Properties of silver nanoparticles influencing their uptake in and toxicity to the earthworm Lumbricus rubellus following exposure in soil

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Physicochemical properties of nanoparticles influence their environmental fate and toxicity, and studies investigating this are vital for a holistic approach towards a comprehensive and adequate environmental risk assessment. In this study, we investigated the effects of size, surface coating (charge) of silver nanoparticles (AgNPs) – a most commonly-used nanoparticle-type, on the bioaccumulation in, and toxicity (survival, growth, cocoon production) to the earthworm Lumbricus rubellus. AgNPs were synthesized in three sizes: 20, 35 and 50 nm. Surface-coating with bovine serum albumin (AgNP_BSA), chitosan (AgNP_Chit), or polyvinylpyrrolidone (AgNP_PVP) produced negative, positive and neutral particles respectively. In a 28-day sub-chronic reproduction toxicity test, earthworms were exposed to these AgNPs in soil (0–250 mg Ag/kg soil DW). Earthworms were also exposed to AgNO3 at concentrations below known EC50. Total Ag tissue concentration indicated uptake by earthworms was generally highest for the AgNP_BSA especially at the lower exposure concentration ranges, and seems to reach a plateau level between 50 and 100 mg Ag/kg soil DW. Reproduction was impaired at high concentrations of all AgNPs tested, with AgNP_BSA particles being the most toxic. The EC50 for the 20 nm AgNP_BSA was 66.8 mg Ag/kg soil, with exposure to AgNP_PVP (neutral) > Chitosan (positive). Size had an influence on uptake and toxicity of the AgNP_PVP, but not for AgNP_BSA nor AgNP_Chit. This study provides essential information on the role of physicochemical properties of AgNPs in influencing uptake by a terrestrial organism L. rubellus under environmentally relevant conditions. It also provides evidence of the influence of surface coating (charge) and the limited effect of size in the range of 20–50 nm, in driving uptake and toxicity of the AgNPs tested.
This work was financially supported by NanoNextNL, a micro- and nano-technology consortium of the Government of The Netherlands and 130 partners; funding was also received from Managing Risks of Nanoparticles, MARINA (EU-FP7, contract CP-FP 263215), and; the Strategic Research Funds titled Novel technologies by the Ministry of Economic Affairs of The Netherlands. Synthesis and characterization of the AgNPs used in this study received support from the QualityNano Project http://www.qualitynano.eu/which is financed by the European Community Research Infrastructures under the FP7 Capacities Programme (Grant No. INFRA-2010-262163).