Spatiotemporal estimates and health risks of atmospheric trace metals across Hong Kong during 2016–2020

Abstract

Trace metals often pose great threats to human health. Although many previous studies have estimated the site-level or national trace metal concentrations in particles, the high-resolution trace metal exposures and health risks at the intra-urban scale still remained poorly understood. To mitigate the hazardous effect of airborne toxic metals, the multi-stage model was firstly developed to construct the long-term and high-resolution trace metal exposures across Hong Kong and to assess the potential health risks associated with these trace metals. The results suggested that the 10-fold cross-validation (CV) R² values of As, Cd, Cr, Fe, Pb, and Se reached 0.65, 0.63, 0.55, 0.64, 0.73, and 0.56, respectively. The higher R² value indicated the robustness of the ensemble model for trace metal prediction. At the spatial scale, As, Cd, Cr, Pb, and Se generally displayed the higher concentrations in the northern part of Hong Kong and gradually decreased from north to south. It was assumed that many energy-intensive industries were located on the northern part of Hong Kong. Moreover, some trace metals derived from industrial emission or power plants could be transported from Mainland China. However, the Fe level showed the higher levels in both of northern part of Hong Kong and Kowloon area. It was assumed that the higher Fe level was enriched in the vehicle brake pads. In addition, the simulated trace metals including As, Cd, Cr, Fe, Pb, and Se in PM₁₀ in Hong Kong displayed significant annual variations. As, Cd, Cr, Fe, Pb, and Se levels increased from 2.84 ± 0.17, 0.59 ± 0.04, 2.44 ± 0.13, 507 ± 39, 15.6 ± 1.11, and 0.45 ± 0.02 ng/m³ to 2.94 ± 0.17, 0.62 ± 0.04, 2.49 ± 0.14, 524 ± 41, 16.4 ± 1.10, and 0.47 ± 0.02 ng/m³ during 2016–2017, respectively. However, they suffered from gradual decreases to 2.35 ± 0.20, 0.53 ± 0.04, 2.22 ± 0.15, 474 ± 42, 13.5 ± 1.20, 0.42 ± 0.02 ng/m³ during 2017–2020, respectively. Our result could facilitate the local environmental management to decrease health risk.