Potential Influences of Polymers after Composting

Positive effects of the application of compost in agriculture are described in numerous publications, e.g., Allison [3], Voelker [4], Gottschall [5] and Hard [6]. The most common effect is fertilisation by mineral nutrition elements. Furthermore, Sekhon and Meelu [7] mention the beneficial effect of organic matter - humus - on the microflora and on the physical properties of less fertile soil. 

Potential hazards caused by the introduction of toxic components (especially heavy metals) in contaminated compost are frequently revealed. These typical impurities are covered by the analytical quality control of the majority of European national regulations, and will lead to the classification of the product as second or third level 

In particular, the collection and composting (or anaerobic digestion) of synthetic biodegradable materials together with traditional biowaste increases the risk of the introduction or generation of unknown and therefore not analysed substances. Hope-Simpson [8] demonstrated for the first time that residues from the composting of coated paper could be toxic to plants and made it impossible to be used as compost in agriculture. The reason was an enrichment of the nutrient element boron up to a toxic level. 

The term compost quality should not be limited to physical and chemical parameters. While such analysis could describe the contents of nntrients and the presence of a small number of selected pollutants very well, the appearance of unidentified metabolites and residues could be detected more reliably by the application of biotests. In particular, artificial polymers may contain ingredients or certain monomers which may resnlt in critical metabolites or intermediates upon biodegradation. 

The increased cost for the additional analysis, performed in advance of the market introduction of new materials, will be rewarded by the confidence of compost plant operators and consumers. Mandatory biotests are needed during the material development phase and are not necessary for the routine quality control of each batch of compost. 

Potential hazards caused by the introduction of toxic components (especially heavy metals) with contaminated compost are revealed very often. These typical impurities are covered by the analytical quality control of most of the national regulations in Europe and will lead to a classification as second or third quality and to a limited use of the compost. These national standards are dealing with well-known contaminants that may derive from typical biowaste and are focussing on heavy metals and a handful of halogenated or aromatic hydrocarbons. The inclusion of bioassays with higher plants in some standards is more to determine the maturity of the compost than with the appearance of ecotoxic effects caused by anything other than the chemicals being determined. 

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