1. Training on Quantitative Health Risk Assessment (QHRA) QHRA : The Context, Concept and Development M. Feroze Ahmed Professor of Civil/Environmental Engineering BUET

2. Definition In water supply context, Quantitative Health Risk Assessment is a technique for estimating predictive disease burden based on water quality as input data. QHRA is O a predictive technique O a modeling technique O a tool to estimate what disease burden might be from the specified water quality and exposure. QHRA is not O an descriptive technique O an empirical technique

3. Applications O A tool to make ‘best estimate’ of disease burden using current available knowledge. OTo understand the relative health risk of different water supply options having health-related water quality of different nature ( diverse hazard). OEstimation of disease burden for estimating heath-based targets in drinking-water safety framework recommended in WHO Guidelines. OAn input in decision-making process in water supply.

4. Risk Assessment of Arsenic Mitigation Options (RAAMO) - An example of use of QHRA O Deep Tubewell O Dug/Ring Well O Rain Water Harvesting O Surface Water Treatment (PSF) O Treatment of Arsenic Contaminated Water O Piped water Supply

5. 1. Problem formulation 2. Hazard identification 3. Exposure Assessment 4. Dose-response Relationship 5. Risk Characterization QHRA PROCESS

6. 1.Problem formulation Which arsenic mitigation option presents the lowest disease burden in a particular setting ? Which arsenic mitigation option presents the lowest disease burden in a particular setting ? Hazard identificationHazard identification What water quality parameters pose maximum health hazard ? 3. Exposure Assessment What is the level of exposure ? In case of water, the concentration in the water multiplied by the quantity of water consumed

7. 4. Dose-Response Relationship What is health effect of exposure to certain dose ? What is health effect of exposure to certain dose ? - Toxicological data - Toxicological data - Human feeding trial - Human feeding trial - Epidemiological data - Epidemiological data - Animal feeding trial - Animal feeding trial 5. Risk Characterization How does QHRA output address the problem statement ? Is the risk acceptable ? How does it compare with the acceptable risk/standard/guidelines ?

8. MODEL INPUT (Water Quality Parameters) O Microbial quality O Iron O ArsenicO Odor O NitrateO Turbidity O Chromium O Color O Boron ( Coastal Area ]O CONDUCTIVITY O ManganeseO Phosphate O LeadOSilica O Lead O Silica O ZincO Ammonia

9. Thermotolerant coliforms (faecal coliforms) Thermotolerant coliforms (faecal coliforms) Indicator E. coli Pathogenic E. coli Pathogenic Total Plate Count Total Coliforms MICROORGANISMS IN THE ENVIRONMENT

10. MODEL INPUT (Water Quality Parameters) Microbial Water Quality Reference Pathogens O Resistant to any treatment processes in place and to any environmental stresses in the exposure medium; O Abundant in the region or area of interest and in the exposure medium; O Infectious to the population of interest; and O Virulent in terms of the extent to which the hazard leads to severe disease endpoints. A reference “worst pathogen” is selected for each of the major classes of pathogens: viruses, bacteria and protozoa

11. Gastrointestinal Route Bacteria Campylobacter spp. E.Coli * Salmonella spp. Shigella spp. Vibrio cholerae Yersinia spp. Protozoa & Helminths Cryptospordium parvum* Dracunculus medinensis Entamoeba histolytica Giardia intestinalis Taxoplasma gondii Ingestion (Drinking) Viruses Adenoviruses Astroviruses Enteroviruses Hepatitis A viruses Hepatitis E viruses Noroviruses Rotaviruses* Sapovirus * Reference pathogens for the model

12. Protozoa(Cryptosporidium) Virus(Rotavirus) Thermotolerant Coliform (TTC) E. Coli Reference Pathogens Bacteria (E. Coli O157) TTC : E. Coli = to be determined TTC : Virus = 100 000 : 1 TTC : Bacteria = 100 000 : 1 TTC : Protozoa = 1 000 000 : 1

13. Measured TTC Measured [ E.Coli ] Locally Measured [ TTC ] Locally Dose of Pathogen Predicted E. coli Ratio [Pathogen] : [ E.coli ] Volume of water consumed E.Coli in sewage Pathogen in Sewage Predicted Pathogen Infection with Rota, Crypto, Shigella Measured Arsenic Ratio [TTC] : [ E.colI ] Disease Burden [DALY] Microbial Dose- Response Dose of Arsenic Cancer of skin, lung & bladder Arsenic Dose- Response LEGEND Model Process Steps Input & Output STRUCTURE OF THE MODEL

14. DALY, a common metric used to express Disease burden (2004 WHO GDWQ) DALYS (Disability Adjusted Life Year), takes account of duration, severity and case fatality of diseases. DALY = YLL+ YLD YLL YLL = year lost due to premature death = D x S (1) YLD YLD = year lost due to disability = D x S Where D = Duration & S = Severity (fraction), S = 1 for Death Arsenic → End points : skin, lung and bladder Cancers Pathogens → Viral, bacterial and protozoal diseases Disease Burden 1 DALY = Loss of 1 Yr. of Life Being ill is like partly dead (alive)

15. DISEASE BURDEN ( DALYS) S = Severity = 0.1 (1/10th dead) D = Duration = 7 days (0.02 yr) DALYs = S x D = 0.002 Life expectancy = 62 years Age at death = 2 year S = Severity = 1 D = Duration = 60 years DALYs = S x D = 60 S = Severity = 0.5 (half alive) D = Duration = 7 days (0.02 yr) DALYs = S x D = 0.01 Infection Full Infection (Naïve host) Superficial Infection (Immune host) No Symptom Recovery Mild Dirrhoea D = 7 days S = 0.1 Recovery Severe Dirrhoea D = 7 days S = 0.5 Death D = Longevity-YL S = 1 20% 80% 95% 90% 98% 10% 5% 2% From Model

16. QUANTITATIVE HEALTH RISK ASSESSMENT MODEL MODEL INPUT O Indicator microbe ( TTC or E. Coli ), number/100 mL O Arsenic concentration, µg/L A single value, 95%ile value, minimum detection limit, maximum & minimum values can be given as input. Additional Optional Input O Daily water consumption, L/day O Average Life expectancy as birth Inbuilt Information Water consumption, Life expectancy, distribution of age group, sex ratio, case fatality rate, TTC -E. coli ratio, dose response relationship.

17. QUANTITATIVE HEALTH RISK ASSESSMENT MODEL MODEL OUTPUT O Total DALYs O Total microbial DALYs O Total arsenic DALYS O Viral DALYS O Bacterial DALYS O Protozoan DALYS O Skin cancer DALYs O Lung cancer DALYS O Bladder cancer DALYs

18. Limitations 1. Ratios of Thermotolerant coliform/E.coli to other pathogens found in a sewage in a country may not be valid for all countries. 2. The dose response relationship for pathogens may not be universally valid because of different levels of immunity. 3. Available dose-response relationship between arsenic and skin, lung, and bladder cancers have been taken into account but there are many uncertainties in health effects of arsenic. 4. The QHR model combining two most important water quality parameters and multiple diseases outcomes is the first of its kind and needs further refinement based on local conditions, further available information and international review.