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INDICATOR PATHOGENS

Indicator pathogens are pathogens whose detectable occurrence 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 (roundworm) 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 roundworm 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 15.5°C (59.90° F) and 35°C (95° F), but the eggs disintegrate at temperatures above 38°C (100.40° F).28 The temperatures generated during thermophilic composting can easily exceed levels necessary to destroy roundworm eggs.

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 cost about $41.00 in Pennsylvania (USA) in 1993, and $33 in 1999. I subjected myself to two stool examinations over a period of two years as part of the research for this book. I had been composting humanure for fifteen years at the time of the testings, and 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, both stool examinations were completely negative.

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 coliforms, 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 warm-blooded 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 (in 1994 around $20.00) by agricultural supply firms, water treatment companies, or private labs.

Table 7.7

AVERAGE DENSITY OF FECAL COLIFORMS
EXCRETED IN 24 HOURS
(million/100ml)

Human 13.0
Duck 33.0
Sheep 16.0
Pig 3.3
Chicken 1.3
Cow 0.23
Turkey 0.29

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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