For those of you interested in economics, you might like to know that ‘one use’ plastic bags are called a ‘market failure’. This is due to the fact that their pricing does not account for external factors such as the impact of litter on wildlife, or the monetary cost to the community to clean up plastic bag pollution.
In Australia alone, 30-35 million plastic bags end up as litter rather than in landfill every year, according to 2007 figures from a report on ‘the investigation of options to reduce the impacts of plastic bags‘.
Degradable and biodegradable plastic bags have been touted as the solution to this problem by a number of prominent supermarkets. However, there is limited evidence that they make a positive difference and more evidence to the contrary! The amount of time plastic bags remain in the environment as litter is unclear but the following facts give you some idea of their possible effects.
The most common degradable bags, oxo-degradable bags, have a ‘pro-degradent’ which causes fast break down into fragments. These then remain in the environment and may take a very long time to completely degrade. The impact of these bags as litter may thus be greater than for a normal plastic bag, which generally remains as one product, not fragments.
Biodegradable plastic bags are made from a mixture of polyethene and starch products and in the right conditions, will break down into elements like carbon dioxide, water and methane. To be considered degradable, these must compost within 12 weeks and fully biodegrade within 6 months. This means they survive long enough to pose a threat to animals if littered, as they may be mistaken for food.
If biodegradable bags are littered and caught in trees, like the plastic bags in the image below, they are unlikely to be exposed to soil microorganisms which assist breakdown and so pose the same problems as regular ‘one-use’ plastic bags.
There are also questions raised about whether there is any benefit of degradable plastic bags even if they are properly disposed and end up in landfill. The Australian government published a report ‘The impact of degradable plastic bags in Australia’, which found that biodegradable plastics are unlikely to degrade in landfill as the microorganisms needed to help the break down, are not found in the dry anaerobic (oxygen deprived) conditions normally found in landfill.
The same report concluded that reusable bags have a lower environmental impact and gave better overall performance than either conventional or degradable ‘one-use’ bags, regardless of the degradability.
So the message is clear – reuse is the better option for the environment.