Ooh just remembered. The last time we had a tin of quality street in school the tin said the plastic wrappers were biodegradeable so we have saved them for next time we teach this so we can compare. I have done this experiment with a low ability class and it usually needs leaving about a week. You can also get students to look at the impact that plastics persisting in the environment have on wildlife. This is a good site http://www.turtlebags.co.uk/_wsn/page6.html It's also worth getting hold of some items made from recycled plastic eg, those little lunch bags they used to have in Boots which were made from 2 'Coke' bottles, fleeces, the pencils that are made from recycled office cups....... Useful to look at the price of the recycled product compared to that made from crude oil. See I knew I'd remember some stuff when I finally woke up!