Microbial Risk Assessment Tool fo Land Application of Biosolids

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1 Microbial Risk Assessment Tool fo Land Application of Biosolids Charles P. Gerba Department of Soil, Water, and Environmental Science And Epidemiology and Biostatistics University of Arizona

2 Biosolids Risk Assessment Team Patrick Gurian (Principal Investigator), Elizabeth Casman, Chuc Gerba, Mike McFarland, Mira Olson, Ian Pepper, Irene Xagorara Colleen Harte, Arun Kumar, Brett Olson

3 Project Objectives! Develop a spread sheet based tool to predic microbial risks of infection! Identity data gaps! Conduct field work to fill data gaps! Evaluate tool with users and test on field dat! Develop a communication program on microbial risks for mangers and the general public

4 Project Approach! Considers several routes of exposure! Can use site specific information or default values! Uses data on concentration of indicators and pathogens collected since 1993 (1000 data sets for biosolids review on indicators and pathogens)! Includes data on concentration of emerging pathogens (e( E. coli 0157:H7)! Collect field data indicator and pathogen fate in cold/high rainfall climate with a shallow water table! Include failure modes in model (child plays in field, water runs off site, less than optimal treatment process proce failure, etc)! Validate model with field studies

5 Risk Assessment is the process of estimating the probability that an event will occur and the magnitude of the adverse effect

6 Application of Microbial Risk Assessment! Set Standards (treatment of drinking water)! Identify critical control points (food industry)! Determine the cost/benefits of different treatment options (vaccines)! Assessing technologies for control of pathogens or various treatment options (treatment options for wastewater reuse)! Compare relative risks between manure and biosol

7 Quantitative Microbial Risk Assessment is an approach that allows the expression risks in a quantitative fashion in terms o infection, illness, or mortality from microbial pathogens

8 What is Risk Assessment?! Risk Assessment has four basic steps:! Hazard Identification - identifying the contaminate (i.e. Salmonella)! Dose-Response Assessment - relationship between the number of organisms ingeste and the probability of becoming infected (i. how many does it take to make you sick)

9 What is Risk Assessment?! Risk Assessment has four basic steps:! Exposure Assessment - Determining the concentration of a pathogen in the biosolid and estimating amount of contact.! Risk Characterization - Estimating the potential impact (infection, disease) of a pathogen based on the severity of its effec

10 Risk Endpoints! Chemical! No observable effect level! mortality! Microbial! Infection! Illness! Mortality

11 Quantitative Microbial Risk Assessmen Identify pathogen of concern Dose-response data from humans Model infection probability Validate model from outbreak data Predict probability of disease from exposure Clinical data estimate proba of disease a mortality

12 Quantitative Microbial Risk Assessmen Concentration of the pathogen in the biosolids Select route of exposure Reduction of pathogen af transport Probability of infection Amount of path ingested o inhaled

13 What is an Acceptable Risk from a Pathogen? Risk is defined as a probability of infection or disease i.e. what are the odds. FOR EXAMPLE The risk of infection from a pathogen in drinking water should not be greater than 1:10,000 per year (Surface Treatment Rule, USEPA) (Law in The Netherlands)

14 Salmonella spp.! More than 2400 serotypes! Second most common cause of foodborn illness in U. S. and Europe! Beef and chicken most common source! Can grow in foods cantaloupe/tomatoes! Can grow in compost

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16 Ascaris

17 Pathogens before and after the 503 Regulations Organism Since 503 Before 503 Number/g dry biosolids Type of treatment (g dry wt) Anaerobic Aerobic Enteroviruses Salmonella Total coliforms 3.5! Fecal coliforms 3.8! Shigella sp ND Fecal streptococci 2.8! 10 4 Not done Not done Ascaris None detected (viable)

18 Pathways of Exposure 1. Inhalation of aerosols from land application sites 5. Consumption of water contaminated by runoff from a land application site Biosolids Land Application 2. Consumption of groundwater contaminated by biosolids 4. Ingestion of plants grown on biosolidsamended fields 3. Direct ingestion of biosolids

19 Steps in Estimating Exposure from Pathogens in Biosolids Pathogen concentration in biosolids A person comes into contac with the biosolids Number of Pathogens after treatment Duration of exposure Amount of hand conta Concentration after land application Amount swallowed

20 Surface Runoff Model: The Joint Green-Ampt Model! Physically-based equation describing the infiltration of water into a soil.! Joint Green-Ampt model developed by combining two existing models (Explicit Green-Ampt and Constant Flux Green Ampt) into a fully explicit model When r<ks, q = r, I = rt When r>ks and t<to q = r, I = rt Constant Flux Green- Ampt When r>ks and t>to, (soil becomes saturated) 2 " 1/ /2 1" 2 S ( ) q = K! + "! +! ! I = Ks " t + t + t + " t + " + t + + t + t " With 2 2 {(1 )! ( 1)![ln(!) ln!]![ln(! ) ln(! / 2)]} " = ( h # h )(! #! ) s f s K S 0 t! = " Kshf! s "! t 0 t + 0 = " r( r " Ks ) ( ) Expl Gree Amp

21 Surface Runoff Spreadsheet Tool ser Interface Select soil type Input Storm event data - rainfall intensity - duration - other field information Results table - Infiltration rate - Cumulative infiltration - Surface runoff Comparison table for different time periods

22 Conceptual Model for Water Pathways Rainfall Biosolids Runoff Infiltration Unsaturated Zone Groundwater table Groundwater flow Saturated Zone! Transport induced by wet-weather events is not included in existing models

23 Groundwater Pathway Rainfall Unsaturated Removal Saturated Transport (1D vertical) Groundwater Transport (1D Horizontal) z R "C "t x R "C "t "[# m C] + $ "C* "t "t %k * $C * % k 0 # m C 0 = #v "C "x + D" 2 C "x 2 # kc = #q "C "z + D" 2 C "z 2 # kc + " [ # C 0 ] m " 2 C = D z # m "t [ ] "z % " qc 2 "z Advec Disper Equati % k# m C Advection- Dispersion Equation V

24 Groundwater Spreadsheet Tool Input water table depth (h), downstream distance (L), rainfall intensity (r), and duration (t) If r"0 and t"0 If r=0 or t=0 h z Rainfall event Non-rainfall period Compare water table (h) to wetting front (z) Pathogen attenuation in unsaturated soil h! z h > z Pathogen transport in saturated soil Pathogen transport in saturated soil Pathogen attenuation in unsaturated soil Pathogen transport in saturated soil

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26 Air Modeling PFU per cubic meter Concentration Time (minutes) (. Q C x, y, z) = - 27U (, av6 & $ ' 0.5y exp $ 2 % 6 y 2 # 4 &! ' 0.5 2exp$! " 23 % 6 z 2 ( z ' h) # & ' 0.5( z + h)! $ + exp " % ( 2 2 y6 z 6 z 2 # 1( + & ' 5x #!/* $! exp "/ 0() % U av "

27 Field Validation of Particulate Dispersion Model

28 Summary! Overall enteric virus and Salmonella levels hav deceased since the 503 regulations went into effect in Class B biosolids! No viable Ascaris have been detected in Class biosolids (4 g)! Models have been developed for major routes exposure! Models are currently being validated! Final tool kit to be available next summer