PLASTIC POLLUTION RESEARCH IN INDONESIA: STATE OF SCIENCE AND FUTURE RESEARCH DIRECTIONS TO REDUCE IMPACTS - EARTHARXIV
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REVIEW
published: 08 June 2021
doi: 10.3389/fenvs.2021.692907
Plastic Pollution Research in
Indonesia: State of Science and Future
Research Directions to Reduce
Impacts
Paul Vriend 1,2*, H. Hidayat 2, J. van Leeuwen 3, M. R. Cordova 4, N. P. Purba 5, A. J. Löhr 6,
I. Faizal 5, N. S. Ningsih 6, K. Agustina 7, S. Husrin 8, D. D. Suryono 8, I. Hantoro 6,9,
B. Widianarko 9, P. Lestari 10,11, B. Vermeulen 1 and Tim van Emmerik 1
1
Hydrology and Quantitative Water Management Group, Wageningen University and Research, Wageningen, Netherlands,
2
Research Center for Limnology, Indonesian Institute of Sciences (LIPI), Bogor, Indonesia, 3Wageningen University,
Environmental Policy Group, Hollandseweg 1, Wageningen, Netherlands, 4Research Center for Oceanography, Indonesian
Institute of Sciences (LIPI), Jl. Pasir Putih 1 Ancol, Jakarta, Indonesia, 5Department of Marine Science, Faculty of Fishery and
Marine Science, Universitas Padjadjaran, Bandung, Indonesia, 6Oceanography Research Group, Faculty of Earth Sciences and
Technology, Bandung Institute of Technology, Bandung, Indonesia, 7The National Plastic Action Partnership, World Resources
Institute (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 Planning
Edited by: and Geo Engineering, Sepuluh Nopember Institute of Technology, Surabaya, Indonesia, 11Department of Agricultural and
Anabela Cachada, Biosystems Engineering, Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia
University of Porto, Portugal
Reviewed by:
Veerasingam S, Several studies have suggested Indonesia to be among the top plastic polluting countries
Qatar University, Qatar globally. Data on the presence and amounts of plastic pollution are required to help design
Kai Zhang,
effective plastic reduction and mitigation strategies. Research quantifying plastic pollution in
City University of Hong Kong, China
Indonesia has picked up in recent years. However, a lack of central coordination in this
*Correspondence:
Paul Vriend research has led to research output with different goals, methods, and data formats. In this
Paul.vriend@wur.nl study we present a meta-analysis of studies published on plastic pollution in Indonesia to
uncover gaps and biases in current research, and to use these insights to suggest ways to
Specialty section:
This article was submitted to improve future research to fill these gaps. Research gaps and biases identified include a clear
Toxicology, Pollution and the preference for marine research, and a bias toward certain environmental compartments within
Environment,
the marine, riverine, and terrestrial systems that have easy to apply methods. Units of
a section of the journal
Frontiers in Environmental Science measurement used to express results vary greatly between studies, making it difficult to
Received: 09 April 2021 compare data effectively. Nevertheless, we identify polypropylene (PP) and polyethylene
Accepted: 17 May 2021 variants (PE, HDPE, LDPE) to be among the most frequently found polymers in both
Published: 08 June 2021
macro- and microplastic pollution in Indonesia, though polymer identification is lacking in a
Citation:
Vriend P, Hidayat H, van Leeuwen J, large part of the studies. Plastic research is mostly done on Java (59% of the studies). We
Cordova MR, Purba NP, Löhr AJ, recommend research methods used to quantify plastic pollution to be harmonized. Moreover,
Faizal I, Ningsih NS, Agustina K,
we recommend a shift in focus of research toward the riverine and terrestrial environments and
Husrin S, Suryono DD, Hantoro I,
Widianarko B, Lestari P, Vermeulen B a shift of focus of environmental compartments analyzed within these systems, an increase in
and van Emmerik T (2021) Plastic spatial coverage of research across Indonesia, and lastly, a larger focus on polymer
Pollution Research in Indonesia: State
of Science and Future Research characterization. With these changes we envision future research which can aid with the
Directions to Reduce Impacts. design of more effective and targeted reduction and mitigation strategies.
