Statistical basis for predicting the need for bacterially induced beach closures: Emergence of a paradigm?

Data collected from four beaches along southern Lake Michigan (USA) during the summer of 2004 were subjected to correlation and time-series regression analyses aimed at identifying an optimal suite of variables that could be used to predict log Escherichia coli concentrations in real time. Although other variables entered into the regression equations, waves, outfalls of bacteria from an adjacent stream, sunshine, temperature, and time of day (morning versus afternoon) turned out to be the most useful and consistent predictive variables. A post-hoc analysis showed that regression models are much more successful than previous day's bacterial concentration at predicting whether or not the beach water quality is above or below the threshold criteria for full body contact established by the USEPA. Additional analyses, using 99% confidence intervals on predicted log E. coli concentrations, indicated that in extreme cases of high or low health threat, model predictions are likely to be accurate about 90% of the time. The findings of this study are consistent with previous work in the region and seem to indicate that real-time monitoring of hydrometeorological variables can provide the basis of an early warning system for protecting the public from the health risk posed by harmful pathogens in beach water.     

Rates of experimental microbiological contamination of fish exposed to polluted water

Fish inhabiting fecally polluted bodies of water are often used for human consumption. Such fish can be contaminated by enteric human pathogens and may pose a potential risk to public health. Controlled experiments with 132 fish of 100 g average weight were conducted to evaluate the rate of contamination of various tissues of fish (tilapia hybrids). The fish were exposed to E. coli introduced into the ambient water at concentrations of up to 10⁶ cfu/ml. Additional experiments were conducted with diluted wastewater containing Aeromonas, enterococci, fecal coliform and F+ coliphages. In another experiment poliovirus I was also added. The highest bacterial concentrations were recovered from the digestive tract (DT), some 5–24 h following exposure, with DT levels essentially similar to those in the inoculated water. In the E. coli experiments, geometric mean levels of about 10² cfu/cm² were recovered from the skin, 26 cfu/g in the spleen and 10² cfu/g in the liver. Most of the muscle samples were not contaminated. Greater contamination was not found under conditions of stress such as high organic load, a water temperature of 37°C or low levels of dissolved oxygen.     

Occurrence and levels of indicator bacteriophages in bathing waters throughout Europe

Somatic coliphages, F-specific RNA bacteriophages, bacteriophages infecting Bacteroides fragilis, Escherichia coli and enterococci were counted in bathing waters in the late spring and summer. We tested fresh and marine bathing waters from North, South, East and West Europe expected to contain between 100 and 500 E. coli per 100 ml, although wider ranges were sometimes found. Bacteriophages were counted after concentration, since a preliminary study proved that this step was necessary to obtain positive counts. During monitoring, a first-line quality control with reference materials for bacteria and bacteriophages was performed by all the laboratories participating in the study. The same microbes were also counted in raw sewage samples from various areas in Europe, where the bacterial indicators and the three groups of bacteriophages were detected in roughly the same numbers. All groups of bacteriophages were detected in both fresh and marine bathing waters throughout Europe. Reliable and complete results from 147 samples showed that for log-transformed values, E. coli and bacteriophages were slightly correlated. However, the slope of the regression line changed according to E. coli concentration and the correlation diminished when this concentration was close to zero per 100 ml. The ratios between E. coli and phages in bathing waters differed significantly from those in sewage. The relative amounts of bacteriophages, mainly somatic coliphages and phages infecting Bact. fragilis RYC2056, increased in bathing waters with low E. coli concentration, especially in seawater samples containing <100 E. coli per 100 ml. The relationship of bacteriophages with respect to enterococci paralleled that of bacteriophages with respect to E. coli. Somatic coliphages and bacteriophages infecting Bact. fragilis are useful to predict the presence of some pathogens with the same origin as present bacterial indicators but with higher survival rates.     

Pathogenic or potentially pathogenic bacteria as contaminants of fresh water from different sources in Araraquara, Brazil

The microbiological quality of various fresh waters in the Araraquara region, state of São Paulo, Brazil was investigated. Ninety-nine water samples were taken from rivers, reservoirs, artesian and non-artesian wells, springs and tap waters, and these waters were analysed using: plate counts of heterotrophic microorganisms (per 1 ml); Most Probable Number (MPN) of fecal coliforms and E. coli (per 100 ml); tests for presence of Salmonella, Shigella, Yersinia, the E. coli pathogens of classes EPEC, ETEC and EIEC and Mycobacterium, Shigella, Yersinia and enteroinvasive E. coli (EIEC) were not isolated. The other types of microorganisms were isolated in varying proportions. We conclude that the waters investigated represent a potential microbiological health risk.     

