scholarly journals Comparing probabilistic microbial risk assessments for drinking water against daily rather than annualised infection probability targets

2009 ◽  
Vol 7 (4) ◽  
pp. 535-543 ◽  
Author(s):  
R. S. Signor ◽  
N. J. Ashbolt
Keyword(s):  
Drinking Water ◽  
Disease Outbreaks ◽  
Assessment Process ◽  
Risk Assessments ◽  
Safe Drinking Water ◽  
Short Term ◽  
Management Planning ◽  
Microbial Risk ◽  
Risk Levels ◽  
Waterborne Pathogen

Some national drinking water guidelines provide guidance on how to define ‘safe’ drinking water. Regarding microbial water quality, a common position is that the chance of an individual becoming infected by some reference waterborne pathogen (e.g. Cryptsporidium) present in the drinking water should <10−4 in any year. However the instantaneous levels of risk to a water consumer vary over the course of a year, and waterborne disease outbreaks have been associated with shorter-duration periods of heightened risk. Performing probabilistic microbial risk assessments is becoming commonplace to capture the impacts of temporal variability on overall infection risk levels. A case is presented here for adoption of a shorter-duration reference period (i.e. daily) infection probability target over which to assess, report and benchmark such risks. A daily infection probability benchmark may provide added incentive and guidance for exercising control over short-term adverse risk fluctuation events and their causes. Management planning could involve outlining measures so that the daily target is met under a variety of pre-identified event scenarios. Other benefits of a daily target could include providing a platform for managers to design and assess management initiatives, as well as simplifying the technical components of the risk assessment process.

scholarly journals Sensitivity of quantitative microbial risk assessments to assumptions about exposure to multiple consumption events per day

2014 ◽  
Vol 12 (4) ◽  
pp. 727-735 ◽  
Author(s):  
N. Van Abel ◽  
E. J. M. Blokker ◽  
P. W. M. H. Smeets ◽  
J. S. Meschke ◽  
G. J. Medema
Keyword(s):  
Drinking Water ◽  
Tap Water ◽  
Daily Intake ◽  
Risk Assessments ◽  
Multiple Time ◽  
Risk Of Infection ◽  
Short Term ◽  
Microbial Risk ◽  
Contamination Events ◽  
The Impact

Quantitative microbial risk assessments (QMRAs) of contaminated drinking water usually assume the daily intake volume is consumed once a day. However, individuals could consume water at multiple time points over 1 day, so the objective was to determine if the number of consumption events per day impacted the risk of infection from Campylobacter jejuni during short-term contamination events. A probabilistic hydraulic and risk model was used to evaluate the impact of multiple consumption events as compared to one consumption event on the health risk from the intake of contaminated tap water. The fraction of the population that experiences greater than 10−4 risk of infection per event at the median dose was 6.8% (5th–95th percentile: 6.5–7.2%) for one consumption event per day, 18.2% (5th–95th: 17.6–18.7%) for three consumption events per day, and 19.8% (5th–95th: 14.0–24.4%) when the number of consumption events varied around 3.49 events/day. While the daily intake volume remained consistent across scenarios, the results suggest that multiple consumption events per day increases the probability of infection during short-term, high level contamination events due to the increased coincidence of a consumption event during the contamination peak. Therefore, it will be important to accurately characterize this parameter in drinking water QMRAs.

scholarly journals Common themes contributing to recent drinking water disease outbreaks in affluent nations

2019 ◽  
Vol 19 (6) ◽  
pp. 1767-1777 ◽  
Author(s):  
S. E. Hrudey ◽  
E. J. Hrudey
Keyword(s):  
Drinking Water ◽  
New Zealand ◽  
Scientific Literature ◽  
Disease Outbreaks ◽  
Disease Outbreak ◽  
Safe Drinking Water ◽  
Waterborne Disease ◽  
George Santayana ◽  
The Past ◽  
Recent Outbreak

