BioCASH Deliverable 3.1 - Report on the safety assessment of different waste streams and their composts

BioCASH aims to create a modelling toolbox that enable scaling up site-specific case studies of biocircular supply chains of waste streams from local to landscape level and thereby creating capacity to assess the socio-economic, environmental and policy impacts on different soil functions and selected modified agricultural production systems and emerging agro-ecological production systems. From the soil perspective, the toolbox should consider the evaluation of indicators related to soil health (e.g. soil biodiversity, carbon sequestration, capacity of water retention, nutrient cycling) and safety (i.e. analysis of contaminants such as metals and plastics). In this regard, one of the objective of WP3 was the development of lab-scale experiments to gain insights into the impact of organic amendments on soil safety and soil health. Accordingly, NIBIO provided samples for analysis to LAMMC and CSIC including composts and feedstocks. The concentration of heavy metals in the waste streams and their composts was determined by LAMMC, and the ecotoxicity of these materials was assessed through germination tests to evaluate the overall toxicity of selected waste streams, regardless of contaminant concentrations. In parallel, the presence of organic pollutants and microplastics in compost samples was evaluated by CSIC to obtain knowledge on the influence of different composting processes. It was observed that heavy metals were generally concentrated through composting. Zinc appeared above the threshold value of 150 mg kg-1 dm (threshold limit for Norway) in only one sample, and all other metals were well below the threshold limits for soil amendment products. There were no significant differences in heavy metal content between the compost treatments, except for lead. Lead was higher in substrate-derived composts and much higher in composts as compared to the feedstocks, indicating that the wood shavings could have been the source (more wood shavings were used to balance the moist substrate in the composting mixtures). Besides, the obtained results showed that organic contaminants are generally strongly bound to the matrix, suggesting a reduced potential for transfer to surrounding water or leaching to groundwater, and low bioavailability and adverse effects on soil organisms in the short term after compost application. In all samples measured, there was a concentration of microplastics in the range 820-1340 fragments/Kg of dry sample. Fragments presented different shape, size and colour. Microplastics were identified by comparing FTIR spectra with open access databases and with our own database. Three polymers represented the totality of plastic items identified: polyethylene (including both low and high density), polyethylene terephthalate and polypropylene in order of abundance. These results confirm the persistent presence of plastics in this food waste compost and highlight one of the major challenges related to the potential for microplastics pollution when applying these wastes as organic fertilizer in agriculture. Finally, according to the results obtained in the germination tests, it can be concluded that neither digestate nor substrate or their composts, with and without biochar additive, has not possessed phytotoxicity on spring wheat seed.