Comparative evaluation of the efficiency of low-cost adsorbents and ligninolytic fungi to remove a combination of xenoestrogens and pesticides from a landfill leachate and abate its phytotoxicity

Abstract

In this study, two widely available low-cost adsorbents, almond shells and a green compost, and two ligninolytic fungi, Pleurotus ostreatus and Stereum hirsutum, were used to remove organic contaminants from a landfill leachate (LLe) and abate its phytotoxicity. The methodology adopted was based on the occurrence of two simultaneous processes, such as adsorption and bioremoval. The leachate was artificially contaminated with a mixture of the xenoestrogens bisphenol A (BPA), ethynilestadiol (EE2) and 4-n-nonylphenol (NP), the herbicide linuron and the insecticide dimethoate at concentrations of 10, 1, 1, 10 and 10 mg L⁻¹, respectively. Three adsorption substrates were prepared: potato dextrose agar alone or the same incorporating each adsorbent. The substrates were either not inoculated or inoculated with each fungus, separately, before to be superimposed on LLe. After 2 months, the residual amount of each contaminant, the electrical conductivity, the pH and the content of total phenols were measured in treated LLe. Germination assays using lettuce, ryegrass and radish were performed to evaluate LLe phytotoxicity. The combination substrate+P. ostreatus showed the best results with average removals of 88, 96, 99, 58 and 46% for BPA, EE2, NP, linuron and dimethoate, respectively. The same treatment considerably reduced the phenol content in LLe compared to no treatment. The combination substrate+S. hirsutum produced average removals of 39, 71, 100, 61 and 32% for BPA, EE2, NP, linuron and dimethoate, respectively. Also uninoculated substrates showed relevant adsorption capacities towards the five contaminants. Most treatments significantly reduced LLe phytotoxicity, especially on lettuce. The best results were obtained with the treatment compost+S. hirsutum, which produced root and shoot lengths and seedling biomass of lettuce, respectively, 2.3, 3.3, and 1.9 times those measured in untreated LLe. In general, germination results were negatively correlated with LLe properties like the residual amount of the contaminants, the electrical conductivity and the pH. These results show that the methodology adopted in the study, i.e., combined adsorption/biodegradation, is suitable not only to remove xenobiotic contaminants from the leachate but also to reduce considerably its inhibition on seed germination.

Keywords:

• Adsorption
• biodegradation
• bioremoval
• landfill leachate
• ligninolytic fungus
• pesticide
• phytotoxicity
• xenoestrogens

Funding

This work was funded by University of Bari Aldo Moro, Italy.