Diurnal trends in redox characteristics of water-soluble and -insoluble PM components

Nirmal Kumar Gali; Guoliang Li; Zhi Ning; Peter Brimblecombe

doi:10.1016/j.envpol.2019.07.009

Diurnal trends in redox characteristics of water-soluble and -insoluble PM components

Environ Pollut. 2019 Nov;254(Pt A):112841. doi: 10.1016/j.envpol.2019.07.009. Epub 2019 Jul 17.

Authors

Nirmal Kumar Gali¹, Guoliang Li², Zhi Ning³, Peter Brimblecombe²

Affiliations

¹ Division of Environment and Sustainability, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region.
² School of Energy and Environment, City University of Hong Kong, Hong Kong Special Administrative Region.
³ Division of Environment and Sustainability, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region. Electronic address: zhining@ust.hk.

PMID: 31369911
DOI: 10.1016/j.envpol.2019.07.009

Abstract

Densely populated cities with a compact urban built environment have concerns over health risks derived from high levels of airborne particulate matter (PM) exposure. Understanding the association between PM and reactive oxygen species (ROS) is an important step towards unravelling the mechanisms behind. This study investigated the role of time-integrated PM sampling on cellular toxicity mechanism on a diurnal scale. The sampling took place in a highly urbanized part of Hong Kong at two contrast roadside and background sites, with simultaneous solid-PM and semi-volatile-PM (SV-PM) collection in both summer and winter seasons. A sampling day consisted three sampling intervals of 6 h each - 04:00-10:00, 12:00-18:00 and 20:00-02:00 h, representing morning rush hours, afternoon and night periods, respectively. Water and organic extracts of PM were prepared, with and without filtration, and exposed to RAW264.7 and A549 cell lines on a dose and time-dependent manner. Solid-PM and SV-PM contribution to total PM_2.5 mass concentration was 9:1, with much higher SV-PM fraction at roadside over urban background (p < 0.001, n = 36). Also, the SV-PM mass concentration increased by 10-20% during 20:00-02:00 h compared to morning and afternoon sampling periods. Organic PM extract was observed to cause 23-29% higher cell death compared to water-soluble PM, which is complemented with increased ROS production in both cell lines. The cellular damage caused by oxidative stress, determined from increased HO-1 and TNF-α expression in RAW264.7 was higher compared to the A549, which demonstrated the greater induction of toxicity from organic PM extract over soluble PM. Similarly, the SV-PM induced greater than 2-fold cellular ROS generation on PM mass basis compared to solid-PM. Lack of phagocytic action in A549 compared to RAW264.7 suggested novel toxicity routes for water-soluble and organic PM that can be expected to occur during human PM inhalation-bronchi-alveolar exposure.

Keywords: Cellular toxicity mechanism; Diurnal oxidative potential; Oxidative stress; Semi-volatile PM; Water-insoluble PM.

MeSH terms

Air Pollutants / analysis*
Cell Line
Cities
Filtration
Hong Kong
Humans
Inhalation Exposure
Oxidation-Reduction
Oxidative Stress
Particulate Matter / analysis*
Reactive Oxygen Species / metabolism
Seasons
Water

Substances

Air Pollutants
Particulate Matter
Reactive Oxygen Species
Water