Microbial Risk from the Philadelphia Water Supply

Anne WolffQiuyan Yuan

Yu-Min SuJian Yang

Outline

• Introduction•Hazard ID• Exposure assessment•Dose response•Risk assessment•Risk management

Problem

•Cryptosporidium presents in surface water, it cause Cryptosporideosis. •What is the risk of Cryptosporideosis

caused by drinking water in Philadelphia?

Objective• Develop a QMRA model to estimate risk of Crypto

from the Philadelphia public water supply.• Use this model to assess what level of removal of

crypto would correspond to the observed risk• Provide some insight into the plausibility of the

claim advanced by these studies that US drinking water is associated with measureable risk of gastrointestinal illness.

Cryptosporidium• First described by Ernest Tyzzer in 1907• Protozoan parasite infecting the

intestinal tract of vertebrates• Currently 26 known species infecting

humans, other mammals, birds, reptiles, fish

• C. parvum and C. hominis are the primary species that infect humans

Carey, C.M., et al, 2003 severntrentservices.com

Cryptosporidiosis

• Gastrointestinal disease caused by Cryptosporidium

• Most common symptom is watery diarrhea but other clinical symptom may include: stomach cramps, nausea, vomiting, fever, dehydration

• Clinical symptoms appear 2 to 10 days after infection and last 1 to 2 weeks.

• Immune compromised, children and the elderly are most vulnerable to infection

• Infection is by fecal-oral route

Cryptosporidium in Drinking Water Supplies

• Cryptosporidium has become a significant pathogen in drinking water outbreaks since the 1980’s• Oocysts are resistant to being killed by the

standard chlorine disinfection • Cryptosporidium pathogens enters water

through the infected feces of animals and humans

Lifecycle and Infection Route

Cryptospiridiosis Statistics from Philadelphia Department of Public Health

Turbidity

• Turbidity is a measure of water clarity • Suspended particles include soil, algae, plankton,

microbes ranging in size from 0.004 -1.0 mm• Microbes in drinking water supply may escape

disinfection by attaching or being hidden by particles• Relationship to Cryptosporidium

Turbidity is used as an indicator for the presence of Cryptosporidium

log10 removal Cryptosporidium oocysts = 0.996 log10 removal turbidity + 0.494 (R2 = 0.71)

• Source: LeChevallier and Norton, 1991.

Framework

Hazard ID

CoagulationGravity Settling

Filtration

Nanofiltration

Daily ingestion

Recovery of method

Children

Adults

Fraction reach to GI

CryptoConcentration

Different treatment

Different population

Risk assessment

Treatment

Adults Children

Exposure assessment

Dose response

K for adult K for children

Parameters• Concentration of Crypto in surface water:

• Recovery efficiency by detection method: 32.3%

Treatment Plant Location

LARGER DATABASEMaximum

cysts per 100 L90th percentile

per 100 LAverage

cysts per 100 L

CRYPTOSPORIDIUMBaxter 100 70 32Queen Lane 1200 200 96Belmont 250 50 43

Parameter

•Water consumption: • Adult ingestion: 2 L/day• Children ingestion: 1 L/day

• The fraction of Crypto that will reach the receptor, assumption: 10%

Parameters• Drinking water treatment method

• log10 removal Cryptosporidium oocysts = 0.996 log10 removal turbidity + 0.494 (R2 = 0.71)

Turbidity log Removal

Crypto log Removal

Crypto removal rate(%)

Coagulation Gravity Settling

Filtration1.6 - 4.0 0.96 -1.87 89.09 - 98.67

Nanofiltration 2.36-2.69 1.35-1.48 95.53 - 96.71

Dose response model

• P(d)=1-exp(-k*dose) Exponential Model

k

Adult 0.0572

Children 0.1 (Assumption)

Crypto in the surface water

Risk assessment

• Risk goal (EPA 1 in 10,000 annual infection risk)• Assumptions (conservative)• Risk assessed at the first downstream

customer• Every crypto measured/reported in raw water

is infectious

Risk assessment

Scenario 1- present

treatmentAdults Children

Scenario 2- present

treatmentAdults Children

5% 2.73E-05 2.56E-05 5% 1.14E-04 1.15E-0450% 4.25E-03 3.09E-03 50% 3.39E-02 2.60E-0295% 2.08E-02 2.56E-02 95% 1.57E-01 1.21E-01Scenario 1-

Nano-filtration

Adults ChildrenScenario 2-

Nano-filtration

Adults Children

5% 2.26E-05 2.21E-05 5% 9.78E-05 1.05E-0450% 2.76E-03 1.96E-03 50% 2.32E-02 1.72E-0295% 1.37E-02 8.06E-03 95% 1.16E-01 8.27E-02

• Scenario 1: Annual average condition• Scenario 2: Spike in turbidity

Risks from literature

The annual risk of contracting Cryptosporidiosis in the United States may range from:• 4 in 1,000 to 1 in 100,000. (Haas, 1994)• 1 in 1,000 to 1 in 100,000 (Haas, 1994; Perz et

al., 1998).• 1 in 10,000 annual risk of infection is 0.003/100L

(95% confidence interval 0.0018 -0.0064/100L) (Haas, 1994).

