Déchets marins et microplastiques

2. What kind of plastic waste ends up in the marine environment?

The source document for this Digest states:

2. Plastics and waste: production, types and uses (sessions E, H)

2.1 Types of plastics

Plastics are man-made, non-metallic polymers of high molecular weight, made up from repeating macromolecules. The term plastic encompasses a wide range of polymeric materials, including, rubbers, technical elastomers, textiles, technical fibers, thermosets and thermoplastics, with some 200 plastics families in production including polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinylchloride (PVC), polyethylene terepthlate (PET), nylon, polyvinyl alcohol (PVA) and acrylonitrile butadiene styrene (ABS) synthetic rubbers. Plastics can be fabricated from feed-stocks derived from petroleum, natural gas, or bio-renewables and have several advantages over other materials, being lightweight, durable, strong and extremely versatile.

2.2 Plastics production

The workshop was informed by PlasticsEurope that Global production of plastics has increased from 1.5 million metric tonnes in 1950 at an average rate of 9% per year to reach 245 million metric tonnes by 2008 with a slight decline to 230 million metric tonnes per year in 2009 According to PlasticsEurope (www.plasticseurope.org), 25% was produced in Europe (EU 27 members states plus Norway and Switzerland; EU27+2), 23% in the NAFTA region including the USA, 16.5% in Asia (excluding China), 15% in China, 8% in the Middle East, 5.5% in Japan 4% in South America and the rest of the world 3%. Plastics production is therefore spread around the globe and can be expected to rise to meet continuing demand. In the EU, as an example of a developed region, albeit with strong N-S and E-W differences, packaging accounts for 40% of the 45 million metric tonnes of plastics consumed in 2009, with low density PE (LDPE), high density PE (LDPE), PP, and PET as the predominant materials. It should be noted that production and consumption vary from region to region, e.g. Europe produced 55 million metric tonnes but only consumed 45 in the same year (2009). Building materials account for 20%, with PVC as the main component followed by HDPE, epoxidised polysulphides (EPS) and polyurethane (PUR), while the automotive and electronics industries account for 7 and 6% respectively, using a much wider range of materials. However, there are significant differences in the pattern of production within Europe. It is known that the cost of raw material may induce the substitution of different polymers for the same purpose in other regions, so the pattern of production and use is not consistent worldwide.

2.3 Waste production and reduction

Of the 45 million metric tonnes of plastics consumed by converters in 2009 in the EU, just over 50% or 23 million metric tonnes goes to waste with 11.2 million metric tonnes being disposed of and 13.1 million metric tonnes being recovered (up from 12.8 in 2008), of which latter quantity, 5.5 million metric tonnes is recycled with 7.6 million metric tonnes being incinerated for energy recovery.

According to the US-EPA municipal solid waste statistics for 2008 (US EPA, 2008) 30 million tons of plastic waste is produced annually, of which only 7.1% is recovered. A further 19.8 million tons of rubber, leather and textiles, containing a substantial polymer component achieved 15% recovery. While overall recovery of plastics for recycling in the USA is relatively small, at 2.1 million tons in 2008, PET soft drink bottles were recovered at a rate of 37% and HDPE milk and water bottle recovery was estimated at about 28%. An additional 12.6% is burned with energy recovery. It is acknowledged by industry and Government alike that recovery of plastics needs to increase dramatically, as does the proportion recycled, and the workshop was informed of efforts by the plastics industry in the EU and the USA over the last 10-15 years to promote recovery and recycling.

PlasticsEurope informed that in the EU the amount of plastic waste going to landfill has been stable in recent years despite rising plastics consumption. A total of 9 of the EU27+2 countries have achieved plastic waste recovery of greater than 80% and of these, Germany as the largest waste producer recycles the highest proportion (ca.35%) of its ca. 4 million metric tonnes of recovered plastic waste annually, most of the rest being combusted with energy recovery. One important feature is that these 9 countries with substantial recycling sectors all have strong legislation restricting the use of landfill sites for plastics disposal. Recovery figures for the remaining 20 EU27+2 countries are all much lower than the above. The UK with the second highest annual plastic waste production of 3.47 million metric tonnes has only a 26% plastic waste recovery rate.

