United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Cincinnati OH 45268
Research and Development EPA-600 '1-82-007, May 1982
&EPA Health Effects of
Land Treatment:
Microbiological
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EPA-600/1-82-007
May 1982
HEALTH EFFECTS OF LAND TREATMENT:
MICROBIOLOGICAL
by
Norman Edward Kowal
Epidemiology Division
Health Effects Research Laboratory
Cincinnati, Ohio 45268
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Health Effects Research Laboratory, U.S.
Environmental Protection Agency, and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or recommendation
for use.
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FOREWORD
The U.S. Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the health and
welfare of the American people. Noxious air, foul water, and spoiled land are tragic
testimony to the deterioration of our national environment. The complexity of that
environment and the interplay among its components require a concentrated and
integrated attack on the problem.
Research and development is that necessary first step in problem solution and it
involves defining the problem, measuring its impact, and searching for solutions.
The primary mission of the Health Effects Research Laboratory in Cincinnati
(HERL) is to provide a sound health effects data base in support of the regulatory
activities of the EPA. To this end, HERL conducts a research program to identify,
characterize, and quantitate harmful effects of pollutants that may result from expo-
sure to chemical, physical, or biological agents found in the environment. In addition
to the valuable health information generated by these activities, new research tech-
niques and methods are being developed that contribute to a better understanding of
human biochemical and physiological functions, and how these functions are altered
by low-level insults.
This report provides a general appraisal of the impact of microbiological contami-
nants in wastewater when applied to land. It is assumed that only a minimum of pre-
application treatment is given so that the land itself serves as part of the treatment
system. With a better understanding of such factors as microbiological densities, die-
off rates, and minimum infective dose, more informed decisions may be made on
proper management practices necessary to protect public health in the community.
James B. Lucas
Acting Director
Health Effects Research Laboratory
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ABSTRACT
The potential health effects arising from the land treatment of wastewater are
examined, and an appraisal of these effects made. The agents, or pollutants, of
concern from a health effects viewpoint are divided into the categories of pathogens
and toxic substances. Only the former are considered in this volume, the latter to be
discussed in a subsequent volume. The pathogens include bacteria, viruses,
protozoa, and helminths. These agents form the basis of the main sections of this
report.
For each agent of concern the types and levels commonly found in municipal
wastewater and the efficiency of preapplication treatment (usually stabilization
pond) are briefly reviewed. A discussion of the levels, behavior, and survival of the
agent in the medium or route of potential human exposure, i.e., aerosols, surface soil
and plants, subsurface soil and groundwater, and animals, follows as appropriate.
Infective dose, risk of infection, and epidemiology are then briefly reviewed. Finally,
conclusions and research needs are presented.
This report covers a period from October 1979 to April 1981 and work was com-
pleted as of April 1981.
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CONTENTS
Foreword iii
Abstract iv
Tables vi
Acknowledgment vii
1. Introduction 1
2. Conclusions 4
3. Recommendations 6
4. Bacteria 7
5. Viruses 26
6. Protozoa 40
7. Helminths 44
References 50
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TABLES
1. Potential Land Treatment Health Effects 2
2. Pathogenic Bacteria of Major Concern in Wastewater 7
3. Pathogenic Bacteria of Minor Concern in Wastewater 8
4. Viable Bacteria in Human Feces 10
5. Pathogenic Bacteria in Feces of Infected Persons 10
6. Bacterial Removal during Wastewater Sedimentation 11
7. Aerosol Bacteria at Land Treatment Sites 14
8. Survival Times of Bacteria in Soil 16
9. Survival Times of Bacteria on Crops 17
10. Soil Penetration of Bacteria at Slow-Rate Land Treatment Sites 20
11. Soil Penetration of Bacteria at Rapid-Infiltration Land
Treatment Sites 21
12. Infective Dose to Man of Enteric Bacteria 23
13. Human Wastewater Viruses 26
14. Levels of Enteric Viruses in U.S. Wastewaters 29
15. Enteric Virus Survival in Wastewater Stabilization Ponds 29
16. Aerosol Enteroviruses at Land Treatment Sites 30
17. Survival Times of Enteric Viruses in Soils 32
18. Survival Times of Enteric Viruses on Crops 33
19. Groundwater Penetration of Viruses at Rapid-Infiltration Land
Treatment Sites 36
20. Oral Infective Dose to Man of Enteric Viruses 38
21. Types of Protozoa in Wastewater 40
22. Levels of Protozoa in Wastewater 41
23. Pathogenic Helminths of Major Concern in Wastewater 44
24. Animal-Pathogenic Helminths in Wastewater 45
25. Helminth Egg Survival in Wastewater Stabilization Ponds 48
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ACKNOWLEDGMENT
The editorial and scientific contributions of Herbert R. Pahren and Elmer W.
