Predicting pathogen risks to aid beach management: The real value of quantitative microbial risk assessment (QMRA)

There has been an ongoing dilemma for agencies that set criteria for safe recreational waters in how to provide for a seasonal assessment of a beach site versus guidance for day-to-day management. Typically an overall ‘safe’ criterion level is derived from epidemiologic studies of sewage-impacted beaches. The decision criterion is based on a percentile value for a single sample or a moving median of a limited number (e.g. five per month) of routine samples, which are reported at least the day after recreator exposure has occurred. The focus of this paper is how to better undertake day-to-day recreational site monitoring and management. Internationally, good examples exist where predictive empirical regression models (based on rainfall, wind speed/direction, etc.) may provide an estimate of the target faecal indicator density for the day of exposure. However, at recreational swimming sites largely impacted by non-sewage sources of faecal indicators, there is concern that the indicator-illness associations derived from studies at sewage-impacted beaches may be inappropriate. Furthermore, some recent epidemiologic evidence supports the relationship to gastrointestinal (GI) illness with qPCR-derived measures of Bacteroidales/Bacteroides spp. as well as more traditional faecal indicators, but we understand less about the environmental fate of these molecular targets and their relationship to bather risk. Modelling pathogens and indicators within a quantitative microbial risk assessment framework is suggested as a way to explore the large diversity of scenarios for faecal contamination and hydrologic events, such as from waterfowl, agricultural animals, resuspended sediments and from the bathers themselves. Examples are provided that suggest that more site-specific targets derived by QMRA could provide insight, directly translatable to management actions.     

Integrated analysis of water quality parameters for cost-effective faecal pollution management in river catchments

In many parts of the world, microbial contamination of surface waters used for drinking, recreation, and shellfishery remains a pervasive risk to human health, especially in Less Economically Developed Countries (LEDC). However, the capacity to provide effective management strategies to break the waterborne route to human infection is often thwarted by our inability to identify the source of microbial contamination. Microbial Source Tracking (MST) has potential to improve water quality management in complex river catchments that are either routinely, or intermittently contaminated by faecal material from one or more sources, by attributing faecal loads to their human or non-human sources, and thereby supporting more rational approaches to microbial risk assessment. The River Ouse catchment in southeast England (U.K.) was used as a model with which to investigate the integration and application of a novel and simple MST approach to monitor microbial water quality over one calendar year, thereby encompassing a range of meteorological conditions. A key objective of the work was to develop simple low-cost protocols that could be easily replicated. Bacteriophages (viruses) capable of infecting a human specific strain of Bacteroides GB-124, and their correlation with presumptive Escherichia coli, were used to distinguish sources of faecal pollution. The results reported here suggest that in this river catchment the principal source of faecal pollution in most instances was non-human in origin. During storm events, presumptive E. coli and presumptive intestinal enterococci levels were 1.1-1.2 logs higher than during dry weather conditions, and levels of the faecal indicator organisms (FIOs) were closely associated with increased turbidity levels (presumptive E. coli and turbidity, r = 0.43). Spatio-temporal variation in microbial water quality parameters was accounted for by three principal components (67.6%). Cluster Analysis, reduced the fourteen monitoring sites to six representative ‘sentinel’ sites. The correlation coefficient between presumptive E. coli and phages of Bacteroides GB-124 was very small (r = 0.05) whilst that between turbidity and suspended solids was high (r = 0.62). Variations in climate, animal and anthropogenic interferences were all, either directly or indirectly, related to faecal contamination. The findings show the importance of meteorological conditions, such as storm events, on microbial water quality, and suggest that any future increases in the frequency of storm events (associated with climate change) are likely to result in a greater incidence of FIO/pathogen loads. This low-cost approach could help to predict spatio-temporal ‘hotspots’ of elevated waterborne disease risk. The work also represents an important step towards integrating novel MST tools into river catchment modelling.     

