 1 1 0 0Total 83 40 37 6

TABLE 2 | Overview of studies included in the meta-analysis, categorized by theenvironmental system and relevant sub-compartment that is studied. Totalsadd up to over 83 since a handful of studies quantified multiple environmentalcompartments and/or environmental systems. Note, review category includesstudies that present overviews of a subset of studies included in this papers(e.g. floating plastic in marine environments).

Compartment Marine Riverine Land Total

Floating 15 5 0 20Column 9 4 0 13Sediment 9 2 0 11Riverbank/beach 29 2 0 31Biota 7 2 0 9Mangrove 4 0 0 4Land surface 0 0 0 0Waste management 0 0 2 2Review 4 0 0 4Other 0 0 2 2Total 77 15 4 96

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929074

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

for the comparison of data between studies that examine the sameenvironmental compartment, the differences in sampling unitsdo not allow for an integrated comparison of plastic pollution inall river compartments.

Besides the size class, the differences in the presentation ofdata also hinder comparing data between differentenvironmental systems. The nature of the measurements thatare done in each system differ. For example, plastic pollution inthe marine environment is often quantified in terms ofconcentration (e.g. kg or items per sample), while plasticpollution in the riverine environment is mostly quantified in

terms of flux (e.g. kg/day, items/day) (Table 3). Thesedifferences are caused by the environmental system itselfsince rivers are often seen as a “conveyor belt” for pollutionto be transported to the oceans. It is therefore important toconsider these factors when trying to compare data between thetwo environmental systems.

Standardization of protocols is needed to allow for better datacomparison. Such a protocol should include what units should beused for reporting data in each environmental compartment. Thiswould facilitate combining and analyzing data from differentstudies on the same environmental compartments. Such analysis

FIGURE 1 | Research output on plastic pollution in Indonesia per environmental system over time. Dark blue represents studies concerning plastic pollution in themarine environment, light blue represents studies concerning pollution in the riverine environment, orange represents research studies concerning plastic pollution in theterrestrial environment, and red represents studies concerning both marine and riverine environment. Output from 1986–2009 was omitted due to incompatibility tocurrent scientific standards, output for 2020 was cut off on October 1, 2020.

TABLE 3 | Overview of units used to express plastic pollution in marine and riverine systems and each of the environmental compartments, where micro is plastic pollution<5 mm and macro is plastic pollution >5 mm. The terrestrial environment was excluded from this table due to the low number of studies performed in this system.

Ocean River

Compartment Micro Macro Micro Macro

Floating Particles/m3 Items/m2 Particles/m3 kg/yearParticles/m2 kg/100m2 particles/l tons/day

kg/surveyRiverbank/beach Particles/m3 Items/m2 - kg/m2

Particles/kg m3/m2 kg/hourkg/m2

Column particles/l Items/m3 particles/l -Particles/m3

Sediment Particles/sample kg/sample Particles/m3

Particles/kg Item/sample Particles/100 g sedimentParticles/100 g dry weight

Biota Particles/organ – Particles/fish –

Particles/animal Particles/m3

Particles/g dry weightMangrove Particles/m2 Items/kg dry weight – –

kg/m2

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929075

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

would lead to better insights into the plastic pollution problemacross Indonesia. Standardization would also allow for a moreconvenient comparison of data between different environmentalcompartments. For example, by ensuring that the mass of itemsfound is included in such a protocol, data can be expressed inboth items and kg per sampling unit.

Frequently Found Materials and ShapesA small portion of studies quantifying plastic pollution inIndonesia report polymer types of the plastic (9 out of 46 formacroplastic, 10 out of 43 for microplastic, Table 4). Whenpolymers are reported, polypropylene (PP) is the most oftenfound polymer type in both macroplastic (56%) and microplastic(90%) pollution. Polyethylene (PE), and its high- and low-densityvariants (HDPE, LDPE) are also among the most abundantplastics for both macro- and microplastic. Other polymersfound in Indonesian aquatic environments include polystyrene(PS) and expanded polystyrene (EPS).

Polymer characterization makes plastic research more labor-intensive, but should be included more frequently in plasticpollution studies. Polymer characterization is easier formacroplastic than for microplastic since certain items haveidentification codes or logos indicating what polymer typesthey are made of. Besides, macroplastic characterization can besimplified by grouping difficult to distinguish polymers, or byusing an item list that indicates what polymers items are mostfrequently made of (e.g. van Emmerik et al., 2018; Vriend et al.,2020). Microplastic polymers are often characterized using a formof spectroscopy (e.g. Fourier transform infrared, Raman) andthermal analysis (e.g. py-GC-MS), which greatly increases thelabor required to gather data (Shim et al., 2017). Thecharacterization of polymers is one of the few ways tocompare macroplastic and microplastic presence directly.Besides, polymer types may give an indication of possiblesources of plastic pollution. Polymer characterization shouldtherefore be encouraged to be included in studies on plasticpollution in Indonesia more often.