Akin are gratefully acknowledged.
vn
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SECTION 1
INTRODUCTION
For centuries Western man has been conscious of the potential value of the appli-
cation of human wastes to the land. Thus, von Liebig, in his 1863 work, The Natural
Laws of Husbandry (Jewell and Seabrook 1979) wrote:
Even the most ignorant peasant is quite aware that the rain falling
upon his dung-heap washes away a great many silver dollars, and that it
would be much more profitable to him to have on his fields what now
poisons the air of his house and the streets of the village; but he looks on
unconcerned and leaves matters to take their course, because they have
always gone on in the same way.
In the context of present-day conventional wastewater treatment we might add
"poisons the rivers and streams" as well. More recently, the Committee on Water
Quality Criteria of the National Academy of Sciences-National Academy of Engi-
neering (1972) stated that:
An expanding population requires new sources of water for irrigation
of crops and development of disposal systems for municipal and other
wastewaters that will not result in the contamination of streams, lakes,
and oceans. Irrigation of crops with wastewater will probably be widely
practiced because it meets both needs simultaneously.
Still more recently the U. S. General Accounting Office (1978) concluded that greater
use of land application as an alternative wastewater treatment technique is needed,
because it provides the benefits of (1) the elimination of point discharge to surface
waters, (2) higher levels of treatment than generally provided by conventional
secondary treatment, and (3) recharge of groundwaters. The GAO felt that land
application techniques have not been widely used because (1) restrictive State pre-
treatment requirements have caused these techniques to compare unfavorably with
conventional treatment alternatives, (2) limited technical and health effects infor-
mation is available, and (3) suitable land may not be available.
The legislative mandate for the greater use of land application treatment tech-
niques is found in the Clean Water Act of 1977 (PL 95-217), Title II (Grants for
Construction of Treatment Works), Section 201, which states that the:
Administrator shall encourage waste treatment management which
results in the construction of revenue producing facilities providing
for (1) the recycling of potential sewage pollutants through the produc-
tion of agriculture, silviculture, or aquaculture products, or any com-
bination thereof. . .
Moreover, the Act requires that a construction grant not be made unless:
the grant applicant has satisfactorily demonstrated to the Adminis-
trator that innovative and alternative wastewater treatment processes
and techniques which provide for the reclaiming and reuse of water,
otherwise eliminate the discharge of pollutants, and utilize recycling
techniques, land treatment, new or improved methods of waste treat-
ment management for municipal and industrial waste (discharged into
municipal systems) and the confined disposal of pollutants, so that
pollutants will not migrate to cause water or other environmental pollu-
1
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tion, have been fully studied and evaluated by the applicant taking into
the account section 201(d) of this Act and taking into account and
allowing to the extent practicable the more efficient use of energy and
resources.
One of the most important of these innovative and alternative wastewater treatment
processes and techniques is land treatment.
There are three types of land treatment systems in general use: slow rate (or
"irrigation"), rapid infiltration (or "infiltration-percolation"), and overland flow.
Slow rate is the most commonly used land treatment system. Wastewater, usually
pretreated by some process, is applied by sprinklers, surface flooding, or ridge-and-
furrow irrigation, at a rate of 2 -20 feet (0.6-6 m) per year. Soils are usually medium
to fine textured with moderate permeability, and percolated water is either collected
by drainage tile or reaches the groundwater. Surface vegetation has included lawns
and golf courses for highly treated wastewater, pastures, and forests, but is most
commonly crops, usually for animal consumption. Climatic constraints often
require some winter storage of wastewater (Reed 1979) Recycling benefits include
moderate groundwater recharge and the utilization of wastewater nutrients in crop
production.