Evaluating short-term changes in recreational water quality during a hydrograph event using a combination of microbial tracers, environmental microbiology, microbial source tracking and hydrological techniques: A case study in Southwest Wales, UK

Quantitative assessment of multiple sources to short-term variations in recreational water quality, as indexed by faecal indicator organism (FIO) concentrations, is becoming increasingly important with adoption of modern water quality standards and catchment-based water quality management requirements (e.g. the EU Water Framework Directive, Article 11 ‘Programmes of Measures’ and the US Clean Water Act, ‘Total Maximum Daily Loads’). This paper describes a study combining microbial tracers, intensive FIO measurement, open channel hydrology and molecular microbial source tracking (MST) to enhance understanding of recreational water quality at Amroth in southwest Wales, UK. Microbial tracers were released from four stream inputs during a moderate hydrograph event. Tracers from two local streams impacted simultaneously with a period of maximum FIO concentrations at the near-shore compliance monitoring site. Connection between these inputs and this site were rapid (9-33 min). Water quality impairment from a more remote stream input followed, 12.85 h after tracer release, sustaining FIO concentrations above desired compliance levels. MST analysis showed dominance of ruminant Bacteroidales genetic markers, associated with agricultural pollution. This integration of tracers and MST offers additional information on the movement and individual sources causing water quality impairment.     

Do we all face the same risk when bathing in the estuary?

With the development of coastal areas, microbial water quality is an emerging public health issue though few studies have focused on risks according to age. A survey was undertaken of faecal contamination in relation to recreational activities in the Peel Harvey estuarine system, Western Australia. Levels of exposure to contaminated water were estimated though social surveys. Follow-up was also conducted to estimate the incidence of disease associated with bathing in the estuary. Pathogen levels exceeded the guideline values recommended by the World Health Organisation (WHO) at most locations throughout the year. The social survey provided information about exposure of the population in age groups. Only 31% of the recreational users belonged to the healthy adult group upon which the WHO quantitative microbial risk assessment model is based. A correlation was established between microbial water quality and incidence of respiratory diseases for children as well as for adults. Exposure to recreational water increased the incidence of respiratory illnesses for the whole population almost by a factor 2. Behaviours which resulted in increased exposures were associated with increased incidence of illnesses were observed, particularly among children aged 11-15 yr, who exhibited the highest odd ratio (OR 4.23 [2.44-6.01], CI 95%, p=0.05). There is a need for combining epidemiology studies with risk assessment processes and complementing them with social surveys for understanding the risk of recreational activities to public health.     

Ecological effects of diffuse mixed pollution are site-specific and require higher-tier risk assessment to improve site management decisions: a discussion paper

Many Dutch ecosystems, whether terrestrial, aquatic or sediment-based, are diffusely polluted by mixtures of contaminants, whose concentrations often exceed regulatory Safe Values or other generic quality criteria. This situation has unclear consequences, especially when local authorities are confronted with such pollution. Water managers are frequently in doubt whether their water systems satisfy the criteria for ‘Good Ecological Status’ as defined in the EU's Water Framework Directive. In case of soils, soil users may wonder whether the soil is ‘fit for use’. In case of nature conservation, the problem is that protected species might suffer from toxic stress. Official regulations in these cases call for appropriate action, but it is unclear whether the diffuse exposure causes adverse effects, and what the action should be. This paper proposes and discusses a site-oriented approach in the risk assessment of diffusely contaminated sites that can be used in addition to the compound-oriented policies from which the abovementioned generic quality criteria were derived. The site-oriented approach can be of help in reducing site-specific risks of diffuse contamination.Reflecting on the results of a large Dutch research effort in systems-oriented ecotoxicological effects, the conclusion is drawn that exposure and effects of diffuse pollution are site-specific in kind and magnitude, determined by the local combination of source-pathway-receptor issues, and often not clearly detectable (though often present). To assist in risk management, higher-tier methods can address various aspects, like addressing local mixture composition, bioavailability, and sensitivity of local species groups. Higher-tier risk assessment methods have as yet been developed mainly for cases of serious contamination, like for pesticide management and Risk-Based Land Management. For diffuse pollution, site-specific information can also be used to obtain site-specific exposure and impact information, while practical and ecology-based approaches can be introduced to obtain an integrated overview of the meaning of site contamination and to derive options for managing and reducing the local risks. These issues are discussed against the background of current major policy shifts, in The Netherlands and elsewhere, from a pollutant-oriented assessment to an additional ecological and site-oriented assessment. The latter is most clearly represented in the Good Ecological Status aim of the EU-Water Framework Directive. The paper assesses, integrates and discusses the results of the Dutch research effort in this policy context.     

