Fungi from a Groundwater-Fed Drinking Water Supply System in Brazil

Occurrence of fungal microbial contamination in drinking water of megacity of Karachi (Pakistan) and their physico-chemical control

The water quality in Karachi (Pakistan) is uncertain due to the occurrence of fungi and other microorganisms. A total of twenty-five water samples were collected from public places, educational institutes, hospitals, water supply systems and surface water of the canal of Karachi (Pakistan). The different fungal species including Acremonium sp., Alternaria alternata, Aspergillus flavus, A. fumigatus, A. sulphureus, Cladosporium sp., Fusarium sp., Clonostachys (Gliocladium) sp., Macrophomina phaseolina, Mucor racemosus, Paecilomyces sp. Penicillium chrysogenum, P. citrinum, P. commune, P. expansum, Rhizoctonia sp. and Stachybotrys sp. were isolated from these drinking water samples. However, the bacteria, microalgae and some other microorganisms were present in low concentrations. The reason for fungi infection and production of mycotoxicity depends upon various factors and the availability of their nutrients in filtration plants. The major threats to human health are fungal mycotoxicity which is responsible for carcinogenic and other lethal diseases. Mostly, the genus Aspergillus was dominated and isolated with a maximum of 88-98% of occurrence in the different samples of drinking water by the direct plate-spread method. For the control of fungi, various Physico-chemical coagulation treatments were used, but Potassium alum, clay pot, and hot water treatment disinfected effectively 69-70% removal of the fungi and its spore or mycelia from the water. In addition, it is concluded that drinking water purifications such as chlorination, filtration and lime did not eliminate thermophilic fungal spores or mycelia including Penicillium, Paecilomyces and Mucor from the water.

Rapid Inactivation of Fungal Spores in Drinking Water by Far-UVC Photolysis of Free Chlorine

Effective and affordable disinfection technology is one key to achieving Sustainable Development Goal 6. In this work, we develop a process by integrating Far-UVC irradiation at 222 nm with free chlorine (UV222/chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV222/chlorine process achieves a 5.0-log inactivation of the A. niger spores at a chlorine dosage of 3.0 mg L-1 and a UV fluence of 30 mJ cm-2 in deionized water, tap water, and surface water. The inactivation rate constant of the spores by the UV222/chlorine process is 0.55 min-1, which is 4.6-fold, 5.5-fold, and 1.8-fold, respectively, higher than those of the UV222 alone, chlorination alone, and the conventional UV254/chlorine process under comparable conditions. The more efficient inactivation by the UV222/chlorine process is mainly attributed to the enhanced generation of reactive chlorine species (e.g., 6.7 × 10-15 M of Cl•) instead of hydroxyl radicals from UV222 photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV222 photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV222/chlorine process over the UV254/chlorine process also include the more effective inhibition of the photoreactivation of the spores after disinfection and the lower formation of chlorinated disinfection byproducts and toxicity.

Fungal identification in the air and water of a hemodialysis unit in Brazil

The presence of fungi in healthcare settings, including hemodialysis units, represents a significant risk for immunocompromised patients. This study aimed to investigate the occurrence of fungi in the air and water of a hemodialysis unit located in a tertiary public hospital in Maceió, Alagoas, Brazil. Over a period of three consecutive months, monthly air samples were collected and analyzed using the spontaneous sedimentation technique on Petri dishes containing Sabouraud Dextrose Agar (SDA). Simultaneously, water samples (100 mL) were collected from four specific water distribution points and subjected plating on SDA. Fungi were phenotypically identified based on their macroscopic and microscopic characteristics. In total, 498 colony-forming units (CFUs) of fungi were isolated, with 86 CFUs originating from the air and 412 CFUs from the water. Regarding the water samples, a higher concentration of fungal CFUs was observed in the potable water from the supply network (229 CFUs). Unexpectedly, 23 CFUs were identified in the reverse osmosis samples and 11 CFUs in the storage tank, which are post-treatment points where the presence of microorganisms is not desired. The fungus Cladosporium spp. was the most prevalent in both air and water samples, followed by Penicillium spp. in the air and Rhodotorula spp. in the water. These findings underscore the need to implement effective control and monitoring measures for fungi in the hemodialysis unit to ensure patient safety.

