Application of hydrodynamic chromatography-ICP-MS to investigate the fate of silver nanoparticles in activated sludge

Detection and characterisation are two of the major challenges in understanding the fate, behaviour and occurrence of engineered nanoparticles (ENPs) in the natural environment. In a previous paper we described the development of hydrodynamic chromatography coupled to plasma mass spectrometry (HDC-ICP-MS) for detecting and characterising ENPs in aqueous matrices. This paper describes the applicability of the approach, to study the behaviour of silver nanoparticles in a much more complex and relevant environmental system i.e. sewage sludge supernatant. Batch sorption studies were performed at a range of nanosilver concentrations. Following completion, the sludge supernatant was characterised by ICP-MS, HDC-ICP-MS and transmission electron microscopy (TEM). It was found that, after a contact time of 6 h, most of the silver had partitioned to the sewage sludge (>90%). However, of the silver remaining in the supernatant, some of this was in the nanoparticle form, implying that closer consideration should be given to the longer-term impact of the release of silver ENPs into aquatic ecosystems. These preliminary data clearly show the utility of HDC-ICP-MS for studying the occurrence and behaviour of ENPs in complex natural environments.