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Plastic bags being surprisingly cheap and durable make it a viable utility option for many supermarkets and convinient stores alike. But these bags aren't always recycled properly and can become a liability to the environment. Plastic bags are made from the unrenewable oil polyethylene. If uncontrolled they can fill up the landfills, oceans and streets that can lead to floods.
Scientists don't know the precise duration for plastic to decompose. One thing is for sure and that is polyethylene does not biodegrade. This was tested on by scientists using respirometry tests. Polyethylene was sealed inside an isloted chamber containing oxygen and microbe rich compost.
Normally after a while bacteria would digest leftover food, fabrics, paper or cardboard producing carbon dioxide as a byproduct. The CO2 level tells us how fast it decomposes -slate.com. Microorganisms do not digest plastic. However unlike glass, it does indeed decompose by UV rays from the sun that break the chemical bonds within plastic. This is called photodegradation and can take up to 20, 500 or 1000 years depending on the amount of sunlight. In landfils where plastic gets buried under heaps of trash, the plastic may reside forever.
Photodegradation is hardly a good thing because although the plastic breaks down into little pieces, it's still there. If plastic manages to photodegrade into the ocean it will release toxic chemicals harming the marine life and harming humans by the consumtion of sea creatures.
Biodegradable plastics may be the solution to a better environment, but according to futurenergia.org, not a solution to laziness. Made from starch or plant based material, biodegradable plastic under the right conditions will successfully biodegrade into carbon dioxide, water and biomass. This means they cannot be disposed to landfils because of the lack of oxygen required by the microbes.
The best way to save the environment from plastic bags is to not use them at all. Converting to cardboard boxes or calico bags may help the earth. Recycling centers are very uncommon in Indonesia. Plastic is either burned, spreading tiny particles of plastic and releasing toxins, or dumped into landfils. Hopefully as the awareness for saving earth increases, the near future will provide convinient places to recycle nearby supermarkets or malls.
http://www.theguardian.com/environment/cif-green/2009/jun/18/greenwash-biodegradeable-plastic-bags