Kinetics and mechanism of sulfate radical-and hydroxyl radical-induced disinfection of bacteria and fungal spores by transition metal ions-activated peroxymonosulfate

Peroxymonosulfate(PMS)-based advanced oxidation process have been recognized as efficient disinfection processes. This study comprehensively investigated the role of sulfate radical (SO4•-) and hydroxyl radical (•OH)-driven disinfection of bacteria and fungal spores by the PMS/metals ions (Me(II)) systems and modeled the CT value based on the relationship between survival and ∫[Radical]dt, with the aim to provide an accurate and quantitative kinetic data of inactivation processes. The results indicated that •OH played a more central role than SO4•- in the inactivation process, and bacteria were more vulnerable to radical attack than fungal spores due to the differences in antioxidant mechanisms and external structures. The k value of •OH -induced inactivation of E. coli was approximately 3-fold higher than that of A. niger, and the shoulder length of •OH -induced inactivation of E. coli was closely 52-fold shorter than that of A. niger after treated with the PMS/Co(II) system. The morphological and biochemical changes revealed that PMS/Me(II) treatment caused membrane damage, intracellular ROS accumulation and esterase activity loss in microorganisms. This study significantly improved the understanding of the contribution of radicals in the process of microbial inactivation by PMS/Me(II) and would provide important implications for the further development of technologies to cope with the highly resistant fungal spores in drinking water.

Occurrence and control of fungi in water: New challenges in biological risk and safety assurance

Recently, the contamination of fungi in water has aroused widespread concern, which will pose a threat to water quality and safety, and raise diseases risk in the immunocompromised individuals. In this review, the characteristics and different physiological state of fungi in water are summarized. A comprehensive evaluation of the control efficiency and mechanism of waterborne fungi by the commonly used disinfection methods is provided as well. During the disinfection processes of chlorine, chlorine dioxide, chloramine and advanced disinfection processes (ADPs) such as O₃-based ADPs and UV-based ADPs, the fungal spores firstly lost their culturability, followed by membrane integrity, and the intracellular reactive oxygen species level increased at the same time, eventually the fungal spores were completely inactivated. The security strategies of drinking water against the contamination of fungi are also discussed in terms of water sources, water treatment plants and pipe network. Finally, future researches need to be explored are proposed: the rapid detection methods, the production laws and control of mycotoxin, and the outbreak conditions of fungi in water. Specifically, exploring efficient, safe and economical technologies, especially ADPs, is still the main direction in the disinfection of fungi in future studies. This review can offer a comprehensive understanding on the occurrence and control of fungi in water to fill the knowledge gap and provide guidance for the future research.

Occurrence of fungal spores in drinking water: A review of pathogenicity, odor, chlorine resistance and control strategies

Fungi in drinking water have been long neglected due to the lack of convenient analysis methods, widely accepted regulations and efficient control strategies. However, in the last few decades, fungi in drinking water have been widely recognized as opportunity pathogens that cause serious damage to the health of immune-compromised individuals. In drinking water treatment plants, fungal spores are more resistant to chlorine disinfection than bacteria and viruses, which can regrow in drinking water distribution systems and subsequently pose health threats to water consumers. In addition, fungi in drinking water may represent an ignored source of taste and odor (T&O). This review identified 74 genera of fungi isolated from drinking water and presented their detailed taxonomy, sources and biomass levels in drinking water systems. The typical pathways of exposure of water-borne fungi and the main effects on human health are clarified. The fungi producing T&O compounds and their products are summarized. Data on free chlorine or monochloramine inactivation of fungal spores and other pathogens are compared. At the first time, we suggested four chlorine-resistant mechanisms including aggregation to tolerate chlorine, strong cell walls, cellular responses to oxidative stress and antioxidation of melanin, which are instructive for the future fungi control attempts. Finally, the inactivation performance of fungal spores by various technologies are comprehensively analyzed. The purpose of this study is to provide an overview of fungi distribution and risks in drinking water, provide insight into the chlorine resistance mechanisms of fungal spores and propose approaches for the control of fungi in drinking water.