Abstract New Zealand experienced its largest waterborne disease outbreak in modern history in August 2016 with 5,500 cases and four fatalities. This recent outbreak is one of 24 drinking-waterborne disease outbreaks in affluent nations that have been reported in the scientific literature since the infamous Walkerton, Ontario, Canada fatal outbreak (2,300 cases, seven fatalities) in May 2000. These disasters were all eminently preventable given the economic and intellectual resources existing in the countries where they occurred. These outbreaks are analysed according to major recurring themes, including: complacency, naiveté and ignorance, failure to learn from experience and chemophobia. Lessons that can be learned to improve preventive approaches for ensuring safe drinking water are based on an extensive and authentic body of evidence in support of meaningful improvements. Philosopher George Santayana captured this need with his famous quote: ‘Those who cannot remember the past are condemned to repeat it.’

Guidelines for the safe use of wastewater in agriculture: revisiting WHO guidelines

2004 ◽  
Vol 50 (2) ◽  
pp. 31-38 ◽  
Author(s):  
R.M. Carr ◽  
U.J. Blumenthal ◽  
D. Duncan Mara
Keyword(s):  
Health Care ◽  
Drinking Water ◽  
Relevant Information ◽  
Epidemiological Studies ◽  
Risk Assessments ◽  
Who Guidelines ◽  
Microbial Risk ◽  
Scarce Resources ◽  
Health Measures ◽  
Hygiene Promotion

The use of wastewater in agriculture is occurring more frequently because of water scarcity and population growth. Often the poorest households rely on this resource for their livelihood and food security needs. However, there are negative health implications of this practice that need to be addressed. WHO developed Guidelines for the Safe Use of Wastewater in Agriculture in 1989. The Guidelines are currently being revised based on new data from epidemiological studies, quantitative microbial risk assessments and other relevant information. WHO guidelines must be practical and offer feasible risk management solutions that will minimize health threats and allow for the beneficial use of scarce resources. To achieve the greatest impact on health, guidelines should be implemented with other health measures such as: health education, hygiene promotion, provision of adequate drinking water and sanitation, and other health care measures.

Toxicological Basis for Drinking Water: Unreasonable Risk to Health Values

1992 ◽  
Vol 11 (3) ◽  
pp. 325-329
Author(s):  
Jennifer Orme Zavaleta
Keyword(s):  
Drinking Water ◽  
Environmental Protection Agency ◽  
Health Effect ◽  
Safe Drinking Water ◽  
Adverse Health Effect ◽  
Short Term ◽  
Water Supplies ◽  
Health Values ◽  
Population Sensitivity

The U.S. Environmental Protection Agency (EPA) administers the Safe Drinking Water Act (SDWA) to ensure that the water obtained from a public water supply is safe to drink. Under the SDWA, EPA establishes enforceable maximum contaminant levels (MCLs) for contaminants that may have an adverse health effect and are known or anticipated to occur in water. Occasionally, public water supplies are unable to meet the MCL at the time it becomes enforceable. The SDWA allows public water supplies to apply to the State for a temporary variance or exemption from an MCL(s) as long as the concentration of the contaminant(s) exceeding the MCL(s) does not result in an unreasonable risk to human health. EPA has developed guidance to assist States in determining what level above the MCL presents an unreasonable health risk. In developing this guidance, the toxicity exhibited by each regulated contaminant is evaluated individually. Consideration is also given to the available risk assessments (short-term and long-term) for each contaminant, comparing carcinogenic risks with noncarcinogenic assessments. Other factors that may be considered on a contaminant by contaminant basis include for example, past exposure and expected duration of the variance or exemption period, population sensitivity, and volatilization of the contaminant from drinking water.

Quantitative microbial risk assessments for drinking water facilities: evaluation of a range of treatment strategies

2019 ◽  
Vol 5 (11) ◽  
pp. 1943-1955
Author(s):  
Joshua G. Elliott ◽  
Liz Taylor-Edmonds ◽  
Robert C. Andrews
Keyword(s):  
Drinking Water ◽  
Treatment Strategies ◽  
Risk Assessments ◽  
Microbial Risk

Impact of treatment on pathogen risk.