A simple test for differentiation between E. coli and A. aerogenes

An important problem in water quality control is the ability to differentiate between E. coli (faecal) and A. aerogenes (non-faecal) coliforms. To perform this differentiation, a simple test, based on a modification of the selective mFC medium and optimal incubation temperature (37°C) is proposed. Under these specific conditions E. coli bacteria develop into dark blue colonies, whereas A. aerogenes into pink ones. The intermediate coliform bacteria appear greenish-blue or pink, depending on their relation (closeness) to E. coli or A. aerogenes.     

Efficacy of monitoring and empirical predictive modeling at improving public health protection at Chicago beaches

Efforts to improve public health protection in recreational swimming waters have focused on obtaining real-time estimates of water quality. Current monitoring techniques rely on the time-intensive culturing of fecal indicator bacteria (FIB) from water samples, but rapidly changing FIB concentrations result in management errors that lead to the public being exposed to high FIB concentrations (type II error) or beaches being closed despite acceptable water quality (type I error). Empirical predictive models may provide a rapid solution, but their effectiveness at improving health protection has not been adequately assessed. We sought to determine if emerging monitoring approaches could effectively reduce risk of illness exposure by minimizing management errors. We examined four monitoring approaches (inactive, current protocol, a single predictive model for all beaches, and individual models for each beach) with increasing refinement at 14 Chicago beaches using historical monitoring and hydrometeorological data and compared management outcomes using different standards for decision-making. Predictability (R²) of FIB concentration improved with model refinement at all beaches but one. Predictive models did not always reduce the number of management errors and therefore the overall illness burden. Use of a Chicago-specific single-sample standard—rather than the default 235 E. coli CFU/100 ml widely used—together with predictive modeling resulted in the greatest number of open beach days without any increase in public health risk. These results emphasize that emerging monitoring approaches such as empirical models are not equally applicable at all beaches, and combining monitoring approaches may expand beach access.     

Photodynamic inactivation of E. coli by immobilized or coated dyes on insoluble supports

The photodynamic inactivation of E. coli by methylene blue, rose bengal and eosin covalently immobilized on polystyrene beads and that of methylene blue coated on granular activated carbon, silica gel and XAD-2 (polystyrene resin) was studied. For the study light-exposed and aerated tap-water contaminated with E. coli subjected to dye sensitized photo-oxidation was used. After 0, 10, 20, 30, 40 and 60 min treatment time, samples were diluted and plated on agar to determine the number of Colony Forming Units (CFU). The study gave the following results: all the light exposed and aerated immobilized dyes (methylene blue, rose bengal and eosin) had an elevated photodynamic action on E. coli. After only 30 min treatment time there was 97.5% inactivation of E. coli by methylene blue, 92.2% by rose bengal and 81.6% by eosin. Methylene blue proved to be the most active. Methylene blue coated on activated carbon, silica gel and XAD-2 also had a high photodynamic action. Activated carbon was found to be the best support; since after 30 min contact it had adsorbed 2 mg g⁻¹ of dye and inactivated 94.4% of E. coli. Comparing the differences in the regression lines of the various methods employed (parallel test) it was found that the effect of each dye was significantly high (P = 0.001) whereas there was no significant difference between methylene blue immobilized and coated on active carbon. From these results it seems that sensitized photo-oxidation using methylene blue coated on activated carbon can be used as an alternative for disinfecting waters for potable purposes, but its effectiveness against other micro-organism present in the water must also be tested.     