Improved strategies and optimization of calibration models for real-time PCR absolute quantification

Real-time PCR absolute quantification applications are becoming more common in the recreational and drinking water quality industries. Many methods rely on the use of standard curves to make estimates of DNA target concentrations in unknown samples. Traditional absolute quantification approaches dictate that a standard curve must accompany each experimental run. However, the generation of a standard curve for each qPCR experiment set-up can be expensive and time consuming, especially for studies with large numbers of unknown samples. As a result, many researchers have adopted a master calibration strategy where a single curve is derived from DNA standard measurements generated from multiple instrument runs. However, a master curve can inflate uncertainty associated with intercept and slope parameters and decrease the accuracy of unknown sample DNA target concentration estimates. Here we report two alternative strategies termed ‘pooled’ and ‘mixed’ for the generation of calibration equations from absolute standard curves which can help reduce the cost and time of laboratory testing, as well as the uncertainty in calibration model parameter estimates. In this study, four different strategies for generating calibration models were compared based on a series of repeated experiments for two different qPCR assays using a Monte Carlo Markov Chain method. The hierarchical Bayesian approach allowed for the comparison of uncertainty in intercept and slope model parameters and the optimization of experiment design. Data suggests that the ‘pooled’ model can reduce uncertainty in both slope and intercept parameter estimates compared to the traditional single curve approach. In addition, the ‘mixed’ model achieved uncertainty estimates similar to the ‘single’ model while increasing the number of available reaction wells per instrument run.     

Reply to comments on "Derivation of numerical values for the World Health Organization guidelines for recreational waters"

The contribution addressed reveals an optimistic design philosophy likely to systematically underestimate risk in epidemiologic studies into the health effects of bathing water exposures. The authors seem to recommend that data on the 'exposure' measure (i.e. water quality) in such studies should be acquired in a similar manner to that used for regulatory sampling. This approach may compromise the quality of the epidemiologic investigations undertaken. It may result in imprecise estimates of exposure because it ignores the fact that regulatory timescales and spatial resolution (even if artificially compressed to a bathing day) can mask large spatial and temporal variability in water quality. If this variability is ignored by taking some mean value and attributing that to all of those exposed in a period at a study location, many bathers may be misclassified and the studies may be biased to a 'no-effect' conclusion. A more appropriate approach is to maximise the precision of the epidemiologic investigations by measurement of individual exposure (or water quality) at the place and time of the exposure, as has been done in randomised volunteer studies in the UK and Germany. The precise epidemiologic relationships linking 'exposure' with 'illness' can then be related to the probability of exposure to particular water quality by a 'normal bather' using the known probability distribution of the exposure variable (i.e. faecal indicator concentration) in the regulated bathing waters. We suggest that any research protocol where poor sampling design for water quality assessment is justified because regulatory monitoring is equally imprecise may be fundamentally flawed. The rationale for this assessment is that the epidemiology is the starting point and evidence-base for 'standards'. If precision is not maximised at this stage in the process it compromises the credibility of the standards design process. The negative effects of the approach advocated in this 'comment' are illustrated using published research findings used to derive the figures illustrated in Wymer et al. [2005. Comment on derivation of numerical values for the World Health Organization guidelines for recreational waters. Water Research 39, 2774-2777].     

Sustainable microbial water quality monitoring programme design using phage-lysis and multivariate techniques

Contamination of surface waters is a pervasive threat to human health, hence, the need to better understand the sources and spatio-temporal variations of contaminants within river catchments. River catchment managers are required to sustainably monitor and manage the quality of surface waters. Catchment managers therefore need cost-effective low-cost long-term sustainable water quality monitoring and management designs to proactively protect public health and aquatic ecosystems. Multivariate and phage-lysis techniques were used to investigate spatio-temporal variations of water quality, main polluting chemophysical and microbial parameters, faecal micro-organisms sources, and to establish ‘sentry’ sampling sites in the Ouse River catchment, southeast England, UK. 350 river water samples were analysed for fourteen chemophysical and microbial water quality parameters in conjunction with the novel human-specific phages of Bacteroides GB-124 (Bacteroides GB-124). Annual, autumn, spring, summer, and winter principal components (PCs) explained approximately 54%, 75%, 62%, 48%, and 60%, respectively, of the total variance present in the datasets. Significant loadings of Escherichia coli, intestinal enterococci, turbidity, and human-specific Bacteroides GB-124 were observed in all datasets. Cluster analysis successfully grouped sampling sites into five clusters. Importantly, multivariate and phage-lysis techniques were useful in determining the sources and spatial extent of water contamination in the catchment. Though human faecal contamination was significant during dry periods, the main source of contamination was non-human. Bacteroides GB-124 could potentially be used for catchment routine microbial water quality monitoring. For a cost-effective low-cost long-term sustainable water quality monitoring design, E. coli or intestinal enterococci, turbidity, and Bacteroides GB-124 should be monitored all-year round in this river catchment.     

