Abstract
Motivation for detecting engineered nanoparticles (ENPs) in the environment comes from a need to understand fate and behavior of these materials in natural matrices. The difficulty lies in the low expected ENP particle number concentration (PNC) and the presence of a large and variable background concentration of natural NPs. We report the PNCs and characteristics of cerium-bearing nanoparticles (Ce-NPs) and titanium-bearing nanoparticles (Ti-NPs) in an aquatic matrix (the Seine River and three of its tributaries) with the use of single particle ICP-MS (spICPMS) and electron microscopy (FEG-SEM). Ce-bearing and Ti-bearing particles were observed in suspended particulate matter collected onto 0.2 μm and 1 kDa filters, using FEG-SEM imaging. At Marnay-sur-Seine, the upstream point, PNCs for Ce-NPs and Ti-NPs were 0.47 ± 0.07 × 106 and 1.35 ± 0.17 × 106 particles as measured by spICPMS. The maximum PNC for both Ce-NPs and Ti-NPs, 1.59 ± 0.10 × 106 particles mL−1 and 5.89 ± 0.10 × 106 particles mL−1, respectively, were found in the Marne River, a major tributary to the Seine. It was shown that downstream of each confluence, an increase in the PNC of the Seine is observed, suggesting a significant contribution of the different tributaries. Mass balance of particles flows and elemental ratios of Ce/La showed that in the Marne and the Oise River, a contribution of natural CeO2 NPs exists. The anthropogenic contribution in TiO2 ENPs for the Marne River was further assessed with Ti/Al, Ti/V, and Ti/Y elemental ratios. Near constant element ratios in the Seine below the Orge River and Paris city suggest neither contribute significantly to Ce or Ti NP concentrations. The study provides further investigation of the strengths and limitations of the application of spICPMS to natural samples and contributes data to the currently highly-limited dataset on natural NP backgrounds in rivers, information that is key to assessing the potential for quantifying the input of ENPs to surface waters. Of the total mass of Ce and Ti, 83 and 90%, respectively, could be detected as particles by spICPMS.
Highlights
Quantifying engineered nanoparticles (ENPs) at relevant analytical concentrations is the key step to assess the fate and behavior of these particles in the environment
The occurrence of CeO2NPs and TiO2NPs were assessed with the use of single particle ICP-MS (spICPMS) showing that millions of particles per milliliter containing Ce and Ti could be measured with this technique with the adequate dilution
The results of the elemental ratios and of the mass balance showed that only the Marne River and the Oise River had a significant contribution in natural CeO2NPs
Summary
Quantifying engineered nanoparticles (ENPs) at relevant analytical concentrations is the key step to assess the fate and behavior of these particles in the environment. Most toxicological studies utilize concentrations higher than that expected in the environment. Even though PECs for most ENPs are low, the flows in the environment are significant (tons per year). Titanium dioxide NPs (TiO2NPs) have been modeled to have a flow from the production, manufacturing and consumption sector to sewage treatment plants of 1,586 tons per year in the United States (Gottschalk et al, 2009). These high flows are mostly due to the important production of ENPs, which keeps increasing over the years because of the industries that incorporate NPs to enhance their products’ properties
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