Physiological characteristics, geochemical properties and hydrological variables influencing pathogen migration in subsurface system: What we know or not?

The global outbreak of coronavirus infectious disease-2019 (COVID-19) draws attentions in the transport and spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in aerosols, wastewater, surface water and solid wastes. As pathogens eventually enter the subsurface system, e.g., soils in the vadose zone and groundwater in the aquifers, they might survive for a prolonged period of time owing to the uniqueness of subsurface environment. In addition, pathogens can transport in groundwater and contaminate surrounding drinking water sources, possessing long-term and concealed risks to human society. This work critically reviews the influential factors of pathogen migration, unravelling the impacts of pathogenic characteristics, vadose zone physiochemical properties and hydrological variables on the migration of typical pathogens in subsurface system. An assessment algorithm and two rating/weighting schemes are proposed to evaluate the migration abilities and risks of pathogens in subsurface environment. As there is still no evidence about the presence and distribution of SARS-CoV-2 in the vadose zones and aquifers, this study also discusses the migration potential and behavior of SARS-CoV-2 viruses in subsurface environment, offering prospective clues and suggestions for its potential risks in drinking water and effective prevention and control from hydrogeological points of view.

Inactivation and subsequent reactivation of Aspergillus species by the combination of UV and monochloramine: Comparisons with UV/chlorine

Ultraviolet (UV)/monochloramine (NH₂Cl) as an advanced oxidation process was firstly applied for Aspergillus spores inactivation. This study aims to: i) clarify the inactivation and photoreactivation characteristics of UV/NH₂Cl process, ii) compared with UV/Cl₂ in inactivation efficiency, photoreactivation and energy consumption. The results illustrated that UV/NH₂Cl showed better inactivation efficiency than that of UV alone and UV/Cl₂, and could effectively control the photoreactivation. For instance, the inactivation rates for Aspergillus flavus, Aspergillus niger and Aspergillus fumigatus in the processes of UV/NH₂Cl (2.0 mg/L) was 0.034, 0.030 and 0.061 cm²/mJ, respectively, which were higher than that of UV alone (0.027, 0.026 and 0.024 cm²/mJ) and UV/Cl₂ (0.023, 0.026 and 0.031 cm²/mJ). However, there was no synergistic effect for Aspergillus flavus and Aspergillus fumigatus. As for Aspergillus niger, the best synergistic effect can reach 1.86-log₁₀. This may be due to their different resistance to disinfectants, which were related to the size, an outer layer of rodlets (hydrophobins) and pigments. After UV/NH₂Cl inactivation, the degree of cell membrane damage and intracellular reactive oxygen species were higher than that of UV alone. UV/NH₂Cl had the advantages of high inactivation efficiency and inhibition of photoreactivation, which provides a new entry point for the disinfection of waterborne fungi.

Inactivation of waterborne fungal spores by 1-bromo-3-chloro-5,5-dimethylhydantoin: Kinetics, influencing factors and mechanisms

Fungal contamination in drinking water source has become a problem worth studying, as waterborne fungi may cause deterioration of water quality and outbreak of diseases. Various disinfection methods have been explored to control fungal spores in drinking water, such as chlor(am)ination, ozonation, chlorine dioxide treatment, but these methods are not appropriate for remote areas, owing to the difficulties in preparation, carriage and storage. In this study, a powdery disinfectant of 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH), which facilitated transportation and preservation, was firstly chosen to inactivate opportunistic pathogens of Aspergillus niger (A. niger) and Penicillium polonicum (P. polonicum). The results revealed that the inactivation kinetics of fungal spores by BCDMH fitted to Chick-Watson model well, with the inactivation rate constant of 0.011 and 0.034 L mg^-1 min^-1 for A. niger and P. polonicum, respectively. Acidic condition and high temperature promoted the inactivation by BCDMH. Compared with chlorine, BCDMH showed relative weaker ability on inactivation of fungal spores. However, it was demonstrated that the inactivation efficiency of BCDMH was obviously enhanced by adding halide ions, with 11 or 36 folds for A. niger and 4 or 15 folds for P. polonicum by adding 40 μM Br^- or I^-. The inactivation mechanisms were detected by flow cytometry and scanning electron microscope. Fungal spores lost their culturability firstly, then membrane integrity was damaged. Meanwhile, the esterase activity and intracellular reactive oxygen species level changed, and finally intracellular adenosine triphosphate released.

