The increasing uses of zinc oxide nanoparticles (ZnONPs) in coatings, paints, personal care products and many other products increase the possibility of the body's exposure to ZnONPs. Accurate and quantitative profiling on the tissue distribution and body clearance of ZnONPs, which is an important factor to clarify the acute and chronic safety concerns of ZnONPs, is interfered by the abundance of the body's endogenous zinc moiety. In this report, radioactive zinc oxide nanoparticles (R-ZnONPs) generated from neutron activation were employed for the in vivo bio-distribution studies using mice as the animal model. Gamma-ray emitting radioactive R-ZnONPs were produced from neutron activation. Zeta potentials of the ZnONPs before and after the neutron irradiation remained about the same, and R-ZnONPs largely remained its original nano-particulate form after neutron irradiation. After intravenous administration into ICR mice, R-ZnONPs exhibited a primary retention in lung (43.6% injected dose (ID)/g tissue wet weight) for the first hour and began to be translocated to intestinal tract for feces excretion at a later stage. This type of labeling free and radioactive nanoparticles retains the surface property and can be a convenient protocol for studying bio-distribution of nanoparticles in pristine chemical form.

Although zinc oxide nanoparticles (ZnONPs) have been applied in nanotechnology, their kinetics and tissue distribution in vivo are unknown. Here we compared the kinetics and tissue distribution of 10 nm (65)ZnONPs, 71 nm (65)ZnONPs and (65)Zn(NO(3))(2) in mice after intravenous injection. The areas under the curves and the half-lives in the second compartment of (65)Zn(NO(3))(2) were greater than those of (65)ZnONPs; the kinetic parameters were similar for both (65)ZnONPs. However, the tissue distributions for the three forms were different. ZnONPs preferentially accumulated in the liver and spleen at 24 h. At day 28, (65)Zn concentration was highest in bone and the proportion of recovered (65)Zn radioactivity was highest in the carcass; these had the same ranking, 10 nm (65)ZnONPs > 71 nm (65)ZnONPs> (65)Zn(NO(3))(2). Although more than 80% of the 10 nm (65)ZnONPs had been excreted by day 28, greater amounts of the 10 nm (65)ZnONPs than the 71 nm (65)ZnONPs or (65)Zn(NO(3))(2) had accumulated in other organs (brain, lung, heart and kidneys). Zn ions seem to have a longer half-life in the plasma, but ZnONPs show greater tissue accumulation. Although the size of the ZnONPs had no obvious effect on the kinetics, nevertheless the smaller ZnONPs tended to accumulate preferentially in some organs.

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