环境水质学国家重点实验室知识库

      隐孢子虫与贾第鞭毛虫(以下简称“两虫”)作为一种水介传播的病原微生物，频频在许多发达国家与发展中国家检出，感染人体引起发烧、呕吐、腹泻脱水甚至死亡。在中国多省份原水中，“两虫”污染严重也十分严重，这应当引起政府足够的关注。
      早在1999 年，英国、美国等国家已经对贾第鞭毛虫和隐孢子虫的浓度或去除率做了限制与规定；我国《生活饮用水卫生标准》已经强制实施十年，但人群感染率依旧偏高。先前评价“两虫”风险的研究中，缺乏对免疫缺陷人群的足够关注，而其过低的免疫力会使“两虫”感染的效能大大提升。除此之外，不同年龄人群敏感性的差异也缺乏相应量化方法。截至目前，国内重点流域“两虫”污染调查积累了大量暴露数据，对“两虫”进行健康风险评价，综合考虑处理工艺可行性、人群感染率与“两虫”健康风险指导水质标准修订建议显得更加重要。
本文以隐孢子虫与贾第鞭毛虫为研究对象，用人口总量平衡法计算人口年龄组结构与流行病调查“两虫”病患年龄组结构的差异用于估算年龄敏感性；建立了浊度—颗粒物关系模型估计了水厂常规工艺“两虫”的去除效率；基于十年原水隐孢子虫与贾第鞭毛虫的暴露数据，结合去除率参数评价了“两虫”的累积健康风险，并研究其控制策略，以期为我国的饮用水安全管理提供技术支撑。
      本研究主要得到结论如下：
      共感染的风险评价：中国重点城市，原水中隐孢子虫、贾第鞭毛虫检出多集中于0-2 个卵囊(孢囊)/10L，与世界范围暴露水平并无显著差异；幼儿感染“两虫”的敏感性是成年人的10.59-17.91 倍，基于敏感性预测全人口感染“两虫”的比例为0.17%-6.59%，与流调结果相吻合；综合考虑敏感性与协同效应计算国内“两虫”暴露共感染的累积风险达38.723×10-6 DALYs，超世卫组织推荐风险。饮水中“两虫”控制策略研究：视“两虫”为颗粒物，建立浊度—颗粒物关系模型以模型选择基准筛选最优模型，以进、出水浊度预测“两虫”的去除率，结果表明：指数模型及二次函数模型分别预测原水、出水浊度—颗粒数表现出较高的稳健性；根据对全国重点城市主力水厂进、出水浊度的检测数据估算“两虫”的去除率中值为2.10 log10 处于世卫组织推荐范围较低水平；基于世卫组织推荐风险（1×10-6 DALYs）推荐原水“两虫”不超过1 个孢囊(卵囊)/20L，建议对长期达标的水质逐渐减少抽检频率；对于检出超标原水，考虑我国工艺和地域差异，建议控制出水浊度不超过0.30 NTU。

       Giardia and Cryptosporidium, as water-borne pathogenic microorganisms, were often detected in many developed and developing countries, which can cause vomiting, diarrhea, fever, and even death after infection. In China, Giardia and Cryptosporidium were frequently detected in many provinces, which should cause us enough attention.

      As early as 1999, the United Kingdom, the United States and other countries had imposed restrictions and regulations on the concentration or removal rate of Giardia and Cryptosporidium. In China, "Standards for drinking water quality " has been enforced for ten years, but the infection rate is still much higher than that of other developing countries. Only lacks large-scale statistics and surveys on the removal rate parameters when reviewing the entire risk assessment process that can not guarantee its accuracy. Previous studies on the risk assessment of pathogens lacked sufficient attention to the immunodeficiency population, and the destruction of the immune barrier caused the infection efficiency of them to be greatly improved. In addition, the differences in age sensitivity between age groups were also lacking in quantitative methods. So far, the survey of Giardia and Cryptosporidium pollution in source water has accumulated enough concentration data. And it is even more important to reevaluate the health risk of Giardia and Cryptosporidium to guide the revision of quality standards.
      In this paper, Cryptosporidium and Giardia were treated as the research object,and the sensitivity of age was estimated according to the difference between the population structure and the epidemic results by the method of population total balancing. The relationship model of turbidity and particle was established to estimate the removal efficiency of particles under conventional process in water plants. Then, based on the 10-year exposure monitoring data of Cryptosporidium and Giardia in China, the cumulative health risks of Cryptosporidium and Giardia were evaluated combining with the removal rate parameters, to guild its control strategy in order to provide technical support for the safe management of drinking water in China. The main conclusions of this study are as follows:
      Risk assessment of co-infection: The detection of Giardia and Cryptosporidium in the source water were mostly concentrated in 0-2 oocysts (cysts)/10L in the major cities in China, which similar with the results in worldwide. The susceptibility being infected with Giardia and Cryptosporidium were estimated to be 10.59-17.91 folds than that of adults. The co-infection rate was estimated to be 0.17% to 6.59%, which similar with and epidemiological survey result. The cumulative risk of co-infection based on exposure is calculated to be 38.723×10-6 DALYs when considering the sensitivity and synergy effect which is much higher than the threshold recommended by World Health Organization.
      Study on control strategy of Cryptosporidium and Giardia in drinking water. The turbidity-particle relationship model was established and the model selection criteria was applied to rating candidate model, to predict the removal rate with the turbidity of the inlet and outlet waters when Cryptosporidium and Giardia were treated as particulate matter. The results show that: The exponential function predicts the relationship of turbidity-particles in source water and the quadratic function predicts in treated water shows a high degree of robustness. Based on the turbidity data in the major cities in China, the intermediate value of the removal rate of Cryptosporidium and Giardia was estimated to be 2.10 log10, slightly lower than the recommended value of the World Health Organization. Based on the recommended risk (1×10-6 DALYs), the concentration of Cryptosporidium or Giardia must be controlled within 1 (oo)cyst per 20 L source water and to gradually reduce the frequency and cycle of sampling for water quality that meets the long-term standards. For the source water exceeding the recommended risk, it is recommended to control the effluent turbidity within 0.30 NTU to control risk, considering the differences in treatment process and geographical in China.