With the aim of developing an understanding of the impact of AgNP on food web interactions and ecological processes, we are currently using the fungal litter-decomposition and algal biofilm system in streams as models to assess effects of nanomaterials in ecosystems. Emphasis is being placed on testing for effects on interactions in simplified food webs (fungi-bacteria-detritivores and algae-bacteria-herbivores, respectively) and on key ecosystem processes (leaf litter decomposition and primary production) upon short-term and long-term exposure. The experiments are carried out in microcosms and indoor experimental stream channels. Assessed responses include growth and activity parameters of fungi, bacteria, algae and invertebrates as well as rates of litter decomposition and primary production. Main results show that depending on the assessed endpoints, AgNP toxicity to litter associated fungi and bacteria as well as biofilms in streams can either be mediated by dissolved Ag+ ions or be directly caused by the particles. Trophic transfer experiments with snails feeding on biofilms contaminated with AgNP show no direct effects on the snail but on the development of hatched eggs as evidenced by malformations of the early snail embryos (SNEP, SNFS NFP 64: PhD thesis C. Gil Allué, Dr. A. Tlili).
Examination of the effects of sulfidized AgNP, which represent a major transformation form of AgNP in waste water effluents, show compared to AgNP no toxicity to various functions of biofilms. However, effects become manifest upon ozonation of the sulfidized particle, due to formation of dissolved Ag+ ions ((SNEP, SNFS NFP 64, Dr. B. Bonet).
A long-term study comparing the effects of ionic and NP silver to periphyton focused on the composition of extracellular substances (EPS) and 3D structure, which are relevant to the interaction with other pollutants and to near-bed hydrology. Reduced diversity, abundance of diatoms and EPS composition were related to the amount of ionic silver, whereas 3D structure was specifically affected by both, particulate and dissolved silver (Ambizione, Dr. A. Kroll, L. Sgier).