Microbiological Decontamination of Water: Improving the Solar Disinfection Technique (SODIS) with the Use of Nontoxic Vital Dye Methylene Blue

Rational use of water is a major challenge for governments and global organizations, with easy and inexpensive interventions being sought by communities that are not supplied with drinking water. In this context, solar disinfection (SODIS) has shown great efficiency for water disinfection. To speed up the process and improve inactivation, we studied the effects of methylene blue (MB) as a photodynamic agent because of its ability to absorb visible light (red wavelength) and generate singlet oxygen as a reactive species, thereby inactivating bacteria and viruses present in water. In this study, samples of clean mineral water were artificially contaminated with Gram‐positive (Staphylococcus epidermidis or Deinococcus radiodurans) or with Gram‐negative strains (Escherichia coli or Salmonella typhimurium) and exposed to traditional SODIS or to MB‐SODIS. A lethal synergistic effect was observed when cultures were illuminated in the presence of MB. The obtained results indicate that bacterial inactivation can be achieved in a much shorter time when using MB associated with SODIS treatment. Therefore, this technique was able to provide safe water for consumption through the inactivation of microorganisms in general, including pathogens and some strains resistant to the traditional SODIS procedure, thus allowing its use in areas usually less exposed to sunlight.     

Solar Water Disinfection to Produce Safe Drinking Water: A Review of Parameters,Enhancements, and Modelling Approaches to Make SODIS Faster and Safer

Solar water disinfection (SODIS) is one the cheapest and most suitable treatments to produce safe drinking water at the household level in resource-poor settings. This review introduces the main parameters that influence the SODIS process and how new enhancements and modelling approaches can overcome some of the current drawbacks that limit its widespread adoption. Increasing the container volume can decrease the recontamination risk caused by handling several 2 L bottles. Using container materials other than polyethylene terephthalate (PET) significantly increases the efficiency of inactivation of viruses and protozoa. In addition, an overestimation of the solar exposure time is usually recommended since the process success is often influenced by many factors beyond the control of the SODIS-user. The development of accurate kinetic models is crucial for ensuring the production of safe drinking water. This work attempts to review the relevant knowledge about the impact of the SODIS variables and the techniques used to develop kinetic models described in the literature. In addition to the type and concentration of pathogens in the untreated water, an ideal kinetic model should consider all critical factors affecting the efficiency of the process, such as intensity, spectral distribution of the solar radiation, container-wall transmission spectra, ageing of the SODIS reactor material, and chemical composition of the water, since the substances in the water can play a critical role as radiation attenuators and/or sensitisers triggering the inactivation process.     

Enumeration of Cryptosporidium spp. in water with US EPA method 1622, USA

The occurrence of Cryptosporidium parvum or other pathogenic Cryptosporidium species in water must be known in order to assess risk and determine the treatment needed to reduce Cryptosporidium oocysts to acceptable levels in finished drinking water. Because Cryptosporidium oocyst occurrence may be sparse, methods must concentrate a large volume of water and correctly identify oocysts in the concentrate. The U.S. Environmental Protection Agency Information Collection Rule (ICR) protozoan method gives low and variable recoveries of Cryptosporidium oocysts, making risk assessment difficult. Therefore, a method giving better oocyst recovery and more consistent results was needed. Method 1622 was developed with existing materials and procedures, and improvements were made in filtration, cleanup, and detection. Absolute porosity filters were used, with cleanup by immunomagnetic separation and detection by direct fluorescent antibody stain with 4',6-diamidino-2-phenylindole (DAPI) staining for additional cell structures. Both the level and consistency of oocyst recovery were improved compared to recovery with the ICR method.     

Both solar UVA and UVB radiation impair conidial culturability and delay germination in the entomopathogenic fungus Metarhizium anisopliae.

