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263
한국해양환경
.
에너지학회지
Journal of the Korean Society
for Marine Environment and Energy
Vol. 18, No. 4. pp. 263-273, November 2015
http://dx.doi.org/10.7846/JKOSMEE.2015.18.4.263
ISSN 2288-0089(Print) / ISSN 2288-081X(Online)
Original Article
물질흐름분석을 활용한 전세계 플라스틱 해양쓰레기의 유입량과
현존량 추정: 예비적 접근
장용창
1
· 이종명
1,†
· 홍선욱
1
· 최현우
2
· 심원준
3
· 홍수연
1
1
(사)동아시아 바다공동체 오션 /한국 해양쓰레기 연구소
2
한국해양과학기술원 해양과학데이터센터
3
한국해양과학기술원 유류유해물질연구단
Estimating the Global Inflow and Stock of Plastic Marine Debris
Using Material Flow Analysis: a Preliminary Approach
Yong Chang Jang
1
, Jongmyoung Lee
1,†
, Sunwook Hong
1
, Hyun Woo Choi
2
,
Won Joon Shim
3
and Su Yeon Hong
1
1
Korea Marine Litter Institute, Our Sea of East Asia Network, 23-96 Jukrim 4-ro, Gwangdo, Tong Yeong, 53013, Korea
2
Oceanographic Data & Information Center, Korea Institute of Ocean Science & Technology, Ansan 15627, Korea
3
Oil and POPs Research Group, Korea Institute of Ocean Science & Technology, 41 Jangmok 1 gil,
Jangmok, Geoje 53201, Korea
요약
전세계 플라스틱 해양쓰레기의 유입량과 현존량을 추정하였다 . 한국에서 플라스틱 해양쓰레기의 연간 유입량(72,956
톤)은 플라스틱의 연간 소비량 (5.2백만톤)의 1.4%로 추정되었다. 유출량이 0이라는 가정과 함께 , 이 1.4% 유입률을
1950년부터 2013년까지 전세계 플라스틱 생산량에 적용함으로써, 2013년 전세계 연간 플라스틱 해양쓰레기 유입량은
4.2백만톤이며, 2013년말 현재 플라스틱 해양쓰레기 현존량은 86백만톤으로 추정되었다. 또한 로지스틱 모델에 따라 ,
석유생산량의 4%가 플라스틱으로 생산될 때 플라스틱 해양쓰레기의 최종 현존량은 199백만톤이 될 것으로 추정되었
다. 유입량과 현존량은 전혀 다른 측정단위이기 때문에 , 유입 저감 정책의 효과성을 평가할 수 있는 개선된 지표가 필
요하다. 또한 , 플라스틱 해양쓰레기 오염은 거의 회복불가능하기 때문에 , 이를 예방하는 대책의 가치는 훨씬 더 높게 평
가되어야 하며, 사전주의의 원칙에 따라 더 강력한 예방 대책이 시행되어야 한다. 본 연구는 제한적인 정보에 근거한 예
비 연구에 해당하므로 플라스틱 해양쓰레기의 유입량과 현존량의 경향을 규명하기 위한 추가 연구가 필요하다.
Abstract −We estimated the global inflow and stock of plastic marine debris. In South Korea, we estimated that
the annual inflow of plastic marine debris (72,956 tons) was about 1.4% of annual plastics consumption (5.2 mil-
lion tons) in 2012. By applying this 1.4% ratio to global plastics production from 1950 to 2013, we estimated that
4.2 million tons of plastic debris entered the ocean in 2013 and that there is a stock of 86 million tons of plastic
marine debris as of the end of 2013, assuming zero outflow. In addition, with a logistic model, if 4% of petroleum
is turned into plastics, the final stock of plastic marine debris shall be 199 million tons at the end. As the inflow and
the stock are different units of measurement, better indicators to assess the effectiveness of inflow-reducing poli-
cies are needed. And, as the pollution from plastic marine debris is almost irreversible, countermeasures to prevent
it should be valued more, and stronger preventive measures should be taken under the precautionary principle. As
this is a preliminary study based on limited information, further research is needed to clarify the tendency of inflow
and stock of plastic marine debris.
