Water-Soluble Ions and Heavy Metal Levels, Source Apportionment, and Health Risk of Indoor Dust in the Mogao Grottoes of Dunhuang, China

Abstract

The direct ingestion of indoor dust particles at historical heritage sites is a primary exposure pathway for employees to heavy metals. Water-soluble ions (WSIs) and heavy metal levels, sources, bioaccessibility, and health risks associated with indoor dust in the Mogao Grottoes were analyzed using comprehensive methods to determine the differences in the concentrations and distribution characteristics of WSIs and heavy metals between statue dust and floor dust. The concentrations of WSIs and heavy metals and the magnetic values of ${\chi }_{\text{lf}}$ and SIRM in indoor dust were higher than those in street dust and topsoil. The mean ${\chi }_{\text{lf}}$ and SIRM of statue dust particles were $100.3\times {10}^{-8}{\text{m}}^3\text{k}{\text{g}}^{-1}$ and $1686.9\times 10^{-5}{\text{Am}}^2\text{k}{\text{g}}^{-1}$ . Specifically, the concentration of Pb was $277\text{mg}\text{k}{\text{g}}^{-1}$ , 15-fold higher than the background value, indicating the continual receipt of heavy metals with high magnetic minerals during dust deposition. WSIs mainly originate from the weathering of surrounding rocks and earthen plaster; Pb originates from the shedding of paint of murals and sculptures; and Zn, Cu, and magnetic minerals originate from traffic sources. The bioaccessibility of heavy metals is high in the gastrointestinal phases of indoor dust. Overall, the health risks posed by heavy metals in indoor dust were low, with moderate to high risks in individual caves. Ingestion presents the highest noncarcinogenic and carcinogenic risk to employees. These results provide essential knowledge on indoor dust characteristics in the Mogao Grottoes, facilitating strategies for dust pollution mitigation and employee health risk control.