Saints or Sinners - are biocompostable plastics as squeaky-green as they seem?

Close-up of Compostable Plastic Cup Logos

The usefulness and cheapness of plastic has made it ubiquitous on our planet. No other material has the capacity to fulfil such a wide range of applications - infinitely replicable, rolling rapidly and cheaply off a production line - which is why it has become so prevalent in such a short space of time (the first fully synthetic plastic, Bakelite, being created in 1907). So then, when we turn around and realise that this wonderstuff is mounting up around us, polluting the very soil and sea we rely on, there is justifiable concern about how we move forward, continuing to enjoy the advances and innovation which seem to be at the very heart of humankind, without taking down our precious planet in the process.

I say "no other material", but of course there are plastic-like substances, derived from plant starch, vegetable oils, wood pulp etc., which can be manufactured to exhibit some or all of the same properties as petrochemical plastics (depending on the application) and are often, at first glance, indistinguishable from their oil-derived cousins:

#1 PETE vs #7 PLA Plastic Lids

Polycarbon or 'Poly-corn' - can you spot the difference?

These are alternatively known as Bioplastics, Ecoplastics, Cornstarch Plastics, Biocompostable Plastics and a host of other names according to the manufacturers' whims, since the science, while not young, is newly booming and has not yet settled on an international glossary of terms. PLA, or Polylactic Acid, for example, is a common bioplastic. (Bioplastics are not to be confused with biodegradable plastic since this is a petrochemical plastic which has been treated with an (often toxic) additive, helping it to override it's longevity and degrade into ever smaller (often harmful) fragments.) Attached as we are to our convenience lifestyles, it is very tempting to see bioplastics as the easy way to continue in the way we have become accustomed 'guilt free' as it were (I am thinking mainly of single-use packaging here). Are these 'green' plastics the answer?

Imagine this: You are hungry and without a snack while out and about (always a good time for plastic to creep in). You see a yummy sandwich, all juicy looking with the filling on display behind the clear wrap. You might have passed it over before, since food-sullied film-type plastics are not easily recyclable and you are trying to be less wasteful. But look! It says 'bioplastic' on the side, great! Pop it in the bin and it'll just break down, right?

Not so fast.

To begin with, not all bioplastics are biodegradable or compostable. Some, although derived from plant material, have been developed to have a similar kind of longevity and resistance to decay as standard petrochemical plastics, with similar disposal issues. There is also concern surrounding the prevalence of GM corn grown as a bioplastic feedstock, and also of the kind of biodiversity-crushing monoculture that would be required to fulfil plastic demand from bioplastics alone. So, realistically, bioplastics are unlikely to save us if we continue to consume plastics at the current rate. But are they a useful stop-gap, a portion of the solution? How about the compostable ones?

In order for a product to be considered to be compostable, it needs to meet an international standard such as EN 13432. The independent Belgian testing institute Vinçotte awards an OK Compost certification (now owned by TÜV AUSTRIA Group) for products that meet EN 13432. The key points are (in laymen's terms):

- The product's composition must be within certain safe limits for volatile compounds, flourine and heavy metals (i.e. toxic substances).

- In an industrial composting unit, 90% of the product must have broken down into carbon dioxide, water and minerals by the action of micro-organisms within 6 months.

- In an industrial composting unit, at least 90% of the product must have broken down physically in order to pass through a 2 x 2mm mesh within 12 weeks.

- The quality of the final compost should not have been adversely affected by the product's decomposition, which should not have left a toxic residue.

A key point above is the use of the industrial composting unit, which has a more vigorous composting action at a higher, constant temperature (55-60 deg C) than a backyard compost heap. The second major criteria is the timescale of 12 weeks/6 months. Most biocompostable plastics are only considered to be compostable in an industrial composting facility (Vinçotte awards a separate, rarer, certification - OK Home Compost - for materials which will break down within specified timescales in a domestic composting environment).

International Compostable Certification Logos

A sample of international Compostable Certification Logos

In the definitions below my mission statement I have explained in more detail why I don't think biocompostable plastics are (at the moment) that practical. The main reason is their disposal, which can be summarised as follows:

- They are not currently recycled, and furthermore will degrade the quality of post-consumer plastic feedstocks if they find their way into the recycling system. Bioplastic must not go into council recycling bins.

- Whilst 'compostable', this is only certified for industrial facilities, and at the moment in the UK these facilities' machines - not being able to distinguish between biocompostable plastics and regular petrochemical plastics - filter out any potential contaminating plastics and send them all to landfill or for incineration. Therefore putting bioplastic into the brown food-waste bin is the same as putting it straight into black bag rubbish.

- Landfill does not provide the right conditions for biocompostable plastics, or other organic matter, to decompose efficiently. Compostable plastics are not expected to break down in landfill any faster than a petrochemical plastic, or for that matter, metal, paper or any other material.

So, what now? And why am I bringing this topic up when I have already semi-covered it?

Well, while not certified home-compostable, there is anecdotal evidence both that bioplastic will break down in a backyard heap, and also that it will not. Some knowledgeable types state that it will break down, but not within the 6 months required to certify it as home compostable, taking closer to 2 years to completely disappear. This second statement is of interest, if it is true, as it may give an ecological solution to those who are prepared to leave their backyard heaps for longer in order to compost ecoplastics. When I was growing up my parents, managing half an acre of vegetable patch and two greenhouses, had a 3-year turnaround on their compost, so this would have been fine for them. There is also, more pressingly, disagreement about how quickly bioplastic litter degrades in the ocean, a place where plastics reap the most harm. Some say 2 years is all that's required for PLA, for instance, to completely break down, whilst this study from the California Department of Resources Recycling and Recovery showed that under test conditions PLA had only biodegraded 0.1% more than the control (petrochemical plastic HDPE) after 1 year.

I feel that there must be people out there like me who want practical answers about what to do with biocompostable plastics that find their way into their households and are baffled by the polychotomy of information out there. I thought this was the ideal time to conduct a couple of backyard science experiments of my own. Why Google yourself stupid looking for the bottom line with bioplastics when you can just roll your sleeves up and test them in real world conditions yourself?

So this post serves as an introduction to two experiments I am proposing:

1) To compost several bioplastic products at home, alongside some organic comparisons and plastic controls and compare their decomposition after 1 year, and then again (if required) after 2 years.

2) To (safely) sink some bioplastics into the sea, along with some organic comparisons and plastic controls, and compare their decomposition at regular intervals over a 2-year period.

Tomorrow's summer solstice seems like a fitting date in the planet's calendar to launch my experiments, so in the morning I shall toss some dross into the domestic dungheap and then head down to the Portsmouth Historic Dockyard to dunk some detritus into the drink, thanks to the IBTC Portsmouth who have kindly lent me a corner of their wet dock in Boathouse 4 for my venture.

The finer details of these experiments will be outlined in their own subsequent posts coming soon, and I'm sure as I go along I will find it hard to resist sharing early findings. It is both excited and nerve-racking. I know the scientist must try to remain impartial, but I do sincerely hope that I will not ultimately conclude that the best place for biocompostable plastic is in landfill with the other 'problem' rubbish.