Fast Multielement Quantification of Nanoparticles in Wastewater and Sludge Using Single-Particle ICP-MS

Quantitatively monitoring the presence of engineered, natural, or incidental nanoparticles (NPs) is essential to understand their potential environmental and ecotoxicological implications. In particular, a significant number of NPs may travel through wastewater treatment plants (WWTPs), as a conduit to their release to the environment, either in treated effluent or in wastewater sludge (biosolids). Here we developed a fast and simple protocol for full quantitative multielement analysis of metallic or metal-containing NPs in wastewater and sludge samples via single-particle ICP-MS. We employed centrifugation to separate NPs from wastewater sludge, with high recoveries (>84%) for Au and Ag NPs, which have rather high densities (19.3 and 10.5 g cm(-3), respectively). In wastewater samples, particle mass concentrations ranged from <1 ng/L for Cd-based NPs to almost 100 mu g/L for Mg particles. Particles from most elements detected in wastewater were <100 nm in size, although TiO2 in raw wastewater was around 250 nm in size, and Mg was >1500 nm in size, well beyond the nanoscale. The efficiency of removal of NPs throughout the WWTP was significantly dependent on the type of metal-containing particles and the influent concentration.