More than half of the studies that studied microplasticpollution characterized the shape of the particles (24 out of43, Table 5). This is in line with the fraction of globalmicroplastic studies that report shapes found by Koelmanset al. (2019). Among the top three most abundant particles,shapes that are more frequently found are fragments (71%),fibers (63%), and films (46%). Shapes that are less frequently

found among the top three most abundant shapes are granulesand foams (both 21%). The shape of particles can be an indicationof the possible sources of the microplastic, though theapplicability of this is still limited. Several potential sources ofparticular shapes of microplastic particles have been studied byFree et al. (2014). However, no studies considered in this meta-analysis tried to identify sources based on the shape of particles.Moreover, Kooi and Koelmans (2019) argue that the shape ofparticles is continuous, and therefore no classification will be ableto accurately capture the full variability of shapes. One of theparticular reasons for this situation is complex degradationmechanisms (photodegradation, mechanical-physical,weathering, even biodegradation) that continuously occur innature, which may breakdown larger plastics intomicroplastics (Kooi and Koelmans, 2019).

Locations of StudiesPlastic research for all size classes and environmental systems ishighly localized on Java Island, especially for riverine andterrestrial focused studies (Figure 2). Studies that quantifyplastic pollution in the marine environment are more evenlyspread across Indonesia, though Java Island is still represented inalmost half of all studies (32 out of 67) focused on marine plasticpollution in seas near Java. Studies quantifying plastic pollution inrivers are either performed on Java (14 out of 15) or Bali Islands(1 out of 15). The same goes for terrestrial focused studies, with sofar only three being done on Java and one on Bali Islands.

Although a larger spread would be ideal, this strong focus onJava Island is reasonable since it houses a large part of theIndonesian population. Lebreton et al. (2017) identified Javaand Sumatra Islands to be areas of concern with theirestimates predicting these islands to be responsible for 14.2%of global annual plastic exports to the oceans. More recently,Meijer et al. (2021) identify 51 rivers on Java Island to be amongthe global top 1,000 most polluting river. However, Java is not theonly Indonesian island with high rates of plastic pollution. Datafrom all Indonesian islands are required to design and prioritizereduction and mitigation strategies, requiring a larger spatialspread of studies.

Another factor that could explain the research focus on Java isthe location of Indonesian institutes that research plasticpollution. Many of these institutes are located on Java island,especially in the Jakarta metropolitan area (Figure 3). BesidesJava, institutes with relatively large plastic research output are

TABLE 4 |Count of polymers found in top three most abundant polymers per study, with abbreviations for the following polymer types: polypropylene (PP), polystyrene (PS),low density polyethylene (LDPE), expanded polystyrene (EPS), polyethylene terephthalate (PET), polyethylene (PE), high density polyethylene (HDPE), and polyamide(also known as nylon, PA).

Studiesthat

reportedpolymers

Percentage of studies that present polymer types in top 3 frequently found polymers

PP (%) PS (%) LDPE (%) EPS (%) PET (%) PE (%) PA (%) HDPE (%)

Macro (n � 46) 9 56 33 33 22 11 22 0 11Micro (n � 43) 10 90 20 30 10 0 40 20 0

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929076

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

located on Sumatra, Bali, and Sulawesi Islands, and the city ofMakassar (Figure 3). When comparing the locations of theseinstitutes with the numbers of studies aggregated to the regionallevel (Figure 2), it can be concluded that regions with largeamounts of studies coincide with the locations of specializedinstitutes, indicating that research is mostly done close to theseinstitutes.

Future Plastic Pollution ResearchDirections in IndonesiaBased on the biases and gaps identified in the meta-analysis, wepropose four directions for future research: 1) Standardization ofresearch methods, 2) expansion of environmental system focus,3) expansion in spatial coverage, and 4) expansion in plasticcharacterization methods. These suggestions aim to ensurereliable and intercomparable data on plastic pollution inIndonesia, which can aid the design of plastic removal andmitigation strategies.

Harmonization of Research Methods andDataWe recommend establishing standard research methods for eachenvironmental system and sub-compartment in Indonesia.Standardizing methods ensures homogeneity in the datagathered and shared by different studies. Current methodsdiffer per study, geographical area, and research group, whichcauses data to be expressed in different units of measurement andplastic items to be categorized differently. This complicates thecomparison of data between studies. Standardized methods canalleviate this problem and would supply easier to interpret datafor policy makers, which will hopefully lead to tailored mitigationand removal strategies. Methods that can be employed to easeharmonization of research methods include the expression ofdata in directly convertible units (Hidalgo-Ruz et al., 2012; Foket al., 2020), or the set-up of plastic research hubs to fostercollaboration (Nel et al., 2021).

