Behaviour of sediment-associated silver nanoparticles and their toxicity to Lumbriculus variegatus

Abstract

The increasing use of silver nanoparticles (AgNPs) in industry and consumer products results in the increasing environmental concentrations of AgNPs. In the aquatic environment, sediment is the major sink for the AgNPs. The behaviour and toxicity of AgNPs in sediments is largely unknown, and therefore the potential risk to the benthic ecosystems is difficult to predict. The aim of this thesis was to study the toxicity and uptake of uncoated AgNPs (uc-AgNPs) and polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs) to Lumbriculus variegatus in sediment exposures. Also, the association of AgNP-originated dissolved Ag with sediment components was studied using a sequential extraction method. Studies were conducted in natural and artificial sediments using silver nitrate (AgNO3) as a positive control for the toxicity and behaviour of silver ions (Ag+). The toxicity of AgNPs was lower than toxicity of AgNO3 in all the tested sediments. The properties of both the sediment and AgNPs were found to influence the environmental behaviour of AgNPs. The PVP-coating on AgNPs increased the bioaccumulation of Ag in alkaline artificial and natural sediments, whereas the bioaccumulation of uc-AgNPs was low. The toxicity of uc-AgNPs and PVP-AgNPs was comparably enhanced in acidic artificial sediment. Firstly, the dissolution of AgNPs was increased by low pH and secondly, the toxicity of Ag+ was further enhanced in acidic sediment. AgNP-originated dissolved Ag was observed to associate strongly with the sediment components, and only a small proportion of Ag was bioaccessible. The bioaccessibility differed among the sediments and was higher with PVP-AgNPs than uc-AgNPs. The toxicity of AgNPs seemed to be a function of Ag+ and no nano-specific toxicity was observed. According to our findings, the acute toxicity of AgNPs to L. varigatus is not expected to be higher than the toxicity of AgNO3.