Characterization and source apportionment of particulate matter and associated culturable bacterial bioaerosols at sites cultivating aromatic and medicinal plants

Abstract

The atmospheric particulate matter (PM) and bioaerosol concentration in agricultural sites varied with agricultural activities and plantation type. In this study, the mass and elemental and ionic composition of PM₁₀ and PM_2.5 were examined at three agricultural sites cultivating Andrographis paniculata, Ocimum basilicum and Ocimum sanctum. The bacterial colony-forming units (CFU) and dominant bacterial species present in PM₁₀ were also examined at three sites. PM₁₀ concentrations ranged from 138.20 to 309.60 μg m⁻³, while PM_2.5 varied between 50.05 and 165.15 μg m⁻³. Elemental analysis revealed the dominance of crustal elements (Ca, Al, and B) along with trace levels of heavy metals (Pb, Cr, and Cd), while the ionic composition was dominated by Ca²⁺, K⁺, NH₄⁺, Cl⁻, SO₄²⁻, and NO₃⁻, indicating agricultural and combustion-related sources. Source apportionment analysis revealed that PM_2.5 was more influenced by secondary aerosols and combustion-related emissions, while PM₁₀ was associated with biological and crustal components. Bioaerosol concentrations ranged from 5.87 to 7.11 log CFU m⁻³, with Bacillus sp., Pantoea sp., and Pseudomonas sp. identified as the dominant bacterial species. A significantly lower load of these bacterial species in bioaerosols at the site cultivating Ocimum sanctum was observed. Overall, the source apportionment demonstrates that agricultural activity is a key source of particulate matter and regulates the concentration of particulate matter in the air.