Another avenue of harmonization that can be explored is thesetting of central research questions which have to be answeredby the research community and linking these to possible researchmethods (e.g. van Emmerik and Vriend. 2021). For example, theIndonesian government could set out a couple of key researchquestions that they need to have answered in order to implementeffective plastic pollution mitigation and reduction strategies.Such question could explore concepts such as determining thecurrent stock of plastic in each environmental system,quantification of the amount of plastic pollution that enterseach environment, and the quantification of plastic pollution

that is exported to the oceans. By setting out their data needs andtheir preferred data format, the Indonesian government ensuresthat research from different parties meet the same standards, andare, therefore, intercomparable.

We suggest a national Indonesian scientific authority to setthese standard methods in collaboration with local andinternational experts. First efforts for standardization havebeen recently published by the Indonesian Institute of Sciences(LIPI) (Nurhati and Cordova, 2020). Moreover, three institutions(LIPI, DCA, and Universitas Padjadjaran) have built marinedebris database to centralize data (https://marinedebris.id). Werecommend this process to be further expanded for methodstandardization and data harmonization of plastic in allenvironmental systems and sub-compartments.

Expansion of Environmental System FocusA shift in research prioritization on specific environmentalsystems is required to get an accurate overview of plasticpollution in Indonesia. In the current form, plastic researchmainly focuses on the marine environment, which is in linewith global research trends (Blettler et al., 2018). However,plastic pollution abundance in the marine environment isdiluted compared to riverine pollution. For example,macroplastic pollution concentrations on riverbanks inIndonesia found in this meta-analysis ranged between 0.007and 0.029°kg/m2, or 7,000–29000°kg/km2 (Owens and Kamil.2020; Widyarsana et al., 2020), while concentrations of floatingmacroplastics in the great pacific garbage patch are estimatedto range between 10–100°kg/km2 (Lebreton et al., 2018). Suchdilution makes the determination of possible sources, and theremoval of plastic pollution more difficult. Therefore,knowledge on plastic pollution transport earlier in itspresence is important for the design of effective removaland mitigation strategies. The research focus should,therefore, be moved higher up in the transport chain,ideally at the source, as well.

The focus of future research should also diversify in terms ofcompartments within environmental systems. The meta-analysisshows that specific compartments within environmental systemare studied more than others (e.g. beaches in the marineenvironment, floating and riverbank in the riverineenvironment). This is mainly due to these compartments beingmore accessible and having easy to apply methods. However, onlyquantifying plastic pollution in these compartments gives a biasedview of the problem. Therefore, we recommend to keep observingpollution in these compartments while also expanding to lesserstudied compartments such as sub-surface plastics in the marineand riverine environments, and surface pollution in the terrestrialenvironment.

TABLE 5 | Count of microplastic shapes found in the top three most abundant shapes per study.

Percentage of studies that present each shape in the top 3 most abundant shapes

Reported shape Fragment (%) Fiber (%) Film (%) Granule (%) Foam (%)

Micro (n � 43) 24 71 63 46 21 21

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929077

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

Environmental system focus can also be further diversified bystudying the time scales that plastic pollution resides in a certainenvironment. We envision time scales plastic pollution to be

studied through two ways. First, historic concentrations of plasticpollution should be studied. Data on historic concentrations canhelp explain how plastic pollution developed in the past decades.

FIGURE 2 | Number of plastic pollution studies performed in Indonesia aggregated to sub-regions, where (A). depicts marine focused literature (land mass closestto research area), (B). depicts studies focused on rivers literature, and (C). represents land focused research.

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929078

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

Such context can be used to suggest ways to reduce plasticpollution in the future. Such data can be gathered by studyingmicroplastic concentrations in sediment cores (e.g. Turner et al.,2019) or through studying use-by dates on accumulatedmacroplastic pollution (e.g. Tramoy et al., 2020). The secondtime scale that should be included in future research is time thatplastic pollution spends in each environmental system. A recentstudy by Tramoy et al. (2020) has shown that retention times ofplastic pollution in estuaries may exceed decades, and research byOlivelli et al. (2020) points at coastal margins and backshores as amajor sink for marine debris. Knowing where plastic pollutionaccumulates for longer periods of time can aid the design oftargeted strategies for removal of it from the environment.Therefore, including these temporal dynamics in plasticpollution will results in better informed intervention strategiesfor plastic pollution.