Municipal waste management: two cases

Malaysia

The workshop was informed that peninsular Malaysia produced ca. 17.5 million metric tonnes of solid waste in 2002, showing a 0.4 million metric tonnes rise in each of 2000 and 2001; between 9 and 17% consisted of plastics. About 76% of waste generated is collected, meaning that 24% is unaccounted for, 1 to 2% is recycled nationally and only about 5% of waste collected in Kuala Lumpur is reused and recycled. Over 40% of 175 disposal sites are operating as dumpsites and intermediate treatment is limited to small- scale thermal treatment plants on tourist resort islands. The waste contains large amounts of organic material (40.6 to 76.8%; wet waste) and many older sites are poorly managed.

The Philippines

In Quezon City, with a population of 2.77 million people, 98% of 736,083 t of solid municipal waste is recovered to controlled disposal, 250,455 t by the informal sector and 476,407t by the formal municipal sector. Only 9,221 t is lost or goes to uncontrolled disposal (compare this to the figures given in the main text on the left). The total valorised or diverted waste is 39.12%, of which 229,842 t by the informal sector and 58,130t by the formal sector. The informal sector is therefore responsible for the majority of recycling. The proportion of polymeric materials reported is: Plastic 16.00% (PET 1.87%, HDPE 1.61%, Film Plastic/LDPE 12.45%), Diapers/Cigarette Butts 4.55%, Textiles 2.88%, Rubber 0.33% (these latter two groups may only be polymeric in part (Source: UN-Habitat, 2009)

2.4 Bio-sourced and “Biodegradable” plastics

The workshop looked specifically at some newer plastic types which are often assumed to be biodegradable and their implications for the problem of marine litter. Bio-plastic (bio-based or bio-sourced) implies that the polymeric product has been made from a biological (living) or renewable source, e.g. corn, or sugar cane. Regarding bio- plastics, the American Chemistry Council supports such innovation but also calls for the application of Life Cycle Assessment (LCA) to assess the trade-offs associated with alternatives to oil or gas based polymers, including:

• the potential to reduce/increase energy consumption and greenhouse gas emissions,
• the true impacts of agricultural production of the feedstock, including water use, fertilizers, eutrophication and especially, the impacts of land-use changes, e.g. deforestation,
• socio-economic factors, including potential impacts on the food supply and foodprices, where a bio-sourced material competes with people for the same (food) resource.

Bio-degradable means that the product may be broken down by living organisms, such as bacteria and fungi (eventually becoming wholly or partly mineralized to CO2 and water). In fact, a polymer can only be legitimately termed biodegradable when it passes a composting test under standard conditions and within a set timeframe1. However, such conditions are not found in the environment at large and such polymers therefore do not biodegrade to any significant extent under natural conditions; this includes the marine environment. Being bio-based does not mean a material is bio-degradable and conversely, being bio-degradable does not mean that a material is bio-based. The California Integrated Waste Management Board (CIWMB, 2007) reported an experimental study on bio-plastics degradation finding that everyday household articles and carrier bags fabricated from: sugar cane, PLA, PHA and ‘Ecoflex’ bags were all mineralised to >60% CO2 and H2O in several experimental and industrial composters within 180 days. Oxo-degradable bags on the other hand showed no degradation. Only PHA bags demonstrated some disintegration in ocean water, while none of the other products disintegrated at all. CIWMB also concluded that biodegradable plastics and plastics that degrade in oxygen or sunlight reduce the quality and impair the mechanical properties of finished products manufactured with recycled content from recovered plastics.

2.5 Sources and inputs of plastic waste to the marine environment

UNEP (2009a) reported that “there are no recent and certain figures on the amounts of marine litter worldwide. Nor are there any such global figures on the annual input of marine litter to the marine and coastal environment”. Our knowledge of the possible quantity of marine litter entering the seas and oceans still relies too heavily estimates such as the US National Academy of Sciences (1975) value of 6.4 million metric tonnes of marine litter per year. This number is compiled exclusively from maritime sources, i.e. “litter generated in the oceans”, such as by shipping, fishing and the military transport and does not include land- based sources. Land-based sources are considered to contribute the largest input of plastics (and therefore micro-plastics) entering the oceans (UNEP, 2009a). Rivers and wastewater discharge are important point sources and estimating the contribution of river systems could be key to quantifying inputs. Rivers fall under national jurisdictions and an improved knowledge of plastics and micro-plastics inputs may encourage local policy making.