The entomopathogenic hyphomycete Metarhizium anisopliae has been used in programs of agricultural pest and disease vector control in several countries. Exposure to simulated solar radiation for a few hours can completely inactivate the conidia of the fungus. In the present study we determined the effect of exposures to full-spectrum sunlight and to solar ultraviolet A radiation at 320-400 nm (UVA) on the conidial culturability and germination of three M. anisopliae strains. The exposures were performed in July and August 2000 in Logan, UT. The strains showed wide variation in tolerance when exposed to full-spectrum sunlight as well as to UVA sunlight. Four-hour exposures to full-spectrum sunlight reduced the relative culturability by approximately 30% for strain ARSEF 324 and by 100% for strains ARSEF 23 and 2575. The relative UV sensitivity of the two more sensitive strains was different under solar UV from that under ultraviolet B radiation at 280-320 nm (UVB) in the laboratory. Four-hour exposures to solar UVA reduced the relative culturability by 10% for strain ARSEF 324, 40% for strain ARSEF 23 and 60% for strain ARSEF 2575. Exposures to both full-spectrum sunlight and UVA sunlight delayed the germination of the surviving conidia of all three strains. These results, in addition to confirming the deleterious effects of UVB, clearly demonstrate the negative effects of UVA sunlight on the survival and germination of M. anisopliae conidia under natural conditions. The negative effects of UVA in sunlight also emphasize that the biological spectral weighting functions for this fungus must not neglect the UVA wavelengths.     

Effectiveness of solar disinfection using batch reactors with non-imaging aluminium reflectors under real conditions: Natural well-water and solar light

Inactivation kinetics are reported for suspensions of Escherichia coli in well-water using compound parabolic collector (CPC) mirrors to enhance the efficiency of solar disinfection (SODIS) for batch reactors under real, solar radiation (cloudy and cloudless) conditions. On clear days, the system with CPC reflectors achieved complete inactivation (more than 5-log unit reduction in bacterial population to below the detection limit of 4CFU/mL) one hour sooner than the system fitted with no CPC. On cloudy days, only systems fitted with CPCs achieved complete inactivation. Degradation of the mirrors under field conditions was also evaluated. The reflectivity of CPC systems that had been in use outdoors for at least 3 years deteriorated in a non-homogeneous fashion. Reflectivity values for these older systems were found to vary between 27% and 72% compared to uniform values of 87% for new CPC systems. The use of CPC has been proven to be a good technological enhancement to inactivate bacteria under real conditions in clear and cloudy days. A comparison between enhancing optics and thermal effect is also discussed.     

Photosensitizing potential of ciprofloxacin at ambient level of UV radiation

Ciprofloxacin is a widely used fluoroquinolone drug with broad spectrum antibacterial activities. Clinical experience has shown incidences of adverse effects related to skin, hepatic, central nervous system, gastrointestinal and phototoxicity. India is a tropical country and sunlight is abundant throughout the day. In this scenario exposure to ambient levels of ultraviolet radiation (UV-R) in sunlight may lead to harmful effects in ciprofloxacin users. Phototoxicity assessment of ciprofloxacin was studied by two mouse fibroblast cell lines L-929 and NIH-3T3. Generation of reactive oxygen species (ROS) like singlet oxygen (1O2), superoxide anion radical (O2*-) and hydroxyl radical (*OH) was studied under the exposure of ambient intensities of UV-A (1.14, 1.6 and 2.2 mW cm(-2)), UV-B (0.6, 0.9 and 1.2 mW cm(-2)) and sunlight (60 min). The drug was generating 1O2, O2*- and *OH in a concentration and dose-dependent manner. Sodium azide (NaN3) and 1,4-diazabicyclo 2-2-2-octane (DABCO) inhibited the generation of 1O2. Superoxide dismutase (SOD) inhibited 90-95% O2*- generation. The drug (5-40 microg mL(-1)) was responsible for linoleic acid peroxidation. Quenching study of linoleic acid peroxidation with SOD (25 and 50 U mL(-1)) confirms the involvement of ROS in drug-induced lipid peroxidation. The generation of *OH radical was further confirmed by using specific quenchers of *OH such as mannitol (0.5 M) and sodium benzoate (0.5 M). 2'-deoxyguanosine (2'-dGuO) assay and linoleic acid peroxidation showed that ROS were mainly responsible for ciprofloxacin-sensitized photo-degradation of guanine base. L-929 cell line showed 29%, 34% and 54% reduced cell viability at higher drug concentration (300 microg mL(-1)) under UV-A, UV-B and sunlight, respectively. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay in NIH-3T3 cell line at higher drug concentration (300 microg mL(-1)) showed a decrease in cell viability by 54%, 56% and 59% under UV-A, UV-B and sunlight, respectively. Results of neutral red uptake assay (NRU) in L-929 cell line were in accordance with MTT assay. The NIH-3T3 cell line showed a higher photosensitizing potential than L-929. The phototoxicity end point shows a time- and concentration-dependent statistically significant (P<0.001) damage. Ciprofloxacin produced ROS by Type I and Type II photodynamic reactions, interacted with nucleic acid moiety and inhibited cell viability. Further, UV-induced photo-peroxidation of linoleic acid accorded the involvement of ROS in the manifestation of drug phototoxicity. Appearance of ciprofloxacin-induced phototoxicity at the ambient level of sunlight is a real risk for the people of India and for those of other tropical countries. We suggest that sunlight exposure should be avoided (especially peak hours) during ciprofloxacin treatment.     