The influence of physical and chemical factors on the transport of E. coli through biological filters for wastewater purification

Transport studies of Escherichia coli were performed in laboratory columns over a period of 15 months. The effects of the filter media properties, effective grain size, specific surface area, pH and cation exchange capacity were examined for loading rates of 25 mm and 50 mm/day applied as 8 doses per day. Distilled water and two solutions of ionic strength 0.00725 and 0.097 M were applied to the columns. Physical factors were found to be the most important for the removal of E. coli. Reduced grain size, hydraulic loading rate and increased specific surface area of the grains significantly reduced transport of E. coli. Chemical factors such as pH, cation exchange capacity and wastewater ionic strength showed less significant effects. The results indicate that the chemical factors in biological wastewater filters have a minor influence on the removal of E. coli after a stabilizing period of three months. Minimum hydraulic retention time (time required for 10% breakthrough of a conservative tracer) was found to be the most relevant parameter for predicting bacterial removal in unsaturated filter systems. Correlation between observed data and a first order removal model, based on minimum retention time, was 0.70.     

Comparative survival and injury of Candida albicans and bacterial indicator organisms in streams receiving acid mine drainage

Microbiological studies were conducted to assess the survival and injury characteristics of Candida albicans and indicator bacteria in streams impacted by acid mine water (AMW) and organic wastes. Persistence of pure cultures of C. albicans in three AMW-polluted streams was studied in situ using environmental membrane diffusion chambers. Survival of the fungus (at least 3 days in AMW) indicated prolonged tolerance to acid conditions. In comparison, Escherichia coli was killed within several hours of acid stress. Persistence studies also demonstrated that C. albicans was less sensitive to seasonal water temperature fluctuations than E. coli or Streptococcus faecium. In addition to its prolonged survival, C. albicans incurred minimal sublethal injury whereas identical conditions of exposure resulted in significant injury to traditional indicator bacteria. The failure of standard microbiological procedures to detect AMW-damaged bacteria compromises the accuracy of public health safety determinations in these waters. On the other hand, the ability of C. albicans to survive in AMW streams with marked resistance to injury suggests its potential as a favorable alternative sanitary indicator organism for such environments.     

Dose—response of Escherichia coli in ozone demand-free phosphate buffer

The intention of this investigation was to determine the mean response of E. coli at predetermined ozone dose levels. By using replicated, randomized, independent batch experiments, precise estimates of the response could be obtained. Particular care was taken in preparing the bacteria and glassware to eliminate effects caused by extraneous ozone demand. A total of 57 batch experiments were conducted at bench-scale using ozone doses of 4.4, 11.45, 200 and 800 μg l⁻¹ at contact times of 30, 60 and 120 s.

The logarithm of the E. coli survival ratio was plotted as a function of applied ozone dose, utilized ozone and contact time. Contact time was found to have some effect for intermediate doses of ozone, but the effects were small relative to those associated with the utilized ozone dose. It was also found that the disinfection reaction was not first-order with respect to the surviving bacteria concentration and two distinct stages were observed; an initial rapid inactivation stage followed by a slower inactivation stage.

Regression analysis of the E. coli response on the logarithm of the dose parameter is typical of dose-response models for water and wastewater disinfection. However, this model form was inadequate when fitted to the data of this study as a result of a significant tailing effect in the log-log dose-response plots. It was postulated that the observed dose-response could be explained by chemical kinetic theory and that the dose-response was affected by the disinfection reaction rates which were dependent upon the surviving number of bacteria and the residual ozone concentration.

For practical application, it was found that an adequate dose-response model for 0–99.99% reduction of E. coli could be developed using the logarithm of utilized ozone as the dose function.     

Inactivation of f2 virus with ferrate (VI)

Disinfection of f2 virus with iron(VI) ferrate in buffered, distilled water and secondary treated sewage effluent has been studied. The relative resistance of f2 virus and Escherichia coli to iron(VI) ferrate has also been examined in buffered, distilled water. Potassium ferrate was found to rapidly inactivate f2 virus at low concentrations at pH = 6, 7 and 8 in pure water systems, and also in secondary effluent. The disinfection reactions observed did not follow first order reaction kinetics. f2 Virus appeared to be equally, or less resistant to potassium ferrate than were most bacteria, including E. coli, in buffered, distilled water at the pH values tested, and also in secondary effluent. Iron(VI) ferrate appears to be a good viricidal agent in raw water and wastewater.     

