An inter-laboratory comparison of high precision stable isotope ratio measurements for nanoparticle tracing in biological samples

Abstract

Stable isotope labeling coupled with high precision isotope ratio measurements by multiple collector-ICP-MS is effective for tracing zinc from zinc oxide nanoparticles (ZnO NPs) in complex media and against a high zinc background. Using this technique, a previous study detected a slightly enhanced uptake of Zn in the blood of human females following dermal exposure to a sunscreen containing ZnO NPs, relative to a sunscreen of the same formulation but with larger ZnO particles (‘bulk’ material). Until now, the results of these exposures and the accuracy of the analyses, which require the resolution of subtle differences in Zn isotope ratios, have not been independently confirmed. Here we compare data from the previous study with results obtained in new, independent analyses of the same and additional samples, that were performed using similar techniques and instrumentation but in a different laboratory. The data sets are in good agreement, with a Pearson correlation coefficient of r ≈ 0.98, thus establishing the usefulness of the methods for tracing engineered ZnO NPs (and other anthropogenic sources of Zn) in Zn-rich biological materials. Previously unanalyzed blood samples from the earlier study provide further evidence for the increased uptake of Zn from ZnO NPs relative to bulk ZnO and they confirm that uptake rates decrease once sunscreen application has ceased.