In rapid infiltration wastewater is flooded, usually intermittently, into shallow
basins at a rate of 20-600 feet (6-183 m) per year. Soils are usually coarse textured
with high permeability, and percolated water moves to groundwater, recovery wells,
or underdrains Surface vegetation is usually absent, and climatic constraints not of
concern (Reed 1979). Groundwater recharge is a recycling benefit.
Overland flow is the least commonly used land treatment system. Wastewater is
applied to the top of gently sloping (2-4 percent) fields at a rate of 10-70 feet (3-21 m)
per year, and moves by sheet flow down the slope to collection ditches at the base.
Soils are usually fine textured with very low permeability. Surface vegetation
consists of water-tolerant grasses, e.g., reed canary grass. Climatic constraints may
require some winter storage of wastewater (Reed 1979). Recycling benefits may
include the utilization of wastewater nutrients in harvested grass for animal forage.
Many of the examples of land application systems in the U.S. utilize wastewater
treated by conventional means up to tertiary level (secondary in the case of overland
flow). The objectives of these systems are usually to produce clean irrigation water
(e.g., for golf course application) or highly treated water for groundwater recharge.
From a wastewater treatment point of view, land application in these systems is a
form of tertiary treatment or effluent "polishing," rather than true land treatment. In
land treatment systems, the subject of this report, raw wastewater is given a mini-
mum preapplication treatment, or "pretreatment," e.g., by a stabilization pond,
before being applied to the land, and the land itself is the site of the major portion of
the wastewater treatment.
With the application to land of large volumes of minimally pretreated wastewater,
it is evident that considerable potential for adverse health effects exists. These poten-
tials have been briefly summarized by Lance and Gerba (1978) in Table. 1. They
identified the greatest health risks as arising from aerosols in slow rate, groundwater
pollution in rapid infiltration, and surface water pollution in overland flow.
TABLE 1. POTENTIAL LAND TREATMENT HEALTH EFFECTS*
Type of land Food Groundwater Surface Water
treatment system contamination pollution pollution Aerosols
Slow rate + + + ++
Rapid infiltration ++
Overland flow : ; ++ +
-Little or no potential problem
+Moderate potential
^Considerable potential
"Source Lance and Gerba 1978
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It is the purpose of this report to examine the potential health effects of land treat-
ment, and to provide an appraisal of these effects. The agents, or pollutants, of
concern from a health effects viewpoint can be divided into the two broad categories
of pathogens and toxic substances. The pathogens include bacteria (e.g., Salmonella
and Shigella), viruses (i.e., enteroviruses, hepatitis virus, adenoviruses, rotaviruses,
and Norwalk-like agents), protozoa (e.g., Entamoeba and Giardia), and helminths
(or worms, e.g., Ascaris, Trichuns, and Toxocara). The protozoa and helminths are
often grouped together under the term, "parasites," although in reality all the patho-
gens are parasites. The toxic substances include organics, trace elements (or heavy
metals, e.g., cadmium and lead), nitrates, and sodium. Nitrates and sodium are
usually not viewed as "toxic" substances, but are here so considered because of their
potential hematological and long-term cardiovascular effects when present in water
supplies at high levels. These agents form the basis of the main sections of this report.
The major health effects of these agents are listed below:
Agent (Pollutant)
Health Effect
Toxic
Bacteria
Viruses
Protozoa
Helminths
Organics
Trace Meta
Nitrates
Sodium
s
_
— Mutagenesis and Carcmogenesis
(cardiovascular, immunological,
hematological, neurological, etc.)
For each agent of concern the types and levels commonly found in municipal
wastewater and the efficiency of preapplication treatment (usually stabilization
pond) are briefly reviewed. A discussion of the levels, behavior, and survival of the
agent in the medium or route of potential human exposure, i.e., aerosols, surface soil
and plants, subsurface soil and groundwater, and animals, follows as appropriate.
