Landfills are an essential component of Hong Kong’s waste management strategy. With a geographically small
size and a large population it is inevitable that many residents will live proximal to landfill sites, and this has
raised public concerns about landfill emissions causing low birth weights, cancer, neurological diseases,
nausea, and hospitalization of diabetics. This project has collected, physico-chemically characterise, and
determined the potential bioreactivity of landfill-derived PM2.5 particulates.
Many studies have demonstrated the health risks posed by landfill sites (Koshy et al., 2009), but unfortunately
there is lack of investigation in the bioactivity of PM2.5 from municipal landfill sites in Hong Kong. This study
has investigated the physicochemical characteristics of PM2.5 samples collected from locations near Municipal
Solid Waste (MSW) landfill sites. We determined the oxidative stress of PM2.5 samples from their generation
of reactive oxygen species. We determined the relationship between physical and chemical characteristics of
PM2.5 and their bioreactivity from particles collected near to the landfill sites and in downwind urban sites.
Five sampling sites were selected for this study. Two sites adjacent to the landfill areas, Two urban sites in a
mixture of residential and commercial areas, and one sampling site is in a remote area far removed from any
anthropogenic activities. The PM2.5 samples were collected simultaneously at all sites with URG PM2.5
samplers. Wind and real-time PM2.5 monitors were installed at two locations in proximity to the landfill sites
in order to determine diurnal variations of particulate level, wind speed and direction. Twenty-four hours
integrated PM2.5 samples were collected in winter (December to March, 2014-15) and summer (July to
November, 2015) in every 3 days intervals. Samples were weighed to a 1 μg precision for the mass
concentration measurements. Field emission scanning electron microscope (FESEM) analysis was used for
particle imaging. Total metal concentrations were analysed using inductively coupled plasma mass
spectrometry (ICP-MS). Ion chromatography (IC) was employed for water-soluble inorganic ions analysis.
Organic carbon (OC) and elemental carbon (EC) were analysed by thermal optical reflectance. Thermal
desorption-gas chromatography-mass spectrometry (TD-GC/MS) was used for polycyclic aromatic
hydrocarbons (PAHs) analysis. A plasmid scission assay (PSA) was used to determine the capability of each
sample to induce plasmid DNA damage. Statistical analysis was performed using SPSS 21.0 software. The
average PM2.5 concentrations were generally higher in winter than summer at all locations and significant
differences between seasons were observed at the landfill sites. The average concentrations of most chemical
species demonstrated summer minimum and winter maximum. The contributions of OC and EC in PM2.5 in
winter are in a range of 17.2-29.1 and 4.4-5.0%, respectively. However, the contributions of OC is lower in
summer. The NO3-, SO42- and NH4+ are the three most abundant inorganic ions, with sulphate contributed in
a range of 6.6-42.3 % in PM2.5 in winter. The amount of damage to the plasmid DNA induced by PM2.5
varied in a range of 24-92 % and 27-96 % in winter and summer, respectively. The DNA damage in summer
were higher than winter in all locations
High PM2.5 levels were observed during daytime downwind from landfills. Significant associations were
observed between DNA damage and heavy metals/PAHs in summer. Emissions from landfill-related
machinery are potential important particle sources. No significant associations were observed between DNA
damage and landfill particles, which indicates that PM2.5 loading from other regional sources was an important
factor for DNA damage