Expansion in Spatial CoveragePlastic research in all environmental systems should have abroader spatial coverage in Indonesia. While plastic pollutionhas been quantified at least once in places with high populationdensities, research is biased toward Java Island. This bias is morepronounced in riverine and terrestrial research where all but onestudy has been performed on Java Island. While Java Island ispredicted to have a considerable contribution towards plasticexports to the ocean by models (e.g. Lebreton et al., 2017), data onplastic pollution in all of Indonesia’s geographic areas arerequired in order to set priorities for mitigation and removalstrategies. We, therefore, recommend expanding the spatialcoverage to all major islands of Indonesia, while keepingresearch focus on areas with predicted high pollution ratessuch as Java and Sumatra Islands. Additionally, Purba et al.(2021) emphasize that plastic pollution is a transboundaryissue in south-east Asian countries. We therefore also suggest

that research should expand to boundary seas. Indonesia has sixsurrounding countries, and more collaboration is needed tomitigate plastic pollution. Increasing insight into how plasticpollution transboundary patterns would help stress theurgency and direction of this transnational collaboration.

Expansion in Plastic CharacterizationMethodsWe recommend both macro- and microplastic characterizationto be expanded by performing research on both size categories atthe same location. 77 out of 83 studies in this meta-analysischaracterize just one plastic size category (macro- ormicroplastic). Integrating macro- and microplastic research atthe same location allows for comparisons to be made between thetwo size classes. This would, in turn, allow for more accuratedetermination of possible sources of plastic pollution, andprovide insights in the relation between presence of macro-and microplastic. Such insights could allow for macroplasticresearch to act as a proxy for microplastic pollution andreduce the need for microplastic research, possibly savingvaluable time and resources (Vriend et al., 2020). Howeverstudies on microplastics occurence and distribution might stillbe of value since they can portray the past behavior of thecommunity in plastic use and disposal.

Characterization methods can be further expanded byincluding polymer analysis more frequently. 19 out of 83studies considered in this meta-analysis characterized plasticpolymers found. Increasing the number of studies that identifypolymers allows for data to be more easily compared betweendifferent environmental systems, compartments, and size classes.This data can in turn be used for the design of more targetedmitigation and removal strategies. We, therefore, recommendincreasing the frequency of polymer analysis in future research.

FIGURE 3 | Location of institutes that published on plastic pollution in Indonesia, and the number of publications they (co-) authored, where red circles indicate onestudy, green triangle represents two studies, blue square represents three studies, blue pentagon represents four to five studies, and the yellow start represents six toseven studies (co-) published per institute.

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 6929079

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

CONCLUSION

Indonesia is suspected to be among the top plastic pollutingcountries in the world. A large body of research has beenpublished that quantifies plastic pollution with the aim tofacilitate the design of effective mitigation and removalstrategies. In this study we perform a meta-analysis of thisbody of literature to identify research biases and gaps, withthe goal to streamline future research.

The majority of the research output on plastic pollution inIndonesia has focused on the marine environment (70 out of 83studies), with first efforts to quantify plastic pollution in otherenvironmental systems (riverine and terrestrial environments)recently being undertaken on Java Island. Research withinenvironmental systems is biased toward compartments thatare easy to access and have already established researchmethods. These compartments include the beach for marineplastic pollution, and floating and riverbank plastics forriverine plastic pollution. Considering research output since2010, macroplastic pollution has been studied more frequentlythan microplastics (43 and 40 studies respectively), and researchwithin environmental systems is biased toward a size class as well.For example, microplastic is mostly characterized in the marineenvironment, while macroplastic is mostly studied in the riverineenvironment. Methods, and with it the measurement units inwhich data is expressed, vary widely between studies, whichcomplicates comparison between studies. Last, the plasticresearch focus is highly area focused, with almost half of allstudies being focused on Java Island.

We recommend four good practices for future research whichcan provide data that can aid the Indonesian government withdesigning monitoring strategies to reduce plastic pollution moreeffectively. These being 1) the harmonization of research

methods, and therefore units used, for each environmentalsystems and sub-compartments across Indonesia, 2) a shift inresearch focus expanding beyond the marine environmenttoward riverine and terrestrial plastic pollution research, 3) anexpansion in spatial coverage to ensure more representativeresearch taking place in the whole of Indonesia, and 4) anexpansion in methods used to characterize plastic pollution,especially in terms of polymer type.

AUTHOR CONTRIBUTIONS

PV, TvE, and HH conceived the idea. PV performed the literaturesearch, extracted data from the identified literature, performedthe data analysis, and prepared the initial draft. All authorsidentified missing literature and wrote the final manuscript.

ACKNOWLEDGMENTS

The work of TvE is supported by the Veni research program TheRiver Plastic Monitoring Project with project number 18211,which is (partly) financed by the Dutch Research Council(NWO). This work has been done as part of the Post-PlasticParadise Project, funded by the ANGIN program of the RoyalNetherlands Academy of Arts and Sciences.

