Endotoxin associated with ambient PM (particulate matter) has been linked to adverse respiratory symptoms, but there have been few studies of ambient endotoxin and its association with co-pollutants and inflammation. Our aim was to measure endotoxin associated with ambient PM10 (particulate matter with aerodynamic diameter<10µm) in summer 2016 at four locations in Chitwan, Nepal, and investigate its association with meteorology, co-pollutants, and inflammatory activity. PM10 concentrations were recorded and filter paper samples were collected using E-samplers; PM1, PM2.5, black carbon (BC), methane (CH4), and carbon monoxide (CO) were also measured. The Limulus amebocyte lysate (LAL) assay was used for endotoxin quantification and the nuclear factor kappa B (NF?B) activation assay to assess inflammatory activity. The mean concentration of PM10 at the different locations ranged from 136 to 189µg/m3, and of endotoxin from 0.29 to 0.53EU/m3. Pollutant presence was positively correlated with endotoxin. Apart from relative humidity, meteorological variations had no significant impact on endotoxin concentration. NF-?B activity was negatively correlated with endotoxin concentration. To the best of our knowledge, this study provides the first measurements of ambient endotoxin associated with PM10 in Nepal. Endotoxin and co-pollutants were positively associated indicating a similar source. Endotoxin was negatively correlated with inflammatory activity as a result of a time-limited forest fire event during the sampling period. Studies of co-pollutants suggested that the higher levels of endotoxin related to biomass burning were accompanied by increased levels of anti-inflammatory agents, which suppressed the endotoxin inflammatory effect.
