Persistence and bioavaiability of manufactured silver nanoparticles in the aquatic environment

The environmental behavior of manufactured nanoparticles (MNPs) has received increasing attention. One of the focuses is whether they exist as particles or as dissolved ions in the environment. The dissolution of MNPs is a key to understand their behaviors in the environment. However, little information is available in dissolution of MNPs in a complex environment, such as sediment, which is believed to be the final sink for released MNPs.
We tested the dissolution of PVP-coated silver nanoparticles (AgNPs) and compared the ion diffusive kinetics with Ag(I) in 3 different media (MilliQ water, seawater and sediment) at a level of 100 µg per g dry weight sediment. A large difference in dissolution in the three media was found in the order: MilliQ water >> seawater > sediment, which suggests that ligands (i.e., organic matter and inorganic ligands) have a large influence on ion release of AgNPs. In MilliQ water, the amount of released ions was 1.6 µg collected in diffusive gradient thin films after 16 days. In sediment, the released ion amount was less than 0.1% of the total amount of AgNPs added. We exposed Capitella teleta to sediment-associated Ag(I) and AgNPs. The results showed that AgNPs were bioavailable and were taken up mainly by worms as particles. The influence of ligands on AgNPs dissolution may have an important influence on bioavailability and toxicity, and we suggest that more studies are needed to examine the effects of ligands on AgNPs dissolution and the influence of dissolution on bioavailability.