Study On Exposure Risk Assessment And Control Of Bioaerosol And Endotoxin In Campus Environment

Air is the fundament for human beings and all living things.Human beings are exposed to large amounts of toxins every day,including bio-aerosols and biohazardous substances such as endotoxin.The people sustained exposure to bio-aerosol,will have fever reaction,decreased immune function and other symptoms,suffering pneumonia,asthma,rhinitis,conjunctivitis,urticaria,lung cancer and other diseases.Therefore,the risk assessment of bioaerosol and airborne endotoxin is important.Research on related control technology is of great significance for human health.At present,there is no uniform standard for the collection and detection of airborne endotoxin.Therefore a systematic optimization of the existing method was conducted.The influence of acquisition time,ultrasonic pretreatment,the choice of absorbent and sampler type on collection efficiency were analyzed.Experimental results showed that endotoxin concentration tended to increase initially and then declined over time,and that the extraction solution reached saturation after 15 min of sampling.The majority of the cells were disrupted by an ultrasonication pretreatment of 500-800 W,allowing more free endotoxins detected by the Limulus amebocyte lysate assay.However,a sonication power greater than 800 W could destroy endotoxin structure.The addition of Tween 20(a solubilizing agent)to the absorbent resulted in bridging between water molecules and endotoxin molecules,which promoted the endotoxin dissolution and0.05%Tween 20 solution had the best solubilization effects.There was a negatively correlation between nozzle aperture size and endotoxin concentration(R~2=0.800).Small pore sizes could enhance airborne endotoxin absorption because they could generate more bubbles with small size and high specific surface area,thereby increasing the interaction between the endotoxins and extraction solution.The bioaerosol,airborne endotoxin,PM2.5,TVOCs,temperature and humidity were tested in typical public places on campus.It was found the places with large population density,more microbial sources,ventilation and cleaning work less,suffered a high level of bioaerosol and endotoxin.The concentration of airborne endotoxin was positively correlated with the concentration of PM2.5 and TVOCs.There was no significant correlation between the concentration of airborne endotoxin and temperature and humidity(p<0.05).The correlation between aerosol and PM2.5,TVOCs,temperature and humidity was not significant neither,sicnce the concentration of bioaerosl was influenced by many factors.The risk of exposure to bioaerosol and airborne endotoxin was evaluated from respiratory inhalation and skin absorption.The results showed respiratory inhalation was the main route of human to take in bioaerosol and endotoxin.The exposure dose of endotoxin was the highest for children,followed by adult males,and then adult females.The Hazard Index of children was 2-3 times higher than that of adults.Spatially,the exposure dose was positively correlated with exposure frequency.The exposure dose in public places for long-term use was greater than that in intermittent public places.Escherichia coli aerosol was inactivated by ultraviolet radiation.The results showed that the inactivation efficiency of was 3.22-log under 185nm,which was the the best sterilization effect.The UV inactivation efficiency of the 254 nm wavelength was 2.97-log.The UV inactivation efficiency of the 365 nm wavelength was only 0.97-log,almost no effect of killing E.coli.What's more,there was no significant change in endotoxin and TOC during the inactivation.