Probabilistic environmental risk assessment of urban wet-weather discharges: an approach developed for Switzerland

Technical solutions aimed at limiting the impacts of urban wet-weather discharges are historically based on an end-of-pipe approach. The characteristics of wet-weather discharges, e.g. intermittent pollution loads, high variations in pollutant concentrations, effects in the receiving waters, etc., are generally not considered. This study presents a new probabilistic approach that links the characteristics of wet-weather discharges to their potential impacts in receiving waters. This new approach involves coupling a model for predicting fluctuating concentrations in rivers along with sediment changes to water quality criteria. The new approach produces a risk profile for receiving waters and includes assessment of uncertainty in input data as well as the uncertainty inherent in local receiving system processes. This new approach is expected to offer a better management of wet-weather discharges, resulting in lower environmental impacts.     

Evaluating the operational utility of a Bacteroidales quantitative PCR-based MST approach in determining the source of faecal indicator organisms at a UK bathing water

Microbial source tracking techniques are used in the UK to provide an evidence-base to guide major expenditure decisions and/or regulatory action relating to sewage disposal. Consequently, it is imperative that the techniques used robustly index faecal indicator organisms (FIOs) that are the regulatory parameters for bathing and shellfish harvesting areas. This study reports a ‘field-scale’ test of microbial source tracking (MST) based on the quantitative PCR analyses of Bacteroidales 16S rRNA genetic marker sequences. The project acquired data to test the operational utility of quantitative Bacteroidales MST data, comparing it with FIO concentrations in streams, effluents and bathing waters. Overall, the data did not exhibit a consistent pattern of significant correlations between Bacteroidales MST parameters and FIOs within the different sample matrices (i.e. rivers, bathing waters and/or effluents). Consequently, there was little evidence from this study that reported concentrations and/or percentages of human and/or ruminant faecal loadings (that are based on Bacteroidales MST gene copy numbers) offer a credible evidence-base describing FIO contributions to receiving water ‘non-compliance’. The study also showed (i) there was no significant attenuation of the Bacteroidales gene copy number ‘signal’ through the UV disinfection process; and (ii) single non-compliant samples submitted for Bacteroidales MST analysis, do not reliably characterise the balance of faecal loadings due to the high variability in the MST signal observed.At this stage in the development of the MST tool deployed, it would be imprudent to use the percentage human and/or ruminant contributions (i.e. as indicated by MST data acquired at a bathing water) as the sole or principal element in the evidence-base used to guide major expenditure decisions and/or regulatory action.     

Estimated human health risks from exposure to recreational waters impacted by human and non-human sources of faecal contamination

This work was conducted to determine whether estimated risks following exposure to recreational waters impacted by gull, chicken, pig, or cattle faecal contamination are substantially different than those associated with waters impacted by human sources such as treated wastewater. Previously published Quantitative Microbial Risk Assessment (QMRA) methods were employed and extended to meet these objectives. Health outcomes used in the analyses were infection from reference waterborne pathogens via ingestion during recreation and subsequent gastrointestinal (GI) illness. Illness risks from these pathogens were calculated for exposure to faecally contaminated recreational water at the U.S. regulatory limits of 35 cfu 100 mL⁻¹ enterococci and 126 cfu 100 mL⁻¹Escherichia coli. The probabilities of GI illness were calculated using pathogen dose-response relationships from the literature and Monte Carlo simulations. Three scenarios were simulated, representing a range of feasible interpretations of the available data. The primary findings are that: 1) GI illness risks associated with exposure to recreational waters impacted by fresh cattle faeces may not be substantially different from waters impacted by human sources; and 2) the risks associated with exposure to recreational waters impacted by fresh gull, chicken, or pig faeces appear substantially lower than waters impacted by human sources. These results suggest that careful consideration may be needed in the future for the management of recreational waters not impacted by human sources.     

