Analysis of Organic Contaminants and In Vitro Cytotoxicity to Test the Suitability of External Organic Matter Processing

External organic matter (EOM), particularly from municipal waste, can contaminate soil when used to amend it. This may limit the benefits of using such an EOM to improve soil health and mitigate climate change. However, certain treatments may reduce the initial contaminant load of EOM. This study aimed to evaluate whether EOM processing can reduce its cytotoxicity and the concentration levels of 34 persistent and emerging organic contaminants. Sewage sludge and a mixture of manure and straw, processed by pyrolysis and anaerobic digestion to generate biochar and digestate, respectively, were selected for this study. An in vitro fish cell cytotoxicity test was performed to assess the toxicity of organic and aqueous extracts from the EOMs. It was found that organic contaminants are generally highly matrix-bound, resulting in low availability, reduced potential for leaching to groundwater, and effects on soil organisms after EOM application. The pyrolysis of sludge resulted in the almost complete removal of bisphenol A, tris(2-chloroisopropyl)phosphate, and octylphenol (removal ≥95%), while the concentration of the other contaminants monitored was reduced, with the exception of polycyclic aromatic hydrocarbons (PAHs) of lower molecular weight. In contrast, anaerobic digestion of manure did not result in a reduction of the contaminant load monitored except for bisphenol A. Cytotoxicity was also observed in aqueous extracts of manure but was reduced by anaerobic digestion. This suggests that anaerobic digestion could reduce potential hazards to groundwater or surface water from manure amendments. Organic EOM extracts were cytotoxic, indicating the presence of toxic products strongly adsorbed to these EOMs and retained in the soil after amendment.