Keywords: Plastic marine debris(플라스틱 해양쓰레기), Inflow(유입량), Stock(현존량), Material flow analysis
(물질흐름분석 ), Policy indicators(정책 지표)
†Corresponding author: sachfem@nate.com
264 장용창 · 이종명 · 홍선욱 · 최현우 · 심원준 · 홍수연
1. Introduction
How much plastic marine debris is there in the ocean? How
much is entering the ocean every year? These questions are
increasingly important (UNGA [2005]; Ryan et al. [2009]) as sci-
entific evidence mounts that marine debris, and plastic marine debris
in particular, is harmful to both human health and marine ecol-
ogy (Rochman et al. [2013]). For example, it is estimated that
plastic marine debris costs approximately US$13 billion per year in
environmental damage to marine ecosystems (UNEP [2014]). A
problem can be managed only when it is adequately under-
stood, and information on the amount of plastic marine debris
is a vital step toward finding a solution (UNEP [2014]).
Previous efforts to answer these questions can be divided
into two groups: those addressing the ‘inflow,’ and those address-
ing the ‘stock’ of marine debris. A ‘flow’ is measured for a certain
period of time, while a ‘stock’ is measured at a specific moment in
time. Regarding inflow, NAS [1975] estimated that 6,360,000 tons of
marine debris enters the ocean every year from ocean-based activi-
ties, while Cantin et al. [1990] estimated that 337,306 tons enter
US waters. Kataoka et al. [2013] estimated that at least 2,115 m
3
of grass flows into Tokyo Bay, Japan annually via rivers. Jang
et al. [2014A] estimated that 91,195 tons of marine debris enters
the ocean from activities on land and at sea. The highest estimates
suggest inflow as high as 7 billion tons per year (GBRMPA [2006]),
though these may be overestimates (Cheshire et al.[2009]).
Likewise, several recent studies have examined the stock of
marine debris. Cozar et al. [2014] estimated that the global stock
of plastic debris in surface waters of the open ocean ranges from
6,600 to 35,200 tons, based on samples collected from 442 sites in
2010. Similarly, Eriksen [2014] estimated that there are 269,000
tons of plastic in global ocean surface waters based on 26 expe-
ditions over 6 years. Jang et al. [2014A] estimated that 152,241
tons of marine debris could be found on the coast, sea floor, sea
surface, and water column of the South Korean sea.
However, these studies provide only a very limited picture of
global pollution from plastic marine debris. The NAS [1975]
estimate is outdated and limited to debris from activities on the
ocean, only 0.7% of which is plastic (Lebreton et al. [2012]);
instead, the estimate includes other materials such as metals,
and even organics such as food waste. The estimate from Cantin et
al. [1990] is also limited to debris from activities in US waters.
Most of the debris described by Kataoka et al. [2013] is grass,
not anthropogenic in origin. Likewise, the findings of Jang et al.
[2014A] are limited to South Korean waters, and the two remaining
estimates of debris stock (Cozar et al. [2014]; Eriksen et al. [2014])
are limited to surface debris, not including debris on the coast
or sea floor.
Here, we estimate the global inflow and stock of plastic marine
debris based on rates of plastic consumption. First, we estimate the
inflow ratio (plastic marine debris inflow / plastic consumption)
from plastic material flow analysis in South Korea. Material
flow analysis is a method of analyzing the amount of materials in a
certain system, and is proper for polluting materials (OECD [2008]).
Second, we apply this inflow ratio to data on the global pro-
duction of plastic (1950-2013) to estimate the global inflow and
stock of plastic marine debris. Third, we speculate on the inflow and
stock of plastic marine debris after 2013, under the assumption
that a constant proportion of petroleum is made into plastics.
Finally, we discuss conceptual differences between plastic marine
debris inflow and stock.
2. Methods
2.1 Inflow ratio of plastic marine debris
We defined the inflow ratio of plastic marine debris as follows:
Inflow ratio of plastic marine debris =
(1)
Here, we applied the inflow ratio for South Korea globally.
The annual plastic marine debris inflow for South Korea was
derived from Jang et al. [2014A], which is a national-level syn-
thesis of previous studies.
Annual plastic consumption in South Korea was estimated
by a material flow analysis (OECD [2008]) of plastics. Material
flow analysis (MFA) is a systematic assessment of the flows
and stocks of materials within a system defined in space and time
(Brunner [2004]). In this case, various data on plastics produc-
tion and consumption in South Korea were used. Under South
Korean law, any large business that manufactures or imports
plastic products (excluding packaging materials) for domestic
consumption must pay a tax for the waste. Moreover, any busi-
ness that manufactures or imports plastic packaging materials
must recycle a certain proportion (about 80%) (Act on the Pro-
motion of Saving and Recycling of Resources [2014]) under
Extended Producers Responsibility regulations (OECD [2001]).
Thus, the government collects various data related to plastics
consumption.
