Potential agricultural use of a sub-product (olive cake) from olive oil industries composting with soil

Context: Olive cake and olive mill wastewater are by-products of olive oil industries. Olive cake is not currently being exploited. Aims: To evaluate the cytotoxicity and genotoxicity induced in Allium cepa root meristems by olive cake in various preparations (aqueous dilutions of olive cake and mixtures of olive cake with soil before and after a composting process). Methods: Olive cake aqueous dilutions as well as fresh and composted olive cake – soil mixtures were obtained. Samples were assayed on Allium cepa L roots and the phenolic content was also determined. Results: Aqueous dilutions showed acute genotoxicity with a mitotic index dramatic reduction and a high number of cell abnormalities. Olive cake induced chromosome aberrations such as bridges, stickiness, and laggard chromosomes and cell aberrations such as strap, folded, giant and binucleated cells. Anomalies increase with polyphenol concentration, both in aqueous dilutions and in mixtures of olive cake – soil without composting. Composted mixtures did not exhibit cell toxicity up to 10% of olive cake although they can decrease the mitotic index, which would produce a reduction in plant growth. Conclusions: Results indicate the varied behavior of olive cake according to sample preparation and suggest the possible use of this by-product incorporated to soils and subjected to composting.