A nose for trouble – the role of off-flavours in assuring safe drinking water

2007 ◽  
Vol 55 (5) ◽  
pp. 239-247 ◽  
Author(s):  
S.E. Hrudey ◽  
E.J. Hrudey
Keyword(s):  
Drinking Water ◽  
Common Factors ◽  
Disease Outbreaks ◽  
Disease Outbreak ◽  
Safe Drinking Water ◽  
Or Efficiency ◽  
Water Utility ◽  
Common Features ◽  
The Past

A detailed review of drinking water disease outbreaks over the past 30 years in 15 affluent countries produced over 70 case studies, some involving fatalities, which revealed a number of common factors in these disasters. Some of these outbreaks involved off-flavours, either as a driver for reducing disinfection and making the system vulnerable to pathogenic contamination or as an early warning of contamination that was not responded to with sufficient urgency or efficiency to avoid a disease outbreak. The characteristics of these outbreaks are recounted and the important link they reveal between aesthetically pleasing drinking water and safety is documented. Our analysis of common features in drinking water outbreaks also supports an argument that the failure of a water utility to be concerned about aesthetic factors makes such water supplies an inherently greater health risk for their consumers.

The Application of Risk Assessment Techniques to Microbial Monitoring Data: A South African Perspective

1993 ◽  
Vol 27 (3-4) ◽  
pp. 145-150 ◽  
Author(s):  
N. Rodda ◽  
A. Amory ◽  
R. Kfir
Keyword(s):  
Risk Assessment ◽  
Drinking Water ◽  
Viral Pathogen ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Risk Levels ◽  
Daily Risk ◽  
Assessment Techniques ◽  
Water Volumes ◽  
Treated Drinking Water

The feasibility of applying microbial risk assessment techniques in South Africa was evaluated by assessing risks associated with enteric viruses in raw and treated drinking water. Maximum daily risks associated with treated drinking water were in the range 2×10−2 − 7×10−1. If levels of viruses in treated drinking water were approximated from those in raw water by assuming reductions during treatmentof 4 log, Slog and 6 log, maximum daily risk estimates were 4×10−2 - 4×10−1, 5×10−3 - 1×10−1 and 5×10−4 - 1×10−2, respectively. A number of complicating factors were identified. Detection limits were high and volumes of water monitored were low. There was no information on viral pathogen removal during treatment. Application of risk assessment techniques within these limitations clearly showed the volume of water monitored to be the most important factor limiting detection of low risk levels. The sampling and concentration of large water volumes (at least 100ℓ) for microbial analysis was identified as an urgent need.

Achieving safe drinking water — risk management based on experience and reality

2007 ◽  
Vol 15 (NA) ◽  
pp. 169-174 ◽  
Author(s):  
Samantha Rizak ◽  
Steve E. Hrudey
Keyword(s):  
Water Quality ◽  
Risk Management ◽  
Drinking Water ◽  
Disease Outbreaks ◽  
Water Quality Monitoring ◽  
Safe Drinking Water ◽  
Water Safety ◽  
Waterborne Disease ◽  
International Consensus ◽  
Developed World

Over recent years there have been a number of high profile water quality incidents in the developed world that have drawn attention to the safety of our drinking water supplies and how we are managing our systems. An analysis of these and other waterborne disease outbreaks reveals some important themes about the underlying causes of outbreak failures and some broader issues about the role of drinking water quality monitoring for the protection of public health. Experience has shown that waterborne disease outbreaks in affluent countries almost universally demonstrate that the outbreaks were eminently preventable and, in most circumstances, the solutions for assuring safety from the risks of drinking water are not complex and rely not so much on implementing stringent water quality standards, as on improved system management and operation. Given these themes, assuring drinking water safety requires a commitment to a comprehensive approach to risk management, one that focuses on prevention and better measures of control extending from catchment and source protection through to the consumer. There is a growing international consensus moving towards this strategy for assuring safe drinking water, which provides the prospects of making water even more safe than it currently is most places in the developed world.

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