Front. Environ. Sci. 9:692907.
doi: 10.3389/fenvs.2021.692907 Keywords: macroplastic, microplastic, indonesia, litter, marine, river, pollution, review
Frontiers in Environmental Science | www.frontiersin.org 1 June 2021 | Volume 9 | Article 692907
Vriend et al. Meta-Analysis Plastic Pollution Indonesia
INTRODUCTION widely in the methods that are used. To gather reliable and
frequent data, a nationally coordinated monitoring strategy is
Plastic pollution has been a topic of rising environmental concern required which, in turn, will form the basis for prioritizing and
in recent years. Model estimates show that between 0.8 and 30 designing effective plastic pollution reduction and mitigation
million metric tonnes of plastic waste enter the aquatic strategies. An overview of the current knowledge and research
environment annually around the globe (Borrelle et al., 2020; gaps and biases is needed to determine what types of monitoring
Lau et al., 2020; Meijer et al., 2021). The majority of plastic data is missing to inform such strategies. These overviews have
pollution is generated on land and transported through rivers to previously been made on a global scale for plastic pollution in
the marine environment (Pawar et al., 2016; Schmidt et al., 2017; freshwater environments (Blettler et al., 2018), for specific
Lebreton and Andrady, 2019). Plastic pollution can have adverse countries (e.g. Chowdhury et al., 2020), and for specific
effects in all three of these systems, which include mortality of environmental systems in Indonesia (Purba et al., 2019).
fauna through ingestion or entanglement, reduction of However, such an overview for plastic pollution across all
livelihoods of those dependent on ecosystem health (e.g. environments in Indonesia does not yet exist.
fishing and tourism), contamination of seafood with This review study provides an overview of the current state of
microplastics with implications for food safety and human knowledge on plastic pollution in Indonesia and provides insights
health, property damage, and an increased risk of floods in into current research biases and knowledge gaps. We then use
urban areas (Gall and Thompson, 2015; Koelmans et al., 2017; these data to suggest ways forward for plastic research in
Conchubhair et al., 2019; Hantoro et al., 2019; Honingh et al., Indonesia to overcome these gaps. This overview was gathered
2020; van Emmerik and Schwarz, 2020). through a review of current literature on plastic pollution in
Indonesia is estimated to be among one of the top emitting Indonesia, and through performing a meta-analysis of the 83
countries of plastic pollution in the world (Meijer et al., 2021). identified peer-reviewed articles published between 1986 and
This is supported by a comparative study of previously published 2020. The goal of this study is to provide insights on what types
field observations, which ranked drains in Jakarta (Indonesia of research questions should be answered to fill research gaps,
Capital City) among the highest polluting rivers globally (van with the aim of having a clear picture for effective policy
Calcar and van Emmerik, 2019). Plastic pollution found in the measures to be implemented and their efficacy to be
Indonesian Seas not only comes from inland, but also from monitored.
several countries surrounding it. The ocean currents transport
this plastic pollution to the inner seas (Purba et al., 2021). High
plastic emission rates are hypothesized to be caused by METHODOLOGY
Indonesia’s high population densities in coastal areas in
combination with improper waste management and Literature Review
insufficient service coverage (Lebreton and Andrady, 2019; The literature search was performed using a snowball method.
Lestari and Trihadiningrum, 2019). Indonesia is located within First, a literature search was performed in the Google Scholar and
the Coral Triangle, a hotspot for global marine biodiversity which ResearchGate databases, using different combinations of the
is highly susceptible to the negative effects of plastic pollution following keywords: plastic, macroplastic, microplastic, litter,
(Tomascik et al., 1997; Spalding et al., 2001; Lasut et al., 2018). marine, river, Indonesia, debris, and waste. Studies that
Reducing plastic emissions in Indonesia will therefore have a quantified environmental plastic pollution in Indonesia were
large impact on both reduction of global plastic emissions to the selected. Studies that considered plastic pollution that could
oceans, and on protecting global biodiversity. The Indonesian not directly be linked to a specific location were excluded
government has committed to reduce plastic pollution. To this from further analysis (e.g. plastic pollution in consumables
end, it has set a target to improve solid waste management and policy studies). Second, selected articles were scanned for
(Presidential Decree No 97/2017) as well as the goal to reduce references to other studies concerning plastic pollution in
marine plastic debris by 70% in 2025. This commitment is Indonesia. These studies were then also added to the review.
followed up by the establishment of the national action plan Lastly, a group Indonesian researchers specialized in plastic
for marine debris management 2018–2025 (Presidential Decree pollution was asked to identify any literature missing in the
No. 83/2018). review. These studies were also added to the literature review.
