Should heavy metals be an issue of concern at olive mill waste disposal areas? The case of nickel

Abstract

Plenty of research works highlight the adverse effects on soil quality caused by the disposal of olive Oil Mill Waste (OMW), focusing mainly on soil organic matter, electrical conductivity, polyphenols, pH, and metals. Apart from few works carried out in the last two decades regarding the possibility of heavy metals contamination at OMW disposal sites, there is currently a considerable gap in knowledge on this issue. To this end, this study focuses on heavy metals leaching from soils that accept OMW, using Nickel (Ni) as an example, and provides evidence on the necessity of thorough future studies on the factors that impact this process. Experimental and field results gathered from soil surveys and lab experiments reveal the relation between Ni leached and soil clay content, waste’’s pH, as well as the impact of the local particularities of the disposal areas, e.g. geomorphology, climatic conditions, and soil properties. A local approach was adopted for the identification of the pollution and ecological risks by taking into account local background Ni concentrations as the latter were determined during an extensive soil survey.