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Estimation of infectious risks in residential populations near a center pivot spraying dairy wastewater

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Estimation of infectious risks in residential populations near a center pivot spraying dairy wastewater

  1. 1. Estimation of Infectious Risks in Residential Populations Near a Center Pivot Spraying Dairy Wastewater Robert S. Dungan, Ph.D. USDA-ARS, Northwest Irrigation and Soils Research Laboratory, Kimberly, Idaho 83341 Voice: 208.423.6553; E-mail: robert.dungan@ars.usda.gov
  2. 2. Dairy Production in Idaho 0 100,000 200,000 300,000 400,000 500,000 600,000 700,000 1975 1985 1995 2005 2015 Number of Milk Cows Magic Valley 70% of cows
  3. 3. Large Quantities of Manure and Wastewater Produced  ~58 kg manure/cow/day  23x106 kg manure/year in southern Idaho  Volume of wastewater?
  4. 4. Land Application of Wastewater  Wastewater is a combination of manure liquids, flush waters, and lot runoff  Source of irrigation water and crop nutrients  Quasi disposal technique
  5. 5. Risk of Exposure to Pathogens  Wastewaters are not treated prior to land application  Variety of zoonotic pathogens present in cattle manures: ◦ Salmonella spp. ◦ E. coli O157:H7 ◦ Campylobacter jejuni ◦ Listeria monocytogenes ◦ Mycobacterium spp. ◦ Leptospira spp. ◦ Yersinia enterocolitica ◦ Cryptosporidium and Giardia spp.
  6. 6. Push to Ban Manure Spraying
  7. 7. Conceptual Model of Human Infection from Land Application of Wastewater Aerosolization/ Evaporation Dispersion Inhalation Risk of infection Dry/wet deposition Produce and fomites Ingestion Small droplets (< 150 um) Large droplets (> 150 um) Deposition
  8. 8. Quantitative Microbial Risk Assessment (QMRA) Approach (Pathogen/Microbial Agent) (Pathogen Dose Inhaled and/or Ingested) (Risk of Infection Based on Dose) (Integration of Information; Estimate Probability of Harm) (Reduce or Eliminate Risks)
  9. 9. Hazard Identification  Campylobacter jejuni, Escherichia coli O157:H7 and non-O157, Listeria monocytogenes, and Salmonella spp.  Based on qPCR, pathogen concentrations in 30 dairy wastewaters were found to range from 103 to 106 cells/100 mL
  10. 10. Exposure Assessment Model  d = ec x br x t x ag  d = number pathogens/dose  ec = airborne pathogen conc. (cells/m3 of air); determined with dispersion model  br = breathing rate (m3/h); set to 0.61 m3/h  t = hours of exposure; 1, 8, or 24 h or multiday (1 h/d for 7 d)  ag = aerosol ingestion rate; set to 0.1
  11. 11. Dose-Response Model  b-Poisson model  Pi = 1- (1 + d/b)-a • where Pi is the probability of infection based on a one-time pathogen exposure • d is the pathogen dose • a and b are dose-response factor from the literature  Probability of infection over a multiday event determined using Pann = 1- (1- Pi)n • where n is the number of days per year
  12. 12. Dispersion Model Setup  AERMOD (Steady-state dispersion model for up to 50 km)  Area source was 396 m x 15 m to mimic droplet pattern from a center pivot with 94 flat plate sprinklers (34 L/min)  Receptors placed at 1, 2, 3, 4, 5, 7, and 10 km from the pivot, with 10 degrees of separation (total of 252 receptors)  Used 5 years of meteorological data (2000 to 2004); April to October only
  13. 13. Receptor Setup in AERMOD