Reliable and frequent data on plastic pollution and its effects The literature search was concluded on October 1, 2020. Studies
on fauna and ecosystems are required for the development and published after this date have therefore not been included in the
assessment of policy measures aimed to reduce plastic emissions subsequent analysis. The corresponding author of this paper read
to the oceans (Conchubhair et al., 2019; Owens and Kamil, 2020; all identified literature (n 83, Supplementary Materials), and
Vriend et al., 2020). Moreover, data on exposure and toxicity are the following information was extracted to a unique dataset:
needed to assess microplastics’ human health risks from exposure
to, for example, contaminated seafood (Hantoro et al., 2019). (1) The environmental system which was studied for plastic
Plastic pollution has been extensively studied in Indonesia (e.g. pollution (e.g. terrestrial, riverine, marine, atmosphere).
Uneputty and Evans, 1997; Rochman et al., 2015; Cordova and (2) The compartment in the system that was studied for
Wahyudi, 2016; Syakti et al., 2017; van Emmerik et al., 2019). plastic pollution (e.g. floating plastic, in the water
However, observations are scattered across the country and vary column, beached plastic, plastic in biota).
Frontiers in Environmental Science | www.frontiersin.org 2 June 2021 | Volume 9 | Article 692907
Vriend et al. Meta-Analysis Plastic Pollution Indonesia
(3) The location of the study (coordinates). compared to 10 studies in the riverine and three in the terrestrial
(4) The size of plastic that was studied (e.g. microplastic, environments. No studies on atmospheric plastic pollution were
macroplastic, or both). identified during the literature search.
(5) The year the study was published. Within environmental systems, there is a bias to study specific
(6) The institutions the authors were affiliated to. sub-compartments (Table 2). For example, plastics on the beach
(7) The top three most frequently found plastic polymer and floating plastic are most frequently studied for the marine
types and/or shapes that were reported in the study. environment (29 and 15 out of 77 studies respectively), while the
(8) The units in which the data were reported. water 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. A
Meta-Analysis similar bias can be identified in riverine plastic research, where
The dataset created through the literature review was used for most research so far has been done on floating plastics (5 out of
several analyses, including a spatial analysis of research locations, 15) and plastics in the water column (4 out of 15), while research
an analysis of research output over time, an analysis of units of on other compartments such as the riverbank (2 out of 15),
measurement in which the data were reported, and an analysis of riverbed (2 out of 15), or in biota (2 out of 15) are lagging behind.
most frequently found polymers and shapes. The observed bias can be attributed to the type of research
The majority of the literature identified during the review used a method available for each system compartment. Some methods
size classification that deviated from more recent definitions. For used to quantify plastics in aquatic environments are cheaper and
example, van Emmerik and Schwarz (2020) define four size classes of easier to apply than others, leading to a preference of application.
plastic pollution, these being macro- (>50 mm), meso- (5–50 mm), For example, method to quantify riverine macroplastic on the
micro-(0.1 µm–5 mm), and nanoplastic (Vriend et al. Meta-Analysis Plastic Pollution Indonesia
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 categories
microplastic (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 0
Riverine 10 5 5 0
Marine 68 30 32 6
Atmosphere 0 0 0 0
Riverine + marine 1 1 0 0
Terrestrial + riverine + marine 1 1 0 0
Total 83 40 37 6
the monitoring of plastic pollution in the riverine and
TABLE 2 | Overview of studies included in the meta-analysis, categorized by the terrestrial environments.
environmental system and relevant sub-compartment that is studied. Totals
add up to over 83 since a handful of studies quantified multiple environmental
compartments and/or environmental systems. Note, review category includes Units of Measurement in Plastic Research
studies that present overviews of a subset of studies included in this papers While all research considered in this study quantifies plastic
(e.g. floating plastic in marine environments). pollution in some capacity, the units of measurements in
Compartment Marine Riverine Land Total which they report their findings differ greatly. Such differences
create difficulties when comparing data from multiple studies
Floating 15 5 0 20 since some units are not compatible with each other. Studies on
Column 9 4 0 13
Sediment 9 2 0 11
macroplastic pollution in Indonesia generally use two types of
Riverbank/beach 29 2 0 31 units to express their results in. They either express results in
Biota 7 2 0 9 items per area, volume or sample, or in a mass per area, volume or
Mangrove 4 0 0 4 sample (Table 3). While some studies report in both types of units
Land surface 0 0 0 0 (e.g. van Emmerik et al., 2018; Cordova and Nurhati, 2019;
Waste management 0 0 2 2
Review 4 0 0 4
Cordova et al., 2021), a large part only reports in one type.