Occurrence of filamentous fungi in drinking water: their role on fungal-bacterial biofilm formation

Water is indispensable to life and safe and accessible supply must be available to all. The presence of microorganisms is a threat to this commitment. Biofilms are the main reservoir of microorganisms inside water distribution systems and they are extremely ecologically diverse. Filamentous fungi and bacteria can coexist inside these systems forming inter-kingdom biofilms. This review has the goal of summarizing the most relevant and recent reports on the occurrence of filamentous fungi in water distribution systems along with the current knowledge and gaps about filamentous fungal biofilm formation. Special focus is given on fungal-bacterial interactions in water biofilms.

Occurrence and diversity of waterborne fungi and associated mycotoxins in treated drinking water distribution system in South Africa: implications on water quality and public health

Despite increased public health concerns on the occurrences of potentially pathogenic/mycotoxigenic fungi in public drinking water system, dissemination of hygienically relevant fungi and their associated mycotoxins via distribution system under the dual burden of ageing infrastructure and ancillary distribution network lacking infrastructure for high-pressure water delivery systems is unknown. In this study, the diversity of fungi and occurrence of mycotoxins at 30 different points along treated piped water supply and ancillary distribution networks in Johannesburg, South Africa, were monitored for 12 months. Mycological analysis using cultural and molecular methods yielded 282 fungi belonging to phylum Ascomycota, having Aspergillus (91%), Penicillium (65%) and Trichoderma (31%) as dominant genera, with Aspergillus fumigatus, Penicillium citrinum, Purpureocillium lilacinum and Aspergillus flavus as the most prevalent species. Communal standpipe and reservoir outlets had significantly higher prevalence than other water samples. There was no strong correlation between total coliforms (r = 0.4266) and residual chlorine (r = - 0.1937), and fungal prevalence at p < 0.05. LC-MS/MS analysis detected aflatoxins B1, M1, G1 and G2 in 50, 9, 9 and 46% of water samples analysed, respectively, ranging between 0 and 3.18 ng/l. Deoxynivalenol (DON), 3-acetyl DON and 15-acetyl DON levels were between 8.4-96.1, 18.7-145.7 and 15.2-71.6 ng/l, respectively. However, the estimated average daily dose (ADD) for detected mycotoxins was below the tolerable daily intake (TDI), suggesting no toxicological risk. Presence of potentially mycotoxigenic fungi, despite the low toxicological risk, demonstrates a need for appropriate monitoring for fungi and mycotoxins in treated drinking water distribution systems for improved water quality and long-term public health assurance.

Broad Diversity of Fungi in Hospital Water

INTRODUCTION

Some studies have reported the occurrence of microorganisms isolated from water. Considering these microorganisms, fungi are known to occur ubiquitously in the environment, including water, and some are pathogenic and may cause health problems, especially in immunocompromised individuals. The aim of this study was to identify fungi in hospital water samples and to correlate their presence with the concentration of free residual chlorine.

METHODS

Water samples (100 mL) were collected from taps (n = 74) and water purifiers (n = 14) in different locations in a university hospital. Samples were filtered through a nitrocellulose membrane and placed on Sabouraud dextrose agar and incubated for 24 hours at 30°C. Fungi were identified according to established methods based on macroscopic and microscopic characteristics (filamentous) and physiological tests (yeasts). Free chlorine residual content was measured at the time of sample collection.

