Déchets marins et microplastiques

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

The term plastic encompasses a wide range of polymeric materials, including rubbers, elastomers, textiles, and thermoplastics. Plastics can be fabricated from raw materials derived from petroleum, natural gas, or bio-renewables and have several advantages over other materials, being lightweight, durable, strong and extremely versatile.

Global production of plastics has increased from 1.5 million metric tonnes in 1950 to reach 245 million metric tonnes in 2008. Plastics production is spread around the globe and can be expected to rise to meet continuing demand.

As an example of main usages, in Europe, packaging accounts for 40% of the 45 million metric tonnes of plastics consumed in 2009, building materials account for 20%, and the automotive and electronics industries account for 7 and 6% respectively. Of these 45 millions tonnes, 23 million goes into the waste cycle and 11 ends up in landfills or in the environment. The rest of the waste is either recycled or burned for energy recovery. It is acknowledged by industry and Government alike that recovery of plastics needs to increase dramatically, as does the proportion recycled.

There are some newer plastic types on the market that are often assumed to be biodegradable. “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.

Bio-degradable means that the product may be broken down by living organisms, and a polymer can only be legitimately termed biodegradable when it passes a composting test under standard conditions and within a set timeframe, being broken down by living organisms in specific conditions into its constituent parts: carbon dioxide, water, inorganic compounds and biomass. These conditions may occur in industrial composters but not in the ocean, and thus many “biodegradable” plastics will not break down in the oceans any faster then other plastics. Truly biodegradable plastics, such as polylactic acid (PLA), tend to be more expensive and are not suitable for many applications requiring durability. “Bio-plastics” are not necessarily bio-degradable, and bio-degradable plastics are not necessarily bio-plastics.

As far as for the amount and types of plastics that make their way into the oceans it is very difficult to estimate because there are no worldwide figures, and current knowledge relies heavily on estimates from decades ago.

The majority of plastic waste entering the seas and oceans is considered to originate from land-based sources, and UNEP 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 transport;
• 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,
• accidental loss or system failure,
• poor waste management practices, and
• illegal disposal.

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