Oxidation potential of PM2.5 in a mechanical processing plant and its association with metal composition

Abstract

Oxidative potential (OP) of particles is an emerging indicator of health that reflects their ability to induce oxidative stress and cause adverse health effects. It offers us a useful tool to evaluate the health effects of particles released by different industrial processes. We measured the OPv (volume normalized OP characterizes overall oxidative burden) and OPm (mass normalized OP characterizes intrinsic toxicity) of PM2.5 from a casting workshop, a machining workshop, a meeting room of a machining processing plant, and outdoors using dithiothreitol (DTT) assay. The observed variations were substantial and varied greatly, underscoring the diverse toxicological profiles of particulates from distinct sources. Overall, PM2.5 mass concentration and OPv were highest in the casting workshop (PM2.5: 669.26 ± 402.62 μg/m3, OPv: 69.55 ± 128.35 nmol/(min·m3)), followed by the machining workshop (PM2.5 = 85.51 ± 41.89 μg/m3, OPv = :5.38 ± 2.68 nmol/(min·m3)), outdoor (PM2.5: 30.77 ± 13.34 μg/m3, OPv: 1.83 ± 0.92 nmol/(min·m3)), and meeting room (PM2.5: 26.97 ± 12.03 μg/m3, OPv: 1.86 ± 1 nmol/(min·m3)). However, localized variances influenced by PM's intrinsic toxicity (OPm) reordered these rankings. For example, PM2.5 mass concentration at the spheroidizing/pouring zone in the casting workshop was the highest, but the OPv was not due to the low intrinsic toxicity of the particles. Spearman's correlation analysis implied that the OPv was significantly correlated with the concentration of transition metals Mn (ρ = 0.47, P < 0.01), Fe (ρ = 0.503, P < 0.01), and Zn (ρ = 0.507, P < 0.01) in addition to PM2.5 mass concentration (ρ = 0.879, P<0.01), and the OPm was significantly correlated with the mass fraction of Zn (ρ = 0.34, P < 0.05) and Al (ρ = 0.333, P < 0.05). Besides, environmental factors (wind speed, temperature relative humidity, CO2) did not contribute to the oxidation potential. Higher oxidation potential (OPv) means higher health risks, our findings underscore the imperative to consider both PM mass concentration and intrinsic toxicity for future air pollution control efforts.