RESULTS

Seventy species of fungi were identified in the water samples and about 56% of the water samples contained culturable fungi. Cladosporium oxysporum, Penicillium spinulosum, and Aspergillus fumigatus were the most common filamentous fungi. Aureobasidium pullulans and Candida parapsilosis were the most common yeasts. Chemical analyses revealed that free residual chlorine was present in 81.8% of the samples within recommended concentrations. Among samples from water purifiers, 92.9% showed low levels of free residual chlorine (<0.2 mg/L). There was no significant association between chlorine concentrations (either within or outside the recommended range) and the presence of filamentous fungi and yeasts.

CONCLUSIONS

This study showed that hospital water can be a reservoir for fungi, some of which are potentially harmful to immunocompromised patients. Free residual chlorine was ineffective in some samples.

Comparison of UV-LEDs and LPUV on inactivation and subsequent reactivation of waterborne fungal spores

Recently, the contamination of fungi in water supply systems has been an area of increasing concern, such as Aspergillus spp. and Penicillium spp. It can cause some waterborne issues such as odor, taste and formation of mycotoxins. Ultraviolet light emitting diodes (UV-LEDs) are considered as a potential alternative to conventional mercury lamps for water disinfection. This study has compared the performance of LPUV (low pressure ultraviolet) and UV-LEDs with emissions at 265, 280 nm and combination emissions at 265/280 nm to test inactivation efficiency, reactivation, viability and electrical energy consumption in the treatment of three water-borne fungal species (Aspergillus niger, Penicillium polonicum, Trichoderma harzianum) at a batch water disinfection system. The results showed that the performances of UV-LEDs were superior for the inactivation of fungal spores compared to the 254 nm (LP), while no statistically differences were observed among the UV-LEDs (p > 0.05). The average photoreactivation rate (k₁) of fungal spores irradiated by UV-LEDs and 254 nm (LP) follows the order: T. harzianum > A. niger > P. polonicum. Compared with LPUV, UV-LEDs irradiation at 280 nm and 265/280 nm more efficiently inhibits photoreactivation, which was attributed to that irradiation of 280 nm and 265/280 nm would cause greater membrane damage and increase intracellular reactive oxygen species level of fungal spores according to the flow cytometric results. The electrical energy consumption of UV-LEDs was higher than that of LPUV, which was due to its lower wall plug efficiency. The results of this study can provide additional and beneficial information for the reasonable exploitation of UV-LEDs in water disinfection.

Aquatic yeasts: diversity, characteristics and potential health implications

There has been a rising interest in the levels, diversity and potential impacts of yeasts in aquatic environments. Some of the species isolated from such niches are known pathogens or have pathogenic and antifungal resistance features. This deems it necessary to understand the characteristics and potential health implications of such environmental yeasts species. Studies on these subjects are limited. Most studies on aquatic yeasts have linked them to water pollution. However, the current gold standards to determine microbial pollution of water use bacteria as the main indicator organisms. Including yeasts in water quality standards may provide a different dimension on the quality of water when determining its fit-for-use properties. Pathogenic yeasts cause superficial infections or life-threatening infections, especially in immunocompromised people. Some of the yeast species isolated in recent studies were resistant to commonly used antifungal agents of clinical and veterinary relevance. With the high prevalence rate of HIV in sub-Saharan Africa, particularly in South Africa, antifungal resistance is a public concern as it poses serious medical and economic challenges. Most available studies are concerned with clinical environments only. There is, thus, a need to review the literature that also focuses on aquatic environments.

Wide diversity of fungal species found in wellwater for human consumption: an analytical cross-sectional study

BACKGROUND

Fungi are ubiquitous in the environment. They are able to grow in water and many of them may be opportunistic pathogens.

OBJECTIVE

The aims were to identify fungi in registered wells (RWs) and nonregistered wells (NRWs) that tap into groundwater; and to correlate the results from physicochemical assays on this water (free residual chlorine and pH) with the presence of fungi.