Other 0 0 2 2 The usage of different units in macroplastic research leads to
Total 77 15 4 96 two challenges when trying to compare data from different
studies. First, data expressed in items per sampling unit
cannot be directly converted into data expressed in mass (e.g.
kg) per sampling unit. Previous studies on floating macroplastic
Marine plastic pollution can negatively impact revenue from pollution in rivers have tried to solve this issue using a conversion
beach tourism (Jang et al., 2014; Petten et al., 2020). rate based on the average mass of macroplastics in rivers (Castro-
Furthermore, microplastic is considered a novel contaminant Jiménez et al., 2019). However, this increases uncertainty in the
expected to pose food safety risks due to consumption of coastal results due to the variability in plastic pollution characteristics
seafood, i.e. bivalves, shellfish and fish (Hantoro et al., 2019). between different locations. A second problem relates to the
Accordingly, several studies have found microplastics sampling unit used. When ignoring the fact that data are
contamination in commercial edible fishes and bivalves in expressed in either items or kg, a range of sampling units is
Indonesia (Rochman et al., 2015; Khoironi et al., 2018; Hastuti used, including macroplastic per volume, per area, and per
et al., 2019; Cordova et al., 2020). sample (Table 3). These differences stem from the use of
To better understand potential sources of plastic pollution, different methods to quantify plastic pollution across
more research is needed to determine the type and sources of environmental compartments (e.g. a sample of water is
pollution in the riverine and terrestrial systems of Indonesia. expressed in volume while a beach sample is taken in a certain
Rivers are widely regarded as the largest sources of marine area).
plastics (Li et al., 2016; van Emmerik and Schwarz, 2020). Similarly, data presented in microplastic research are difficult
Plastic pollution is in turn produced through the consumption to compare because a wide range of sampling units are used.
and improper disposal of waste on land, and is transported to While most microplastic research expresses their results in terms
the oceans by rivers (Schmidt et al., 2017; Lebreton and of particles per sampling unit (Table 3), the sampling units range
Andrady, 2019; Lestari and Trihadiningrum. 2019). Here, from particles per volume, mass, and mass of tissue. Again, these
plastic pollution is dispersed over a large volume of water, differences are caused by the methods that are utilized for each
which causes the plastic pollution to be more diluted in the environmental compartment: volumetric samples are mostly
ocean compared to plastic pollution in the riverine and taken in the water column (e.g. Cordova and Hernawan,
terrestrial environments. Quantifying plastic pollution 2018), tissue samples are taken from biota (e.g. Rahmawati
earlier in its journey from land to sea allows for the and Patria, 2019), and samples based on area and/or depth are
quantification of more plastic while using fewer resources. taken from riverbanks, beaches, and from sediment at the bottom
We, therefore, underscore the importance of the shift towards of the waterbody (e.g. Syakti et al., 2018). While these units allow
Frontiers in Environmental Science | www.frontiersin.org 4 June 2021 | Volume 9 | Article 692907Vriend et al. Meta-Analysis Plastic Pollution Indonesia
FIGURE 1 | Research output on plastic pollution in Indonesia per environmental system over time. Dark blue represents studies concerning plastic pollution in the
marine environment, light blue represents studies concerning pollution in the riverine environment, orange represents research studies concerning plastic pollution in the
terrestrial environment, and red represents studies concerning both marine and riverine environment. Output from 1986–2009 was omitted due to incompatibility to
current scientific standards, output for 2020 was cut off on October 1, 2020.
for the comparison of data between studies that examine the same terms of flux (e.g. kg/day, items/day) (Table 3). These
environmental compartment, the differences in sampling units differences are caused by the environmental system itself
do not allow for an integrated comparison of plastic pollution in since rivers are often seen as a “conveyor belt” for pollution
all river compartments. to be transported to the oceans. It is therefore important to
Besides the size class, the differences in the presentation of consider these factors when trying to compare data between the
data also hinder comparing data between different two environmental systems.
