Position Papers
Residues
Fragmentation occurs during degradation of both oxo-biodegradable and hydro-biodegradable plastics.
It is not of course acceptable to apply conventional plastics to the soil even if they are fragmented, since physical shredding alone does not transform plastic into a biodegradable product. However, the properties of oxo-biodegradable plastic on exposure to the environment are quite different from those of the original plastic. The transformed plastic behaves in the same way as nature's wastes. It is bio-assimilated by the same bacteria and fungi, and they convert the degraded plastic to cell biomass, just like lignocellulosic materials such as straw, leaves and twigs.
Eco-toxicity tests1 have demonstrated that oxo-biodegradable plastic produces no immediate, or cumulative, adverse effects on the soil, whether from the plastic itself or from the additive. The major elements of organic additives are naturally bio-degradable, and the traces remaining after degradation are in such minor parts per million (in some cases, per billion) that no harmful effects will occur. Some of these materials can also be found in hydro-biodegradable products.
Oxo-biodegradable plastics do not contain "heavy metals"2 Metal compounds used in oxo-biodegradable polymers and listed in European Directive 67/548/EC are not banned. The Directive simply controls their marketing and use, and they are marketed and used accordingly.
The UK Food Standards Agency's Expert Group on Vitamins and Minerals3 has carried out a risk assessment on trace elements and has shown that all the metal salts used in commercial oxo-biodegradable plastics are in fact trace-elements necessary for healthy plant and human growth.
Like lignocellulose (and unlike the hydro-biodegradable plastics which discharge their CO2 to atmosphere during composting), oxo-biodegradable plastics are sequestered by the soil and enhance the "land carbon sink
1. See G. Scott and D.M. Wiles, Degradable Polymers: Principles and Applications, Kluwer, 2002, Chapter 13, Section 9.11, page 472, et seq
2. The term "heavy metal" has never been defined by any authoritative body. Over the 60 years or so in which it has been used in chemistry, it has been given such a wide range of meanings by different authors that it is effectively meaningless……Even if the term "heavy metal" should become obsolete because it has no coherent scientific basis, there will still be a problem with the common use of the term "metal" to refer to a metal and all its compounds. This usage implies that the pure metal and all its compounds have the same physicochemical, biological, and toxicological properties. Thus, sodium metal and sodium chloride are assumed by this usage to be equivalent. However, no one can swallow sodium metal without suffering life-threatening damage, while we all need sodium chloride (salt) in our diet. (Pure Appl. Chem., Vol. 74, No. 5, pp. 793–807, 2002).
3. UK Food Standards Agency (2003) Expert Group on vitamins and minerals" Part 3 Trace Elements, Risk Assessment.