69th SWCS International Annual Conference “Making Waves in Conservation: Our Life on Land and Its Impact on Water” July 27-30, 2014 Lombard, IL

1. Conservation practices and produce food safety
in California
Rob Atwill, D.V.M., Ph.D.
University of California-Davis

2. Reported annual foodborne illness in USA, CDC, 2013
9.4 million illnesses, 55,961 hospitalizations, 1351 deaths
Bacterial Chemical Parasitic Viral
Fish & shellfish 4% 62% 33% 4%
Dairy, egg, meat 64% 13% 0.1% 30%
Produce 27% 19% 30% 60%
TOTAL 3.6 250 230 5.5
million thousand thousand million

3. Reported annual foodborne illness in USA, CDC, 2013
9.4 million illnesses, 55,961 hospitalizations, 1351 deaths
Bacterial Chemical Parasitic Viral
Fish & shellfish 4% 62% 33% 4%
Dairy, egg, meat 64% 13% 0.1% 30%
Produce 27% 19% 30% 60%
TOTAL 3.6 250 230 5.5
million thousand thousand million
leafy greens tomatoes cantaloupe
Foods eaten
raw at risk

4. Fall 2006 spinach outbreak of E. coli O157:H7
Product originated from a field in San Benito County, CA
Outbreak in
late Aug to early September

5. Are these produce outbreaks the result of irrigation
water, winter runoff, livestock grazing and/or wildlife?
What is the source and process of connectivity?

6. Microbiological safety of irrigation water

7. E. coli concentrations in California irrigation water
(industry data, 2/2007 to 11/2010, n=44,000)
77%
11% 8%
2%
1% 0.8%
0.1%
0.5% 0.4%
0%
20%
40%
60%
80%
100%
1
10
100
1,000
10,000
100,000
Proportion
Frequency
E. coli concentration (MPN/100mL)
0 1-5 6-25 26-50 51-100 101-200 201-235 236-567 >567

8. Microbiological safety of irrigation reservoirs
and tailwater ponds (sediment basins)

9. E. coli concentrations (MPN/100mL)
Seasons Well Reservoir Difference % Increase
Winter 1.0 18.5 17.5 >1800
Spring 9.8 21.5 11.7 >200
Summer 19.4 77.6 58.2 400
Fall 20.8 65.4 44.6 >300
Overall 13.9 50.6 36.7 >300
Changes in water quality: well to surface storage
central coastal California, 2/2007 – 11/2010
Data reproduced from Atwill, 2011
9

10. Fencing to exclude fecal deposition by terrestrial wildlife
Chemical treatments
Dewater in fall, dry out the sediments
Removal
Other ideas

11. Key processes driving waterborne pathogen transmission
A. Vertebrate pathogen loading: domestic and wild populations
B. Hydrological transport: linking fecal sources with water
C. Inactivation kinetics: survival during transport

12. CA data: rangeland buffers can retain >95%
of key pathogens in winter and spring;
>99.9% achievable under certain conditions

13. Herd pos n prev (%)
A 0 489 0.0
B 7 480 1.5
C 0 200 0.0
D 44 434 10.1
E 0 61 0.0
F 6 386 1.6
G 2 271 0.7
H 9 256 3.5
Total 68 2715 2.5
Cow-calf herds, central coastal CA, 2008-2010
E. coli O157 infection ranged from 0% to 10%

14. Key focus: pathogen sources and modes of transport
Irrigation water, proximity to livestock, rangeland runoff,
wildlife intrusion, soil amendments
Runoff in winter, outbreaks in late summer/fall?
Longitudinal survey, 4/2008 to 11/2011
Soil samples 0.4% (10/2450)
Produce samples 0.0% ( 0/2462)
Water samples 0.4% ( 1/242)
Livestock 2.5% (68/2715)

15. Key focus: pathogen sources and modes of transport
Irrigation water, proximity to livestock, rangeland runoff,
wildlife intrusion, soil amendments
Runoff in winter, outbreaks in late summer/fall?
Longitudinal survey, 4/2008 to 11/2011
Soil samples 0.4% (10/2450)
Produce samples 0.0% ( 0/2462)
Water samples 0.4% ( 1/242)
Livestock 2.5% (68/2715)

16. E. coli O157:H7, 2008-10
Feral pig 10/200 (5%)
Coyote 2/95 (2%)
Am. crow 5/93 (5%)
Cowbird 2/60 (3%)
Rabbit 0/108 (0%)
Skunk 0/63 (0%)
Blackbird 0/112 (0%)
Raccoon 0/28 (0%)
Beef cattle 68/2715 (2.5%)
Clarify sources of Ec O157
and we can better design:
• fencing style
• modify specific habitat
• target specific wildlife
E. coli O157:H7 in wildlife
and cattle

17. Rodent species Cryptosporidium Giardia
CA parasitic mouse 11% 13%
Deer mouse 33% 27%
Dusky-footed wood rat 17% 17%
TOTAL 28% 25%
Prevalence of pathogens in wild rodents in
produce production fields, central California
Preliminary data: Crypto appears human infectious, Giardia mostly not
E. coli O157:H7 2/1,043 (0.2%)
Salmonella 30/1,043 (2.9%)

18. When wildlife congregate
then food safety risks are magnified

19. Randomized field trials of romaine lettuce
Salinas Valley, 2011 & 2012

20. scat
BED BED
FURROW

21. 20 to 30% of nearby heads of lettuce
contaminated with E. coli O157:H7
Add in 2 hours of irrigation

22. 0
1
100
10,000
1,000,000
10 15 20 25
Distance between lettuce and scat (inches)
E.coliO157:H7/headlettuce E. coli O157:H7 per head of Romaine lettuce

23. 10
100
1,000
10,000
100,000
0 10 20 30 40 50 60 70 80
Age of scat (hrs) prior to irrigation
E.coliO157:H7/headlettuce E. coli O157:H7 per head of Romaine lettuce
Animal intrusion <24 hrs prior

24. Drip irrigation versus overhead sprinkler
regarding fecal splash

25. Exclude wildlife by fencing, trapping
and habitat modification,
dust abatement

26. Vegetative or Bare Ground Buffers
• Bare ground may reduce food and cover for some rodents.
• Con: eliminates pathogen reduction benefits of vegetation.
• Con: causes soil erosion & sedimentation.
• Con: degrades water quality & aquatic habitat.
Daniel Mountjoy, NRCS

27. Vegetative Conservation Practice in Question:
Grassed Waterways
• Pro: Convey runoff without
causing erosion or flooding.
• Pro: Reduce gulley erosion.
• Pro: Protect and improve water
quality.
• Pro: Can be mowed and
maintained to discourage rodents.
• Con: Considered by some as
possible cover for rodents or
amphibians (foreign object
concern).
Daniel Mountjoy, NRCS

28. Benefits to food safety versus costs to conservation

29. Questions?