Quantifying Nanoparticle Associated Ti, Ce, Au, and Pd Occurrence in 35 U.S. Surface Waters

Mass flux models have predicted environmental concentrations of released engineered nanoparticles (ENPs), but their validation with field studies at high geographic scale has been limited. Additionally, baseline levels of natural and incidental nanoparticle (NP) occurrence are not well-established. This study begins to address these knowledge gaps by investigating the Au, Ce, Ti, and Pd NP content of 241 water samples from 35 drinking water sources across the U.S. over 6-9 months using single particle inductively coupled plasma-mass spectrometry. Ce and Ti NPs were commonly detected, with Ce concentrations (0.3-230 μg L-1) exceeding both ENP predictions and reports of natural abundance. The Ti NP concentrations (3-2400 μg L-1) were greater than modeled ENP release and similar to the expected natural abundance. Although Au and Pd NPs were rarely detected, they were present at parts per billion levels in some samples. The NP concentrations and sizes did not differ between geographic regions but were highly variable at individual sites over time, suggesting that local changes to release rates and precipitation may cause temporary hot spots. The regional NP concentrations and sizes provided here will be useful to inform continued ENP release and risk assessment studies.