To simplify the calculation, we assumed that the lifetime of
all plastic products is less than one year. That is, the amounts of
plastic production, consumption, and waste in a given year were
Annual plastic marine debris inflow to the ocean
Annual plastic consumption
물질흐름분석을 활용한 전세계 플라스틱 해양쓰레기의 유입량과 현존량 추정 : 예비적 접근 265
assumed to be the same, although some products are in use for
longer periods. For example, the percentage of packaging material
in the usage of plastic is 37% in the United Kingdom (Hopewell et
al. [2009]) and 39% in the Europe (Plastics Europe [2013]).
However, even when the lifetime of products are longer than
one year, it does not affect the final discharge amount of debris,
as there shall be only time gap.
For the material flow analysis, the study site was defined as
the territory and sea of South Korea, and the time as the calendar
year 2013, except where 2013 data were not available, in which
case 2012 data were used.
2.2 Global inflow and stock of plastic marine debris
(1950-2013)
Next, the inflow ratio was applied to data on global plastic
production estimated by Plastics Europe (2011, 2012, 2013,
and 2014) to estimate the global inflow and stock of plastic
marine debris from 1950 to 2013. For this purpose, we assumed
that plastic marine debris outflow, such as beach cleanup efforts or
plastic biodegradation, does not occur. That is, although there
are in fact some outflows, we assumed there were none for
simplicity, an assumption we address below. We also assumed
that the inflow ratio is the same irrespective of nation or year.
Under these assumptions, the accumulation of inflow from 1950
to a certain year becomes the stock at the end of that year (Eq. 2).
We discuss the reliability of these assumptions in the discus-
sion section below.
Stock of plastic marine debris at the end of a certain year
= Accumulated sum of the inflow of plactic marine debris
from 1950 to that year (2)
2.3 Speculating on the plastic marine debris level after 2013
We speculatively estimated the potential level of plastic marine
debris after 2013, assuming that the ratio of plastic marine
debris inflow to plastic production, and the ratio of plastic pro-
duction to petroleum production, are both constant over time.
About 4% of total petroleum is made into plastics (Hopewell et
al. [2009]; British Plastics Federation [2012]), and a further 4%
is used for this production (Thompson et al. [2011]). Although
plastics can be produced from other sources such as coal and
gas, we analyzed plastics made from petroleum only, and used
speculative petroleum production data from Gallagher [2011].
If 4% of petroleum is made into plastics, and the same pro-
portion of plastics becomes marine debris each year, then the
plastic marine debris will follow the same pattern as petroleum
production—a logistic curve (Hubbert [1956]). The well-known
logistic function (Verhulst [1838]) is given by Eq. (3):
(3)
where S(y) is the stock of plastic marine debris in tons as a
function of time (year); K is the final stock of plastic marine
debris (carrying capacity); S
0
is the initial stock; r is the growth
rate, which is the same as that for petroleum production; and y is
the year (time).
As we assumed that plastic marine debris follows the same
pattern as petroleum production, r is the same as for petroleum,
and K is calculated as a portion (4% × inflow ratio) of the final
cumulative petroleum production.
As a special feature of the logistic curve, maximum inflow
occurs when the stock is half of the final stock, K (Gallagher[
2011]). Thus, the inflow curve is shaped like a bell or peak, of
which the center is the maximum.
3. Results
3.1 Inflow ratio of plastic marine debris into the ocean
To determine the inflow ratio of plastic marine debris into the
ocean, we conducted a material flow analysis of plastics and
plastic marine debris (Fig. 1). In 2012, 13,355,000 tons (‘B’ in
Fig. 1) of plastic pellets (a precursor to most plastic products) were
produced in South Korea; 7,487,000 tons (‘D’) were exported,
an additional 465,000 tons (‘E’) were imported, and 5,868,000
tons (‘C’) were used to produce 6,333,000 tons (‘F’) of plastic
products (Korea Plastic Manufacturing Cooperatives, 2014). In
2013, 5,176,358 tons (‘J’) of plastic products were consumed,
comprising 4,036,358 tons (‘G’) of products manufactured
domestically and 1,140,000 tons (‘I’) imported (Korea Packaging
Recycling Cooperative, 2014; Korea Ministry of Environment,
2014). After consumption, 4,500,351 tons (‘K’) were treated at
waste plants (Korea Environment Corporation, 2012).
The annual inflow of marine debris in 2012 was estimated at
72,956 tons (‘R’ in Fig. 1). This was calculated by multiplying
the total annual inflow (91,195 tons in South Korea; Jang et al.
