污水处理厂微生物气溶胶的暴露风险评价

为了给污水处理厂微生物气溶胶的健康风险评价提供定量依据,于2011年6—7月利用Andersen 6级撞击式空气微生物采样仪对西安市第三污水处理厂氧化沟单元内不同距离处的细菌气溶胶进行现场采样,利用平皿培养和菌落计数对细菌进行分析。选用适于我国国情的暴露因子参数,建立暴露风险评价模型,对污水处理厂的工人及周围居民的健康风险进行评价。评价点的细菌气溶胶浓度采用修正的高斯模型计算。结果表明,呼吸吸入是人体(儿童和成人)摄入微生物气溶胶的主要途径,暴露非致癌风险商随距离的增加而逐渐降低。同种途径在同样位置,儿童的风险商是成年男性或成年女性的2~3倍。经呼吸途径的风险商从大到小为儿童、成年男性、成年女性,经皮肤接触途径的风险商从大到小为儿童、成年女性、成年男性。

Exposure hazard assessment of microbial aerosol generated in sewage treatment plant

The paper is engaged in a research on how to improve the exposure hazard assessment of microbial aerosol generated in the sewage treatment plant.For this purpose,we have carried out a series of theoretical and field study in hoping to indentify and quantify the exposure hazard associated with the microbial aerosol generated in sewage treatment plant(STP) and in turn to provide necessary quantitative reference for the health hazard assessment in this connection.For the above said purpose,we have first of all collected bacterial aerosols by means of an Andersen 6-stage cascade impactor at a Xi’an STP and observing the oxidation ditch process from June,2011 to July,2011.To be exact,we have selected three sampling sites at a distance of 2 m,5 m,10 m in the downwind direction from the oxidation ditch.We have also employed the plate culture and colony-counting method to determine the concentrations and size distributions of airborne bacteria.Next,we began to use the data collected from the oxidation ditch to generate microbial release rate.The downward-wind concentrations of the bacteria in the air were then calculated by the modified Gaussian model of air pollutant diffusion,which is considered to be the microorganisms decay.And,subsequently,based on the framework of the up-to-date American EPA exposure factors handbook and the corresponding Chinese literatures on the exposure factors in Chinese convention,we have developed an exposure model to measure the daily average exposure level from inhalation to skin contact.And,finally,we have applied the health hazard assessment model we have proposed to evaluating the liability of non-carcinogenic hazards of airborne bacteria for the workers in the STP and the surrounding residents.The results of our investigation indicate that the exposure hazard rate via inhalation is 105 times as high as via skin contact for children and adults,which implies that the inhaling is the chief way of bioaerosol intake for human sufferers.At the same time,the exposure hazard rate is found to drop gradually with the increase of windward distance.In addition,the exposure hazard rate for children tends to be generally 2-3 times as high as that for adults at each site.The order of exposure hazard rates via inhalation and by skin touch proves to be children>men>women and children>women>men,respectively,whereas the hazard rate for children is much higher than that for adult women and men.The liability gap between adult female and the adult male is minor.