Proton exchange kinetics from the bound waters on the oxo-centered rhodium(III) trimer [Rh3(mu3-O)(mu-O2CCH3)6(OH2)3]+: a variable pH and temperature 1H NMR study

Proton exchange from the bound to the bulk waters on the oxo-centered rhodium(III) trimer, [Rh(3)(micro(3)-O)(micro-O(2)CCH(3))(6)(OH(2))(3)](+)(abbreviated as Rh(3)(+)), was investigated over the temperature range of 219.1-313.9 K using a (1)H NMR line-broadening technique. By solving the modified Bloch equations for a two-site chemical exchange, lifetimes (tau) for proton transfer at pH = 2.7, 3.6, and 7.0 ([Rh(3)(+)]= 26 mM, T= 298 K) were determined to be 0.3 (+/-.08) ms, 2 (+/-0.3) ms, and 0.2 (+/-0.2) ms, respectively. From the temperature dependence of the rate, the activation parameters were determined to be DeltaH(++)= 16.2 (+/-0.5) kJ mol(-1) and DeltaS(++)=- 123 (+/-2) J mol(-1) K(-1), DeltaH(++)= 14.9 (+/-0.5) kJ mol(-1) and DeltaS(++)=- 141 (+/-2) J mol(-1) K(-1), and DeltaH(++)= 45 (+/-2) kJ mol(-1) and DeltaS(++)=- 22 (+/-5) J mol(-1) K(-1) for pH = 2.7, 3.6 and 7.0, respectively. All results are reported for a mixed solvent system [acetone : 250 mM NaClO(4)(aq)(3:1)], which was necessary to depress the freezing point of the solution so that the (1)H NMR signal due to bound water could be observed. The pK(a) of Rh(3)(+) was measured to be 8.9 (+/-0.2) in the mixed solvent, which is near the pK(a) for an aqueous solution (8.3 (+/-0.2)). Surprisingly, the lifetimes for protons on Rh(3)(+) are close to those observed for the Rh(OH(2))(6)(3+) ion, in spite of the considerable difference in structure, Br?nsted acidity of the bound waters and average charge on the metal ion.     

饮用水中氯酸盐、亚氯酸盐的离子色谱测定方法

建立了饮用水中微量氯酸盐以及亚氯酸盐的离子色谱测定方法。结果表明,亚氯酸盐和氯酸盐在0～0.50 mg/L范围内线性良好,精密度高,亚氯酸盐r2=0.999 8,样品加标平均回收率91.5%～99.4%,相对标准偏差(RSD)0.64%～1.78%,检出限为3.98μg/L;氯酸盐r2=0.999 6,样品加标平均回收率94.7%～101.6%,相对标准偏差(RSD)0.94%～1.35%,检出限为4.65μg/L;方法操作简单、快速、准确、灵敏度高、干扰少,适用于饮水消毒副产物亚氯酸盐和氯酸盐的检测。     

A novel fiber optical device for ultraviolet disinfection of water

Since there are several problems in traditional UV disinfection techniques, a highly efficient, reliable and economical method, using quartz optical fibers to deliver UV light is proposed. The principle of the experimental setup is that ultraviolet rays are gathered by a reflector and converge on a light point, the diameter of approximately 5mm. In this way UV light can be transferred into water to kill the bacteria in the water. This paper presents preliminary results on water disinfection using this new UV disinfection setup. Its suitability for application could be shown in experiments with E. coli (ATCC8099) as test microorganisms. We have optimized the distribution of the optical fibers in the water in bench-scale study. This result can provide guidance for pilot-scale and field-scale study of this new technique. The results show that the new technique had a good performance under different conditions as follows: (a) turbidity level=10.2 NTU, (b) ferric ion concentration=0.3 mg/L, and (c) humic acid concentration=5 mg/L. The new technique provides a promising approach to disinfection treatment of drinking water.     

