Abstract:
Sri Lanka experienced a transboundary haze event in December 2022. The air quality
index changed significantly during this period. This study aims to determine the impact
of haze events on bacterial consortia and the total microbial load (TML) of air collected
during hazy and non-hazy days. Air sampling was done three times daily during the
hazy days (9th-16th December 2022) at a place located 1.7 Km away from Kandy
city. Control samples were collected during non-hazy days at the same location. A
fine particulate air sampler with two different impactor systems consisting of sterile
filter papers was used for sampling. Impactor A: collected fine particulate matter ≤ 2.5
microns; B: collected particulate matter in the 2.5−10 microns range. After 30 minutes
of sample collection, filter papers were cut into fine pieces and shaken in 8 mL sterile
distilled water at 100 rpm for 2 hours. After centrifugation, the pellet was cultured
on Luria-Bertani (LB) culture media. TML was determined using the flow cytometry
technique. Ten different culturable bacterial species were identified. Among them, 48%
were gram-positive bacilli. Pseudomonas spp. and Bacillus spp. were predominantly
identified during the hazy days, while Bacillus spp. was predominantly reported on
non-hazy days. TML was ∼3.5-fold higher on hazy days (2.86 × 105 cells/m3) than on
non-hazy days (8.21×104 cells/m3). The highest TML was obtained on the fourth day
of the sample collection, and it was at its peak at noon, 6.67 × 105 cells/m3 air. The
microbial load was significantly higher in particulate matter deposited on the impactor
system A than in B (p < 0.001). The findings suggest that pathogenic bacterial species
with the highest microbial load were reported in a recent haze event. The bacteria could
reach into the lower respiratory tract along with fine particulate matter (< 2.5 microns)
causing lower respiratory distress.
