Biotic and abiotic factors affect microcystin-LR concentrations in water/sediment interface

Area of Science:

• Environmental Science
• Aquatic Toxicology
• Microbiology

Background:

• Harmful cyanobacterial blooms are increasing globally, leading to elevated cyanotoxin concentrations.
• Microcystins (MCs) are prevalent freshwater cyanotoxins posing risks to aquatic life and human health.
• The fate of MCs in aquatic systems, including sediment interactions, is crucial for risk assessment.

Purpose of the Study:

• To investigate the fate of microcystins (MCs) in a shallow coastal lagoon.
• To estimate the potential return of pre-existing MCs from sediment to the water column.
• To evaluate MC-LR adsorption to sediment and biodegradation under lagoon-specific conditions.

Main Methods:

• Experiments simulating lagoon conditions (temperature, pH, aeration) were conducted with sediment and water samples.
• MC-desorption, adsorption of MC-LR to sediment, and biodegradation were assessed.
• Bacterial community composition in sediment and interstitial water was analyzed.

Main Results:

• No significant MC-desorption from sediment was detected under tested conditions.
• Sediment facilitated a 50% reduction in soluble MC-LR concentration, enhanced by higher temperatures and aeration.
• Biodegradation of MCs was confirmed in sediment and interstitial water, with identified MC-degrading bacterial genera.

Conclusions:

• Sediment plays a critical role in the fate of MC-LR in shallow coastal lagoons.
• Stable adsorption and biodegradation by sediment-associated bacteria effectively remove MCs from the water column.
• Sediment acts as a sink, mitigating MC contamination risks in these environments.