气相色谱法同时测定水中12种挥发性消毒副产物

建立液-液萃取气相色谱法电子捕获检测器(GC/ECD)同时测定饮用水中12种挥发性消毒副产物(Disinfection byproducts, DBPs)的方法.采用过程标准校正降低预处理过程中引入的误差,方法检出限为0.08~0.21 μg/L, 全部组分在21.50 min内测定完成.不同浓度的DBPs在自来水和地表水中的回收率为80.9%~115.7%,相对标准偏差在0.9%~9.9%之间.各组分在0.5~200 μg/L浓度范围内线性关系良好,相关系数R>0.99.应用本方法测定了饮用水和地表水及其氯化后样品中DBPs的含量.本方法简便、快速、稳定,满足饮用水中挥发性DBPs的检测要求.     

Comprehensive chemical derivatization for gas chromatography-mass spectrometry-based multi-targeted profiling of the major phytohormones

In the present investigation we report selection of the N-methyl-N-(tert.-butydimethylsilyl)trifluoroacetamide (MTBSTFA) reagent as the most comprehensive derivatization protocol among 17 tested reactions covering trifluoroacetylation, pentafluorobenzylation, methylations, and trimethylsilylations. MTBSTFA allowed easy and robust tert.-butyldimethylsilyl derivatization of 1-aminocyclopropane-1-carboxylic acid, indole-3-acetic acid, (+/-)-jasmonic acid, salicylic acid, (+/-)-abscisic acid, meta-topolin, and trans-zeatin. Detection limits as analysed by selected ion monitoring quadrupole GC-MS were 0.2, 0.01, 1.0, 0.02, 0.3, 0.3, and 0.9 pmol of injected substance, respectively. Analysis of gibberellic acid A3, trans-zeatin riboside and (+/-)-abscisic acid-beta-D-glucopyranosyl ester was best when coupled by splitting extracts and trimethysilylation. The MTBSTFA derivatization protocol was optimised, and validated. The preparation was insensitive to 2% residual water and to < or = 1 day storage at room temperature. The final scheme was highly reproducible and successfully applied to extracts from approximately 300 mg (fresh mass) of tobacco (Nicotiana tabacum) root and Arabidopsis thaliana seedling.     

Stability studies of propoxur herbicide in environmental water samples by liquid chromatography-atmospheric pressure chemical ionization ion-trap mass spectrometry

Liquid chromatography-atmospheric pressure ionization ion-trap mass spectrometry has been investigated for the analysis of polar pesticides in water. The degradation behavior of propoxur, selected as a model pesticide belonging to the N-methylcarbamate group, in various aqueous matrices (Milli-Q water, drinking water, rain water, seawater and river water) was investigated. Two interfaces of atmospheric pressure ionization, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), were compared during the study. Propoxur and its transformation product (N-methylformamide) were best ionized as positive ions with both APCI and ESI, while another transformation product (2-isopropoxyphenol) yielded stronger signals as negative ions only with APCI. In addition, the effects of various pH, matrix type and irradiation sources (sunlight, darkness, indoor lighting and artificial UV lamp) on the chemical degradation (hydrolysis) were also assessed. From the kinetic studies of degradation, it was found that the half-life of propoxur was reduced from 327 to 161 h in Milli-Q water with variation of irradiation conditions from dark to sunlight exposure. Degradation rates largely increased with increasing pH. The half-life of the target compound dissolved in Milli-Q water under darkness decreased from 407 to 3 h when the pH of Milli-Q water was increased from 5 to 8.5. These suggest that hydrolysis of propoxur is light-intensity and pH-dependent. In order to mimic contaminated natural environmental waters, propoxur was spiked into real water samples at 30 microg/l. The degradation of propoxur in such water samples under various conditions were studied in detail and compared. With the ion trap run in a time-scheduled single ion monitoring mode, typical limits of detection of the instrument were in the range of 1-10 microg/l.     

