According to the intermediate result of an ongoing study on the documentation, evaluation and prevention of microplastic in composts and digestate from biowaste recycling units and their discharge into agricultural soil (MiKoBo), just under 450 tonnes of microplastics are discharged annually throughout Germany via composts and liquid digestate products. Of this, plastic sheet and film account for 146 tonnes and rigid plastics for 302 tonnes. The research project is funded by the German State of Baden-Württemberg and also involves the universities of Stuttgart, Hohenheim and Bayreuth as well as the Fraunhofer Institute for Chemical Technology, ICT.

 

The intermediate results from the project, which was launched in 2018, were presented during the Stuttgart Waste Forum in summer last year by Prof. Martin Kranert from the University of Stuttgart.  The results are, in fact, on the same scale as those stemming from the special study "Compost and digestate" from 2020, and from the report "Plastics in the environment" (2021), both compiled by Conversio Strategy and Research GmbH on behalf of the BKV.  According to Kranert, the 450 tonnes a year of microplastics in the soil are equivalent to around 5.5 g per person per year. Although this amount should not be ignored, it is not a reason for ringing the alarm bells, says Kranert, who, to visualise this quantity, compares it with the abrasion from shoe soles, which amounts to around 190 g per person per year. Samples taken in the course of the project showed a concentration of 0 to 100 plastic particles per litre in the composts and digestate. The microplastics, of both polyethylene and biodegradable plastics, were still present after twelve weeks, and, even after 230 days, had not yet decomposed. Despite the small quantity involved, the discharges should be further reduced, says Kranert. With regard to the effects of microplastics on the soil function, the research team was unable to establish any negative effects. At the concentrations of 20 kg of microplastics (PE and biodegradable plastics) per hectare, which were analysed as part of the MiKoBo project, they did not find any reduction in the grain yield. Nevertheless, Kranert is of the opinion that the discharge of plastics should be further reduced.

 

The German Quality Assurance Organisation for Compost (BGK) is of the same opinion. Its figures more or less correspond to those obtained in the MiKoBo study. According to the BGK, around 400 tonnes of plastics are currently discharged, of which some 250 tonnes end up on agricultural land.

 

As part of the MiKoBo project, a risk estimate will now be carried out with the aid of ecotoxicity studies.

 

More information:

• Project overview
• Intermediate report
• The special report "Compost and digestate (Conversio 2020)" and the report "Plastics in the Environment in Germany(Conversio 2021)" mentioned in the text can be ordered free of charge. In German language from here. The report "Plastics in the Environment" also in English from here here.

 

Sources:

• Euwid Recycling und Entsorgung 29/2021 (20.7.21)
• Kompost.de (H&K aktuell Q2/2021)
• Photo: @ Degrande / Pixabay