Mitigating Activity of Humic Substances: Direct Influence on Biota

Mitigating activity of HS can be defined as a phenomenon of lowering the adverse effects of contaminants toxicity and of those of abiotic stress factors such as unfavourable temperature, pH, salinity, etc. As a rule, it is related to the detoxifying properties of HS or to their beneficial effects on biota. This review focuses on the latter effects and considers the possible mechanisms of mitigating activity of humic materials in terms of biological activity of HS. The beneficial effects of HS on biota are segregated into the four categories according to the underlying mechanism of their action: an influence on the organism development; an enhancement in nutrient supply; catalysis of the biochemical reactions; and an antioxidant activity. The published data on the mentioned essential biological functions of HS are reviewed.

The given review shows that in spite of the numerous reports published recently to elucidate the mechanisms underlying biological effects of HS, the data reported are quite contradictory. The main reason is the complexity of HS structure. A wide variety of the effects observed can be explained by the polyfunctionality of HS. The general conclusion can be made — all biological effects of HS have been more pronounced under stress conditions independent of what stress factors are involved. Thus, HS can be considered as an environmental modulator mitigating the harmful consequences of stress factors.