Electrochemical biosensor for detecting DNA sequences from the pathogenic protozoan Cryptosporidium parvum

An electrochemical hybridization biosensor was developed for the detection of short DNA fragments specific to the deadly waterborne pathogen Cryptosporidium. The sensor relies on the immobilization of a 38-mer oligonucleotide unique to the Cryptosporidium DNA onto the carbon-paste transducer, and employs a highly sensitive chronopotentiometric transduction mode for monitoring the hybridization event. Variables of the probe-immobilization, hybridization and indicator-detection steps are optimized to offer convenient quantitation of ng ml(-1) levels of the Cryptosporidium DNA target, in connection with short (3-15 min) hybridization times. The suitability for direct detection of the spiked Cryptosporidium DNA target in untreated drinking and river water samples is demonstrated. Similar performance characteristics are observed at DNA-coated microfabricated thick-film carbon strips. This and similar developments hold great promise for field screening of Cryptosporidium and other microorganisms in environmental samples.     

A pumpless cell culture chip with the constant medium perfusion-rate maintained by balanced droplet dispensing

This paper presents a pumpless cell culture chip, where a constant-rate medium perfusion is achieved by balanced droplet dispensing. Previous pumpless cell culture chips, where the gravity-driven flow is induced by gradually decreasing the hydraulic-head difference, Δh, between source and drain reservoirs, result in a decreasing perfusion-rate. However, the present pumpless cell culture chip, where autonomous droplet dispensers are integrated on the source reservoirs, results in a constant perfusion-rate using a constant Δh maintained by balanced droplet dispensing between the source-inlet and the drain-outlet. In the experimental study, constant perfusion-rates of 0.1, 0.2, and 0.3 μl min(-1) are obtained by Δh of 38, 76, and 114 mm, respectively. At the constant perfusion-rate (Q=0.2 μl min(-1)), H358 lung cancer cells show the maximum growth-rate of 57.8 ± 21.1% d(-1), which is 1.9 times higher than the 30.2 ± 10.3% d(-1) of the static culture. At a perfusion-rate varying between 0.1-0.3 μl min(-1) (average=0.2 μl min(-1)), however, the H358 cells show a growth-rate of 46.9 ± 8.3% d(-1), which is lower than that of the constant Q of 0.2 μl min(-1). The constant-rate perfusion culture (Q=0.1, 0.2, and 0.3 μl min(-1)) also results in an average cell viability of 89.2%, which is higher than 75.9% of the static culture. This pumpless cell culture chip offers a favorable environment to cells with a high growth-rate and viability, thus having potential for use in cell-based bio-assays.     

Estimation of biologically damaging UV levels in marine surface waters with DNA and viral dosimeters

We have surveyed the biologically harmful radiation penetrating the water column along a transect in the western Gulf of Mexico using dosimeters consisting of intact viruses or naked calf-thymus DNA (ctDNA). The indigenous marine bacteriophage PWH3a-P1, which lytically infects the heterotrophic bacterium Vibrio natriegens (strain PWH3a), displayed decay rates for infectivity approaching 1.0 h(-1) in surface waters when deployed in a seawater-based dosimeter. The accumulation of pyrimidine dimers in ctDNA dosimeters provided a strong correlation to these results, with pyrimidine dimers representing more than 0.3% (up to ca 3800 dimers Mb(-1) DNA) of the total DNA in dosimeters exposed to sea surface levels of solar radiation. The results demonstrate a strong correlation between the dimer formation in the DNA dosimeters, the decay rates of viral infectivity and the penetration of UVB radiation into the water column. The decay of viral infectivity attenuated with depth in a manner similar to the decay of solar radiation and was still significant at 10 m in offshore oligotrophic water and at dimer frequencies less than 0.1% (ca 200-300 dimers Mb(-1) DNA).     