Federal Regulation• Crypto is regulated by the federal government as

a primary drinking water contaminant.• Community size based (10,000)• 12 month sampling every 5 years to determine

the removal treatment process.

Risk Management• Treatment (Removal & Inactivation)

• Other mitigations (BWA, research, etc.)• Early warnings (Turbidity, E coli, particle count, etc.)• Multi-barrier, event management, customer education, research;

Conventional Treat

Lime Softening Credit CFE Credit IFE Credit

Bin 3 Treatment

Log Removal 3 3.5 4 4.5 5

C 0.96 0.00096 0.000303579 0.000096 3.03579E-05 0.0000096Inf 0.028 0.028 0.028 0.028 0.028 0.028Consu 1.2 1.2 1.2 1.2 1.2 1.2

DR 0.032256 0.000032256 1.02002E-05 3.2256E-06 1.02002E-06 3.2256E-07

Ann Risk 1.00E+00 1.12E-02 3.56E-03 1.13E-03 3.57E-04 1.13E-04 TEXAS COMMISSION ON ENVIRONMENTAL QUALITY PTR SECTION STAFF GUIDANCE

Vulnerable populations: immunocompromised, children, elderly;For extra stringency suggest installing home water filters with one of the following on label:Reverse osmosis (with or without NSF 53 or NSF 58 labeling)Absolute pore size of 1 micron or smaller (with or without NSF 53 or NSF 58 labeling)Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst removalTested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst reduction

Risk Communication and Management for the Public

Risk Management

• Turbidity removal followed by:• UV• Chlorination• Ozone

References• Carey, C.M., H. Lee, & J.T. Trevors.(2004). Biology, persistence and detection of Cryptosporidium parvum and Cryptosporidium hominis

oocyst. Water Research, 38, 818–862.• Centers for Disease Control. “Parasites: Cryptosporidium”. Retrieved from http://www.cdc.gov/parasites/crypto/index.html• City of Philadelphia Department of Public Health. (2013). Division of Disease Control Annual Report• Efficiency of the activated carbon filtration in the natural organic matter removal• EPA Guidance Manual- Turbidity Provisions. 1999.• EPA, Exposure Factors Handbook Chapter 3—Ingestion of Water and Other Select Liquids. 2011.• EPA, Cryptosporidium: Drinking Water Health Advisory, 2001• Haas, C.N., Crockett, C.S., Rose, J.B., Gerba, C.P., and Fazil, A.M. 1996. Assessing the risk posed by oocysts in drinking water. J. AWWA,

88:9:131-136.• Haas, C.N., Hornberger, J., Ammangandla, U., Heath, M., and Jacangelo, J.G. 1994. A volumetric method for assessing Giardia inactivation.

J. AWWA, 86:2:115-120.• J. Hatt, E. Germain, S. Judd, 2013, Granular activated carbon for removal of organic matter and turbidity from secondary wastewater,

Water Science & Technology, 67(4), 846-853.• M. Jenkins, S. Tiwari, J. Darby, 2011, Bacterial, viral and turbidity removal by intermittent slow sand filtration for household use in

developing countries: Experimental investigation and modeling, Water Science, 45, 6227-6239.• M. LeChevallier, W. Norton, 1992. Examining Relationships Between Particle Counts and Giardia, Cryptosporidium, and Turbidity. J. AWWA.• M. Lechevallier, W. Norton, R. Lee, 1991, Giardia and Cryptosporidium spp. in filtered drinking water supplies, Applied and Environmental

Microbiology, 57 (9), 2617-2621.• M. Sato, A. Galvani, J. Padula, A. Nardocci, M. Lauretto, M. Razzolini, E. Hachich, 2013, Assessing the infection risk of Giardia and

Cryptosporidium in public drinking water delivered by surface water system in Sao Paulo State, Brazil, Science of the Total Environment, 442, 389-396.

• Perz, J.F., Ennever, F.K., and LeBlancq, S.M. 1998. Cryptosporidium in tap water: comparison of predicted risks with observed levels of disease. Am. J. Epidemiol., 147:3:289-301.

• R. Aboytes, G. Di Giovanni, F. Abrams, C. Rheinecker, W. McElory, N. Shaw, M. Lechevallier, 2004, Detection of infectious cryptosporidium in filtered drinking water, J. AWWA.

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