environmental systems. The nature of the measurements that Standardization of protocols is needed to allow for better data
are done in each system differ. For example, plastic pollution in comparison. Such a protocol should include what units should be
the marine environment is often quantified in terms of used for reporting data in each environmental compartment. This
concentration (e.g. kg or items per sample), while plastic would facilitate combining and analyzing data from different
pollution in the riverine environment is mostly quantified in studies on the same environmental compartments. Such analysis
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. 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
3 2 3
Floating Particles/m Items/m Particles/m kg/year
Particles/m2 kg/100m2 particles/l tons/day
kg/survey
Riverbank/beach Particles/m3 Items/m2 - kg/m2
Particles/kg m3/m2 kg/hour
kg/m2
Column particles/l Items/m3 particles/l -
Particles/m3
Sediment Particles/sample kg/sample Particles/m3
Particles/kg Item/sample Particles/100 g sediment
Particles/100 g dry weight
Biota Particles/organ – Particles/fish –
Particles/animal Particles/m3
Particles/g dry weight
Mangrove Particles/m2 Items/kg dry weight – –
kg/m2
Frontiers in Environmental Science | www.frontiersin.org 5 June 2021 | Volume 9 | Article 692907Vriend et al. Meta-Analysis Plastic Pollution Indonesia
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).
Studies Percentage of studies that present polymer types in top 3 frequently found polymers
that
reported
polymers
PP (%) PS (%) LDPE (%) EPS (%) PET (%) PE (%) PA (%) HDPE (%)
Macro (n 46) 9 56 33 33 22 11 22 0 11
Micro (n 43) 10 90 20 30 10 0 40 20 0
would lead to better insights into the plastic pollution problem found among the top three most abundant shapes are granules
across Indonesia. Standardization would also allow for a more and foams (both 21%). The shape of particles can be an indication
convenient comparison of data between different environmental of the possible sources of the microplastic, though the
compartments. For example, by ensuring that the mass of items applicability of this is still limited. Several potential sources of
found is included in such a protocol, data can be expressed in particular shapes of microplastic particles have been studied by
both items and kg per sampling unit. Free et al. (2014). However, no studies considered in this meta-
analysis tried to identify sources based on the shape of particles.
Frequently Found Materials and Shapes Moreover, Kooi and Koelmans (2019) argue that the shape of
A small portion of studies quantifying plastic pollution in particles is continuous, and therefore no classification will be able
Indonesia report polymer types of the plastic (9 out of 46 for to accurately capture the full variability of shapes. One of the
macroplastic, 10 out of 43 for microplastic, Table 4). When particular reasons for this situation is complex degradation
polymers are reported, polypropylene (PP) is the most often mechanisms (photodegradation, mechanical-physical,
found polymer type in both macroplastic (56%) and microplastic weathering, even biodegradation) that continuously occur in
(90%) pollution. Polyethylene (PE), and its high- and low-density nature, which may breakdown larger plastics into
variants (HDPE, LDPE) are also among the most abundant microplastics (Kooi and Koelmans, 2019).
plastics for both macro- and microplastic. Other polymers
found in Indonesian aquatic environments include polystyrene Locations of Studies
(PS) and expanded polystyrene (EPS). Plastic research for all size classes and environmental systems is
Polymer characterization makes plastic research more labor- highly localized on Java Island, especially for riverine and
intensive, but should be included more frequently in plastic terrestrial focused studies (Figure 2). Studies that quantify
pollution studies. Polymer characterization is easier for plastic pollution in the marine environment are more evenly
macroplastic than for microplastic since certain items have spread across Indonesia, though Java Island is still represented in
identification codes or logos indicating what polymer types almost half of all studies (32 out of 67) focused on marine plastic
they are made of. Besides, macroplastic characterization can be pollution in seas near Java. Studies quantifying plastic pollution in
simplified by grouping difficult to distinguish polymers, or by rivers are either performed on Java (14 out of 15) or Bali Islands
using an item list that indicates what polymers items are most (1 out of 15). The same goes for terrestrial focused studies, with so
frequently made of (e.g. van Emmerik et al., 2018; Vriend et al., far only three being done on Java and one on Bali Islands.
