Biodegradable Plastics - The "Compostable" Controversy

The "Compostable" Controversy

While "biodegradable" broadly means that an object can be biologically broken down, specifying "compostable", as it is usually understood, means that such a process will result in compost, or humus. Many plastic manufacturers throughout Canada and the US have released products indicated as being compostable, however this practice can be debatable if the manufacturer is submitting to the, now withdrawn, ASTM standard definition of the word, as it applies to plastics:

"that which is capable of undergoing biological decomposition in a compost site such that the material is not visually distinguishable and breaks down into carbon dioxide, water, inorganic compounds and biomass at a rate consistent with known compostable materials." (ASTM D 6002)

There is a major discrepancy between this definition and what one would expect from a backyard composting operation. With the inclusion of "inorganic materials", the above definition allows that the end product might not be humus, an organic substance. The only criteria the ASTM standard definition does outline is that a compostable plastic has to disappear at the same rate as something that we have already established as being compostable, under the traditional definition.