scholarly journals Quantitative Microbial Risk Assessment Models for Consumption of Raw Vegetables Irrigated with Reclaimed Water

2006 ◽  
Vol 72 (5) ◽  
pp. 3284-3290 ◽  
Author(s):  
Andrew J. Hamilton ◽  
Frank Stagnitti ◽  
Robert Premier ◽  
Anne-Maree Boland ◽  
Glenn Hale
Keyword(s):  
Risk Assessment ◽  
Reclaimed Water ◽  
Quantitative Microbial Risk Assessment ◽  
Risk Of Infection ◽  
Worst Case ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Risk Assessment Models ◽  
Crop Type ◽  
Annual Risk

ABSTRACT Quantitative microbial risk assessment models for estimating the annual risk of enteric virus infection associated with consuming raw vegetables that have been overhead irrigated with nondisinfected secondary treated reclaimed water were constructed. We ran models for several different scenarios of crop type, viral concentration in effluent, and time since last irrigation event. The mean annual risk of infection was always less for cucumber than for broccoli, cabbage, or lettuce. Across the various crops, effluent qualities, and viral decay rates considered, the annual risk of infection ranged from 10−3 to 10−1 when reclaimed-water irrigation ceased 1 day before harvest and from 10−9 to 10−3 when it ceased 2 weeks before harvest. Two previously published decay coefficients were used to describe the die-off of viruses in the environment. For all combinations of crop type and effluent quality, application of the more aggressive decay coefficient led to annual risks of infection that satisfied the commonly propounded benchmark of ≤10−4, i.e., one infection or less per 10,000 people per year, providing that 14 days had elapsed since irrigation with reclaimed water. Conversely, this benchmark was not attained for any combination of crop and water quality when this withholding period was 1 day. The lower decay rate conferred markedly less protection, with broccoli and cucumber being the only crops satisfying the 10−4 standard for all water qualities after a 14-day withholding period. Sensitivity analyses on the models revealed that in nearly all cases, variation in the amount of produce consumed had the most significant effect on the total uncertainty surrounding the estimate of annual infection risk. The models presented cover what would generally be considered to be worst-case scenarios: overhead irrigation and consumption of vegetables raw. Practices such as subsurface, furrow, or drip irrigation and postharvest washing/disinfection and food preparation could substantially lower risks and need to be considered in future models, particularly for developed nations where these extra risk reduction measures are more common.

scholarly journals Microbial risk assessment of local handling and use of human faeces

2006 ◽  
Vol 5 (1) ◽  
pp. 117-128 ◽  
Author(s):  
Caroline Schönning ◽  
Therese Westrell ◽  
Thor Axel Stenström ◽  
Karsten Arnbjerg-Nielsen ◽  
Arne Bernt Hasling ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Incidence Rates ◽  
Quantitative Microbial Risk Assessment ◽  
Risk Of Infection ◽  
Accidental Ingestion ◽  
Storage Container ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Local Use ◽  
Annual Risk

Dry urine-diverting toilets may be used in order to collect excreta for the utilisation of nutrients. A quantitative microbial risk assessment was conducted in order to evaluate the risks of transmission of infectious disease related to the local use of faeces as a fertiliser. The human exposures evaluated included accidental ingestion of small amounts of faeces, or a mixture of faeces and soil, while emptying the storage container and applying the material in the garden, during recreational stays to the garden, and during gardening. A range of pathogens representing various groups of microorganisms was considered. Results showed that 12-months' storage before use was sufficient for the inactivation of most pathogens to acceptable levels. When working or spending time in the garden the annual risk of infection by Ascaris was still slightly above 10-4 in these scenarios, although the incidence rate for Ascaris is very low in the population in question. Measures to further reduce the hygienic risks include longer storage, or treatment, of the faeces. The results can easily be extended to other regions with different incidence rates.