2020). Microplastic polymers are often characterized using a form Although a larger spread would be ideal, this strong focus on
of spectroscopy (e.g. Fourier transform infrared, Raman) and Java Island is reasonable since it houses a large part of the
thermal analysis (e.g. py-GC-MS), which greatly increases the Indonesian population. Lebreton et al. (2017) identified Java
labor required to gather data (Shim et al., 2017). The and Sumatra Islands to be areas of concern with their
characterization of polymers is one of the few ways to estimates predicting these islands to be responsible for 14.2%
compare macroplastic and microplastic presence directly. of global annual plastic exports to the oceans. More recently,
Besides, polymer types may give an indication of possible Meijer et al. (2021) identify 51 rivers on Java Island to be among
sources of plastic pollution. Polymer characterization should the global top 1,000 most polluting river. However, Java is not the
therefore be encouraged to be included in studies on plastic only Indonesian island with high rates of plastic pollution. Data
pollution in Indonesia more often. from all Indonesian islands are required to design and prioritize
More than half of the studies that studied microplastic reduction and mitigation strategies, requiring a larger spatial
pollution characterized the shape of the particles (24 out of spread of studies.
43, Table 5). This is in line with the fraction of global Another factor that could explain the research focus on Java is
microplastic studies that report shapes found by Koelmans the location of Indonesian institutes that research plastic
et al. (2019). Among the top three most abundant particles, pollution. Many of these institutes are located on Java island,
shapes that are more frequently found are fragments (71%), especially in the Jakarta metropolitan area (Figure 3). Besides
fibers (63%), and films (46%). Shapes that are less frequently Java, institutes with relatively large plastic research output are
Frontiers in Environmental Science | www.frontiersin.org 6 June 2021 | Volume 9 | Article 692907Vriend et al. Meta-Analysis Plastic Pollution Indonesia
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
located on Sumatra, Bali, and Sulawesi Islands, and the city of that is exported to the oceans. By setting out their data needs and
Makassar (Figure 3). When comparing the locations of these their preferred data format, the Indonesian government ensures
institutes with the numbers of studies aggregated to the regional that research from different parties meet the same standards, and
level (Figure 2), it can be concluded that regions with large are, therefore, intercomparable.
amounts of studies coincide with the locations of specialized We suggest a national Indonesian scientific authority to set
institutes, indicating that research is mostly done close to these these standard methods in collaboration with local and
institutes. international experts. First efforts for standardization have
been recently published by the Indonesian Institute of Sciences
(LIPI) (Nurhati and Cordova, 2020). Moreover, three institutions
Future Plastic Pollution Research (LIPI, DCA, and Universitas Padjadjaran) have built marine
Directions in Indonesia debris database to centralize data (https://marinedebris.id). We
Based on the biases and gaps identified in the meta-analysis, we recommend this process to be further expanded for method
propose four directions for future research: 1) Standardization of standardization and data harmonization of plastic in all
research methods, 2) expansion of environmental system focus, environmental systems and sub-compartments.
3) expansion in spatial coverage, and 4) expansion in plastic
characterization methods. These suggestions aim to ensure Expansion of Environmental System Focus
reliable and intercomparable data on plastic pollution in A shift in research prioritization on specific environmental
Indonesia, which can aid the design of plastic removal and systems is required to get an accurate overview of plastic
mitigation strategies. pollution in Indonesia. In the current form, plastic research
mainly focuses on the marine environment, which is in line
with global research trends (Blettler et al., 2018). However,
Harmonization of Research Methods and plastic pollution abundance in the marine environment is
Data diluted compared to riverine pollution. For example,
We recommend establishing standard research methods for each macroplastic pollution concentrations on riverbanks in
environmental system and sub-compartment in Indonesia. Indonesia found in this meta-analysis ranged between 0.007
Standardizing methods ensures homogeneity in the data and 0.029°kg/m2, or 7,000–29000°kg/km2 (Owens and Kamil.