Waterborne rotavirus: A risk assessment

A risk assessment approach was used to estimate the public health impacts from exposure to human rotavirus in drinking and recreational waters. Rotavirus is the major cause of viral gastroenteritis worldwide and several waterborne outbreaks have been documented. This results in a significant economic impact on society in terms of direct medical costs, loss of work, quality of life and mortality. The virus is common in domestic wastewater and polluted surface waters. Dose-response data in human adult volunteers indicate that it is the most infective of all the enteric viruses, and this was used to develop a microbial risk assessment model to estimate daily and yearly risks of infection, morbidity and mortality for exposure via drinking and recreational waters using existing information on the occurrence of rotavirus. The disease is most severe for the very young, the elderly, and the immunocompromised. Case fatality rates in the United States are 0.01% in the general population, 1% in the elderly, and up to 50% in the immunocompromised. Analysis indicates that significant risks of disease (5 × 10⁻¹−2.45 × 10⁻³) could result for drinking and recreational waters in which rotavirus has been detected. The major limitation in assessing the risks of waterborne rotaviral infections at present is the lack of data on its occurrence in water and the potential for human exposure.     

A study on subjective preference to daylit residential indoor environment using conjoint analysis

This paper reports a study of the subjective preference to daylit indoor environment of a residential room using conjoint analysis, which is a highly reputable method used to analyze the mutual relationships among different attributes. Seven influential attributes were selected in the view of daylight performance assessment. They include ‘general brightness’, ‘desktop brightness’, ‘perceived glare’, ‘sunlight penetration’, ‘quality of view’, ‘user friendliness of shading control’ and ‘impact on energy’. Each of them has two levels. A total of eight combinations (profiles) of attributes with various levels were established by adopting fractional factorial design. Subjects were asked to rank-order the eight profiles according to their preference in terms of daylit environment of a residential room. The study aims at finding out the relative impact of the seven selected attributes to the overall daylight performance and seeking an organized assessment method for a residential daylit environment. Conjoint analysis found that the seven attributes have importance level in the order of ‘quality of view’, ‘general brightness’, ‘impact on energy’, ‘user friendliness of shading control’, ‘perceived glare’, ‘desktop brightness’ and ‘sunlight penetration’.     

Uncertainty of measurement or of mean value for the reliable classification of contaminated land

Classification of contaminated land is important for risk assessment and so it is vital to understand and quantify all of the uncertainties that are involved in the assessment of contaminated land. This paper uses a case study to compare two methods for assessing the uncertainty in site investigations (uncertainty of individual measurements, including that from sampling, and uncertainty of the mean value of all measurements within an area) and how the different methods affect the decisions made about a site. Using the ‘uncertainty of the mean value’ there is shown to be no significant possibility of ‘significant harm’ under UK guidance at one particular test site, but if you consider the ‘uncertainty of the measurements’ a significant proportion (50%) of the site is shown to be possibly contaminated. This raises doubts as to whether the current method using ‘uncertainty of the mean’ is sufficiently robust, and suggests that ‘uncertainty of measurement’ information may be preferable, or at least beneficial when used in conjunction.     

Decay of intestinal enterococci concentrations in high-energy estuarine and coastal waters: towards real-time T90 values for modelling faecal indicators in recreational waters

Intestinal enterococci are the principal 'health-evidence-based' parameter recommended by WHO for the assessment of marine recreational water compliance. Understanding the survival characteristics of these organisms in nearshore waters is central to public health protection using robust modelling to effect real-time prediction of water quality at recreation sites as recently suggested by WHO and the Commission of the European Communities Previous models have more often focused on the coliform parameters and assumed two static day-time and night-time T90 values to characterise the decay process. The principal driver for enterococci survival is the received dose of irradiance from sunlight. In the water column, transmission of irradiance is determined by turbidity produced by suspended material. This paper reports the results of irradiated microcosm experiments using simulated sunlight to investigate the decay of intestinal enterococci in relatively turbid estuarine and coastal waters collected from the Severn Estuary and Bristol Channel, UK. High-turbidity estuarine waters produced a T90 value of 39.5 h. Low-turbidity coastal waters produced a much shorter T90 value of 6.6 h. In experiments receiving no irradiation, high-turbidity estuarine waters also produced a longer T90 of 65.1 h compared with corresponding low-turbidity coastal waters, T90 24.8 h. Irradiated T90 values were correlated with salinity, turbidity and suspended solids (r>0.8, p<0.001). The results suggest that enterococci decay in irradiated experiments with turbidity >200 NTU is similar to decay observed under dark conditions. Most significantly, these results suggest that modelling turbidity and or suspended solids offers a potential means of predicting T90 values in 'real-time' for discrete cells of a hydrodynamic model.     

