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PERSISTENCE OF PATHOGENS IN SOIL, CROPS, MANURE, AND SLUDGE

According to Feachem et al. (1980), the persistence of fecal pathogens in the environment can be summarized as follows:

IN SOIL

Survival times of pathogens in soil are affected by soil moisture, pH, type of soil, temperature, sunlight, and organic matter. Although fecal coliforms can survive for several years under optimum conditions, a 99% reduction is likely within 25 days in warm climates (see Figure 7.1). Salmonella bacteria may survive for a year in rich, moist, organic soil, although 50 days would be a more typical survival time. Viruses can survive up to three months in warm weather, and up to six months in cold. Protozoan cysts are unlikely to survive for more than ten days. Roundworm eggs can survive for several years.

The viruses, bacteria, protozoa, and worms that can be passed in human excrement all have limited survival times outside of the human body. Let's take a look at their survival times when deposited raw into soil (refer to Tables 7.8 through 7.12).

SURVIVAL OF PATHOGENS ON CROPS

Bacteria and viruses cannot penetrate undamaged vegetable skins. Furthermore, pathogens are not taken up in the roots of plants and transported to other portions of the plant.30 However, pathogens can survive on the surfaces of vegetables, especially root vegetables. Sunshine and low air humidity will promote the death of pathogens. Viruses can survive up to two months on crops but usually live less than one month. Indicator bacteria may persist several months, but usually only last less than one month. Protozoan cysts usually survive less than two days, and worm eggs usually last less than one month. In studies of the survival of Ascaris eggs on lettuce and tomatoes during a hot, dry summer, all eggs degenerated enough after 27 to 35 days to be incapable of infection.31

Lettuce and radishes in Ohio sprayed with sewage inoculated with Poliovirus I showed a 99% reduction in pathogens after six days; 100% were eliminated after 36 days. Radishes grown outdoors in soil fertilized with fresh typhoid-contaminated feces four days after planting showed a pathogen survival period of less than 24 days. Tomatoes and lettuce contaminated with a suspension of roundworm eggs showed a 99% reduction in eggs in 19 days and a 100% reduction in four weeks. These tests indicate that if there is any doubt about pathogen contamination of compost, the compost should be applied to long-season crops at the time of planting so that sufficient time ensues for the pathogens to die before harvest.

PATHOGEN SURVIVAL IN SLUDGE AND FECES/URINE

Viruses can survive up to five months, but usually less than three months in sludge and night soil. Indicator bacteria can survive up to five months, but usually less than four months. Salmonellae survive up to five months, but usually less than one month. Tubercle bacilli survive up to two years, but usually less than five months. Protozoan cysts survive up to one month, but usually less than ten days. Worm eggs vary depending on species, but roundworm eggs may survive for many months.

Table 7.8

SURVIVAL OF ENTEROVIRUSES IN SOIL

Soil Type pH % Moisture Temp. (°C) Days of Survival
(less than)
Sterile, sandy 7.5 10 - 20% 3 - 10 130 - 170
    10 - 20% 18 - 23 90 - 110
  5.0 10 - 20% 3 - 10 110 - 150
    10 - 20% 18 - 23 40 - 90
Non-sterile, sandy 7.5 10 - 20% 3 - 10 110 - 170
    10 - 20% 18 - 23 40 - 110
  5.0 0 - 20% 3 - 10 90 - 150
    10 - 20% 18 - 23 25 - 60
Sterile, loamy 7.5 10 - 20% 3 - 10 70 - 150
    10 - 20% 18 - 23 70 - 110
  5.0 10 - 20% 3 - 10 90 - 150
    10 - 20% 18 - 23 25 - 60
Non-sterile, loamy 7.5 10 - 20% 3 - 10 110 - 150
    10 - 20% 18 - 23 70 - 110
  5.0 10 - 20% 3 - 10 90 - 130
    10 - 20% 18 - 23 25 - 60
Non-sterile, sandy 7.5 10 - 20% 18 - 23 15 - 25

