Yamuna River case study

1. Microbial Risk in a
Hypothetical Indian
River
QMRA Workshop, Drexel university
Woo Hyoung Lee, Qiaozhi li,
Sharada Prasad, Matthew Verbyla
1/10/14
1

2. Objective
Stream AA (near Delhi,
India) is polluted with
domestic wastewater and
surface runoff from Village
BB.
Objective: Assess
microbial risks for
drinking, swimming, and
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irrigating spinach and
2

3. Hazard (I): Vibrio
• Comma-shaped, gram-negative bacillus (1-3µm(L)x 0.5-0.8µm(D))
• Infection: Fecal-oral transmission by food or water supply
• 2nd transmission: seasonal effect  dense population ↑
• Symptom/Disease: Diarrhea, dehydration, hypovolemic shock/death
• Incubation time: 4hrs-5 days (avg. 2-3 days)
• Mortality rate: <1% (treated), >50% (untreated)
• 0.5 cases/106 population (U.S., 2003-2008)
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3

4. Hazard (II): Shigella
• Rod-shaped, gram-negative bacteria
• Infection: person-to-person contact , contaminated food and water
• 2nd transmission: mass outdoor gathering (+) vs. handwashing (-)
• Symptom/Disease: Diarrhea, dysentery, acute colitis
• Incubation time: 1-4 days
• Mortality rate: <1% (developed country)
20-25% (East & Middle East)
• 3.8 cases/106 population (U.S., 2010)
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5. Hazard (III): Salmonella
• Rod-shaped, gram-negative enterobacteria (2-5µm(L)x0.7-1.5µm(D))
• Infection: Ingestion of bacteria in contaminated food or water
• 2nd transmission: direct contact (e.g., laundry personnel)
• Symptom/Disease: Diarrhea, fever, and abdominal cramps
• Incubation time: few hrs- 1 day
• Mortality rate: 400-600 deaths/year (U.S., 2007)
• 1.4 million infection/year (U.S., 2003-2008)
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6. Exposure Assessment
What do we know about this location?
The concentration of fecal
coliforms in this river is
1.5x107 (SD = 800)
At least one town discharges
raw wastewater to the river
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People living 5km downstream of the
point of sample collection in this river
Drink from it (no treatment)
◦
Bathe in it 2x/week (May – August)
◦
Use it to irrigate cucumbers & spinach
◦
6

7. Concentrations of Bacterial
Pathogens and Pathogen Indicators
CFC = 1.5e7 MPN/100ml (SD =
8.0e2)
1:58,100
1:35,200
1:418,000
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CSalmonella = 1.5e7 / 58,100 = 258
iMPN/100ml
(SD = 0.014)
CShigella = 1.5e7 / 418,000 = 36 iMPN/100ml
(SD = 0.002)
CVibrio = 1.5e7 / 35,200 = 426 iMPN/100ml
(SD = 0.023)
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8. Exposure Assessment
(Swimming and Drinking)
Pathways
Drinking
untreated water
Swimming
(accidental
water ingestion)
[1]
Exposed
Subgroup
Quantity Ingested
per event1
Calculation:
Dose per Event
Frequency
(events/year)
Everyone
2 liters
=
CFC/fFC:path·(2000ml)
350
Adults
80 ml
(20 ml/hr, 4 hrs)
=
CFC/fFC:path·(100ml)
32
Children
200 ml
(50 ml/hr, 4 hrs)
=
CFC/fFC:path·(200ml)
32
U.S. EPA. Highlights of the Exposure Factors Handbook (Final Report). U.S. Environmental Protection Agency, Washington, DC,
EPA/600/R-10/030, 2011.
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9. Exposure Assessment
(Consumers & Producers of Crops)
Pathways
Working in
the field
Exposed
Subgroup
Quantity Ingested
per event3
Calculation:
Dose per Event2
Frequency
(events/year)
Farmers
100 mg
soil
=
CFC/fFC:path·φ·(0.1/ρ)
50 – 125
=
Consumers
100 g
CFC/fFC:path·Vcuc·(10
50 – 150
cucumber
Consuming crops (cucumber)
0g)
irrigated with
=
river water
Consumers
100 g
CFC/fFC:path·Vspi·(10
75 – 225
(spinach)
spinach
[2]
Hamilton, A. J., et al. (2006). Quantitative Microbial Risk Assessment Models for Consumption of Raw Vegetables Irrigated with
0g)
Reclaimed Water. Applied & Environmental Microbiology, 72(5), 3284–3290. Vcuc ~ N(0.108,0.019)ml/g; Vspi ~ N(0.0036,0.0012)ml/g
[3]
Mara, D.D. (2008). Quantifying health risks in wastewater irrigation. UNESCO Encyclopedia of Life Support Systems. EOLSS
Publishers.
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10. Dose Response
Agent
Best fit
model
Salmonella
anatum
β-Poisson
Salmonella
meleagridis
β-Poisson
Salmonella
Typhi
β-Poisson
Shigella
flexneri
β-Poisson
Vibrio
cholerae
β-Poisson
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Optimized
parameters
α=3.18E-01,
N50=3.71E+0
4
α=3.89E-01 ,
N50=1.68E+0
4
α=1.75E-01,
N50=1.11E+0
6
α= 2.65E-01,
N50=1.48E+0
3
α= 2.50E-01,
N50=2.43E+0
2
LD50/ID50
Host
Route
Dose units
endpoint
3.71E+04
human
oral, with
eggnog
inferred
MPN/ml
positive stool
culture
1.68E+04
human
oral, with
eggnog
inferred
MPN/ml
infection
1.11E+06
human
oral
inferred
MPN/ml
disease
1.48E+03
human
oral(in milk)
inferred
MPN/ml
positive stool
isolation
2.43E+02
human
oral (with
NaHCO3)
inferred
MPN/ml
infection
10