DATA AND SETTING

Analytical cross-sectional quantitative study on groundwater wells in São José do Rio Preto, São Paulo, Brazil.

METHODS

52 samples of 500 ml of water were collected from RWs and 107 from NRWs. These were sent to a microbiology laboratory to identify any fungi that were present. In addition, free residual chlorine and pH were measured immediately after sample collection. Several statistical analysis tests were used.

RESULTS

Fungal contamination was present in 78.8% of the samples from RWs and 81.3% from NRWs. Filamentous fungi were more prevalent than yeast in both types of wells. There was no significant difference in presence of fungi according to whether chloride and pH were within recommended levels in RWs; or according to whether pH was within recommended levels in NRWs. Furthermore, there was no statistical difference in the levels of fungal contamination between RWs and NRWs.

CONCLUSION

Both RWs and NRWs are potential reservoirs for many types of fungi. Many of these may become opportunistic pathogens if they infect immunosuppressed individuals. Furthermore, this study confirms that fungi are able to grow even when chlorine and pH parameters are within the standards recommended.

Succession of bacterial and fungal communities within biofilms of a chlorinated drinking water distribution system

Understanding the temporal dynamics of multi-species biofilms in Drinking Water Distribution Systems (DWDS) is essential to ensure safe, high quality water reaches consumers after it passes through these high surface area reactors. This research studied the succession characteristics of fungal and bacterial communities under controlled environmental conditions fully representative of operational DWDS. Microbial communities were observed to increase in complexity after one month of biofilm development but they did not reach stability after three months. Changes in cell numbers were faster at the start of biofilm formation and tended to decrease over time, despite the continuing changes in bacterial community composition. Fungal diversity was markedly less than bacterial diversity and had a lag in responding to temporal dynamics. A core-mixed community of bacteria including Pseudomonas, Massillia and Sphingomonas and the fungi Acremonium and Neocosmopora were present constantly and consistently in the biofilms over time and conditions studied. Monitoring and managing biofilms and such ubiquitous core microbial communities are key control strategies to ensuring the delivery of safe drinking water via the current ageing DWDS infrastructure.

Opportunistic Water-Borne Human Pathogenic Filamentous Fungi Unreported from Food

Clean drinking water and sanitation are fundamental human rights recognized by the United Nations (UN) General Assembly and the Human Rights Council in 2010 (Resolution 64/292). In modern societies, water is not related only to drinking, it is also widely used for personal and home hygiene, and leisure. Ongoing human population and subsequent environmental stressors challenge the current standards on safe drinking and recreational water, requiring regular updating. Also, a changing Earth and its increasingly frequent extreme weather events and climatic changes underpin the necessity to adjust regulation to a risk-based approach. Although fungi were never introduced to water quality regulations, the incidence of fungal infections worldwide is growing, and changes in antimicrobial resistance patterns are taking place. The presence of fungi in different types of water has been thoroughly investigated during the past 30 years only in Europe, and more than 400 different species were reported from ground-, surface-, and tap-water. The most frequently reported fungi, however, were not waterborne, but are frequently related to soil, air, and food. This review focuses on waterborne filamentous fungi, unreported from food, that offer a pathogenic potential.

Solar photocatalytic disinfection of agricultural pathogenic fungi (Curvularia sp.) in real urban wastewater

