The 3-hydroxy fatty acids as biomarkers for quantification and characterization of endotoxins and Gram-negative bacteria in atmospheric aerosols in Hong Kong

Abstract

Abstract Endotoxins from Gram-negative bacteria have received much attention because they could elicit strong pro-inflammatory responses in the human respiratory tract. In this study, 3-hydroxy fatty acids (3-OH FAs) with carbon chain lengths from 10 to 18 (C10–C18) were employed as biomarkers to quantify and characterize the endotoxins and Gram-negative bacterial community in atmospheric aerosols. Gas chromatography–mass spectrometry (GC–MS) was utilized for quantification of this biomarker in fine (PM 2.5 ) and coarse (PM 2.5–10 ) particulates collected by high volume samplers simultaneously at a rural and an urban site in Hong Kong. The geometric mean concentrations of the endotoxins were 5.5 and 1.35 ng m −3 in fine and coarse particulates at the rural site, respectively. At the urban site, the corresponding concentrations were 9.4 and 2.80 ng m −3 in fine and coarse particulates, respectively. It is found that 70–80% of the total endotoxins are associated with the fine particulates. Significant higher endotoxin levels at the urban site were observed throughout the 8-month study period. This could possibly relate to the heavier human activities in the urban areas. The distribution patterns of the 3-OH FAs with respect to carbon number are similar between the rural and urban sites regardless of particle sizes. The C10 and C16 were predominant and accounted for about 40–50% of the total 3-OH FAs. Furthermore, the odd carbon chain length 3-OH FAs constituted a non-negligible fraction (15–25%) of the total 3-OH FAs. The biologically active endotoxins estimated as the sum of C12 and C14 portions in this study ranged from 0.6–3.7 and 1.9–4.8 ng m −3 at the rural and urban sites, respectively. Applying the biomarker-to-microbial mass conversion factors, the dry mass loading of the Gram-negative bacteria are in the order of 10–10 2 ng m −3 in atmospheric aerosol. This study also demonstrates that the biomarker (3-OH FAs) approach yields much more quantitative information such as the mass loading, total endotoxin concentration and estimation of potent endotoxin level in the atmospheric aerosol.