Application of Microbial Risk Assessment to the Development of Standards for Enteric Pathogens in Water Used To Irrigate Fresh Produce

2005 ◽  
Vol 68 (5) ◽  
pp. 913-918 ◽  
Author(s):  
SCOTT W. STINE ◽  
INHONG SONG ◽  
CHRISTOPHER Y. CHOI ◽  
CHARLES P. GERBA
Keyword(s):  
Risk Assessment ◽  
Irrigation Water ◽  
Fresh Produce ◽  
Enteric Bacteria ◽  
Irrigation Event ◽  
Risk Of Infection ◽  
Probable Number ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Annual Risk

Microbial contamination of the surfaces of cantaloupe, iceberg lettuce, and bell peppers via contact with irrigation water was investigated to aid in the development of irrigation water quality standards for enteric bacteria and viruses. Furrow and subsurface drip irrigation methods were evaluated with the use of nonpathogenic surrogates, coliphage PRD1, and Escherichia coli ATCC 25922. The concentrations of hepatitis A virus (HAV) and Salmonella in irrigation water necessary to achieve a 1:10,000 annual risk of infection, the acceptable level of risk used for drinking water by the U.S. Environmental Protection Agency, were calculated with a quantitative microbial risk assessment approach. These calculations were based on the transfer of the selected nonpathogenic surrogates to fresh produce via irrigation water, as well as previously determined preharvest inactivation rates of pathogenic microorganisms on the surfaces of fresh produce. The risk of infection was found to be variable depending on type of crop, irrigation method, and days between last irrigation event and harvest. The worst-case scenario, in which produce is harvested and consumed the day after the last irrigation event and maximum exposure is assumed, indicated that concentrations of 2.5 CFU/100 ml of Salmonella and 2.5 × 10−5 most probable number per 100 ml of HAV in irrigation water would result in an annual risk of 1:10,000 when the crop was consumed. If 14 days elapsed before harvest, allowing for die-off of the pathogens, the concentrations were increased to 5.7 × 103 Salmonella per 100 ml and 9.9 × 10−3 HAV per 100 ml.

QMRA (quantitative microbial risk assessment) and HACCP (hazard analysis and critical control points) for management of pathogens in wastewater and sewage sludge treatment and reuse

2004 ◽  
Vol 50 (2) ◽  
pp. 23-30 ◽  
Author(s):  
T. Westrell ◽  
C. Schönning ◽  
T.A. Stenström ◽  
N.J. Ashbolt
Keyword(s):  
Risk Assessment ◽  
Hazard Analysis ◽  
Treatment Plant ◽  
Storage Site ◽  
Control Points ◽  
Quantitative Microbial Risk Assessment ◽  
Worst Case ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Critical Control Points

Hazard Analysis and Critical Control Points (HACCP) was applied for identifying and controlling exposure to pathogenic microorganisms encountered during normal sludge and wastewater handling at a 12,500 m3/d treatment plant utilising tertiary wastewater treatment and mesophilic sludge digestion. The hazardous scenarios considered were human exposure during treatment, handling, soil application and crop consumption, and exposure via water at the wetland-area and recreational swimming. A quantitative microbial risk assessment (QMRA), including rotavirus, adenovirus, haemorrhagic E. coli, Salmonella, Giardia and Cryptosporidium, was performed in order to prioritise pathogen hazards for control purposes. Human exposures were treated as individual risks but also related to the endemic situation in the general population. The highest individual health risk from a single exposure was via aerosols for workers at the belt press for sludge dewatering (virus infection risk = 1). The largest impact on the community would arise if children ingested sludge at the unprotected storage site, although in the worst-case situation the largest number of infections would arise through vegetables fertilised with sludge and eaten raw (not allowed in Sweden). Acceptable risk for various hazardous scenarios, treatment and/or reuse strategies could be tested in the model.

scholarly journals Improved methods for modelling drinking water treatment in quantitative microbial risk assessment; a case study of Campylobacter reduction by filtration and ozonation

2008 ◽  
Vol 6 (3) ◽  
pp. 301-314 ◽  
Author(s):  
P. W. M. H. Smeets ◽  
Y. J. Dullemont ◽  
P. H. A. J. M. Van Gelder ◽  
J. C. Van Dijk ◽  
G. J. Medema
Keyword(s):  
Risk Assessment ◽  
Drinking Water ◽  
Rare Events ◽  
Monitoring Data ◽  
Average Risk ◽  
Quantitative Microbial Risk Assessment ◽  
Risk Of Infection ◽  
Microbial Risk Assessment ◽  
Microbial Risk

