"Tumbleweed" wrote in message
. ..

"Nick Maclaren" wrote in message
...

In article , (dmc) writes:
| In article , Huge

wrote:
| (dmc) writes:
|
| Had a couple full of gravel at the bottom of the garden for a few
years.
| Both have gone very brittle - the one I attempted to empty and move
just
| crumbled.
|
| That's not biodegrading. The UV in the sunlight has destroyed them.
|
| Hmm. Good point. They had turned to dust though. Nasty poisonous dust
| maybe

No. Polythene and polypropylene break down into harmless chemicals,
and I believe that the other ingredients aren't particularly toxic
or permanent.

| What actually has to happen to something in order for it to have
"biodegraded"?
| Break down into component chemicals?

To have broken down as result of biological action.



Indeed. So something that is biodegradeable may break down to harmful
chemicals, whilst something that is inert (and thus not biodegradable),
for
example glass, may have no effect on the environment (after its
manufacture).

Usually (always?) there is an implicit 'its a good thing' associated with
the word biodegradeable, for no good reason AFAICS.

Biodegradation is being eaten by bugs, worms fungi etc. It is not breaking
down into harmful chemicals. Although I've never seen a chemical analysis of
worm dung. :-))

Steve