Indicator pathogens are pathogens whose detection in soil or water serves as evidence that fecal contamination exists. The astute reader will have noticed that many of the pathogenic worms listed in Table 7.6 are not found in the United States. Of those that are, the Ascaris lumbricoides (round-worm) is the most persistent, and can serve as an indicator for the presence of pathogenic helminths in the environment. A single female roundworm may lay as many as 27 million eggs in her lifetime.21 These eggs are protected by an outer covering that is resistant to chemicals and enables the eggs to remain viable in soil for long periods of time. The egg shell is made of five separate layers: an outer and inner membrane, with three tough layers in between. The outer membrane may become partially hardened by hostile environmental influences.22 The reported viability of round-worm eggs (Ascaris ova) in soil ranges from a couple of weeks under sunny, sandy conditions,23 to two and a half years,24 four years,25 five and a half years,26 or even ten years27 in soil, depending on the source of the information. Consequently, the eggs of the roundworm seem to be the best indicator for determining if parasitic worm pathogens are present in compost. In China, current standards for the agricultural reuse of humanure require an Ascaris mortality of greater than 95%.
Ascaris eggs develop at temperatures between 15.50C (59.90° F) and 350C (950 F), but the eggs disintegrate at temperatures above 380C (100.40° F).28 The temperatures generated during thermophilic composting can easily exceed levels necessary to destroy roundworm eggs.
Survival Times of Fecal Coliforms in Soil
Figure 7.1 — Source: Recycling Treated Municipal Wastewater and Sludge Through Forest and Cropland. Edited by William E. Sopper and Louis T. Kardos. 1973. p. 82. Based on the work of Van Donsel, et al., 1967.
AVERAGE DENSITY OF FECAL COLIFORMS EXCRETED IN 24 HOURS (million/100ml)
One way to determine if the compost you're using is contaminated with viable roundworm eggs is to have a stool analysis done at a local hospital. If your compost is contaminated and you're using the compost to grow your own food, then there will be a chance that you've contaminated yourself. A stool analysis will reveal whether that is the case or not. Such an analysis is relatively inexpensive.
I subjected myself to three stool examinations over a period of twelve years as part of the research for this book. I had been composting humanure for fourteen years at the time of the first testing, and 26 years at the time of the third. I had used all of the compost in my food gardens. Hundreds of other people had also used my toilet over the years, potentially contaminating it with Ascaris. Yet, all stool examinations were completely negative. As of this writing, nearly three decades have passed since I began gardening with humanure compost. During those years, I have raised several healthy children. Our toilet has been used by countless people, including many strangers. All of the toilet material has been composted and used for gardening purposes in our home garden.
There are indicators other than roundworm eggs that can be used to determine contamination of water, soil or compost. Indicator bacteria include fecal coliforms, which reproduce in the intestinal systems of warm blooded animals (see Table 7.7). If one wants to test a water supply for fecal contamination, then one looks for fecal col-iforms, usually Escherichia coli. E. coli is one of the most abundant intestinal bacteria in humans; over 200 specific types exist. Although some of them can cause disease, most are harmless.29 The absence of E. coli in water indicates that the water is free from fecal contamination.
Water tests often determine the level of total coliforms in the water, reported as the number of coliforms per 100 ml. Such a test measures all species of the coliform group and is not limited to species originating in warm-blooded animals. Since some coliform species come from the soil, the results of this test are not always indicative of fecal contamination in a stream analysis. However, this test can be used for ground water supplies, as no coliforms should be present in ground water unless it has been contaminated by a warmblooded animal.
Fecal coliforms do not multiply outside the intestines of warm-blooded animals, and their presence in water is unlikely unless there is fecal pollution. They survive for a shorter time in natural waters than the coliform group as a whole, therefore their presence indicates relatively recent pollution. In domestic sewage, the fecal coliform count is usually 90% or more of the total coliform count, but in natural streams, fecal coliforms may contribute 10-30% of the total coliform density. Almost all natural waters have a presence of fecal coliforms, since all warm-blooded animals excrete them. Most states in the U.S. limit the fecal coliform concentration allowable in waters used for water sports to 200 fecal coliforms per 100 ml.
Bacterial analyses of drinking water supplies are routinely provided for a small fee by agricultural supply firms, water treatment companies or private labs.
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:
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 excreted in humanure all have limited survival times outside of the human body. Tables 7.8 through 7.12 reveal their survival times in soil.
Bacteria and viruses are unlikely to penetrate undamaged vegetable skins. Furthermore, pathogens are unlikely to be taken up in the roots of plants and transported to other portions of the plant,30 although research published in 2002 indicates that at least one type of E. coli can enter lettuce plants through the root systems and travel throughout the edible portions of the plant.AA
Some pathogens can survive on the surfaces of vegetables, especially root vegetables, although 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 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.
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