Direct and Indirect Detoxification Effects of Humic Substances

Lydia Bondareva,Nadezhda Kudryasheva

doi:10.3390/agronomy11020198

Abstract

The review summarizes studies on the detoxification effects of water-soluble humic substances (HS), which are products of the natural transformation of organic substances in soils and bottom sediments that serve as natural detoxifying agents in water solutions. The detoxifying effects of HS on microorganisms are quite complex: HS neutralize free pollutants (indirect bioeffects) and also stimulate the protective response of organisms (direct bioeffects). Prospects and potential problems of bioluminescent bacteria-based assay to monitor toxicity of solutions in the presence of HS are discussed. The main criterion for the bioassay application is versatility and ease of use. The detoxification efficiency of HS in different pollutant solutions was evaluated, and the detoxification mechanisms are discussed. Particular attention was paid to the direct and complex direct + indirect effects of HS. The review focuses on the protective function of HS in solutions of radionuclides and salts of stable metals, with special consideration of the antioxidant properties of HS.

Highlights

Humic substances (HS) are complex mixtures of high-molecular organic compounds of natural origin
To identify HS–organism interactions, priority should be given to understanding the functional mechanisms that have the highest impact on abiotic stress protection
Interact with biochemical components and affect the signaling pathways, eliciting dynamic signaling crosstalk inside the microorganisms in the course of various types of stresses involving the toxic impact of anthropogenic pollutants [78,79]

Summary

Introduction

Humic substances (HS) are complex mixtures of high-molecular organic compounds of natural origin. HS do neutralize free pollutants in solutions (indirect bioeffects), but may stimulate the protective response of organisms (direct bioeffects). These effects are a topic of interest due to the multiple interrelations between HS and microorganisms including the humification of organic matter in soils and sediments. HS may act as natural xenobiotics, which produce various biological effects and may influence water communities; the different mechanisms involved in these changes are under consideration [7,8]. Special attention is paid to the protective function of HS in the solutions of radionuclides and salts of stable metals

Influence of HS on Living Organisms

Antioxidant Properties of HS via Bacterial Bioassay

Conclusions