Hazard Identification And Risk Factor Characterization Of Reclaimed Water Inhalation Exposures

Water resources have become increasingly scarce around the world,and urban use of reclaimed water from municipal wastewater significantly reduces the stress of water shortage.Various countries and regions issued water reuse guidelines or quality standards to guarantee human health and ecological safety during the appliation of reclaimed water under different circumstances.Those guidelinesare generally based on the related studies of risk assessment.However,previous researches mainly focused on the risk of pathogens and carcinogenic compounds in water such as enterovirus,THMs,and heavy metals.In addition,it was hypothesized that the accidental ingestion is the main exposure route of reclaimed water,and the common method for risk analysis is mathematical model including Monte Carlo simulation.The deficiencies of present studies arethe ignorance of a ubiquitous exposure route,inhalation,especially in urban use,and a potent risk of endotoxin,which is from gram-negative bacteria and often has a high concentration in reclaimed water.Epidemiological data indicatethat occupational exposureof organic dusts which was rich in endotoxin could cause asthma,fever and bronchitis in people engaged in related jobs.Thus the objective of our work is to establish an animal model to detect possible health effects of acute inhalation exposure of reclaimed water,identify dominating factors in reclaimed water,calculate health threshold of the main risk factor,and find possible lung damage after exposure and recovery periods.A mouse inhalation exposure model was established,and it was observed that the reclaimed water could induce strong lung inflammation after acute exposure.The most sensitive and stable effect in blood and lung is the proportion of polymorphonuclear(PMN)in bronchioalveolar lavage fluid(BALF).Moreover,after ultra-filtration,the exposure will not cause any inflammation in lung,indicating that only microorganisms and macro-molecules in water were capable of inducing inflammation in lung.Eleven water samples from 5 different plants were collected and used to treat animals,and the resulted PMN incretion in lung was positively correlated to the endotoxin level in the water.Based on the fact that in reclaimed water,the endotoxin activity was from both of free-endotoxin and cell-bound endotoxin,we used LPS standard and randomly selected gram-negative bacteria to treat animals.The dose-response relationship of real water samples and LPS water is similar,compared to bacteria samples.A polymyxin B affinity adsorption column was used to treat water samples,to remove free endotoxin as far as possible,and the result of inhalation exposure display that the effect from samples that both before and after adsorption were in good accordance with the prediction of dose-response model.Use BMDS to fit the data,and choose PMN proportion in BALF as a critical endpoint to calculate the threshold of acute inhalation of reclaimed water in mice,the resulted BMDL is 185EU/kg,corresponding to 264 EU/mL endotoxin level in water under the same exposure condition.We also summarized human data of acute LPS inhalation,the threshold derived from human study is corresponding to 120EU/mL in water.Thus we confirmed that by means of inhalation,human were also more sensitive to LPS exposure than mice.Sub-chronic inhalation exposure,in which the maximum exposure duration is 12 weeks,proved that repeated long term reclaimed water inhalation leads to apoptosis of epithelial cell in lung,plus over accumulation of collagenous fibers,and inevitably induced pulmonary dysfunction.The phenotypepersisted 4 weeks after the last exposure,means that the injury is irreversible.Moreover,the data from immunoglobulin tests proved that reclaimed water inhalation cannot induce allergy in lung,the elevated immunoglobulin(IgG,IgA)was mainly responsible for mucosal immunity.In conclusion,based on the experimental animal model,the current study firstly finished the hazard identification and risk factor screening of inhalation exposure of reclaimed water.Together with LPS threshold value from former researchers,and documented data of LPS level in reclaimed water,this study also revealed that the risk from inhalation is commom.Finally,after subchronic exposure,the present study confirmed that long term inhalation of reclaimed water will cause significant lung damage in mice.