gathered and shared by different studies. Current methods 2020; Widyarsana et al., 2020), while concentrations of floating
differ per study, geographical area, and research group, which macroplastics in the great pacific garbage patch are estimated
causes data to be expressed in different units of measurement and to range between 10–100°kg/km2 (Lebreton et al., 2018). Such
plastic items to be categorized differently. This complicates the dilution makes the determination of possible sources, and the
comparison of data between studies. Standardized methods can removal of plastic pollution more difficult. Therefore,
alleviate this problem and would supply easier to interpret data knowledge on plastic pollution transport earlier in its
for policy makers, which will hopefully lead to tailored mitigation presence is important for the design of effective removal
and removal strategies. Methods that can be employed to ease and mitigation strategies. The research focus should,
harmonization of research methods include the expression of therefore, be moved higher up in the transport chain,
data in directly convertible units (Hidalgo-Ruz et al., 2012; Fok ideally at the source, as well.
et al., 2020), or the set-up of plastic research hubs to foster The focus of future research should also diversify in terms of
collaboration (Nel et al., 2021). compartments within environmental systems. The meta-analysis
Another avenue of harmonization that can be explored is the shows that specific compartments within environmental system
setting of central research questions which have to be answered are studied more than others (e.g. beaches in the marine
by the research community and linking these to possible research environment, floating and riverbank in the riverine
methods (e.g. van Emmerik and Vriend. 2021). For example, the environment). This is mainly due to these compartments being
Indonesian government could set out a couple of key research more accessible and having easy to apply methods. However, only
questions that they need to have answered in order to implement quantifying plastic pollution in these compartments gives a biased
effective plastic pollution mitigation and reduction strategies. view of the problem. Therefore, we recommend to keep observing
Such question could explore concepts such as determining the pollution in these compartments while also expanding to lesser
current stock of plastic in each environmental system, studied compartments such as sub-surface plastics in the marine
quantification of the amount of plastic pollution that enters and riverine environments, and surface pollution in the terrestrial
each environment, and the quantification of plastic pollution environment.
Frontiers in Environmental Science | www.frontiersin.org 7 June 2021 | Volume 9 | Article 692907Vriend et al. Meta-Analysis Plastic Pollution Indonesia FIGURE 2 | Number of plastic pollution studies performed in Indonesia aggregated to sub-regions, where (A). depicts marine focused literature (land mass closest to research area), (B). depicts studies focused on rivers literature, and (C). represents land focused research. Environmental system focus can also be further diversified by studied through two ways. First, historic concentrations of plastic studying the time scales that plastic pollution resides in a certain pollution should be studied. Data on historic concentrations can environment. We envision time scales plastic pollution to be help explain how plastic pollution developed in the past decades. Frontiers in Environmental Science | www.frontiersin.org 8 June 2021 | Volume 9 | Article 692907
Vriend et al. Meta-Analysis Plastic Pollution Indonesia
FIGURE 3 | Location of institutes that published on plastic pollution in Indonesia, and the number of publications they (co-) authored, where red circles indicate one
study, green triangle represents two studies, blue square represents three studies, blue pentagon represents four to five studies, and the yellow start represents six to
seven studies (co-) published per institute.
Such context can be used to suggest ways to reduce plastic that research should expand to boundary seas. Indonesia has six
pollution in the future. Such data can be gathered by studying surrounding countries, and more collaboration is needed to
microplastic concentrations in sediment cores (e.g. Turner et al., mitigate plastic pollution. Increasing insight into how plastic
2019) or through studying use-by dates on accumulated pollution transboundary patterns would help stress the
macroplastic pollution (e.g. Tramoy et al., 2020). The second urgency and direction of this transnational collaboration.
time scale that should be included in future research is time that
plastic pollution spends in each environmental system. A recent
study by Tramoy et al. (2020) has shown that retention times of Expansion in Plastic Characterization
plastic pollution in estuaries may exceed decades, and research by Methods
Olivelli et al. (2020) points at coastal margins and backshores as a We recommend both macro- and microplastic characterization
major sink for marine debris. Knowing where plastic pollution to be expanded by performing research on both size categories at
accumulates for longer periods of time can aid the design of the same location. 77 out of 83 studies in this meta-analysis
targeted strategies for removal of it from the environment. characterize just one plastic size category (macro- or
Therefore, including these temporal dynamics in plastic microplastic). Integrating macro- and microplastic research at
pollution will results in better informed intervention strategies the same location allows for comparisons to be made between the
for plastic pollution. two size classes. This would, in turn, allow for more accurate
determination of possible sources of plastic pollution, and
Expansion in Spatial Coverage provide insights in the relation between presence of macro-
Plastic research in all environmental systems should have a and microplastic. Such insights could allow for macroplastic
broader spatial coverage in Indonesia. While plastic pollution research to act as a proxy for microplastic pollution and
has been quantified at least once in places with high population reduce the need for microplastic research, possibly saving
densities, research is biased toward Java Island. This bias is more valuable time and resources (Vriend et al., 2020). However
pronounced in riverine and terrestrial research where all but one studies on microplastics occurence and distribution might still
study has been performed on Java Island. While Java Island is be of value since they can portray the past behavior of the
predicted to have a considerable contribution towards plastic community in plastic use and disposal.