The interest in developing alternative water disinfection methods that increase the access to irrigation water free of pathogens for agricultural purposes is increasing in the last decades. Advanced Oxidation Processes (AOPs) have been demonstrated to be very efficient for the abatement of several kind of pathogens in contaminated water. The purpose of the current study was to evaluate and compare the capability of several solar AOPs for the inactivation of resistant spores of agricultural fungi. Solar photoassisted H₂O₂, solar photo-Fenton at acid and near-neutral pH, and solar heterogeneous photocatalysis using TiO_2, with and without H₂O₂, have been studied for the inactivation of spores of Curvularia sp., a phytopathogenic fungi worldwide found in soils and crops. Different concentrations of reagents and catalysts were evaluated at bench scale (solar vessel reactors, 200mL) and at pilot plant scale (solar Compound Parabolic Collector-CPC reactor, 20L) under natural solar radiation using distilled water (DW) and real secondary effluents (SE) from a municipal wastewater treatment plant. Inactivation order of Curvularia sp. in distilled water was determined, i.e. TiO₂/H₂O₂/sunlight (100/50mgL^-1)>H₂O₂/sunlight (40mgL^-1)>TiO₂/sunlight (100mgL^-1)>photo-Fenton with 5/10mgL^-1 of Fe²⁺/H₂O₂ at pH3 and near-neutral pH. For the case of SE, at near neutral pH, the most efficient solar process was H₂O₂/Solar (60mgL^-1); nevertheless, the best Curvularia sp. inactivation rate was obtained with photo-Fenton (10/20mgL^-1 of Fe²⁺/H₂O₂) requiring a previous water adicification to pH3, within 300 and 210min of solar treatment, respectively. These results show the efficiency of solar AOPs as a feasible option for the inactivation of resistant pathogens in water for crops irrigation, even in the presence of organic matter (average Dissolved Organic Carbon (DOC): 24mgL^-1), and open a window for future wastewater reclamation and irrigation use.

Inactivation of three genera of dominant fungal spores in groundwater using chlorine dioxide: Effectiveness, influencing factors, and mechanisms

Fungi in aquatic environments received more attention recently; therefore, the characteristics of inactivation of fungal spores by widely used disinfectants are quite important. Nonetheless, the inactivation efficacy of fungal spores by chlorine dioxide is poorly known. In this study, the effectiveness of chlorine dioxide at inactivation of three dominant genera of fungal spores isolated from drinking groundwater and the effects of pH, temperature, chlorine dioxide concentration, and humic acid were evaluated. The inactivation mechanisms were explored by analyzing the leakage of intracellular substances, the increase in extracellular adenosine triphosphate (ATP), deoxyribonucleic acid (DNA), and proteins as well as the changes in spore morphology. The kinetics of inactivation by chlorine dioxide fitted the Chick-Watson model, and different fungal species showed different resistance to chlorine dioxide inactivation, which was in the following order: Cladosporium sp.>Trichoderma sp. >Penicillium sp., which are much more resistant than Escherichia coli. Regarding the three genera of fungal spores used in this study, chlorine dioxide was more effective at inactivation of fungal spores than chlorine. The effect of disinfectant concentration and temperature was positive, and the impact of pH levels (6.0 and 7.0) was insignificant, whereas the influence of water matrices on the inactivation efficiency was negative. The increased concentration of characteristic extracellular substances and changes of spore morphology were observed after inactivation with chlorine dioxide and were due to cell wall and cell membrane damage in fungal spores, causing the leakage of intracellular substances and death of a fungal spore.

Free chlorine and monochloramine inactivation kinetics of Aspergillus and Penicillium in drinking water

Fungi are near-ubiquitous in potable water distribution systems, but the disinfection kinetics of commonly identified fungi are poorly studied. In the present study, laboratory scale experiments were conducted to evaluate the inactivation kinetics of Aspergillus fumigatus, Aspergillus versicolor, and Penicillium purpurogenum by free chlorine and monochloramine. The observed inactivation data were then fit to a delayed Chick-Watson model. Based on the model parameter estimation, the Ct values (integrated product of disinfectant concentration C and contact time t over defined time intervals) for 99.9% inactivation of the tested fungal strains ranged from 48.99 mg min/L to 194.7 mg min/L for free chlorine and from 90.33 mg min/L to 531.3 mg min/L for monochloramine. Fungal isolates from a drinking water system (Aspergillus versicolor and Penicillium purpurogenum) were more disinfection resistant than Aspergillus fumigatus type and clinical isolates. The required 99.9% inactivation Ct values for the tested fungal strains are higher than E. coli, a commonly monitored indicator bacteria, and within a similar range for bacteria commonly identified within water distribution systems, such as Mycobacterium spp. and Legionella spp.