  14. 14. Pathogen Emissions Rates for use in AERMOD Scenario Flow rate (l/min) Pathoge n conc. (cells/100 mL) Waste- water (%) Sprinkler impact factor Aerosol- ization efficiency (%) Pathogen emission rate (cell/s) A (low) 3217 103 5 0† 0.1 2.7 x 101 B (Medium) 3217 104 10 0 1.5 8.0 x 103 C (High) 3217 105 10 0 1.5 8.0 x 104 D (Very high) 3217 106 20 0 3.0 3.2 x 106 † Sprinkler impact on microorganism viability was determined to be minimal, thus the Impact Factor (I) was set to zero
  15. 15. Sensitivity Analysis (Effect of Averaging Period and Emission Rate) Downwind (km) 2 4 6 8 10 Pathogen(cellsm-3ofair) 0 2 4 6 8 10 12 1-h 3-h 24-h 2 4 6 8 10 0 50 100 150 200 2.7x101 cells s-1 8.0x103 cells s-1 8.0x104 cells s-1 3.2x106 cells s-1
  16. 16. Additional QMRA Assumptions  All bioaerosols were < 100 mm in aerodynamic diameter  Aerosol density was 1.1 g/cm3  Only dry deposition was considered  Deposition behavior among pathogens was similar  Inactivation of airborne pathogens occurred  Aerosol age (ad) based on average wind speed of 4.4 m/s
  17. 17. Microorganism Die-Off Factor  Md = e-lad • where l is the viability decay rate (/s) • ad is the aerosol age (s)  Aerosol age ranged from 3.8 to 38 min  To account for daytime or nighttime conditions, respective decay rates of 0.07/s or 0.002/s were used  The airborne pathogen concentration was then corrected for die-off
  18. 18. Risk of Infection After a 1-h Exposure Event at 1 km Downwind (Daytime)LogRiskofInfection -16 -14 -12 -10 -8 -6 -4 -2 0 -16 -14 -12 -10 -8 -6 -4 -2 0 Scenario A (Low) Scenario B (Medium) Scenario C (High) Scenario D (Very High) C. jejuni E. coli O157:H7 Non-O157 Listeria Salmonella C. jejuni E. coli O157:H7 Non-O157 Listeria Salmonella
  19. 19. Risk of Infection After a 1-h Exposure Event (Nighttime) -14 -12 -10 -8 -6 -4 -2 0 Scenario A (Low) 1 5 10 km 1 5 10 km 1 5 10 km 1 5 10 km 1 5 10 km C. jejuni E. coli O157:H7 Non-O157 Listeria Salmonella LogRiskofInfection -14 -12 -10 -8 -6 -4 -2 0 Scenario C (High) Scenario B (Medium) C. jejuni E. coli O157:H7 Non-O157 Listeria Salmonella 1 5 10 km 1 5 10 km 1 5 10 km 1 5 10 km 1 5 10 km Scenario D (Very High)
  20. 20. Campylobacter jejuni (1 km, Daytime) -14 -12 -10 -8 -6 -4 -2 0 Scenario A Scenario B Scenario C Scenario D 1h 8h 24h LogRiskof Infection
  21. 21. Campylobacter jejuni (1 km, Nighttime) -14 -12 -10 -8 -6 -4 -2 0 Scenario A Scenario B Scenario C Scenario D 1h 8h 24h LogRiskof Infection
  22. 22. E. coli non-O157 (1 km, Daytime) -16 -14 -12 -10 -8 -6 -4 -2 0 Scenario A Scenario B Scenario C Scenario D 1h 8h 24h LogRiskof Infection * Risk of infection near zero *
  23. 23. E. coli non-O157 (1 km, Nighttime) -16 -14 -12 -10 -8 -6 -4 -2 0 Scenario A Scenario B Scenario C Scenario D 1h 8h 24h LogRiskof Infection
  24. 24. Salmonella (1 km, Daytime) -16 -14 -12 -10 -8 -6 -4 -2 0 Scenario A Scenario B Scenario C Scenario D 1h 8h 24h * * * Risk of infection near zero LogRiskof Infection
  25. 25. Salmonella (1 km, Nighttime) -16 -14 -12 -10 -8 -6 -4 -2 0 Scenario A Scenario B Scenario C Scenario D 1h 8h 24h LogRiskof Infection
  26. 26. Conclusions and Recommendations  Risk assessment is not an exact science  This QMRA provides a useful starting point to understand and manage infectious risks associated with the spray irrigation of dairy wastewaters  Residential populations ≥ 1 km downwind should have a very low risk of infection during daytime applications  Infectious risks will likely be higher during nighttime applications (infection  disease)  Wastewater should be applied during daylight hours when dilution and microbial die-off are highest  Apply the lowest possible percentage of wastewater to decrease the number of aerosolized pathogens
  27. 27. Thank You

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