I understand that it depends, but who came up with these numbers like 450 years for PET bottle do degarde and how?

Hi Stjepan

That's a good question. I dont have the exact answer, but I suppose some type of carbon dating must be involved with determining the age of current degraded plastics and the rate of degradation of current plastics. Or by doing small scale experiments with softer plastics you can possibly extrapolate to harder plastics  I read this paper ter Halle et al. 2016 attached, which mentions measuring the free radical reactions from UV exposure which can be linked to the age of the plastic via the degradation of the polymers (pg 5673).

Hi, thanks for the link to apapr, its really intersting.

What Im REALLY interested in what mathod or what assumptions were made when they came up with these numbers on this poster (eg styrofoam cup 50, plastic bag 10-20, plastic bottle 450)?!

http://oceancrusaders.org/wp-content/uploads/2015/09/How-Long.jpg

I too see lots of figures on the Internet, but little substantiation in the research literature. I think that it is a hot topic, ready for some real research, not sponsored by the paper manufacturers. 

How do you define half-life of a container? Half the mass left? Have you got access to a rubbish dump or beach, where you can date the containers via date codes / product redesign dates?

What are the degrading factors? UV?, Friction? Heat?

plastic bottle degradation needs 450 years and aluminum tin need only 200 years?? is it true?

I think all numbers available are just assumptions, after all. The most "honest" predictions on the life-span of plastics are in the order of "hundreds to thousands of years" (see for example Barnes, D. K., et al., Accumulation and fragmentation of plastic debris in global environments, Biological Sciences). Unfortunately there is no way to know the truth yet, but it would be interesting to start monitoring plastic debris now, and let future generations see the results.

Thanks Marina!

You are right, and the terminoloy ´´life span´´ of plastic, is also tricky because of fragmentation etc.

Life span of Plastic depends on environmental factors. Whereas, mean values about its degradation remain just assumptions. But, we can guarantee at least 100 years as we found plastics in nature coming from old activities (debut of the last century).