For the pathogens, infective dose, risk of infection, and epidemiology are then briefly
reviewed. Finally, conclusions and research needs are presented.
Surface water pollution from land treatment site runoff is not considered since
proper system design should prevent direct runoff to surface waters (Sorber and
Outer 1975, Reed 1979). Surface discharge of overland flow effluent may have
similar consequences to those of conventional treatment, but little is known in this
area since examples are so few.
The present volume is devoted to the pathogens. A subsequent volume will cover
the toxic substances.
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SECTION 2
CONCLUSIONS
The types and levels in wastewater of most pathogens are fairly well understood.
However, viruses are less well understood. The occurrence of virus in an environ-
mental setting should probably be based on viral tests rather than bacterial
indicators since failures in this indicator system have been reported.
Although untreated wastewater should never be used for irrigation, the level of
preapplication treatment required for the protection of public health may be as little
as properly-designed sedimentation at land treatment sites with limited public
access, where crops are protected by appropriate crop choice and waiting periods,
and groundwater is protected by appropriate hydrological studies and selection of
application rate. Where protection of groundwater cannot be assured, wastewater
stabilization ponds should be considered for virus removal. Because of potential
contamination of crops and infection of animals, slow-rate irrigation and overland-
flow systems should have complete removal of helminth eggs. These relatively simple
pretreatment requirements would be appropriate for many land treatment systems in
the United States, e.g., for many slow-rate sites where crops for animal feed are
grown
This appraisal assumes only a minimum level of preapplication treatment, i.e.,
properly-designed sedimentation. In situations with greater public access (e.g., water
disposal on golf courses), shorter waiting periods before grazing or harvest of crops
(e.g., agriculture in arid areas), or threat of groundwater contamination (e.g.,
shallow water table), more extensive preapplication treatment may be required. This
treatment may consist of wastewater stabilization ponds, conventional treatment
unit processes, or even disinfection. The exact degree of pretreatment required for
these situations is site-specific, and recommendations should be determined sepa-
rately for each system.
Because of the potential exposure to aerosolized viruses at land treatment sites, it
would be prudent to limit public access to 100-200 m from a spray source. At this
distance bacteria are also unlikely to pose a significant risk. Human exposure to
pathogenic protozoa or helminth eggs through aerosols is extremely unlikely.
Suppression of aerosol formation by the use of downward-directed, low-pressure
nozzles, ridge-and-furrow irrigation, or drip irrigation is recommended where these
application techniques are feasible.
The survival times of pathogens on soil and plants are summarized as follows.
Since pathogens survive for a much longer time on soil than plants, the recom-
mended waiting periods before harvest are based upon probable contamination with
soil.
Pathogen
Bacteria
Viruses
Protozoa
Helminths
Absolute
maximum
1 year
6 months
10 days
7 years
Soil
Common
maximum
2 months
3 months
2 days
2 years
Plants
Absolute
maximum
6 months
2 months
5 days
5 months
Common
maximum
1 month
1 month
2 days
1 month
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Aerial crops with little chance for contact with soil should not be harvested for
human consumption for at least one month after the last wastewater application;
subsurface and low-growing crops for human consumption should not be grown at a
land treatment site for at least six months after last application. These waiting
periods need not apply to the growth of crops for animal feed, however.
Properly designed slow-rate land treatment systems pose little threat of bacterial
or viral contamination of groundwater.
Considerable threat of bacterial contamination exists, however, at rapid-infil-
tration sites where the water table is shallow, particularly if the soil is porous.
Likewise, considerable potential for viral contamination of groundwater exists at
rapid-infiltration sites, and appropriate preapplication treatment or management
techniques should be instituted, e.g., intermittent application of wastewater. Until
then, groundwater drawn for use as potable water supplies should be disinfected.
Human exposure to pathogenic protozoa or helminths through groundwater is
extremely unlikely.
There appears to be little danger of bacterial, viral, or protozoal disease to animals
grazing at land treatment sites if grazing does not resume until four weeks after
application. Removal of helminth eggs during preapplication treatment should
eliminate the potential of disease from those long-lived parasites.
Because of the possibility of picking up an infection, it would be wise for humans
to maintain a minimum amount of contact with an active land treatment site.
