Are you confused about what happens to a plastic bag when you throw it away? You should be! The terminology regarding plastic bags and compostable and biodegradable properties is very confusing, so here are some generally accepted definitions.

Compostable:

materials are capable of undergoing biological decomposition in a compost site, to the extent that they are not visually distinguishable and break down to carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials (e.g. cellulose). Compostable materials leave no toxic residue and therefore, the resulting humus is a safe and healthy contribution to soil.

In order to be classified compostable, the degradation must meet certain specified criteria such as rate biodegradation, maximum residue of material left at a specific point in time and a requirement for the material to have no harmful impact on the final compost or the composting process. All compostable plastic is therefore also biodegradable. The most commonly used standards for compostable plastic are the American standard ASTM #D6400-99, the European standard EN-13432 and DIN V-54900.

The important thing to remember with a compostable plastic bag is that when you can no longer use it (and you can re-use them!) then you need to compost what’s left.

Biodegradable:

materials will degrade from the action of naturally occurring micro-organisms, such as bacteria, fungi etc. Biodegradable material is not necessarily compostable, as the residue may be toxic and is, therefore, not considered compostable. For biodegradation to take place the micro-organisms also need oxygen and moisture.

Biodegrade sounds good, doesn’t it? However there are three important things to remember when a bag is labelled ‘biodegradable’

• The conditions have to be RIGHT for a bag to biodegrade. If the conditions aren’t right; the bag WON’T biodegrade well. Conditions are generally NOT RIGHT in your bin; landfill sites; the local river; the sea or up a tree. Typically it can take years for biodegradation to occur in a landfill, if it happens at all.

• IF a bag biodegrades and that is a big IF; it may still leave a toxic residue.

• ‘Biodegradable’ plastic is bad news for recycling. It is not recommened to mix ‘biodegradable’ plastic with ‘normal’ plastic. If plastic recycling is contaminated with ‘biodegradable’ plastic the subsequent product could be corrupted and weakened.

• ‘Biodegradable’ bags are not the answer to environmental plastic bag litter because the conditions required for full biodegradation are not met.
  
  

Photo-degrade

To break down by the action of natural daylight. Plastic that can only be broken down in this way just gets smaller and smaller but still remains a plastic.

Degradable

A confusing term because it is used in different ways. All of the above processes are forms of degradation. If someone says that they have a degradable product, ask them how it degrades. It may be that you’ve found a great product which composts. On the other hand it may be a product that just, well, degrades. Degrade just means to break something down. You can degrade something by tearing it up into smaller and smaller pieces. So, most things are degradable. On its own this term says nothing about how long it may take or what is left in the end. When it comes to plastic what is left in the end are lots of small pieces of plastic.

Plastic Facts

80% of marine waste comes from land based sources and up to 80% of that is plastic.

Most of the marine debris in the world is comprised of plastic materials. The average proportion varies between 60 to 80% of total marine debris.

Gregory, M.R., Ryan, P.G. 1997. Pelagic plastics and other seaborne persistent synthetic debris: a review of Southern Hemisphere perspectives. In Coe, J.M., Rogers, D.B. (Eds.), Marine Debris- Sources, Impacts, Solutions. Springer-Verlag, New York, pp.49-66.

Nearly 80% of marine debris comes from land-based sources.

Faris, J. and Hart, K., Seas of Debris: A Summary of the Third International Conference on Marine Debris, N.C. Sea Grant College Program and NOAA, 1994, title page.

Most of the land-based rubbish is conveyed to oceans through storm drains. The main sources of plastic and other types of human-made debris in urban runoff include: litter (mostly bags, packaging and single-use disposable products), industrial discharges, garbage transportation, landfills, construction debris, and debris from commercial establishments and public venues.

Algalita Marine Research Foundation

The ocean is especially susceptible to plastic pollution. It takes longer for the sun to break apart plastic in the ocean than on land because of the oceans’ cooling capacity. Plastic pieces can attract and hold elements like PCB and DDT. PCBs are persistent organic pollutants and have entered the environment through both use and disposal. PCB’s are banned because they are carcinogenic. DDT is an organochlorine insecticide that was banned in the UK in 1984.

Algalita Marine Research Foundation

Sharks with plastic rings wrapped around their gills and mouths caught in southeast Brazil.

Sazima, I. Gadig, O.B.F. Namora, R.C. Motta, F.S. Plastic debris collars on juvenile carcharhinid sharks (Rhizoprionodon lalandii) in southwest Atlantic. Marine Pollution Bulletin, Volume 44, Issue 10, October 2002, pp. 1149-1151

The world produces over 200 million tonnes plastic annually. Around half of this is used for disposable items of packaging that are discarded within a year. This debris is accumulating in landfill and the problem is growing.

Dr Richard Thompson. Marine Ecologist at the University of Plymouth.

UK beaches contain on average 2000 pieces of litter for every kilometre.

Marine Conservation Society.

Globally, over 1 million and 100 thousand marine mammals and turtles die every year from entanglement or ingestion of plastic.

LAIST. 1997

Conservative estimates show 8 billion lightweight plastic carrier bags are issued in the UK annually.

DEFRA 2003

That’s approximately 166 bags per adult annually.

-on average we use each plastic bag for 12 minutes before disposing of it

United Nations Environmental Programme.