In order to determine the best means of disposal of a given product, it is important to know whether it is degradable, biodegradable, or compostable.
A degradable item will naturally break down into smaller parts. The processes which cause this include thermal (oxidative) or ultraviolet (photo-degradable). For example a tin can will degrade over time through weathering and oxidation.
Biodegradable items are composed mainly of materials which occur naturally. Through microbial action, they can be degraded into simple, stable compounds which can be absorbed into the ecosystem (such as carbon dioxide and water).
A biodegradable item will only biodegrade if it is in an environment which includes moisture, heat, and microorganisms. Without those three components, there will be no bio-degradation.
Compostable items biodegrade rapidly in the presence of oxygen into carbon dioxide, water, inorganic compounds, and biomass. During composting, the material also disintegrates into particles which are visually indistinguishable from one-another.
Bio-degradation occurs rapidly, at around the rate at which cellulose (paper) biodegrades.
Disintegration is important - the resulting particles must be very small.
The resulting compost must be free of heavy metals and other toxins, and useful as organic fertilizer.
Existing compo stability standards include European Norm EN13432 and American Society for Testing and Materials (ASTM) D6400-99. Of these, EN13432 is the strictest, requiring 90% bio-degradation in 90 days, while ASTM D6400-99 requires 60% bio-degradation in 180 days. Both set limits of required disintegration in addition to stipulating allowable levels of toxins.
Biodegradability is certified by The International Standards Organization (ISO) 14855, which requires 60% bio-degradation in 180 days, though makes no stipulations regarding disintegration or toxins remaining.