[2014A]) by the 80% ratio of plastics in marine debris (Der-
raik [2002]), and is the sum of the inflows from activities in the
sea (‘M’ = 58,370 tons × 80% = 46,696) and on land (‘N’ = 32,825
tons × 80% = 26,260). Thus, the plastic marine debris inflow ratio
is approximately 1.4% (72,956 / 5,176,358 = 1.4%) (Table 1).
3.2 Global inflow and stock of plastic marine debris
To estimate the stock of plastic marine debris, we applied the
Sy() K/1 k
s
o
----1–
⎝⎠
⎛⎞
e
ry–
+
⎝⎠
⎛⎞
=
266 장용창 · 이종명 · 홍선욱 · 최현우 · 심원준 · 홍수연
1.4% ratio (Table 1) to data on global plastic production pro-
vided by Plastics Europe (2011, 2012, 2013, 2014). However,
as only general production trends in plastic production are pub-
lically available in these documents, we obtained specific data
for each year via personal communication with Plastics Europe.
Though plastics were produced before 1950, this was dismissed
for simplification. Annual plastics production information is
attached as an appendix below.
Using these data, we calculated the global plastic marine debris
stock at the end of 2013 as 86 million tons and the plastic marine
Fig. 1. Material flow analysis of plastics and plastic marine debris in South Korea in 2013. (Drawn by this research based on data from Korea Plas-
tic Manufacturing Cooperatives (2014), Korea Packaging Recycling Cooperative (2014), Korea Ministry of Environment (2014), Korea
Environment Corporation (2012), and Jang et al. (2014A)).
Table 1. Plastic marine debris inflow ratio for South Korea (2013)
Items Amount (weight, ton) References
Annual marine debris inflow 91,195 Jang et al. [2014A]
Ratio of plastics in marine debris 80% Derraik [2002]; #1
Annual plastic marine debris inflow 72,956 91,195×80%=72,956
Annual plastic consumption (‘J’ in Fig. 1.) 5,176,358 MOK [2014]; KPRC [2014]
Plastic marine debris inflow ratio 1.4% 72,956 / 5,176,358 = 1.4%
#1. Though Derraik [2002] has shown 60 to 80% are plastic, 80% was applied for simplification.
Fig. 2. Plastic marine debris inflow and stock worldwide, under the assumption that 1.4% of plastic production enters the ocean. As the
stock is the accumulation of the inflow, the stock is around 20-fold larger than the yearly inflow as of 2013.
물질흐름분석을 활용한 전세계 플라스틱 해양쓰레기의 유입량과 현존량 추정 : 예비적 접근 267
debris inflow for the single year 2013 as 4.2 million tons (Fig. 2).
As the stock is the accumulation of the inflow, the stock is around
20 times larger than the yearly inflow as of 2013.
3.3 Speculation on plastic marine debris levels after 2013
According to Gallagher [2011], the total accumulated pro-
duction (carrying capacity) of petroleum will ultimately be 2.24
trillion barrels, and peak oil occurred in 2009. Next, we apply
the 4% ratio of petroleum turned into plastics and the 1.4% ratio of
plastic marine debris inflow. As 1 barrel equals 0.1589 tons, the
final total plastic marine debris stock (K in the Eq. 3) will be
about 199 million tons (= 2.24 trillion barrels × 0.1589 × 0.04
× 0.014), and the maximum inflow of plastic marine debris will
be 2.9 million tons (30.2 billion tons × 0.1589 × 0.04 × 0.014) in 2009
(Fig. 3). As the maximum inflow occurs when the stock is half
of K, the stock in 2009 is 99 million tons (half of 199 m tons).
Although these estimates of petroleum production may change
if new petroleum resources are found, this figure gives a glimpse
into the potential plastic marine debris volume of the future.
The speculative estimate of plastic marine debris inflow and
stock based on petroleum production (Fig. 3) differs from the
estimate based on plastic production (Fig. 2). For example, for
the year 2009, the inflow is similar but not the same (3.5 million
tons
≠
2.9 million tons), and the stock is likewise (70 million tons
≠
99 million tons). Such differences are brought about by dif-
ferent input factors, such as growth rates, initial stock, and carry-
ing capacity. In particular, for the speculative estimate after 2013,
we assumed that only petroleum, and no other material, was used
to make plastics.
