Silver nanoparticle effects on stream periphyton during short-term exposures

Area of Science:

• Environmental Science
• Ecotoxicology
• Aquatic Ecology

Background:

• Silver nanoparticles (AgNP) are common antimicrobials in consumer products.
• AgNP released into aquatic environments interact with vital microbial communities like periphyton.
• The impact of nanoparticles on periphyton's ecosystem functions is largely unknown.

Purpose of the Study:

• To investigate the effects of silver nanoparticles (AgNP) and silver ions on stream periphyton.
• To assess impacts on key ecosystem processes including photosynthesis, respiration, and enzyme activity.
• To differentiate between nanoparticle-specific toxicity and toxicity from dissolved silver ions.

Main Methods:

• Experimental microcosms were used to expose periphyton to citrate-coated AgNP and silver nitrate (AgNO3).
• Five functional endpoints were measured: photosynthetic yield, respiration potential, and three extracellular enzyme activities.
• A chelating ligand was used to distinguish between dissolved silver ion toxicity and potential nanoparticle effects.

Main Results:

• Both AgNP and AgNO3 significantly inhibited periphyton photosynthesis and respiration after 2-hour exposure.
• Activities of two out of three extracellular enzymes were inhibited by both AgNP and AgNO3.
• While most AgNP toxicity was attributed to dissolved Ag(I), one enzyme (leucine aminopeptidase) was inhibited by AgNP independently of dissolved silver.

Conclusions:

• Silver nanoparticles and silver ions can disrupt fundamental metabolic functions in stream periphyton.
• Toxicity is primarily driven by dissolved silver ions, but direct nanoparticle effects on specific enzymes also occur.
• These findings highlight the potential ecological risk of AgNP to primary producers in freshwater ecosystems.