Determination of fluoride in drinking water and in urine of adolescents living in three counties in Northern Chihuahua Mexico using a fluoride ion selective electrode

This study was carried out to determine fluoride in drinking water and in urine of adolescents, ages 15-20 years, living in Northern Chihuahua Mexico. Participants are from a cross-sectional study on health effects of chronic fluoride exposure from drinking water. A total of 201 participants (106 female and 95 male) in the study were recruited from three counties. Samples of drinking water of each county were collected and analyzed using the U.S. EPA Fluoride Ion-Selective Method. Statistically significant difference of fluoride content in water was found among the three counties of recruitment (Cd. Juarez; 0.3 mg/L, Samalayuca, 1.0 mg/L, and Villa Ahumada, 5.3 mg/L). Fluoride content in wells and tap water samples of Villa Ahumada ranged from 5.0 to 5.7 mg/L. Fluoride content of these samples was above the level permitted by Mexican regulations. The fluoride content in bottled water obtained from local stores in Villa Ahumada ranged from 0.3 to 3.7 mg/l.Fluoride in urine samples of each participant was also analyzed using the U.S. EPA Ion-Selective Method. The mean fluoride urine concentration (reported in mg/g creatinine) in adolescents living in these counties was 0.792±0.39, 1.33±0.67 and 2.22±1.16 (Cd. Juarez, Samalayuca and Villa Ahumada), respectively. The high fluoride urinary levels found in participants from Villa Ahumada may be associated to the high fluoride level (5.3 mg/L) in dinking water.The accuracy of measurements was assessed with reference materials in water and in urine. Mean fluoride recovery was 99.0% and 99.6% in water and in urine, respectively. The levels obtained were within the assayed 5% confidence levels.     

Role of surface proteins in the deposition kinetics of Cryptosporidium parvum oocysts

A radial stagnation point flow system was used to investigate the influence of Cryptosporidium parvum surface properties on oocyst deposition kinetics onto solid surfaces. To determine the role of oocyst surface proteins in adhesion, the deposition kinetics of viable oocysts were compared with the deposition kinetics of oocysts treated (inactivated) with either heat or formalin. Results showed a significantly higher deposition rate with formalin and heat-treated oocysts compared to viable oocysts under identical solution ionic strengths. Low deposition rates and corresponding attachment efficiencies were observed with viable oocysts over the entire range of solution conditions investigated, even at high ionic strengths where DLVO theory predicts the absence of an electrostatic energy barrier. An "electrosteric" repulsion between the viable Cryptosporidium oocyst and the quartz substrate, attributed to proteins on the oocyst surface, is surmised to cause this low deposition rate. Inactivation of the oocysts with either formalin or heat resulted in increased attachment efficiencies over the entire range of ionic strengths examined. It is hypothesized that formalin and heat treatments alter the structure of surface proteins and thus reduce steric repulsion. Formalin treatment was also found to impart an increased hydrophobicity to the oocyst surface and thus greater enhancement in oocyst deposition kinetics compared to heat treatment.     

Simple and automatic determination of aldehydes and acetone in water by headspace solid-phase microextraction and gas chromatography-mass spectrometry

We describe a simple and automatic method to determine nine aldehydes and acetone simultaneously in water. This method is based on derivatization with 2,2,2-trifluoroethylhydrazine (TFEH) and consecutive headspace-solid-phase microextraction and gas chromatography-mass spectrometry. Acetone-d(6) was used as the internal standard. Aldehydes and acetone in water reacted for 30 min at 40°C with TFEH in a headspace vial and the formed TFEH derivatives were simultaneously vaporized and adsorbed on polydimethylsiloxane-divinylbenzene. Under the established condition, the method detection limit was 0.1-0.5 μg/L in 4 mL water and the relative standard deviation was less than 13% at concentrations of 0.25 and 0.05 mg/L. This method was applied to determine aldehydes and acetone in 5 mineral water and 114 surface water samples. All mineral water samples had detectable levels of methanal (24.0-61.8 μg/L), ethanal (57.7-110.9 μg/L), propanal (11.5-11.7 μg/L), butanal, pentanal (3.3-3.4 μg/L) and nonanal (0.3-0.4 μg/L). Methanal and ethanal were also detected in concentration range of 2.7-117.2 and 1.2-11.9 μg/L, respectively, in surface water of 114 monitoring sites in Korea.