University of Campinas - School of Civil Engineering, Architecture and Urban Design, Department of Sanitation and Environment, Avenida Albert Einstein, 951 - Cidade Universitária, 13083852, Campinas, SP, Brazil.
University of Campinas, Institute of Biology, Department of Animal Biology. Rua Monteiro Lobato, 255, 13083862, Campinas, SP, Brazil.
Chemosphere. 2019 Jan;214:764-770. doi: 10.1016/j.chemosphere.2018.09.164. Epub 2018 Sep 29.
The protozoan Giardia duodenalis is one of the parasites of primary concern in drinking water treatment plants, due to its resistance to chlorination. Another matter of concern regarding chlorination of drinking water is the formation of disinfection by-products in the presence of precursors such as natural organic matter (NOM). In this study, the effects of ozonation (5 mg L) on G. duodenalis cysts in raw surface water from a drinking water treatment plant were evaluated, and the presence and alteration of NOM were assessed, as an indicative of the potential to prevent total organic halogen (TOX) formation during post-chlorination. Following ozone treatment, the presence of damaged cysts was observed by direct immunofluorescence assay (IFA) and confirmed by the molecular approach propidium monoazide-polymerase chain reaction (PMA-PCR). Using an animal model, analysis of the intestinal tissues revealed that 80% of the animals inoculated with ozonated water were positive for trophozoites. This study shows that analysis of intestinal fragments is imperative to accurately assess animal infection following inoculation of treated cysts. More importantly, considering the low infective dose of Giardia cysts in susceptible hosts, an ozone dosage usually applied in drinking water treatment plants did not completely inactivate G. duodenalis cysts in surface water. Nonetheless, the results suggest that competitive reactions with NOM have occurred, and the applied ozone dosage has proven useful to remove NOM reactivity, and thus prevent halogenated DBP formation during post-chlorination.
原虫贾第虫是饮用水处理厂中首要关注的寄生虫之一，因为它对氯化作用具有抗性。另一个与饮用水氯化有关的问题是在存在天然有机物 (NOM) 等前体的情况下形成消毒副产物。在这项研究中，评估了臭氧化 (5 mg/L) 对饮用水处理厂原地表水中华支睾吸虫包囊的影响，并评估了 NOM 的存在和变化情况，以指示在后氯化过程中防止总有机卤素 (TOX) 形成的潜力。臭氧处理后，通过直接免疫荧光分析 (IFA) 观察到受损包囊的存在，并通过分子方法吖啶橙单叠氮 - 聚合酶链反应 (PMA-PCR) 得到证实。使用动物模型，对肠道组织进行分析表明，接种臭氧水的动物中有 80% 呈滋养体阳性。本研究表明，分析肠道片段对于准确评估接种处理包囊后动物感染至关重要。更重要的是，考虑到易感宿主中贾第虫包囊的低感染剂量，饮用水处理厂通常应用的臭氧剂量并不能完全使地表水中华支睾吸虫包囊失活。尽管如此，结果表明已经发生了与 NOM 的竞争反应，并且所应用的臭氧剂量已被证明有助于去除 NOM 反应性，从而防止在后氯化过程中形成卤代 DBPs。
