There is obviously a lot of confusion around the materials plastic shopping bags are made from and the compostability, biodegradability and recyclability of them.

A blog published on edie earlier this week underlines just how easy it is to misunderstand this complex issue. Evidently, the association I represent is not doing enough to get clearer evidence across to businesses and the public.

So, here’s my right of reply to that blog; my own attempt to bust some of the myths that evidently still exist when it comes to the sustainability of plastic bags.

1) Bio-based and biodegradable plastics

These are made of polymers that come from renewable, bio-based sources (starches, sugars, cellulose) as well as non-renewable sources (oil- based). Actually, one can make totally biodegradable plastics from oil as well as making totally non-biodegradable materials from plants. Confused? Yes, this isn’t an easy process to get your head around.

Biodegradability does not exist as a legal concept when discussing bioplastics. Compostability does, and the European standard EN13432 has certified the compostability of packaging materials in the UK since 2002. This asks for a minimum of 90% biodegradation in composting over a 180-day period.

The blog published earlier in the week made the statement that as these only decompose to 90% that residual plastics remain thereafter. This is incorrect. The current best laboratory test considers CO2 evolution in relation to a known biodegradable material, e.g. cellulose.

Ninety percent is the pass limit in the biodegradation test for two reasons: firstly, since the test uses naturally occurring microbes and materials (compost) there is some variability.

And secondly, not all of the biodegradable plastic will be converted to CO2, because during the metabolism of the substrate (biodegradable plastic), water and biomass are also produced. However, given these other products may be consumed or used by other means or microbes in the compost, it is not possible to measure them accurately.