4. Discussion
4.1 Review of assumptions
In this study, we assumed that the inflow ratio (annual plas-
tic marine debris inflow per unit of plastic consumption) was
the same for all countries and years from 1950 to 2013. But the
inflow ratio can change. For example, Liu et al. [2013] found
that strong recycling policies regarding plastic bags and bottles
decreased these types of debris on beaches in Taiwan vs. the USA.
We can generally assume that the inflow ratio will decrease as
waste management improves. Although we assumed that the
inflow ratio was the same for all countries and years, further
studies are needed to determine the inflow ratios for specific
countries and years.
We further assumed that plastic is not degraded in the ocean.
The final stage of degradation is called mineralization, wherein
carbon in polymers is converted into CO
2
(and ultimately incor-
porated into biomass), and there are some polymer types, such as
aliphatic polyesters, that progress to this stage (Andrady [2011]).
There are several methods of measuring polymer degradation,
including molecular weight loss (Shah et al. [2008]). For exam-
ple, Kim et al. [2006] found that polybutylene succinate (PBS)
lost about 13% of its molecular weight while high-density poly-
ethylene (HDPE) lost almost nothing when they were kept on
experimental compost soil for 80 days. Thus, our assumption of
no plastic degradation is not always true.
Although plastics might degrade in the marine environment,
we can assume that this occurs very slowly. For example, Lam-
bert et al. [2013] found that many nano-sized plastic particles
are produced when the molecular weight of the plastic is lost.
That is, more harmful pollutants are made when the original
plastics are seemingly degraded, if they are not completely miner-
alized. And, as sunlight and oxygen, important factors in deg-
radation, are limited in the marine environment, degradation is
likely much slower in the ocean than on land (Andrady [2011]).
The degradation speed of plastics is unknown, especially in
the ocean. If we suppose that plastics degrade in 600 years, for
example, then the stock of plastic marine debris will lose 1/600
of its weight each year. In this case, the plastic marine debris
stock in the year 2013 would be calculated as follows:
Plastic marine debris stock in the year 2013 (with 600 years
of degradation)
= ∑ Inflow of plastic marine debris each year × (1 - (2013 - year)
/ 600)) = 84 million tons
Here, 84 million tons is about 98% of the 86 million tons we
originally estimated. Thus, the assumption of no biodegrada-
Fig. 3. Speculation on plastic marine debris stock and inflow after
1950 with the assumption that 4% of petroleum is turned into plastics and
that 1.4% of plastics become marine debris.
268 장용창 · 이종명 · 홍선욱 · 최현우 · 심원준 · 홍수연
tion does not significantly affect the result.
We also assumed that plastic marine debris collection is zero.
Although a certain amount of plastic debris is collected around
the world, the amount is insufficient to significantly influence
the result. For example, only 570 tons of debris was removed for
the 10 years from 1997 to 2006 in the USA (NOAA [2008]). Glob-
ally, 52,617 tons of debris was removed by millions of partici-
pants in the International Coastal Cleanup campaigns in the 21
years from 1986 to 2006 (NOAA [2008]).
For the speculative estimate after 2013, we used the peak oil
estimate from Gallagher [2011]. Although there are fierce debates
on the extent of petroleum reserves and the timing of peak oil
(Chapman [2014]), this is not the focus of our study. Regard-
less of the extent of petroleum resources, it appears certain that
the stock of plastic marine debris will hardly decline even if the
production of plastics decreases in the future.
4.2 Comparison with previous estimates
In this study, the inflow ratio (annual plastic marine debris
inflow / annual plastic consumption) was estimated at 1.4% (72,956
ton / 5,176,358 tons = 1.4%) in South Korea and then extrapolated
worldwide. However, both debris inflow and plastic consumption
may be underestimated. For example, to estimate marine debris
inflow, we used data from the Han River in 2000 (Incheon City
[2001]) as the inflow from land sources. That study used a
5-cm mesh net to collect debris from the river and, consequently,
debris smaller than 5 cm, such as micro-beads (Fendall and
Sewell [2009]), is not included in the inflow estimate. Plastic
consumption was also underestimated because small businesses
are not taxed for waste and are exempted from reporting the
manufacture or importation of plastic (Korea Ministry of the
Environment [2014]). Thus, it is unclear whether 1.4% is an
over- or under-estimate.
Thompson [2006] suggested that upto 10% of plastics enter
the ocean (Cole et al. [2011]). If 1.4% changes to 10%, then the
inflow in 2013 would be 30 million tons and the stock at the end
of 2013 615 million tons, based on our estimates (see Appendix).