Shipping is a major source of marine litter in some regions (van Franeker et al., 2009) and although Annex V of the Marpol 73/78 convention covering garbage is currently being reviewed (See Section 5.2), data still remain scarce as to how much plastic enters the sea from ships and offshore platforms. A fuller overview of marine litter sources is given at the end of this section.

Ribic et al. (2010) provided decadal trend data for beach debris along the Eastern Atlantic seaboard of the USA, noting that:

1. The Southeast Atlantic region had low land-based and general-source debris loads and no increases despite the largest percentage increase in coastal population;
2. The Northeast region, with a smaller percentage population increase, also had low land-based and general-source debris loads and no increases;
3. The Mid-Atlantic fared the worst, with an increasing coastal population and heavy land-based and general-source debris loads that increased over time;
4. Ocean-based debris did not change in the Northeast region where the fishery is relatively stable while it declined significantly over the Mid-Atlantic and Southeast regions.

Bravo et al. (2009; see Table 1 below) summarized the densities of anthropomorphic marine debris world-wide, expressed in numbers of items per m2. These numbers show (outliers removed) that there are on average 1.3 plastic items for every m2 of the worlds’ shoreline (201 beaches on all five continents) and often much more. This however gives no impression of size or type of the items involved.

Table 1. Densities of ‘anthropogenic marine debris’ reported from beaches throughout the world. Adapted from Bravo et al. (2009).

Table 2 below, shows relative proportions of different types of items being listed in Center for Marine Conservation/Ocean Conservancy reports from 1989 to 2007 (UNEP, 2009a) and provides a clear indication of the prevalence of plastic being washed up on beaches.

Table 2. ‘Top ten’ marine debris items; adapted from UNEP (2009a), compiled from annual ICC data reports, Center for Marine Conservation/Ocean Conservancy (1989-2007).

UNEP (2009a) provides statistics on ‘standing stocks’ of litter (kg/km) on beaches around the world, collected through UNEP Regional Seas participation in ICC events in 2005, 2006 and 2007. Cleaner beaches have generally a few kg/km of litter, intermediate beaches have tens to hundreds of kg/km and occasionally, heavily littered beaches have one to several tonnes/km of coastline.

The North Western Pacific Action Plan (NOWPAP, 2009), a UNEP Regional Seas Programme reported a survey of marine litter in Japan, which demonstrated between 2.2 and 46 tonnes/km/year of marine litter on 11 beaches monitored during a 1 year survey; this consisted for 11 to 39% of plastics.

The majority of plastic waste entering the seas and oceans is considered to originate from land-based sources, and UNEP (2009a) identified the following:

• street litter which is washed, blown or discharged into nearby waterways by rain, snowmelt, and wind,
• inappropriate or illegal dumping of domestic and industrial rubbish, public littering
• inadequately covered waste containers and waste container vehicles
• poorly managed waste dumps
• manufacturing sites, plastic processing, and transport2;
• sewage treatment and combined sewer overflows
• people using the sea for recreation or shore fishing
• shore-based solid waste disposal and processing facilities

A lesser proportion can be attributed to maritime transport, exploration and drilling platforms as well as fishing, although it is recognised that in some localities, these may be dominant sources of marine litter and plastics. Some debris enters the water from accidental loss or system failure, while other debris comes from poor waste management practices, and illegal disposal.

To the above sources, the GESAMP workshop added the following:

• sewage sludge dumping grounds at sea;
• sea-based aquaculture activities: some recent studies (Hinojosa & Thiel, 2009; Astudillo et al, 2009) have identified aquaculture activities as major sources of marine plastic debris.

Source & ©: ,  Proceedings of the GESAMP International Workshop
on micro- plastic particles as a vector in transporting persistent, bio- accumulating and toxic substances in the oceans. 28-30th June 2010, UNESCO-IOC,
Paris. 2. Plastics and waste: production, types and uses (sessions E, H), p.12-17.