Justin White, of Balclutha Primary School, asks :-

Why do we use plastic for packaging when it takes so long to break down in a landfill?

Stephen Moratti, an organic chemist at the University of Otago, responded.

Packaging needs to perform lots of roles. It needs to keep microbes and dirt out, and often air. It often needs to be transparent, should be strong, lightweight, cheap and capable of being printed on. Only plastic fully meets all these needs. It does suffer from the problem of not breaking down in landfills, but up to now people just ignored this and dug more holes to bury it in. It should be noted that some food packaging can really help to prevent waste by extending the life of the products.

One would think that paper would be better for the environment. But paper-cardboard containers tend to be only used once and thrown way. The paper making industry is quite polluting and requires lots of energy. If you can reuse plastic items many times (lunch bags, reusable shopping bags) then plastic may actually be better for the environment. For one off items (e.g. wrapping meat) you are better off using paper, though supermarkets don't like doing that as paper can let liquids like blood seep through. No reason not to use paper bags for fruit though. I suspect supermarkets like plastic bags even there as they are cheaper, take up less room, and are less likely to break spilling all your apples on the floor. Paper is used in supermarkets for items such as warm bread, as plastic cant let the moisture out so the outside of the bread can get a little soggy.

Scientists are now developing plastics that can degrade. Some are based on starch - and in Australia you can buy chocolate boxes where the case is starch. Other polymers such as polylactic acid that can degrade are being increasingly used. However, these plastics tend to be more expensive and not quite as strong. Another option is to chemically recycle the plastic, and the plastic in fizzy bottles (PET) is a good example where this can be done very efficiently. The trouble with most plastic waste streams is that there are a whole mix of dozens of types of plastics, and unless one is able to separate them cleanly which is almost impossible, one can't cleanly recycle them.

Other options include chopping up the plastics finely and using them as fillers for say road and concrete. Burning them as using the heat to generate electricity might be possible, but often the additives and inks used can make the smoke toxic.

The take home message is that plastics are superb in the role of packaging but we still need to find better ways of stopping the waste. At home you can help by reusing your bags as much as possible, and refilling plastic containers (e.g. ketchup) from the cardboard brix they sell at the supermarket.

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