Chemical transformations of nanoscale zinc oxide in simulated sweat and its impact on the antibacterial efficacy

• Published in: Journal of hazardous materials Vol. 410; p. 124568
• Main Authors: Qian, Xiaoting, Gu, Zhouhang, Tang, Qing, Hong, Aimei, Xu, Zhenlan, Dai, Yihong, Bian, Xinyun, Lou, Haijin, Mortimer, Monika, Baalousha, Mohammed, Li, Lingxiangyu
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.05.2021
• Subjects: Bioavailability; Nanoscale zinc oxide; Phosphate-induced transformation; Selective dissolution; Simulated sweat; Simulated sweat; Selective dissolution; Nanoscale zinc oxide; Phosphate-induced transformation; Bioavailability
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2020.124568

Nanoscale zinc oxide (n-ZnO) is widely used in personal care products and textiles, thus, it would likely be released into human sweat. To better evaluate the potential human health risks of n-ZnO, it is essential to understand its chemical transformations in physiological solutions, such as human sweat, and the resulting changes in the n-ZnO bioavailability. Here, two types of n-ZnO, ZnO nanoparticles (ZnO-NPs) and nanorod-based ZnO nanospheres (ZnO-NSs) were synthesized and incubated in 3 types of simulated sweat with different pH values and phosphate concentrations. The content of Zn3(PO4)2 in the transformed n-ZnO was quantified by selective dissolution of Zn3(PO4)2 in 0.35 M ammonia solution where 100% and 5.5% of Zn3(PO4)2 and ZnO were dissolved, respectively. The kinetics analysis indicated that by 24–48 h the content of Zn3(PO4)2 reached the maximum, being 15–21% at pH 8.0 and 45–70% at pH 5.5 or 4.3. Interestingly, no correlation was observed between the rate constants of Zn3(PO4)2 formation and the specific surface areas of n-ZnO, implying that chemical transformations from n-ZnO to Zn3(PO4)2 in the simulated sweat might not be simply attributed to dissolution and precipitation. Using a variety of characterization techniques, we demonstrated the formation of a ZnO‒Zn3(PO4)2 core-shell structure with the shell consisting of amorphous Zn3(PO4)2 at pH 8.0 and additionally of crystalline Zn3(PO4)2 and Zn3(PO4)2•4H2O at pH 5.5 or 4.3. The phosphate-induced transformation of n-ZnO in the simulated sweat at pH 5.5 and 4.3 greatly reduced the antibacterial efficacy of n-ZnO through moderating the nanoparticle dissolution, indicating limited bioavailability of the NPs upon transformation. The results improve the understanding of the fate and hazards of n-ZnO. [Display omitted] •Nanoscale ZnO could undergo chemical transformations in the simulated sweat.•Selective dissolution of Zn3(PO4)2 against ZnO was established by ammonia solution.•Chemical transformations of nanoscale ZnO was affected by pH of the simulated sweat.•Transformations of nanoscale ZnO affected its antibacterial efficacy to E. coli.