As there is no scientific basis on the 10% assumption of Thompson
[2006], it is unclear if 10% is relatively large or small. Again,
more work must be done to estimate the inflow ratio. In this
respect, a recent attempt to estimate plastic debris inflow from
the land on a per-country basis (Jambeck et al. [2015]) is highly
valuable. The estimate of plastic marine debris inflow from the
land in 2010 in South Korea (33,747 tons) by Jambeck et al. [2015]
is not much different from our own estimate (26,260 tons).
However, because debris inflow from activities in the ocean can
exceed that from activities on land in some countries (Jang et
al. [2014B]), it is important to also consider debris inflow from
activities in the ocean.
Our estimate of plastic marine debris inflow from activities
in the ocean is much smaller than that of NAS [1975], which
estimated it at 6,360,000 tons in 1975. This is markedly larger
than our estimates of 560,000 tons of inflow in 1975 and 4.2
million tons in 2013 (see Appendix). Such a difference can be
explained in part by the fact that the NAS [1975] estimate
occurred before MARPOL 73/78 (IMO [1997]) which prohib-
ited pollution from ships, including plastics and other materi-
als such as metal (cargo boxes) and food waste. Notably, 88%
(5,600,000 / 6,360,000 tons) of the garbage from NAS [1975] was
lost cargo from merchant shipping, and such losses have been
dramatically reduced with the development of shipping tech-
nology. Moreover, only 0.7% (44,520 tons) of the 6,360,000 tons
of NAS [1975] was plastic (Lebreton et al. [2012]).
The two previous estimates of stock, 6,600-35,200 tons (Cozar et
al. [2014]) and 269,000 tons (Eriksen [2014]), are much smaller
than our estimate of 86 million tons. This difference can be explained
in part by the fact that a large portion of plastic marine debris
accumulates on the sea bottom. For example, Jang et al. [2014A]
estimated that 90% of marine debris stock (152,241 tons) is on
the sea floor, 8% on the beaches, and only 2% in the water col-
umn and on the sea surface in South Korean waters. If we take
2% of our 86,219,000-ton stock estimate, we obtain 1,724,380
tons as an estimate of plastic marine debris on the sea surface
and in the water column. This is still larger than 269,000 tons;
however, the estimates of Eriksen [2014] and Cozar et al. [2014]
consider only plastic marine debris on the surface and would
presumably be higher if they included debris in the water col-
umn.
Regarding plastic marine debris on the sea floor, we must
remember that formerly floating debris can eventually become
submerged. Although some plastics are lighter than water, these
light plastics can gain weight and accumulate on the sea floor
for various reasons, such as plankton fouling (Andrady [2011]).
Likely because of this, there are reports of plastic marine debris
on the sea floor as deep as 1000 m (Debrot et al. [2014]; Eryasa et
al. [2014]; and Galgani et al., [2000]). Furthermore, fishing nets
and ropes made of polypropylene and polyethylene (Jang et al.
[2014B]) are the main components of marine debris collected
from the sea bottom in South Korea (MLTM [2009]). Again, Cozar
et al. [2014] and Eriksen [2014] considered only the water sur-
face, and did not consider plastic marine debris in the water
column.
물질흐름분석을 활용한 전세계 플라스틱 해양쓰레기의 유입량과 현존량 추정 : 예비적 접근 269
4.3 The value of preventive measures against irreversible
pollution and adequate indicators
If biodegradation of plastic debris in the ocean is close to zero, we
might say that pollution from plastic marine debris is irreversible,
much as the discharge of non-degradable pesticides is irrevers-
ible (Arrow and Fisher [1974]). If a certain type of pollution is
irreversible, countermeasures to prevent it should be valued
more, and stronger preventive measures should be taken under
the Precautionary Principle (Gollier et al. [2000]). Moreover, when
pollution is irreversible, reducing the stock is almost infinitely
costly. Thus, we must develop more policies to reduce the inflow
of plastic marine debris into the ocean.
However, the effectiveness of policies to reduce the inflow
of plastic marine debris should be measurable and evidence-
based (Sanderson[2002]). If certain policies are more effective
in reducing plastic debris inflow, they should be more supported
financially. To that end, the conceptual difference between inflow
and stock should be clarified when developing policy indicators.
In other words, we need to understand that current flow-reducing
policy has very little effect on the marine debris stock. According
to our estimate, for example, there is a stock of 86 million tons
of plastic marine debris as of the end of 2013, yet only 4.2 mil-
lion tons entered the ocean in 2013. Thus, even if marine debris
inflow were completely eliminated in 2014, the stock at the end
of 2014 would still be 86 million tons. Clearly, the effectiveness of
policies to reduce inflow can hardly be measured by indicators
based on marine debris stock.