Comment on "Derivation of numerical values for the World Health Organization guidelines for recreational waters"

The subject paper describes a procedure for adjusting a risk model based upon a measure of personal exposure (the "UK personal exposure model") in order to attribute an expected rate of gastroenteritis among a group of swimmers to a mean recreational water quality value (enterococci per 100mL). We term the resulting model for group risk the "UK ecologic exposure model." The distinction is essential to establishing recreational water quality guidelines because exposures of individual bathers are not known from a water monitoring program, the only assessment available being some form of ecologic exposure such as a mean log indicator density. While the authors of the subject paper solved the UK ecologic exposure model for only a single point (that value of mean log10 enterococcus density which is expected to result in five extra cases of gastroenteritis per 100 swimmers), we extend their model to show the entire curve over a relevant range of densities. The resulting exposure-response curve is seen to not differ substantially from the existing USEPA model for "highly credible gastrointestinal illness" in marine waters. However, particularly since such correspondence is not guaranteed for future studies or for other existing epidemiological studies, we recommend the direct approach to evaluating ecologic exposure, such as used in the USEPA studies, rather than the indirect approach of the UK ecologic exposure model, given the number of untested assumptions that are necessary for accomplishing the latter.     

Impact of particles on sediment accumulation in a drinking water distribution system

Discolouration of drinking water is one of the main reasons customers complain to their water company. Though corrosion of cast iron is often seen as the main source for this problem, the particles originating from the treatment plant play an important and potentially dominant role in the generation of a discolouration risk in drinking water distribution systems. To investigate this thesis a study was performed in a drinking water distribution system. In two similar isolated network areas the effect of particles on discolouration risk was studied with particle counting, the Resuspension Potential Method (RPM) and assessment of the total accumulated sediment. In the ‘Control Area’, supplied with normal drinking water, the discolouration risk was regenerated within 1.5 year. In the ‘Research Area’, supplied with particle-free water, this will take 10-15 years. An obvious remedy for controlling the discolouration risk is to improve the treatment with respect to the short peaks that are caused by particle breakthrough.     

Deliberate ignorance in project risk management

The management of project risk is considered a key discipline by most organisations involved in projects. Best practice project risk management processes are claimed to be self-evidently correct. However, project risk management involves a choice between which information is utilized and which is deemed to be irrelevant and hence excluded. Little research has been carried out to ascertain the manifestation of barriers to optimal project risk management such as ‘irrelevance’; the deliberate inattention of risk actors to risk. This paper presents the results of a qualitative study of IT project managers, investigating their reasons for deeming certain known risks to be irrelevant. The results both confirm and expand on Smithson’s [Smithson, M., 1989. Ignorance and Uncertainty. Springer-Verlag, New York] taxonomy of ignorance and uncertainty and in particular offer further context related insights into the phenomenon of ‘irrelevance’ in project risk management. We suggest that coping with ‘irrelevance’ requires defence mechanisms, the effective management of relevance as well as the setting of, and sticking to priorities.     

我国水质标准与国外水质标准/基准的对比分析

系统分析了我国现行的两个水质标准《地表水环境质量标准》(GB 3838—2002)和《生活饮用水卫生标准》(GB 5749—2006),并与WHO的《饮用水水质准则》、美国环境保护局2001年《国家饮用水水质标准》和《美国国家推荐水质基准:2002》进行了比较,在此基础上提出了我国水质标准在实际执行和环境管理过程中存在的问题和需进一步改进、完善的地方,以及开展我国水质基准研究的重要性和紧迫性。结合我国水环境标准管理体系的现状,对我国水质标准体系的制/修订、如何有效建立完善的水环境标准管理体系提出了对策。