11. Fate & Transport Model
Assumptions
Flow
Maximum Velocity
velocity:
m/s
1.66E+00
Minimum Velocity
m/s
5.50E-02
Reference on Velocity
Mamta Rani, 2013
5km
Travel Time (= Distance/Velocity):
Minimum Transportation Time
hr
8.37E-01
Maximum Transportation time
hr
2.53E+01
Decay Rate:
Pathogen
Distribution
Median
St. dev for log(UF)
Reference
Salmonella spp.
Shigella spp.
Vibrio cholerae
log-Normal
log-Normal
log-Normal
9.59E-03
4.40E-03
2.27E-03
1.40E+00
1.80E+00
1.80E+00
John, 2005
Henis, 1987
Ramaiah, 2004
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Concentration at DD =
Concentration at BB * EXP(-Decay
Rate*Transportation Time)
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12. Fate & Transport
<1 log reduction in
all scenarios during
transport 5km
downstream
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Pathogen
Salmonella
Shigella
Vibrio
Log Reduction
0.003 (high flow)
0.105 (low flow)
0.002 (high flow)
0.048 (low flow)
0.001 (high flow)
0.025 (low flow)
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13. Risk Characterization – Bathing
(Assume no decay)
Risk Per Event
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Annual Risk
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14. Risk Characterization – Eating
Cucumber
(Assume no decay)
Risk Per Event
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Annual Risk
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15. Risk Characterization – Farming
(Assume no decay)
Risk Per Event
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Annual Risk
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16. Summary of Risk Characterization
Annual Median Risk
Pathway
(given certain pathogen reductions)
Exposed Subgroup
No reduction
1-log
2-log
3-log
4-log
Drinking water
Everyone
>99%
>99%
>99%
>99%
99%
Swimming
(accidental water
ingestion)
Adults
>99%
>99%
~79%
~16%
~2%
Children
>99%
>99%
~97%
~34%
~4%
Working in the field
Farmers
~11%
~1%
<1%
<1%
<1%
~88%
~20%
~2%
<1%
<1%
>99%
>99%
~65%
~10%
~1%
Consuming crops Consumers (cucumber)
irrigated with water Consumers (spinach)
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17. Limitations
Only considers risk from three bacterial pathogens
Only ingestion considered
Based on EPA handbook for exposure, which may not be
relevant in this context
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18. The importance of good
assumptions
200 ml / swim
50 ml / swim
P(inf) =
78%
P(inf) =
50%
(median)
(median)
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19. Risk Characterization &
Management
1.
Based on the risks you are able to assess, do they appear to be “de minimus” or more substantial?
Substantial
2.
Which groups of people are most at risk and due to what activities?
Drinking water is the riskiest activity; children & raw produce consumers are at higher risk than farmers
3.
Rank exposure routes in decreasing order of their annual risks of infection and comment on risk
management approaches for minimizing these exposure risks?
Drinking water; recreational bathing; consumption of produce; farming
4.
How much reduction in fecal coliforms would you recommend to meet the USEPA allowable annual risks of
microbial infection guideline for recreational water contact?
A 6-7 log reduction (and more data collection) is recommended to presumably control risk to 1:10,000
level
5.
What are important uncertainties in your analysis? What could be done to reduce them? 19
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20. Risk Management
International recommendations: Annual risk of infection < 10-4
- 6-7 log reduction in pathogen concentration is required
Strategies and challenges for risk reduction:
- Waste control at Village BB
- Build water treatment Infrastructure upstream of Village DD
- Local population: boil drinking water
- Spinach and cucumber consumers:
W
a Water Treatment Infrastructure
t
e
r
Wash spinach and cucumbers before consumption
- For farmers: wear protective mask while irrigating
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21. Risk Management
Cost-effective analysis:
- Cost and effect of achieving different level of risk reduction
through different strategies
Social-community factors on decision making:
- Risk communication
- Policy
- Funding resources
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22. Thank You
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