Harmful effects of silver nanoparticles on a complex detrital model system

Area of Science:

• Environmental Science
• Ecotoxicology
• Microbiology

Background:

• Silver nanoparticles (AgNP) are increasingly prevalent in industrial and environmental applications.
• Realistic toxicity assessments require understanding AgNP interactions within complex ecosystems.
• Stream ecosystems rely on microbial decomposers for crucial ecological functions.

Purpose of the Study:

• To assess the acute toxicity of carbonate-coated AgNP and silver ions (Ag+) in a model stream ecosystem.
• To differentiate between particle-mediated toxicity and toxicity from dissolved silver ions.
• To evaluate the impact of AgNP on microbial growth and key ecosystem processes.

Main Methods:

• Utilized a model system of decomposing plant litter with associated fungal and bacterial communities.
• Assessed the stability of AgNP size and surface charge throughout the experiment.
• Measured bacterial protein biosynthesis, fungal ergosterol synthesis, fungal reproduction, and enzyme activities (alkaline phosphatase, leucine aminopeptidase, β-glucosidase).
• Investigated the role of cysteine in mitigating AgNP toxicity.

Main Results:

• AgNP significantly inhibited bacterial growth (EC50 = 0.3 μM) and fungal growth (EC50 = 47 μM), showing greater toxicity than Ag+.
• Fungal reproduction was stimulated by AgNP but not Ag+ at tested concentrations.
• AgNP affected various enzyme activities, with distinct impacts compared to Ag+.
• Cysteine addition did not alleviate AgNP toxicity, confirming particle-mediated effects.

Conclusions:

• AgNP exhibit significant particle-mediated toxicity to microbial communities in aquatic ecosystems.
• AgNP disrupt bacterial growth and alter key microbial processes, with potential severe consequences for ecosystem functioning.
• Toxicity assessments must consider the physical form of silver (nanoparticles vs. ions) for accurate environmental risk evaluation.