SUPPLEMENTARY MATERIAL

The SupplementaryMaterial for this article can be found online at:https://www.frontiersin.org/articles/10.3389/fenvs.2021.692907/full#supplementary-material

REFERENCES

Blettler, M. C. M., Abrial, E., Khan, F. R., Sivri, N., and Espinola, L. A. (2018).Freshwater Plastic Pollution: Recognizing Research Biases and IdentifyingKnowledge Gaps. Water Res. 143, 416–424. doi:10.1016/j.watres.2018.06.015

Borrelle, S. B., Ringma, J., Law, K. L., Monnahan, C. C., Lebreton, L., McGivern,A., et al. (2020). Predicted Growth in Plastic Waste Exceeds Efforts toMitigate Plastic Pollution. Science 369 (6510), 1515–1518. doi:10.1126/science.aba3656

Castro-Jiménez, J., González-Fernández, D., Fornier, M., Schmidt, N., andSempéré, R. (2019). Macro-litter in Surface Waters from the Rhone River:Plastic Pollution and Loading to the NW Mediterranean Sea. Mar. Pollut. Bull.146, 60–66. doi:10.1016/j.marpolbul.2019.05.067

Chowdhury, G. W., Koldewey, H. J., Duncan, E., Napper, I. E., Niloy, M. N. H.,Nelms, S. E., et al. (2020). Plastic Pollution in Aquatic Systems in Bangladesh: AReview of Current Knowledge. Amsterdam, Netherlands: Science of The TotalEnvironment, 143285.

Conchubhair, D. Ó., Fitzhenry, D., Lusher, A., King, A. L., van Emmerik, T.,Lebreton, L., et al. (2019). Joint Effort Among Research Infrastructures toQuantify the Impact of Plastic Debris in the Ocean. Environ. Res. Lett. 14 (6),065001. doi:10.1088/1748-9326/ab17ed

Cordova, M. R., and Hernawan, U. E. (2018). “Microplastics in SumbaWaters, East Nusa Tenggara”, in IOP Conference Series: Earth andEnvironmental Science (Bristol, United Kingdom: IOP Publishing),Vol. 162, 1012023.

Cordova, M. R., and Nurhati, I. S. (2019). Major Sources and MonthlyVariations in the Release of Land-Derived marine Debris from theGreater Jakarta Area, Indonesia. Scientific Rep. 9 (1), 1–8. doi:10.1038/s41598-019-55065-2

Cordova, M. R., and Wahyudi, A. a. J. (2016). Microplastic in the Deep-SeaSediment of Southwestern SumatranWaters.Mar. Res. Indonesia 41 (1), 27–35.doi:10.14203/mri.v41i1.99

Cordova, M. R., Riani, E., and Shiomoto, A. (2020). Microplastics Ingestion by BluePanchax Fish (Aplocheilus sp.) from Ciliwung Estuary, Jakarta, Indonesia.Mar.Pollut. Bull., 161, 111763. doi:10.1016/j.marpolbul.2020.111763

Cordova, M. R., Nurhati, I. S., Riani, E., Nurhasanahand Iswari, M. Y.(2021). Unprecedented Plastic-Made Personal Protective Equipment(PPE) Debris in River Outlets into Jakarta Bay during COVID-19Pandemic. Chemosphere, 268, 129360. doi:10.1016/j.chemosphere.2020.129360

DIVA-GIS (n.a.). Indonesia – Administrative Areas. via: http://www.diva-gis.org/gData. (Accessed on 16-10-2020).

Fok, L., Lam, T. W. L., Li, H.-X., and Xu, X.-R. (2020). A Meta-Analysis ofMethodologies Adopted by Microplastic Studies in China. Sci. Total Environ.718, 135371. doi:10.1016/j.scitotenv.2019.135371

Free, C. M., Jensen, O. P., Mason, S. A., Eriksen, M., Williamson, N. J., andBoldgiv, B. (2014). High-levels of Microplastic Pollution in a Large,Remote, mountain lake. Mar. Pollut. Bull. 85, 156–163. doi:10.1016/j.marpolbul.2014.06.001

Gall, S. C., and Thompson, R. C. (2015). The Impact of Debris on marine Life.Mar.Pollut. Bull. 92 (1-2), 170–179. doi:10.1016/j.marpolbul.2014.12.041

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 69290710

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

González-Fernández, D., and Hanke, G. (2017). Toward a HarmonizedApproach for Monitoring of Riverine Floating Macro Litter Inputs tothe marine Environment. Front. Mar. Sci. 4, 86. doi:10.3389/fmars.2017.00086

Hantoro, I., Löhr, A. J., Van Belleghem, F. G. A. J., Widianarko, B., and Ragas, A. M.J. (2019). Microplastics in Coastal Areas and Seafood: Implications for FoodSafety. Food Addit. & Contam.: A 36 (5), 674–711. doi:10.1080/19440049.2019.1585581

Hantoro, I., Widianarko, Y. B., and Retnaningsih, C. (2020). Protokol HW1-TPUNIKA: Metode Deteksi Dan Identifikasi Mikroplastik Dengan ATR-FTIRMikroskopi Pada Sampel Hasil Laut. Yogyakarta: Wahana ResolusiUnikaRepository.