Quantitative microbial risk assessment (QMRA) is increasingly applied to estimate drinking water safety. In QMRA the risk of infection is calculated from pathogen concentrations in drinking water, water consumption and dose response relations. Pathogen concentrations in drinking water are generally low and monitoring provides little information for QMRA. Therefore pathogen concentrations are monitored in the raw water and reduction of pathogens by treatment is modelled stochastically with Monte Carlo simulations. The method was tested in a case study with Campylobacter monitoring data of rapid sand filtration and ozonation processes. This study showed that the currently applied method did not predict the monitoring data used for validation. Consequently the risk of infection was over estimated by one order of magnitude. An improved method for model validation was developed. It combines non-parametric bootstrapping with statistical extrapolation to rare events. Evaluation of the treatment model was improved by presenting monitoring data and modelling results in CCDF graphs, which focus on the occurrence of rare events. Apart from calculating the yearly average risk of infection, the model results were presented in FN curves. This allowed for evaluation of both the distribution of risk and the uncertainty associated with the assessment.

scholarly journals Quantitative microbial risk assessment used to evaluate seasonal wastewater treatment limits: case study in Vacaville, CA

2017 ◽  
Vol 18 (3) ◽  
pp. 910-925 ◽  
Author(s):  
Edmund Seto ◽  
Adam W. Olivieri ◽  
Richard E. Danielson
Keyword(s):  
Risk Assessment ◽  
Wastewater Treatment ◽  
Treatment Plant ◽  
Enteric Viruses ◽  
Secondary Effluent ◽  
Quantitative Microbial Risk Assessment ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Annual Risk ◽  
Receiving Water

Abstract A quantitative microbial risk assessment (QMRA) was conducted to support renewal of the City of Vacaville wastewater discharge permit and seasonal (summer) filtration requirements. Influent and final disinfected effluent from the city's wastewater treatment plant, as well as 11 receiving water stations, were monitored for indicator organisms (i.e. total and fecal coliforms, Escherichia coli, Enterococcus, male-specific bacteriophage (MS2), and the Bacteroidales) and several pathogens (i.e. Giardia cysts, Cryptosporidium oocysts, infectious Cryptosporidium, and Norovirus GI and GII). QMRA annualized risks of infection for selected pathogens enteric viruses, Giardia and Cryptosporidium. Estimated median annualized risk for recreational exposure in either disinfected secondary and/or filtered disinfected secondary effluent is on the order of 1.1 × 10−3 per person per year (pppy) for enteric viruses and would be roughly one order of magnitude lower if local receiving water dilution of the treatment plant effluent was taken into account. Estimated median annual risk for recreation exposure in disinfected secondary effluent is 1.8 × 10−3 pppy for Cryptosporidium and 1 log10 less with filtration during the summer months. The estimated median annual risk for landscape exposure (e.g. golfing) to secondary disinfected effluent is 7.6 × 10−7 pppy for enteric viruses. Estimated median annualized risk is 1.7 × 10−7 pppy for enteric viruses and 3.0 × 10−5 to 3.6 × 10−6 pppy for parasites for use of secondary disinfected effluent with irrigated agriculture. Estimated annualized risks for recreational exposure to the local receiving waters were approximately 10 to 1,000 times greater than direct recreational exposure to the final filtered and disinfected effluent. All risk estimates associated with exposure to final treated plant effluent (i.e. secondary filtered and disinfected) were close to or lower than the California level of acceptable annual risk of infection of 10−4 pppy for recreational exposure. Risk estimates provide further evidence to support the use of seasonal treatment limits requiring summer filtration for public health protection.

scholarly journals Quantitative microbial risk assessment (QMRA) for water re-use via aquifers

2009 ◽  
Vol 30 (1) ◽  
pp. 20
Author(s):  
Declan Page ◽  
Simon Toze
Keyword(s):  
Risk Assessment ◽  
Reclaimed Water ◽  
Managed Aquifer Recharge ◽  
Urban Water ◽  
Quantitative Microbial Risk Assessment ◽  
Aquifer Recharge ◽  
Microbial Risk Assessment ◽  
Microbial Risk ◽  
Wide Range ◽  
Potential Risks

Worldwide, there is an increasing interest in the recharge of aquifers as a method for augmenting urban water supplies. Managed aquifer recharge (MAR) can utilise a variety of non-traditional source waters including urban stormwater and reclaimed water from sewage effluent. However, these alternate water sources may contain a wide range of pathogenic hazards that pose risks to human health. Hence the safe use of recycling water via aquifers requires potential risks to be reduced to acceptable levels. This article outlines the approach recommended by the draft Australian Guidelines for Water Recycling (AGWR) (Phase 2C Managed Aquifer Recharge) to quantify the aquifer treatment using a quantitative microbial risk assessment (QMRA) approach.

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