Freitag, 11. März 2016

Global marine plastic debris amount estimation


Several estimates about the amount of plastics entering the ocean each year exist. Jambeck et al. (2015) estimate that amount to be about 8 million t, Hammer et al (2012) say it is 6.4 million t and Plastics Europe (2015) state it to be 10% of the plastics produced, thus 31 million t. Further, Eriksen et al. (2014) estimate that more than 260 000 t float on the surface while Cózar et al. (2014) say the floating mass should be some 10 000 t - and that it should be more, so a lot is removed by nano-fragmentation and ingestion, other sinks. So their number is still by far within the Eriksen estimate.
 
If these estimates are combined now - about 260 000 t floats (15%), then 260 000 t is washed ashore (15%) and 1 200 000 t sinks to the sea floor (70%) (Barnes et al, 2009). This is then 1.7 million t in total - but the annual input, according to Jambeck then is 8 million t. If any of the 3 input estimates here (6.4 million t, 8 million t or 31 million t) is anywhere near correct, then the total mass already existing in the ocean from about 50 year of incessantly increasing plastics production cannot be in the order of 1,7 t in total. With 15% washed ashore, where the waste still is in a marine ecosystem, maybe half of that is cleaned up. But a tiny part of the floating debris is cleaned up now and then as well and some other processes remove plastics that are ingested etc. Then in total approximately 10% of the debris entering the ocean is actually removed some way or another, which likely is an optimistic estimate. This would mean that 90% of the debris entering the ocean stays there. With lifetimes of the order of hundreds of year, the plastic can only be fragmented, but not biodegraded. Global annual plastic production started off with 1.5 million t in 1950, increasing steadily to over 300 million t nowadays (see Figure 2). The estimates from literature could probably be averaged to 10 million t for 2015, which is about 3% of the plastics produced. This number can then be used to calculate the total amount of plastic waste that must have entered the ocean since plastic production began in the 1950ies, which is approximated to be about 200 million tons (see Figure 3).  So instead of the given 1.7 million t of total marine debris from literature, the more fitting number of 200 million t in total will be used for illustrations and considerations of the marine debris picture. 

Figure 2: Growth in global plastic production 1950-2014, from Plastics Europe, the facts 2015










Year
plastic amount
estimated waste
Year
plastic amount
estimated waste
1950
1.5
0.045
1983
77
2.31
1951
2
0.06
1984
80
2.4
1952
3
0.09
1985
82
2.46
1953
4
0.12
1986
85
2.55
1954
5
0.15
1987
90
2.7
1955
6
0.18
1988
96
2.88
1956
7
0.21
1989
100
3
1957
8
0.24
1990
107
3.21
1958
9
0.27
1991
112
3.36
1959
10
0.3
1992
120
3.6
1960
11
0.33
1993
125
3.75
1961
12
0.36
1994
130
3.9
1962
13
0.39
1995
137
4.11
1963
14
0.42
1996
140
4.2
1964
15
0.45
1997
150
4.5
1965
16
0.48
1998
155
4.65
1966
18
0.54
1999
160
4.8
1967
20
0.6
2000
172
5.16
1968
25
0.75
2001
185
5.55
1969
28
0.84
2002
200
6
1970
30
0.9
2003
208
6.24
1971
32
0.96
2004
215
6.45
1972
35
1.05
2005
225
6.75
1973
38
1.14
2006
230
6.9
1974
40
1.2
2007
240
7.2
1975
44
1.32
2008
245
7.35
1976
50
1.5
2009
250
7.5
1977
55
1.65
2010
270
8.1
1978
62
1.86
2011
279
8.37
1979
65
1.95
2012
288
8.64
1980
68
2.04
2013
299
8.97
1981
70
2.1
2014
311
9.33
1982
75
2.25
2015
320
9.6




6773
203



Figure 3: Approximated marine debris amount in million t, calculated with 3% of the plastics produced enter the ocean




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