Hastuti, A. R., Lumbanbatu, D. T., and Wardiatno, Y. (2019). The Presence ofMicroplastics in the Digestive Tract of Commercial Fishes off Pantai IndahKapuk Coast, Jakarta, Indonesia. Biodiversitas J. Biol. Divers. 20 (5), 1233–1242.doi:10.13057/biodiv/d200513

Hidalgo-Ruz, V., Gutow, L., Thompson, R. C., and Thiel, M. (2012). Microplasticsin the marine Environment: a Review of the Methods Used for Identificationand Quantification. Environ. Sci. Technol. 46 (6), 3060–3075. doi:10.1021/es2031505

Honingh, D., van Emmerik, T., Uijttewaal, W., Kardhana, H., Hoes, O., and van deGiesen, N. (2020). Urban River Water Level Increase through Plastic WasteAccumulation. Front. Earth Sci. 8, 28. doi:10.3389/feart.2020.00028

Jang, Y. C., Hong, S., Lee, J., Lee, M. J., and Shim, W. J. (2014). Estimation of LostTourism Revenue in Geoje Island from the 2011 marine Debris Pollution Eventin South Korea. Mar. Pollut. Bull. 81 (1), 49–54. doi:10.1016/j.marpolbul.2014.02.021

Khoironi, A., Anggoro, S., and Sudarno (2018). “The Existence of Microplastic inAsian green Mussels”, in IOP Conference Series: Earth and EnvironmentalScience (Bristol, United Kingdom: IOP Publishing), 131, 1012050. doi:10.1088/1755-1315/131/1/012050

Koelmans, A. A., Besseling, E., Foekema, E., Kooi, M., Mintenig, S., Ossendorp, B.C., et al. (2017). Risks of Plastic Debris: Unravelling Fact, Opinion, Perception,and Belief. Washington, D.C.: ACS Publications.

Koelmans, A. A., Mohamed Nor, N. H., Hermsen, E., Kooi, M., Mintenig, S. M.,and De France, J. (2019). Microplastics in Freshwaters and Drinking Water:Critical Review and Assessment of Data Quality. Water Res. 155, 410–422.doi:10.1016/j.watres.2019.02.054

Kooi, M., and Koelmans, A. A. (2019). Simplifying Microplastic via ContinuousProbability Distributions for Size, Shape, and Density. Environ. Sci. Technol.Lett. 6 (9), 551–557. doi:10.1021/acs.estlett.9b00379

Lasut, M. T., Weber, M., Pangalila, F., Rumampuk, N. D. C., Rimper, J. R. T. S. L.,Warouw, V., et al. (2018). “FromCoral Triangle to Trash Triangle-How the HotSpot of Global Marine Biodiversity Is Threatened by Plastic Waste,” inProceedings of the International Conference on Microplastic Pollution inthe Mediterranean Sea. Cham: Springer, 107–113. doi:10.1007/978-3-319-71279-6_15

Lau, W. W. Y., Shiran, Y., Bailey, R. M., Cook, E., Stuchtey, M. R., Koskella, J., et al.(2020). Evaluating Scenarios toward Zero Plastic Pollution. Science 369 (6510),1455–1461. doi:10.1126/science.aba9475

Lebreton, L., and Andrady, A. (2019). Future Scenarios of Global Plastic WasteGeneration and Disposal. Palgrave Commun. 5 (1), 1–11. doi:10.1057/s41599-018-0212-7

Lebreton, L. C., Van Der Zwet, J., Damsteeg, J. W., Slat, B., Andrady, A., andReisser, J. (2017). River Plastic Emissions to theWorld’s Oceans.Nat. Commun.8, 15611. doi:10.1038/ncomms15611

Lebreton, L., Slat, B., Ferrari, F., Sainte-Rose, B., Aitken, J., Marthouse, R., et al.(2018). Evidence that the Great Pacific Garbage Patch Is Rapidly AccumulatingPlastic. Scientific Rep. 8 (1), 1–15. doi:10.1038/s41598-018-22939-w

Lestari, P., and Trihadiningrum, Y. (2019). The Impact of Improper Solid WasteManagement to Plastic Pollution in Indonesian Coast and marineEnvironment. Mar. Pollut. Bull. 149, 110505. doi:10.1016/j.marpolbul.2019.110505

Li, W. C., Tse, H. F., and Fok, L. (2016). Plastic Waste in the marine Environment:A Review of Sources, Occurrence and Effects. Sci. Total Environ. 566-567,333–349. doi:10.1016/j.scitotenv.2016.05.084