Coliphages as an indicator of faecal pollution in water. Its relationship with indicator and pathogenic microorganisms

The study was designed to test the proposal that Escherichia coli specific bacteriophages might serve as universal faecal pollution indicators in water. A highly specific, sensitive and rapid technique for the detection and quantification of these virus particles was developed. The numerical relationship between E. coli and its parasitic phages was investigated in three different aqueous ecosystems such as sea water in the vicinity of sewage outfalls, river water contaminated by domestic and industrial sewage discharges, and estuarine waters, and found to be very close. In addition, the results obtained indicate that the coliphages are good indicators of the presence of the pathogenic microorganisms studied. In nearly all the water samples tested, the results suggest that coliphages are better indicators of faecal pollution than the classical indicator systems currently employed.     

Effects of the nuisance algae, Cladophora, on Escherichia coli at recreational beaches in Wisconsin

Recreational beaches constitute a large part of the 12 billion dollar per year tourism industry in Wisconsin. Beach closures due to microbial contamination are costly in terms of lost tourism revenue and adverse publicity for an area. Escherichia coli (E. coli), is used as an indicator of microbial contamination, as high concentrations of this organism should indicate a recent fecal contamination event that may contain other, more pathogenic, bacteria. An additional problem at many beaches in the state is the nuisance algae, Cladophora. It has been hypothesized that mats of Cladophora may harbor high concentrations of E. coli. Three beaches in Door County, WI were selected for study, based on tourist activity and amounts of algae present. Concentrations of E. coli were higher within Cladophora mats than in surrounding water. Beaches displayed an E. coli concentration gradient in water extending away from the Cladophora mats, although this was not statistically significant. Likewise, the amount of Cladophora observed on a beach did not correlate with E. coli concentrations found in routine beach monitoring samples. More work is needed to determine the impact of mats of Cladophora on beach water quality, as well as likely sources of E. coli found within the mats.     

Tracer study and profiling of a tertiary lagoon in the United Kingdom: II

Monitoring data over a year showed that the performance of a tertiary lagoon system in the United Kingdom was very variable. Distinct seasonal patterns were seen for all the determinands. Tracer studies and profile sampling of one of the lagoons were carried out in order to investigate the factors affecting performance. The tracer studies, using sodium fluoride, indicated that the hydraulic regime was dispersed plug flow. The mean retention time was found to be 26 h, but the peak in tracer concentration occurred after 12 h, showing significant short-circuiting. During the profile sampling, the pH, temperature, DO and conductivity were measured down through the lagoon at 16 positions and four depths. E. coli, enterococci and total coliform numbers were measured in samples taken from the surface and the base of the lagoon. The results showed temperature decreased down through the lagoon, but the other parameters increased with depth, indicating that the short-circuiting was caused by the cooler influent sinking to the base of the lagoon.     

Evidence for localized bacterial loading as the cause of chronic beach closings in a freshwater marina

We conducted a comprehensive regional spatial assessment of bacterial water quality in order to determine the points of entry of fecal pollution into a swimming beach area on Lake Michigan that historically has had numerous water quality advisories for elevated levels of Escherichia coli (E. coli). Intensive, consecutive-day water samples were collected during dry and rainy conditions across multiple shoreline and offshore sites, and E. coli levels were enumerated from these samples. For both dry and rainy days, shoreline sites demonstrated significantly higher E. coli levels than offshore regions. We found that offshore (10-150m from shore) E. coli levels did not exceed 235CFU/100ml in more than 5% of the samples collected for 19 surveys (n=209). In contrast, samples taken at the beach area exceeded 235CFU/100ml in 66% of the samples collected for 43 shoreline surveys (n=675). Locally high E. coli levels coincided with bird presence and stormwater at the swimming beach located within the marina, and were unrelated to E. coli levels in connecting harbor waters. We conclude that beach water quality may be impacted by local, persistent contamination, which may confound routine beach monitoring and prevent the detection of regional pollution from other sources.     

Nitrate concentration in wetlands: assessing the contribution of deeper groundwater from anions

Denitrification in wetlands is useful for removing nitrate from the surface water, although it can be difficult to assess wetland functioning particularly where it overlies a hard-rock aquifer whose fractures and joints form pathways that mix waters with different chemical composition. The variability of NO3 concentrations in such waters, which partly transit through wetlands, can obscure the effect of denitrification. To address this question, we monitored groundwater chemistry at different depths on three pilot sites overlying (mica)schist aquifers with almost no NO3 contamination at depth, probably due to denitrification. The spatial variability of NO3 concentrations, both along the flowpath and with depth, is related in each site to at least one of the following factors: (1) upward flux of deeper NO3-free groundwater; (2) in situ heterotrophic denitrification; (3) application of different types of fertilizer and other amendments. These factors are efficiently discriminated by the monitoring of just three, easily affordable, parameters: NO3, SO4 and Cl.     