As the effects of policy intervention differ according to the type
of policy instrument used, the indicators should also differ
(Table 2). For reducing debris inflow, the main policy indicator
should be the amount of debris entering the ocean in a given period.
For example, we might ask fishermen how much litter they pro-
duced during the past year. For reducing debris stock, the policy
indicator should be the amount of debris found in the ocean. For
example, we might measure the amount of marine debris on
beaches at a certain point in time. The various types of policy
strategies to cope with marine debris are listed on ‘The Honolulu
Strategy: A Global Framework for Prevention and Management of
Marine Debris’ (NOAA and UNEP [2011]. Unfortunately, there
are few studies on the inflow of plastic marine debris, while many
studies focus on the abundance—the stock—of marine debris
in the ocean (Ryan et al. [2009]; Cheshire et al. [2009]; Cole et
al. [2011]).
4.4 Future studies needed
Our study has many limitations. Many of the parameters
used generally in this study are derived from the specific case
of South Korea. Thus, more research is needed. First, plastic
consumption should be investigated in more detail for specific
countries. UNEP [2014] also emphasized that any problems ‘can
be managed when measured.’ However, while UNEP [2014] is
calling for participation from the business sector in measuring
plastics, government should play the central role in this regard,
as government policy impacts the management of plastic con-
sumption and pollution. Material flow analysis will be a useful
approach, of which Mutha et al. [2006] present a good exam-
ple from India.
Second, estimating plastic marine debris inflow at the national
level is vital but challenging. Jang et al. [2014A] reviewed sev-
eral previous studies for this purpose in South Korea. These
included (1) measuring debris inflow from rivers by capturing
debris with nets across the Han River (Incheon City [2001]);
(2) measuring debris inflow from rivers during a flood event
(Geoje City [2013]); (3) measuring lost fishing gear and gen-
eral garbage produced by ships via interviews with fishermen
(MLTM [2009]); and (4) measuring lost aquaculture buoys via
interviews with fishermen. These data were combined with
governmental statistics to estimate the marine debris inflow.
Though the accuracy of these types of measurement may be
questioned, they appear to be the best of the methods currently
available; clearly, better methods are needed. In particular, dump-
ing, which determines debris inflow, is a human activity, and
might be measured using social scientific methods.
Third, when estimating the stock of plastic marine debris,
Table 2. Examples of policy instruments and indicators for reducing marine debris flow and stock
Classification Policy instruments Policy indicators
Reducing
marine
debris
inflow
(1) Collecting debris in rivers with booms.
(2) Changing aquaculture practices.
(3) Increasing the legally required ratio of recycling
certain products via Extended Producers Responsibility.
(1) Amount of debris collected in a given period.
(2) Fishermen’s responses to the question of how much litter they
produced in a given period.
(3) Actual recycling ratio for the products.
Reducing
marine
debris
stock
(1) Collecting from beaches.
(2) Collecting from the seabed.
(3) Collecting from the water surface and column.
(1) Amount of marine debris on beaches at a given point in time.
(2) Amount of marine debris on the seabed at a given point in time.
(3) Amount of marine debris on the water surface and in the column
at a given point in time.
270 장용창 · 이종명 · 홍선욱 · 최현우 · 심원준 · 홍수연
debris travel must be considered. For example, debris on beaches
moves between the beach and sea many times each day (Kako
et al. [2010]). Thus, care should be taken when estimating debris
stock on beaches based on observations on beaches alone,
because a beach is part of the sea. Estimating the stock on the
sea surface might have the same challenges. As floating plastic
debris moves through the water column via the process of plankton
fouling (Andrady [2011]) and the water surface is part of the ocean,
we should be careful when interpreting the abundance of float-
ing plastic debris. Monitoring the abundance of plastic debris
on the sea floor is also limited by technology and financial cost as
huge sample sizes are required to overcome the very large spatial
heterogeneity in plastic litter (Ryan et al. [2009]).
5. Conclusion
In this study, we estimated global plastic marine debris inflow
and stock by applying material flow analysis of plastic marine
debris in South Korea to global plastic production. We estimated
that there is 86 million tons of plastic marine debris stock as of
the end of 2013, 20-fold greater than the annual inflow (4.2 mil-
lion tons for 2013). Thus, even if we reduce further inflow to zero,
the stock will still be considered. Consequently, the effective-
ness of inflow-reducing policies cannot be measured using indi-
cators showing changes in the stock. As pollution from plastic
marine debris is irreversible, the value of reducing debris inflow
is much greater than for reversible pollution. Therefore, we must
develop more methods of reducing inflow. As policies are more
supported if their effectiveness is clear, better indicators are needed
to show changes in inflow. To this end, we must pay careful atten-
tion to the conceptual difference between inflow and stock.