Meijer, L. J. J., van Emmerik, T., van der Ent, R., Schmidt, C., and Lebreton, L.(2021). More Than 1000 Rivers Account for 80% of Global Riverine Plastic

Emissions into the Ocean. Sci. Adv. 7 (18). eaaz5803. doi:10.1126/sciadv.aaz5803

Michida, Y., Chavanich, S., Chiba, S., Cordova, M. R., Cozsar Cabanas, A., Glagani,F., et al. (2019). Guidelines For Harmonizing Ocean Surface MicroplasticMonitoring Methods. Version 1.1. Chiyoda-ku, Tokyo, Japan: Ministry ofthe Environment Japan. doi:10.25607/OBP-867

Nel, H. A., Naidoo, T., Akindele, E. O., Nhiwatiwa, T., Fadare, O. O., and Krause, S.(2021). Collaboration and Infrastructure Is Needed to Develop an AfricanPerspective on Micro (Nano) Plastic Pollution. Environ. Res. Lett. 16 (2),021002. doi:10.1088/1748-9326/abdaeb

Nurhati, I. S., and Cordova, M. R. (2020). Marine Plastic Debris in Indonesia:Baseline Estimates (2010-2019) and Monitoring Strategy (2021-2025). Mar.Res. Indonesia 45 (2), 1–6. doi:10.14203/mri.v45i2.581

Olivelli, A., Hardesty, B. D., and Wilcox, C. (2020). Coastal Margins andBackshores Represent a Major Sink for marine Debris: Insights from acontinental-scale Analysis. Environ. Res. Lett. 15 (7), 074037. doi:10.1088/1748-9326/ab7836

OSPAR Commission (2010). Guideline for Monitoring Marine Litter on theBeachers in the OSPAR Maritime Area. London: OSPAR commission.

Owens, K. A., and Kamil, P. I. (2020). Adapting Coastal Collection Methods forRiver Assessment to Increase Data on Global Plastic Pollution: Examples fromIndia and Indonesia. Front. Environ. Sci. 7, 208. doi:10.3389/fenvs.2019.00208

Pawar, P. R., Shirgaonkar, S. S., and Patil, R. B. (2016). Plastic marine Debris:Sources, Distribution, and Impacts on Coastal and Ocean Biodiversity. PENCILPubl. Biol. Sci. 3 (1), 40–54.

Petten, L., Schalekamp, J., Viool, V., and Gupta, A. (2020). The price Tag of PlasticPollution – an Economic Assessment of River Plastic. Amsterdam: Deloitte. via:https://www2.deloitte.com/nl/nl/pages/strategy-analytics-and-ma/articles/the-price-tag-of-plastic-pollution.html. (Accessed on 04-11-2020).

Purba, N. P., Handyman, D. I. W., Pribadi, T. D., Syakti, A. D., Pranowo, W. S.,Harvey, A., et al. (2019). Marine Debris in Indonesia: A Review of Research andStatus. Mar. Pollut. Bull. 146, 134–144. doi:10.1016/j.marpolbul.2019.05.057

Purba, N., Faizal, I., Cordova, M., Abimanyu, A., Afandi, N., Indriawan, D., et al.(2021). Marine Debris Pathway across Indonesian Boundary Seas. J. Ecol. Eng.22 (3), 82–98. doi:10.12911/22998993/132428

Rahmawati, N. H., and Patria, M. P. (2019). “Microplastics Dissemination fromFish Mugil Dussumieri and Mangrove Water of Muara Teluknaga, Tangerang,Banten,” in Journal of Physics: Conference Series (Bristol, United Kingdom:IOP Publishing), 1282, 1012104. doi:10.1088/1742-6596/1282/1/012104

Rochman, C. M., Tahir, A., Williams, S. L., Baxa, D. V., Lam, R., Miller, J. T., et al.(2015). Anthropogenic Debris in Seafood: Plastic Debris and Fibers fromTextiles in Fish and Bivalves Sold for Human Consumption. Scientific Rep.5, 14340. doi:10.1038/srep14340

Schmidt, C., Krauth, T., and Wagner, S. (2017). Export of Plastic Debris by Riversinto the Sea. Environ. Sci. Technol. 51 (21), 12246–12253. doi:10.1021/acs.est.7b02368

Shim, W. J., Hong, S. H., and Eo, S. E. (2017). Identification Methods inMicroplastic Analysis: a Review. Anal. Methods 9 (9), 1384–1391. doi:10.1039/c6ay02558g

Spalding, M., Spalding, M. D., Ravilious, C., and Green, E. P. (2001).World Atlas ofCoral Reefs. Oakland, CA Univ of California Press.