Source: Feachem et al., 1980


Table 7.9

SURVIVAL TIME OF E. HISTOLYTICA PROTOZOA IN SOIL

Protozoa Soil Moisture Temp. (°C) Survival
E. histolytica loam / sand Damp 28 - 34 8 - 10 days
E. histolytica soil Moist ? 42 - 72 hours
E. histolytica soil Dry ? 18 - 42 hours

Source: Feachem et al., 1980


Table 7.10

SURVIVAL TIME OF SOME BACTERIA IN SOIL

Bacteria Soil Moisture Temp. (°C) Survival
Streptococci loam ? ? 9 - 11 weeks
Streptococci sandy loam ? ? 5 - 6 weeks
S. typhi various soils ? 22 2 days - 400 days
Bovine tubercule bacilli soil & dung ? ? less than 178 days
Leptospires varied varied summer 12 hours - 15 days

Source: Feachem et al., 1980


Table 7.11

SURVIVAL TIME OF POLIOVIRUSES IN SOIL

Soil Type Virus Moisture Temp. (°C) Days of Survival
Sand dunes Poliovirus dry ? Less than 77
Sand dunes Poliovirus moist ? Less than 91
 
Loamy fine sand Poliovirus 1 moist 4 90% reduction in 84
Loamy fine sand Poliovirus 1 moist 20 99.999% reduction in 84
 
Soil irrigated w/ effluent, pH=8.5 Polioviruses 1, 2 & 3 9 - 20% 12 - 33 Less than 8
 
Sludge or effluent, irrigated soil Poliovirus 1 180mm total rain -14 - 27 96 - 123 after sludge applied
      -14 -27 89 - 96 after effluent applied
    190mm total rain 15 - 33 less than 11 days after sludge or effluent applied

Source: Feachem et al., 1980


Table 7.12

SURVIVAL TIME OF SOME PATHOGENIC WORMS IN SOIL

Worm Soil Moisture Temp. (°C) Survival
Hookworm larvae Sand ? room temp less than 4 months
  Soil ? open shade, Sumatra less than 6 months
  Soil Moist Dense shade 9 - 11 weeks
      Mod. shade 6 - 7.5 weeks
      Sunlight 5 - 10 days
  Soil Water covered varied 10 - 43 days
  Soil Moist 0 less than 1 week
      16 14 - 17.5 weeks
      27 9 - 11 weeks
      35 less than 3 weeks
      40 less than 1 week
 
Hookworm ova (eggs) Heated soil with night soil water covered 15 -27 9% survival after 2 weeks
  Unheated soil with night soil water covered 15 - 27 3% survival after 2 weeks
 
Roundworm ova Sandy, shaded   25 - 36 31% dead after 54 days
  Sandy, sun   24 - 38 99% dead after 15 days
  Loam, shade   25 - 36 3.5% dead after 21 days
  Loam, sun   24 - 38 4% dead after 21 days
  Clay, shade   25 - 36 2% dead after 21 days
  Clay, sun   24 - 38 12% dead after 21 days
  Humus, shade   25 - 36 1.5% dead after 22 days
  Clay, shade   22 - 35 more than 90 days
  Sandy, shade   22 - 35 less than 90 days
  Sandy, sun   22 - 35 less than 90 days
  Soil irrigated with sewage   ? less than 2.5 years
  Soil   ? 2 years

Source: Feachem et al., 1980


Table 7.13

PARASITIC WORM EGG DEATH

Eggs Temp. (°C) Survival
Schistosome 53.5 1 minute
Hookworm 55.0 1 minute
Roundworm -30.0 24 hours
Roundworm 0.0 4 years
Roundworm 55.0 10 minutes
Roundworm 60.0 5 seconds

Source: Compost, Fertilizer, and Biogas Production from Human and Farm Wastes in the People's Republic of China, (1978),
M.G. McGarry and J. Stainforth, editors, International Development Research Center, Ottawa, Canada. p. 43.

Source: The Humanure Handbook. Jenkins Publishing, PO Box 607, Grove City, PA 16127. To order, phone: 1-800-639-4099.
www.jenkinspublishing.com


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