Epidemiological studies to date suggest little effect of land treatment on disease
incidence. However, well planned and implemented prospective studies have not
been completed.
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SECTION 3
RECOMMENDATIONS
This appraisal brought out a number of areas where additional research is needed
to fill gaps in knowledge or substantiate information which has an insufficient data
base. Research areas recommended are:
1. Develop better methods to recover and detect viruses, since only a small fraction
of the total viruses in wastewater and other environmental samples may actually
be detected.
2. Survival of viruses and protozoan cysts in storage ponds and waste stabilization
ponds.
3. Determination of the effect of dry ing of the soil between wastewater applications
on the survival of surface-soil viruses.
4. The factors controlling the migration of viruses in soils and the survival of
viruses and bacteria in groundwater at rapid-infiltration sites.
5. The role of animals in transmitting human diseases at land application sites
to animals or man off site.
6. The comparison of the respiratory infective dose of enteric viruses with the oral
infective dose.
7. Well-planned and funded prospective acute disease epidemiological studies at
land treatment sites involving a large number of exposed people should be
completed.
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SECTION 4
BACTERIA
TYPES AND LEVELS IN WASTEWATER
The pathogenic bacteria of major concern in wastewater are listed in Table 2. All
have symptomless infections and human carrier states, and many have important
nonhuman reservoirs as well. The pathogenic bacteria of minor concern are listed in
Table 3; this list is perforce somewhat arbitrary since almost any bacterium can
become an opportunistic pathogen under appropriate circumstances, e.g., in the
immunologically compromised or in the debilitated. Recent reviews of pathogens in
wastewater include those by Benarde (1973), Burge and Marsh (1978), Elliott and
Ellis (1977), Kristensen and Bonde (1977), and Menzies (1977).
TABLE 2. PATHOGENIC BACTERIA OF MAJOR CONCERN IN
WASTEWATER
Name Nonhuman reservoir
Campylobacter jejuni Cattle, dogs, cats, poultry
Escherichia co//(pathogenic strains) —
Leptospira spp. Domestic and wild mammals, rats
Salmonella paratyphi (A, B, Q* —
Salmonella typhi —
Salmonella spp. Domestic and wild mammals, birds,
turtles
Shigella sonnei, S. f/exneri, S. boydii, —
S. dysenteriae
Vibrio cholerae —
Yersinia enterocolitica. Y. pseudo- Wild and domestic birds and mammals
tuberculosis
"Correct nomenclature Salmonella paratyphi A, S schotlmuellen, S htrschfeldit. respectively
Campylobacter jejuni (formerly C. fetus subsp. jejuni) is a recently-recognized
cause of acute gastroenteritis with diarrhea. It is now thought to be as prevalent as
the commonly recognized enteric bacteria Salmonella and Shigella, having been
isolated from the stools of 4-8% of patients with diarrhea (MMWR 1979).
Pathogenic strains of the common intestinal bacterium Escherichia coli are of
three types—enterotoxigenic, enteropathogenic, and enteroinvasive (WHO Scien-
tific Working Group 1980). All produce acute diarrhea, but by different mecha-
nisms. Fatality rates may range up to 40% in newborns. Outbreaks occasionally
occur in nurseries and institutions, and the disease is common among travelers to
developing countries.
Leptospira spp. are bacteria excreted in the urine of domestic and wild animals,
and enter municipal wastewater primarily from the urine of infected rats inhabiting
sewers. Leptospirosis is a group of diseases caused by the bacteria, and may manifest
itself through fever, headache, chills, severe malaise, vomiting, muscular aches, and
conjunctivitis, and occasionally meningitis, jaundice, renal insufficiency, hemolytic
anemia, and skin and mucous membrane hemorrhage. Fatality is low, but increases
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TABLE 3. PATHOGENIC BACTERIA OF MINOR CONCERN
IN WASTEWATER
Aeromonas spp
Bacillus cereus
Brucella spp.
Citrobacter spp.
Clostndium perfringens
Coxiella burnetii
Enterobacter spp.
Erysipelothrix rhusiopathiae
Francisella tularensis
Klebsiella spp.
