Effects of silver nanoparticles on survival, biomass change and avoidance behaviour of the endogeic earthworm Allolobophora chlorotica.

Increasing commercial application of silver nanoparticles (Ag NP) and subsequent presence in wastewater and sewage sludge has raised concerns regarding their effects in the aquatic and terrestrial environment. Several studies have employed standardised acute and chronic earthworm-based tests to establish the toxicological effects of Ag NP within soil. These studies have relied heavily on the use of epigiec earthworm species which may have limited ecological relevance in mineral soil. This study assessed the influence of Ag NP (uncoated 80nm powder) and AgNO on survival, change in biomass and avoidance behaviour in a soil dwelling (endogiec) species, Allolobophora chlorotica. Earthworms were exposed for 14 days to soils spiked with Ag NP or AgNO at 0, 12.5, 25, 50 and 100mgkg either separately for survival and biomass measurement, or combined within a linear gradient to assess avoidance. Avoidance behaviour was shown to provide the most sensitive endpoint with an observable effect at an Ag NP/AgNO concentration of 12.5mgkg compared with 50mgkg for biomass change and 100mgkg for survival. Greater mortality was observed in AgNO (66.7%) compared with Ag NP-spiked soils (12.5%) at 100mgkg, attributed to increased presence of silver ions. Although comparison of results with studies employing Eisenia fetida and Eisenia andrei suggest that the A. chlorotica response to Ag NP is more sensitive, further research employing both epigeic and endogeic earthworms under similar experimental conditions is required to confirm this observation.