Gel immobilization improves survival of Escherichia coli under temperature stress in nutrient-poor natural water

Viable Escherichia coli cells were entrapped in agar gel layers to form artificial biofilms. Sessile-like bacteria and planktonic (suspended) counterparts were exposed for 28 d to natural (spring)water at two temperatures (4°C and 18°C). Culturabilities on non-selective and selective solid media were monitored over the exposure period, together with cell viability that was determined by using a fluorescent viability probe and confocal scanning laser microscopy analysis. The number of planktonic organisms recovered on non-selective medium decreased by 3 logarithmic units during exposure at 4°C and was reduced to an undetectable level at 18°C. Whatever the temperature of the spring water microcosm, however, the immobilized-cell population did not decrease by more than one log unit over the exposure period. Cell counts on coliform-selective, lactose–deoxycholate agar plates confirmed the enhanced resistance of gel-entrapped cells to environment stress as compared to planktonic organisms: at the two tested temperatures, sublethal injury of suspended E. coli reached more than 80% whereas it did not exceed 65% for immobilized cells. Viability studies indicated that planktonic cells rapidly died. These results show that the ability of microorganisms to colonize aquatic ecosystems in the fixed state (i.e. as biofilms) must be considered in studies evaluating cell survival in these environments.     

Fecal indicator bacteria are abundant in wet sand at freshwater beaches

Potential fecal contamination of sand in the wave-washed zone of public bathing beaches is overlooked in beach monitoring programs. Activity in this zone can bring pathogens to the sand surface or into the water, presenting a health risk to sensitive populations. On a unit weight basis (colony forming units per 100g), the mean summer abundance of the fecal indicator bacteria enterococci and Escherichia coli was 3-38 times higher in the top 20 cm of wet-sand cores than in the water column at six freshwater bathing beaches. E. coli were 4 times more abundant than enterococci in water but counts were similar in the sand. A correlation (r=0.60) existed between E. coli counts in the water and in the top 5 cm of sand only, whereas no relationship existed between enterococci abundance in water and sand. In general, enterococci were most numerous in the 5-10 cm sand stratum and E. coli in the 0-5 cm stratum. These preliminary data show that wet freshwater beach sand is a reservoir of fecal indicator bacteria. Enteric pathogens may also be present in beach sand.     

Alteration to lake trophic status as a means to control arsenic mobility in a mine-impacted lake

The relationship between lake trophic status, sedimentary redox conditions and As mobility was examined in mine-impacted Balmer Lake, Canada. Under the current redox regime, the reductive dissolution of As-bearing Fe(III) oxyhydroxides occurs in close proximity to the sediment–water interface, resulting in the remobilization of dissolved As in the shallow porewaters to values as high as 8.5 mg L⁻¹. The shallow depth of the oxic zone limits the extent to which As can be re-sorbed in the interfacial horizons, and as a result, a proportion of the remobilized As escapes into the water column where it poses a water quality concern. Examination of the relationship between summer average chlorophyll a and total P at spring overturn in the lake water column demonstrates that Balmer Lake is currently eutrophic as a result of mining-derived inputs of P (domestic waters) and N (blasting residues and cyanide breakdown products). The results suggest that actively pushing the system towards oligotrophy by reducing non-natural P loadings to the system will decrease rates of in situ production and associated sediment oxygen demand, which will in turn result in increased thickness of the aerobic zone and enhanced As scavenging. Such conclusions are supported by porewater data which indicate that the flux of As to the water column is significantly reduced when the Fe(III) redox cline is situated at deeper sediment depths. In the absence of detailed P-loading data, it is recommended that P inputs be reduced to 10% of the estimated pre-mining P loading of 200 kg yr⁻¹. This implies reducing the collective P-loadings from the two mine sites adjacent to the lake from the approximate current value (150 kg yr⁻¹) to 20 kg yr⁻¹. It is proposed that establishment of oligotrophy in the lake should significantly mitigate the current level of dissolved As in lake waters.