Syakti, A. D., Bouhroum, R., Hidayati, N. V., Koenawan, C. J., Boulkamh, A.,Sulistyo, I., et al. (2017). Beach Macro-Litter Monitoring and FloatingMicroplastic in a Coastal Area of Indonesia. Mar. Pollut. Bull. 122 (1-2),217–225. doi:10.1016/j.marpolbul.2017.06.046

Syakti, A. D., Hidayati, N. V., Jaya, Y. V., Siregar, S. H., Yude, R., Suhendy, L., et al.(2018). Simultaneous Grading of Microplastic Size Sampling in the SmallIslands of Bintan Water, Indonesia. Mar. Pollut. Bull. 137, 593–600. doi:10.1016/j.marpolbul.2018.11.005

Tomascik, T., Mah, A. J., Nontji, A., and Moosa, K. M. (1997). The Ecology of theIndonesian Seas. Oxford, England: Oxford University Press.

Tramoy, R., Gasperi, J., Colasse, L., and Tassin, B. (2020). Transfer Dynamic ofMacroplastics in Estuaries - New Insights from the Seine Estuary: Part 1. LongTerm Dynamic Based on Date-Prints on Stranded Debris. Mar. Pollut. Bull.152, 110894. doi:10.1016/j.marpolbul.2020.110894

Turner, S., Horton, A. A., Rose, N. L., and Hall, C. (2019). A Temporal SedimentRecord of Microplastics in an Urban lake, London, UK. J. Paleolimnol 61 (4),449–462. doi:10.1007/s10933-019-00071-7

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 69290711

Vriend et al. Meta-Analysis Plastic Pollution Indonesia

Uneputty, P., and Evans, S. M. (1997). The Impact of Plastic Debris on the Biota ofTidal Flats in Ambon Bay (Eastern Indonesia). Mar. Environ. Res. 44 (3),233–242. doi:10.1016/s0141-1136(97)00002-0

van Calcar, C. J., and van Emmerik, T. H. M. (2019). Abundance of Plastic Debrisacross European and Asian Rivers. Environ. Res. Lett. 14 (12), 124051. doi:10.1088/1748-9326/ab5468

Emmerik, T., and Schwarz, A. (2020). Plastic Debris in Rivers.WIREs Water 7 (1),e1398. doi:10.1002/wat2.1398

van Emmerik, T., and Vriend, P. (2021). Roadmap Litter Monitoring in DutchRivers. Wageningen, Netherlands: Wageningen University & Research. doi:10.18174/537439

van Emmerik, T., Kieu-Le, T. C., Loozen, M., van Oeveren, K., Strady, E., Bui,X. T., et al. (2018). A Methodology to Characterize Riverine MacroplasticEmission into the Ocean. Front. Mar. Sci. 5, 372. doi:10.3389/fmars.2018.00372

van Emmerik, T., Loozen, M., Van Oeveren, K., Buschman, F., and Prinsen, G.(2019). Riverine Plastic Emission from Jakarta into the Ocean. Environ.Res. Lett. 14 (8), 084033. doi:10.1088/1748-9326/ab30e8

Vriend, P., Roebroek, C. T. J., and van Emmerik, T. (2020). Same butDifferent: A Framework to Design and Compare Riverbank PlasticMonitoring Strategies. Front. Water 2, 31. doi:10.3389/frwa.2020.563791

Widyarsana, I. M. W., Damanhuri, E., Ulhusna, N., and Agustina, E. (2020). “APreliminary Study: Identification of Stream Waste Quantity and Compositionin Bali Province, Indonesia,” in E3S Web of Conferences (Paris, France: EDPSciences), Vol. 148, 05005.

Willoughby, N. G. (1986). Man-made Litter on the Shores of the Thousand IslandArchipelago, Java. Mar. Pollut. Bull. 17 (5), 224–228. doi:10.1016/0025-326x(86)90605-3

Conflict of Interest: KA is employed by the World Resources Institute.

The remaining authors declare that the research was conducted in the absence ofany commercial or financial relationships that could be construed as a potentialconflict of interest.

Copyright © 2021 Vriend, Hidayat, van Leeuwen, Cordova, Purba, Löhr, Faizal,Ningsih, Agustina, Husrin, Suryono, Hantoro, Widianarko, Lestari, Vermeulen andvan Emmerik. This is an open-access article distributed under the terms of theCreative Commons Attribution License (CC BY). The use, distribution orreproduction in other forums is permitted, provided the original author(s) andthe copyright owner(s) are credited and that the original publication in this journal iscited, in accordance with accepted academic practice. No use, distribution orreproduction is permitted which does not comply with these terms.

Frontiers in Environmental Science | www.frontiersin.org June 2021 | Volume 9 | Article 69290712

Vriend et al. Meta-Analysis Plastic Pollution Indonesia