Acknowledgments
We thank Dr. Yan van Franeker at the IMARES Institute for
Marine Resources and Ecosystem Studies for sharing informa-
tion on annual plastic production obtained from Plastics Europe,
and Plastics Europe for making their data available. W.J.S was
supported by a research project titled “Environmental Risk
Assessment of Microplastics in the Marine Environment” from
the Ministry of Oceans and Fisheries.
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물질흐름분석을 활용한 전세계 플라스틱 해양쓰레기의 유입량과 현존량 추정 : 예비적 접근 273
Appendix. Calculation of inflow and stock of global plastic marine debris under the assumption that 1.4% of plastics enter the ocean and none
is collected or biodegraded
Year
Plastics
production
(a)
Plastic marine
debris inflow
(b = a×1.4%)
Plastic marine debris
stock (c = accumulation
of ‘b’)
Year
Plastics
production
(a)
Plastic marine
debris inflow
(b = a×1.4%)
Plastic marine debris stock
(c = accumulation of ‘b’)
1950 1,700,000 23,800 23,800 1982 63,000,000 882,000 11,403,000
1951 2,000,000 28,000 51,800 1983 69,000,000 966,000 12,369,000
1952 1,900,000 26,600 78,400 1984 74,000,000 1,036,000 13,405,000
1953 2,400,000 33,600 112,000 1985 78,000,000 1,092,000 14,497,000
1954 2,700,000 37,800 149,800 1986 83,000,000 1,162,000 15,659,000
1955 3,500,000 49,000 198,800 1987 90,000,000 1,260,000 16,919,000
1956 4,000,000 56,000 254,800 1988 96,000,000 1,344,000 18,263,000
1957 4,600,000 64,400 319,200 1989 99,000,000 1,386,000 19,649,000
1958 4,900,000 68,600 387,800 1990 105,000,000 1,470,000 21,119,000
1959 6,300,000 88,200 476,000 1991 109,000,000 1,526,000 22,645,000
1960 7,200,000 100,800 576,800 1992 116,000,000 1,624,000 24,269,000
1961 8,000,000 112,000 688,800 1993 121,000,000 1,694,000 25,963,000
1962 9,500,000 133,000 821,800 1994 133,000,000 1,862,000 27,825,000
1963 10,900,000 152,600 974,400 1995 138,000,000 1,932,000 29,757,000
1964 13,000,000 182,000 1,156,400 1996 148,000,000 2,072,000 31,829,000
1965 15,000,000 210,000 1,366,400 1997 158,000,000 2,212,000 34,041,000
1966 17,600,000 246,400 1,612,800 1998 165,000,000 2,310,000 36,351,000
1967 19,700,000 275,800 1,888,600 1999 178,000,000 2,492,000 38,843,000
1968 23,600,000 330,400 2,219,000 2000 187,000,000 2,618,000 41,461,000
1969 28,000,000 392,000 2,611,000 2001 192,000,000 2,688,000 44,149,000
1970 30,000,000 420,000 3,031,000 2002 204,000,000 2,856,000 47,005,000
1971 33,000,000 462,000 3,493,000 2003 212,000,000 2,968,000 49,973,000
1972 38,000,000 532,000 4,025,000 2004 225,000,000 3,150,000 53,123,000
1973 44,000,000 616,000 4,641,000 2005 230,000,000 3,220,000 56,343,000
1974 45,000,000 630,000 5,271,000 2006 245,000,000 3,430,000 59,773,000
1975 40,000,000 560,000 5,831,000 2007 257,000,000 3,598,000 63,371,000
1976 47,000,000 658,000 6,489,000 2008 245,000,000 3,430,000 66,801,000
1977 51,000,000 714,000 7,203,000 2009 250,000,000 3,500,000 70,301,000
1978 55,000,000 770,000 7,973,000 2010 265,000,000 3,780,000 74,081,000
1979 61,000,000 854,000 8,827,000 2011 280,000,000 3,920,000 78,001,000
1980 60,000,000 840,000 9,667,000 2012 288,000,000 4,032,000 82,033,000
1981 61,000,000 854,000 10,521,000 2013 299,000,000 4,186,000 86,219,000
