We're being warned not to throw contact lenses down the loo or sink. A study by Arizona State University says the plastic ends up in waste water treatment plants. It's then spread on farmland as sewage sludge which then ends up in the oceans when it's washed away by heavy rain. Around 14 billion lenses are thrown away in the US which adds up to around 200,000 kgs of plastic waste a year. It's another form of plastic affecting our environment.