Analysis of engineered nanomaterials (Ag, CeO and FeO) in spiked surface waters at environmentally relevant particle concentrations.

Quantification of engineered nanomaterials (ENMs) concentrations in surface waters remains one of the key challenges in environmental nanoscience and nanotechnology. A promising approach to estimate metal and metal oxide ENM concentrations in complex environmental samples is based on the increase in the elemental ratios of ENM-contaminated samples relative to the corresponding natural background elemental ratios. This contribution evaluated the detection and quantification of Ag, CeO, and FeO ENMs spiked in synthetic soft, or in natural river waters using the elemental ratio approach, and evaluated the effect of extractants including sodium hydroxide (NaOH), sodium oxalate (NaCO) and sodium pyrophosphate (NaPO) on the recovery of ENMs from the spiked waters. The extracted ENM concentrations were higher in NaPO-extracted suspensions than in NaOH- and NaCO-extracted suspensions due to the higher efficiency of NaPO to break up natural and engineered nanomaterial heteroaggregates. The size distributions of the extracted suspensions were determined by asymmetrical flow-field flow fractionation coupled to inductively coupled plasma-mass spectrometer (AF4-ICP-MS). These size distribution analysis demonstrated that Ag ENMs were extracted from the spiked river water as both primary particles and small (<100 nm) aggregates, whereas CeO ENMs were extracted from the spiked river water as aggregates of particles in the size range 0-200 nm. The number particle size distribution of the extracted suspensions confirmed that Ag ENMs were extracted as a mixture of primary and aggregated Ag ENMs. Small Ag ENMs (i.e. <20 nm) were detected by AF4-ICP-MS, but these particles were not detected by single particle (sp)-ICP-MS due to high size detection limit of sp-ICP-MS. This study illustrates that the elemental ratio approach is a promising approach to detect and quantify ENMs in surface waters. This study also illustrates the need for a multi-method approach, including extraction, filtration, AF4-ICP-MS and sp-ICP-MS, to detect, quantify, and characterize ENMs in surface waters.