Evaluating Earthworms’ Potential for Remediating Soils Contaminated with Olive Mill Waste Sediments

Abstract

The olive-oil industry generates large amounts of residues that, in the past, were accumulated in evaporating ponds in many Mediterranean countries. Currently, these open-air ponds pose a serious environmental hazard because of toxic chemicals that concentrate in their sediments. Bioremediation of olive mill waste (OMW) sediments has emerged as a viable option for managing this environmentally problematic residue. Here, we postulate that inoculation of an OMW-soil mixture with earthworms may be a complementary bioremediation strategy to that using native microorganisms only. A laboratory study assessed the ecotoxicity of OMW-amended soils (10%, 20%, 40% and 80% w/w) combining earthworm biomarker responses and soil enzyme activities. The doses of 40% and 80% were toxic to earthworms, as evidenced by the high mortality rate, loss of body weight and signs of oxidative stress after 30 d of soil incubation. Conversely, doses ≤ 20% w/w were compatible with earthworm activity, as indicated by the significant increase of soil enzyme activities. Total concentrations of phenolic compounds decreased by more than 70% respect to initial concentrations in 10% and 20% OMW treatments. These results suggest that OMW sediments intentionally mixed with soils in an up to 20% proportion is a workable bioremediation strategy, where earthworms can be inoculated to facilitate the OMW degradation.

Sewage Sludge-Induced Effect on Growth, Enzyme Inhibition, and Genotoxicity can be Ameliorated Using Wheat Straw and Biochar in Pheretima posthuma Earthworms

“…Our study showed that the sewage sludge induces changes in the activity of crucial enzymes of earthworms responsible for the metabolism of the energy, neurotransmission, and oxidation systems. The dosedependent response was observed by increasing the concentration of sewage sludge enzyme inhibition (Sanchez-Hernandez et al, 2020). In the case of sewage sludge, acid phosphatase activity was affected by sewage sludge followed by biochar and at the same concentrations of these amendments also caused inhibition of acetylcholinesterase activity within earthworms.…”