EOM4Soil Deliverable 5.4 - Report on toxicity of EOM and effect of pre-processing

External organic matter (EOM), particularly from urban residues, is a known source of soil contamination when used as soil amendment. In this context, the benefits of EOM in terms of climate change mitigation and soil health can, in some cases, be limited by the contamination resulting from its use and its eventual toxicity. However, some treatments may reduce the initial contamination load of EOM. Accordingly, this work aimed to evaluate the efficacy of EOM treatment in reducing the toxicity of different EOMS. Cytotoxicity and phytotoxicity were evaluated by a short-term in vitro test using fish-derived cells and by a germination test, respectively. Municipal (sewage sludge) and agricultural (manure) side-streams were selected as the original EOMs and pyrolysed and digested to produce biochar and digestate, respectively. Besides, the cytotoxicity of a compost sample together with its corresponding feedstocks (biogas digestate, garden waste and biochar in 42:53:5 weight ratio) was also evaluated. Organic EOM extracts from both sewage sludge and especially biochar were cytotoxic, indicating the presence of toxic products that are strongly adsorbed to these EOMs and could remain in the soil after amendment. On the contrary, manure exhibited cytotoxicity to aquoeus extracts, which was reduced by digestion. This suggests that the main hazard of this EOM without treatment is related to a potential source of pollution to groundwater or surface water if it is not treated before.

This work is part of the project “EOM4Soil: External organic matters for climate mitigation and soil health” in the framework of the European Joint Programme for SOIL “Towards climate-smart sustainable management of agricultural soils” (EJP SOIL) funded by the EU Horizon 2020 Research and Innovation Programme (Grant Agreement No. 862695).

Peer reviewed