Humic substances. Part 2: Interactions with organisms.

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Aquatic Ecology

Background:

• Freshwater bodies dominated by humic substances (HS) are globally prevalent.
• Direct interactions of HS with aquatic organisms are often overlooked.
• HS are natural environmental chemicals with significant ecological implications.

Purpose of the Study:

• To review and synthesize current knowledge on the direct ecological effects of dissolved HS on freshwater organisms.
• To challenge existing paradigms regarding the inertness of HS in aquatic ecosystems.
• To explore novel perspectives on HS-mediated stress and its potential role in aging and fitness.

Main Methods:

• Comprehensive review of international and grey literature on humic substance ecology.
• Inclusion of results from ongoing experimental studies.
• Focus on direct organism-HS interactions, excluding indirect effects like light attenuation.

Main Results:

• HS adversely affect photosynthesis and growth in macrophytes and algae, with varying responses among species.
• HS suppress cyanobacteria more than eukaryotic algae, likely due to quinone content.
• HS exhibit hormone-like properties, causing feminization in fish and amphibians, and modulate reproduction in nematodes.
• HS induce molecular chaperones, biotransformation enzymes, and oxidative stress, potentially leading to teratogenic effects.
• Field studies indicate reduced fish yield in lakes with higher HS concentrations.

Conclusions:

• Dissolved HS act as significant abiotic ecological drivers, influencing aquatic ecosystems.
• HS induce various stress responses in organisms, consuming energy and potentially impacting metabolism.
• Mild HS exposure may confer stress resistance and extend lifespan, aligning with new theories on aging.
• The ecological consequences of HS interactions remain incompletely understood and require further investigation.