Bioactive and total endotoxins in atmospheric aerosols in the Pearl River Delta region, China

Endotoxin, a toxic and pyrogenic substance in gram-negative bacteria in atmospheric aerosols was measured over a period of one year at Nansha, Guangzhou and Hong Kong in the Pearl River Delta region, China. Atmospheric aerosols were collected by high-volume samplers. The bioactive endotoxin levels in the samples were determined using the Limulus Amebocyte Lysate (LAL) assay after extraction with pyrogen-free water while the total endotoxin levels were measured by quantifying the biomarker, 3-hydroxy fatty acids (3-OHFAs) with GC–MS. Results showed that there was no significant difference (0.19 < p < 0.81) in the bioactive endotoxin level in PM10 among sites (average concentrations ranged from 0.34 to 0.39 EU m−3). However, Hong Kong showed a significantly lower (p < 0.05) total endotoxin level in PM10 (average of 17.4 ng m−3) compared with Nanshaʹs 29.4 ng m−3 and Guangzhouʹs 32.7 ng m−3. The bioactive endotoxins were found to be associated with the coarse mode (PM2.5-10) of the particulates of natural origins while the total endotoxins were associated more with the fine mode (PM2.5) of the particulates of anthropogenic origins. When normalized with particulate mass, the endotoxin loading is much higher in summer as a result of the increased growth of the bacteria when climatic conditions are favorable. The chemically determined total endotoxins were 3–4 orders of magnitude higher than the bioactive endotoxins quantified using the LAL assay. Correlation analyses between the bioactive endotoxins and 3-OHFAs with different carbon length were analyzed. Results showed that the correlations detected vary among sites and particulate sizes. Although no generalization between the total and bioactive endotoxins can be drawn from the study, the levels reported in this study suggests that the discrepancies between the two measurement approaches, and the bioactive potential of 3-OHFAs with individual carbon chains deserve further investigation.