exports to the ocean by models (e.g. Lebreton et al., 2017), data on Characterization methods can be further expanded by
plastic pollution in all of Indonesia’s geographic areas are including polymer analysis more frequently. 19 out of 83
required in order to set priorities for mitigation and removal studies considered in this meta-analysis characterized plastic
strategies. We, therefore, recommend expanding the spatial polymers found. Increasing the number of studies that identify
coverage to all major islands of Indonesia, while keeping polymers allows for data to be more easily compared between
research focus on areas with predicted high pollution rates different environmental systems, compartments, and size classes.
such as Java and Sumatra Islands. Additionally, Purba et al. This data can in turn be used for the design of more targeted
(2021) emphasize that plastic pollution is a transboundary mitigation and removal strategies. We, therefore, recommend
issue in south-east Asian countries. We therefore also suggest increasing the frequency of polymer analysis in future research.
Frontiers in Environmental Science | www.frontiersin.org 9 June 2021 | Volume 9 | Article 692907Vriend et al. Meta-Analysis Plastic Pollution Indonesia
CONCLUSION methods, and therefore units used, for each environmental
systems and sub-compartments across Indonesia, 2) a shift in
Indonesia is suspected to be among the top plastic polluting research focus expanding beyond the marine environment
countries in the world. A large body of research has been toward riverine and terrestrial plastic pollution research, 3) an
published that quantifies plastic pollution with the aim to expansion in spatial coverage to ensure more representative
facilitate the design of effective mitigation and removal research taking place in the whole of Indonesia, and 4) an
strategies. In this study we perform a meta-analysis of this expansion in methods used to characterize plastic pollution,
body of literature to identify research biases and gaps, with especially in terms of polymer type.
the goal to streamline future research.
The majority of the research output on plastic pollution in
Indonesia has focused on the marine environment (70 out of 83 AUTHOR CONTRIBUTIONS
studies), with first efforts to quantify plastic pollution in other
environmental systems (riverine and terrestrial environments) PV, TvE, and HH conceived the idea. PV performed the literature
recently being undertaken on Java Island. Research within search, extracted data from the identified literature, performed
environmental systems is biased toward compartments that the data analysis, and prepared the initial draft. All authors
are easy to access and have already established research identified missing literature and wrote the final manuscript.
methods. These compartments include the beach for marine
plastic pollution, and floating and riverbank plastics for
riverine plastic pollution. Considering research output since ACKNOWLEDGMENTS
2010, macroplastic pollution has been studied more frequently
than microplastics (43 and 40 studies respectively), and research The work of TvE is supported by the Veni research program The
within environmental systems is biased toward a size class as well. River Plastic Monitoring Project with project number 18211,
For example, microplastic is mostly characterized in the marine which is (partly) financed by the Dutch Research Council
environment, while macroplastic is mostly studied in the riverine (NWO). This work has been done as part of the Post-Plastic
environment. Methods, and with it the measurement units in Paradise Project, funded by the ANGIN program of the Royal
which data is expressed, vary widely between studies, which Netherlands Academy of Arts and Sciences.
complicates comparison between studies. Last, the plastic
research focus is highly area focused, with almost half of all
studies being focused on Java Island. SUPPLEMENTARY MATERIAL
We recommend four good practices for future research which
can provide data that can aid the Indonesian government with The Supplementary Material for this article can be found online at:
designing monitoring strategies to reduce plastic pollution more https://www.frontiersin.org/articles/10.3389/fenvs.2021.692907/
effectively. These being 1) the harmonization of research full#supplementary-material
Cordova, M. R., and Nurhati, I. S. (2019). Major Sources and Monthly
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