As plastic, like oil, wood, animals, vegetables and us, is mainly hydrocarbon i.e molecules mainly composed of carbon and hydrogen atoms, plus a few others, then when any of these oxidise e.g. by rotting, burning, composting, or by digestion after being eaten, then the product is mainly CO2 and H2O - no escaping that, as most kinds of 'natural' degradation are by oxidation. It's the 'easy' default reaction that happens when nature's animals (as opposed to plants) are left to get on with it - 'easy' because it requires no energy input, in fact oxidation is exothermic i.e. gives off heat. So as well as 'carbon dioxide, water, organic material and a small amount of inorganic residue', these decomposing plastic bags also give off heat, which just goes to waste. (There's also anaerobic degradation, as in the airless depths of a landfill, plus other kinds of man-created chemical breakdown).

If I get your drift, I think you're right Mike - rather than eco-fashionable bio-degradation of plastics, better to store plastics safe and undegraded in deep holes in the ground, aka landfill, where it can one day be 'quarried' as a valuable raw material for re-processing, once oil gets so expensive it can't be used ad-lib any more.

So this is another acceptable way of emitting CO2?

In any case doesn't the fact that it takes at least 4yrs to degrade, defeat the argument for the protection of seagulls [I cant see my plastic potato bags getting anywhere near turtles no matter what becomes of them]

Because ones not packaged in plastic are inconvenient to get hold of, especially at Christmas. Sad but true, guilty as charged

Biff, of course we can vote with our feet and refuse such things. But would it make any difference if a couple of thousand even million people did so? I don't think so. The way forward is to ban plastic packaging. In my view oil derived products should only be used where there is not a sustainable alternative capable of meeting the demand.

Posted By: Henry SearsThere are too many people on the planet. You ban plastic packaging and the demand for paper packaging would just move the problem elsewhere.

So ban all disposable packaging and bring our reusable bags to the grocers for re-filling? Nice idea, but something about flying pigs springs to mind...

I agree with you Henry, but the dwindling supply of oil means that plastic will probably become too expensive to use for packaging anyway so the problem of what to do about it is coming sooner or later. A ban on carrier bags now would for example force people to re-use the ones in circulation.

Posted By: biffvernonWe are all agreed that there are too many plastic bags and too many people but we have to deal with the possible. It is possible to take your own shopping bag to the greengrocers and the more people that do it the more the government will feel empowered to encourage the rest. Of course it is much preferable to follow the Modbury example and act without the need for government legislation. There's no point saying it can't be done when we can see that it has been done. Getting rid of people is much trickier so it's best not to try. Just accept the population total and learn to live with it.

Biff, Your proposal is one solution and probably the best if it would work. Unfortunately, if those of us who accept there is a problem cannot agree with your solution, how are the rest of the population to be persuaded. That's why I think legislation is needed to kickstart the change in thinking

I agree with most of that Chris, but with this exception: If we take the example of the potato bags, the choice of whether to re-use the bags is outside that of the consumer. The fact is that most potatoes in supermarkets come in plastic bags. Okay, greengrocers are different but what percentage of people buy their potatoes from greengrocers?

I think the supermarkets continue to user such packaging on the basis of the bio-degradable greenwash I mentioned above. I think the only way to stop them doing this is to ban them.

I dont think this would be detrimental to the electorates political thinking of Government either; and it would highlight the issue a little more and subsequently educate people into re-using the bags they do have a choice about.

Give this policy a couple of years to sink in and then go for a blanket ban on carrier bags as well. Alternatively slap a 10p a bag tax on them

Yes, that's a good point, measures like this are small potatoes [ha ha] compared to the consumer debt bubble

Posted By: Chris WardleUnless we address the issue of population control and manage the world population down to a sustainable level

And just what does 'manage' mean? Are you goiing to commit suicide, murder, or merely force your sister to not have a baby?
The best, nay only, way to stabilise population is to go for women's education, child healthcare, and social security in old age. All of which mean tackling the economic calamity that Peak Oil foreshadows.

Government should not need to waste it's time on plastic carrier bags. Surely we are grown up enough to buy our potatoes sensibly without Nanny State telling us what a shopping bag is for.

To answer the original question, I believe that supermarkets have moved to bio-degradable plastics in response to pressure to reduce the environmental impact of packaging used in their products. This is a deliberate choice - plastics that degrade in reasonably short times are relatively novel and have to be designed to do so. It's infinitely preferable for plastics to degrade as they would otherwise add to the vast quantities of landfill that we produce every day. Unfortunately most consumers associate plastic with convenience and cleanliness so supermarkets find it hard to develop alternative packaging. In the case of potatoes, the supermarkets would have to unilaterally change to paper, because most consumers would not buy spuds that they can't conveniently see and would just pick the ones in clear plastic bags (despite the fact they don't keep as well and go green).

You can't 'mine' existing plastics and re-use them as the different types in common use don't mix well and many cannot be reformed into anything that is usable. Plastics come in a variety of different forms, with different physical and chemical properties that are usually incompatible with each other. So unless you could separate the different types, mixing them would just produce a chemical powder that would be of no use to anyone as anything other than a filler material (which itself would have unpredictable characteristics due to the mix). There is currently no technique for identifying different types of plastic, which is why the few plastic recycling schemes in existence at present are very strict on what you can put in to them.

Plastics in building products are not the same and are chosen for physical characteristics that provide the desired lifetime. Many that do degrade, do so by becoming brittle and cracking rather than decomposing in any way. The question to ask for building products is whether their designed lifespan is long enough and their performance is consistent throughout that life time.

Thanks for your post Tuna, that's a very clear picture.

Posted By: biffvernonThe critical thing is whether we can roll out the alternative generation facility fast enough

Biff, that-type statement should always be accompanied by 'and drastically reduce demand' - because official thinking still hasn't really linked the two up. Lovelock would not have so infamously espoused nuclear energy if he'd had the knowledge that exists on this forum - the real possibility of taking (almost) the entire building stock off-grid, for heat vent & cooling. There's massive opportunity for similar in industrial process power, and I've no doubt there's a forum somewhere discussing comparable possibilities for transportation.

Just a comment on the population issue. We can't sustain 6 billion let alone 9 billion sustainably on this planet. I would be susprised if we could manage more than 2 billion using renewable energy alone. This is self evident when you look at the correlation between growth in fossil fuel use and population growth. The logical conclusion to draw from this is that unless we find methods to reduce world population in a humane way faster than total energy production falls, people will die in tragic circumstances in vast numbers, e.g. through famine and war.

Billions are spent on development aid each year. If some of that money was used to provide supplementary pensions for women who agreed to be sterilised after the birth of their first healthy child (no compulsion whatsoever), I think you would see a welcome drop in the birth rate all over the world. Other similar voluntary financial incentives could be devised.

It is a depressing thought that every extra person who enters the world means one extra life to end in tragic circumstances somewhere later this century and a greater risk of the synchronous failure of whole societies. Unfortunately, in a world of finite resources, population is ultimately a zero sum game.

Posted By: fostertom

Posted By: TunaYou can't 'mine' existing plastics and re-use them

Not today but undoubtedly in the future. I've previously posted a link to a great Independent article that's sadly no longer available online, about an Australian mining co. that's developing its expertise in just this, and has already won contracts in the Midlands to manage landfills on that basis.

It's interesting that you suggest this, as surely this is exactly the argument being used against nuclear power - that you can't just stick the waste product in the ground and hope that some future generation will have figured out a way to deal with it. The difference is that we already generate millions and millions of tonnes of plastic waste on an annual basis and store it in sites across the UK - you're never more than a few miles from a landfill site.