Twenty-five years ago they didn’t exist. Now, compact discs (CDs) and digital video discs (DVDs) are everywhere. We buy them from music shops, we copy our music onto them, all our computer programmes and games come on CDs, and we use them to back up our work on the computer. CDs have become so popular that we even get them free with magazines.

Compared to the old vinyl records, or cassettes, or even floppy discs, CDs offer a lot of advantages. They are smaller and lighter and they hold much more information, be it music, text, programmes or pictures. They are convenient to carry around, last longer and whatever you record on them is safer, in that you are not likely to lose the information. DVDs hold a lot more information so we use them to store programmes, watch and record movies. Since laser beams read CDs and DVDs and no mechanism comes into contact with the recording medium, these discs are not prone to damage, as are tapes and records.

A CD usually comes in a slim box called a ‘jewel case’ made out of moulded plastic. This protects the CD, makes it easy to stack and to carry around, and provides space for information on the disc’s contents.

CDs are also getting cheaper to make, and therefore cheaper to buy. In 2000, more than 700 compact disc factories were operating worldwide.

So where’s the hitch?

The problem with CDs is their popularity: the International Recording Media Association estimates world demand for CDs at around 9 billion annually! When we don’t need them anymore, where will these billions of discs end up? All you can do with them is throw them away; from the trash can they’ll end up in a landfill or be burnt in an incinerator. In the US alone, each month more than 45 tonnes of CDs become unwanted. Each year, over 55 million boxes of software go to landfills and incinerators, and people throw away millions of music CDs along with the jewel cases they came in.

The fact that CDs are oil derived should indeed have set alarm bells ringing (see plastic bags) a long while ago.

CDs and DVDs are made out of a layered combination of materials, plastics, metals and dyes. The base is a piece of clear plastic called polycarbonate that is around 1.2 mm thick. Polycarbonates are a particular group of plastics derived, as most plastics are, from oil. They are called polycarbonates because they are long chains of molecules linked together by carbonate groups (-O-CO-O-).

Then next layer is a very thin (50 nano metres!) reflective layer of aluminium (sometimes gold is used for very high quality CDs). A thin layer of lacquer or acrylic plastic is then sprayed over the aluminium to protect it. This last layer can be printed on. DVDs are the same diameter and thickness as CDs. They are made from the same materials and manufacturing methods as CDs, but they have more layers. The aluminium coating is only 55-70 microns thick, and the lacquer and printing account for approximately 20 microns of the overall thickness.

The metals are so thin they are not worth recycling, only the polycarbonate is. But, in order to recycle the polycarbonate the coatings must first be removed. Therefore it’s not worth recycling small numbers of CDs.

The material used to make CDs and their jewel cases is not biodegradable: they don’t break down into harmless or biologically useful substances in landfills. And, as is typical of plastics, when burnt CDs and CD cases release extremely poisonous dioxins and furans as gases. These are produced when plastic burns in the presence of even a small quantity of chlorine. It is very difficult to totally ensure a chlorine-free area in an incinerator; in fact, dioxins can even be formed outside the chimney, where the incinerator gases are released.

The jewel case is worse in this regard. A standard CD jewel case is often made from polyvinyl chloride, more commonly known as PVC, a plastic that itself contains chlorine. A particular danger of dioxins and furans is that they ‘bio-accumulate’, meaning that even if they are originally present in tiny quantities they are stored in the body where they slowly build up to a dangerous level.

A problem perhaps particular to India and other developing countries is that the analysis of dioxins requires very expensive equipment and highly trained staff, of the sort available only in a limited number of laboratories. Worldwide, only around 100 laboratories are able to do this and most of these can only test soil or water samples. Testing for dioxins in food or biological samples -- such as the blood of exposed people -- is much more difficult and only about 20 laboratories can do this. A test could cost anything between US$ 1,200 for a single biological sample, to more than US$ 10,000 for a complete assessment of an incinerator.

Of the actual CD, one of most dangerous products in the breakdown process is something called bisphenol-A (BPA). BPA is formed as polycarbonate material slowly breaks down in landfills, a leaching process that takes place quicker in the presence of oils or fats. It can soak into the ground and into nearby water sources. BPA is an endocrine disruptor, which means that it is similar to natural chemicals called hormones that are found in animal and human bodies. Hormones are essential to the normal functioning of the body and control important aspects of life like growth, sexual and mental development. If endocrine disruptors get into the body they can cause damage by mimicking these natural chemicals and hence giving the wrong signals to the body. Laboratory tests have shown BPA to cause serious damage, including to brain chemistry, behaviour, the immune system, and male and female reproductive systems.

At one time, water bottles, especially those used by children, used to be made from polycarbonates. When the danger of BPA leaching was discovered these bottles were immediately banned, as were other polycarbonate food storage items. This gives a small idea of just how dangerous BPA is thought to be.

There is some hope on the horizon though. One of the positive things about polycarbonates is that if collected in large enough quantities they can be recycled quite well compared to other plastics. Some companies in Europe and the US do recycle old CDs and DVDs into high-quality plastic. And, better still, last year the electronics company Sanyo claimed to have developed a disc based on a plastic-like substance made from corn, which, it claims, is as easy to use as polycarbonate but will biodegrade when thrown away. The company says that around 85 corn kernels are needed to produce one disc, which means an average ear of corn can produce around 10 discs!

But before such biodegradable options become commonplace, one thing you could do is reuse your CDs as often as possible. Always buy re-recordable CDs instead of single-use ones whenever possible. And when they can no longer be used to record, or when you get sick of what used to be your favourite band, don’t throw them away. Use them around the house for as long as possible. Old CDs can be used as drink coasters or as reflectors on bicycles. They can also be used in gardens as bird-chasers, as hung CDs seem to frighten away birds as they shine and spin in the breeze.

-- Manoj Nadkarni

InfoChange News & Features, June 2006