Investigation on the impacts of raw and bioremediated olive oil mill waste on agroecosystems

Agricultural practices, such as olive growing and related olive oil extraction processes can impact agroecosystems due to the large amounts of olive mill waste (OMW) that are produced and spread on land. The main aim of our study was to investigate the effects of raw olive mill wastewater and olive mill semi-solid waste on different components of agroecosystems. OMW (olive mill semi-solid waste and olive mill wastewater) were collected at two different oil mills in Tuscany and subjected to a bioremediation process based on bioaugmentation. Fungi strains able to metabolize polyphenols were isolated from OMW, grown and added to olive semi-solid waste or olive mill wastewater, composted with chopped straw and olive leaves. Polyphenol concentrations and pH were detected in OMW before and during bioremediation process which last 6 months. Specimens of Eisenia fetida and Gambusia affinis were exposed to both kinds of OMW, before and after the bioremediation treatment. A set of biomarkers was applied to investigate eventual neurotoxic affects (AChE inhibition), oxidative stress (LPO, catalase), and genotoxicity (Comet and ENA assays) of raw and bioremediated OMW. Mortality was also measured. Maize seeds were differently treated by incubating seeds with either water and raw or bioremediated olive mill wastewater, at different times, Germination Index was computated. Tobacco and tomato plants were grown in pots in presence of raw or bioaugmented OMW. Photosynthesis-related molecules, such as content of RuBisCO (ribulose-1,5- bisphosphate carboxylase oxygenase) and of the photosynthetic pigments lutein, chlorophylls, and β-carotene were investigated in tobacco. Growth tests were carried out on tobacco and tomato plants. This study provides valuable information on the potential impact of OMW on agroecosystems. In particular, negative effects were found both on animals, such as mortality, neurotoxicity, oxidative stress and genotoxicity, and on plants such as inhibition of germination and root growth, alterations of photosynthetic parameters and plant growth. OMW is a complex mixture in which surely the high levels of polyphenols play a key role for toxicity, but the possible presence of other chemical compounds used in agriculture should not be overlooked. The bioaugmentation treatment in which the decrease in the levels of polyphenols and acidity was highlighted resulted in a net decrease in toxicity and the new byproducts obtained can be proposed as fertilizers.