Toxicological and genotoxicological assessment of water extracts of sewage sludge and other biogenic wastes: A piece of the SLURP jigsaw puzzle

Given the considerable quantities of biogenic matrices employed in agricultural applications, there is growing concern about the potential negative effects resulting from the presence of harmful contaminants. The project “SLURP - SLUdge Recovery in Agriculture: Environment and Health Protection” planned a multi-stage approach in which the application of a wide battery of bioassays was proposed as an effective tool to measure the direct interaction of matrices with the different components of the ecosystem, from the molecular to the whole organism level. The aim of the present study, which is a part of the “SLURP” project, was to characterise the toxicological and genotoxicological properties of water extracts from biogenic wastes using several assays based on plant, bacterial and human cells. The aqueous extracts of four sewage sludges, a liming material, two manure slurries of swine and bovine origin, a digestate from bovine manure and a compost were chemically characterised for inorganic ions and heavy metals. Then the extracts were analysed using tests on A.cepa, C.sativus, L.sativum, S.typhimurium and human hepatoma cell line (HepG2) to assess toxicity (seed germination, root elongation, proliferation), mutagenicity and genotoxicity (primary DNA damage, chromosomal aberrations). The extracts exhibited chemical heterogeneity. Ammonia nitrogen, Ca²⁺, Fe and Zn were the most abundant elements. Toxic effects were caused on A.cepa and L.sativum by all extracts, while there were non-toxic effects on human cells. Genotoxic effects on A.cepa and L.sativum were instead caused by almost all the extracts, at least at the highest dose tested, while only four samples from one sewage sludge, liming material, digestate, and compost, caused DNA damage on human cells. None of the extracts induced mutagenic effects in S.typhimurium. A comprehensive interpretation of these results can only be achieved through the integrated evaluation of all eco-toxicological and chemical data obtained throughout the entire project.