Legionella pneumophila
Listeria monocytogenes
Mycobactenum tuberculosis
M. spp
Proteus spp.
Pseudomonas aeruginosa
Serratia spp.
Staphylococcus aureus
Streptococcus spp.
with age, and may reach 20% or more in patients with jaundice and kidney damage
(Benenson 1975). In the U.S., 498 cases were reported in 1974-78 (Martone and
Kaufmann 1980). Direct transmission from humans is rare, with most infection
resulting from contact with the urine of infected animals, e.g., by swimmers, outdoor
workers, sewer workers, and those in contact with animals.
Salmonella paratyphi (A, B, C) causes paratyphoid fever, a generalized enteric
infection, often acute, with fever, spleen enlargement, diarrhea, and lymphoid tissue
involvement. Fatality rate is low, and many mild attacks exhibit only fever or tran-
sient diarrhea. Paratyphoid fever is infrequent in the U.S. (Benenson 1975).
Salmonella typhi causes typhoid fever, a systemic disease with a fatality rate of
10% untreated or 2-3% treated by antibiotics (Benenson 1975). It occurs sporadi-
cally in the U.S., where 647 cases were reported in 1979 (MMWR 1980a), but is more
common in the developing countries.
Salmonella spp., including over 1000 serotypes, cause salmonellosis, an acute
gastroenteritis characterized by abdominal pain, diarrhea, nausea, vomiting, and
fever. Death is uncommon except in the very young, very old, or debilitated
(Benenson 1975). In 1979, 30,476 cases were reported to the Center for Disease
Control (CDC) (MMWR 1980a).
Shigella sonnei, S. flexneri, S. bovdii, and 5. dysenteriae cause shigellosis, or
bacillary dysentery, an acute enteritis primarily involving the colon, producing
diarrhea, fever, vomiting, cramps, and tenesmus. There is negligible mortality
associated with shigellosis (Butler et al. 1977). In 1979, 15,265cases were reported to
CDC (MMWR 1980b).
Vibrio cholerae causes cholera, an acute enteritis characterized by sudden onset,
profuse watery stools, vomiting, and rapid dehydration, acidosis, and circulatory
collapse. Fatality rates are about 50% untreated, but less than 1% treated (Benenson
1975). Cholera is rare in the U.S., there being no reported cases between 1911 and
1972, although one case occurred in 1973 in Texas and 11 in 1978 in Louisiana (Blake
et al. 1980).
Yersmia enterocolitica and Y. pseudotuberculosis cause yersiniosis, an acute
gastroenteritis and/or mesentenc lymphadenitis, with diarrhea, abdominal pain,
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and numerous other symptoms Death is uncommon. Yersiniosis occurs only
sporadically in the U.S., and its transmitted from either infected animals or humans.
At this point it might be useful to clarify a few points of bacterial terminology. The
term, "enteric bacteria," includes all those bacteria whose natural habitat is the
intestinal tract of humans and animals, including members of several families,
particularly Enterobacteriaceae and Pseudomonadaceae (e.g., Pseudomonas). They
are all aerobic, gram-negative, nonsporeforming rods (Jawet? et al. 1978). The
family Enterobacteriaceae includes the following tribes and genera (Holt 1977).
Escherichieae
Escherichia
Edwardsiella
Citrohacter
Salmonella (including Arizona)
Klebsielleae
Klebsiella
Enterobacter
Hafnta
Serratia
Proteeae
Proteus
Yersinieae
Yersima
Erwimeae
Erwinia
The terms, "total coliform" and "fecal coliform," are operationally-defined entities
used for indicator purposes. Their taxonomic composition is variable, but all are
members of the Enterobacteriaceae. A recent study of fecally-contaminated drinking
water (Lamka et al. 1980) found the following composition:
Total Coliform Species
Cit robacter freundii 46%
Klebsiella pneumoniae 18%
Escherichia coll 14%
Enterobacter agglomerans 12%
E. cloacae 4%
E. hafniae 3%
Serratia liquifaciens 1%
Fecal Coliform Species
Escherichia coli 73%
Serratia liquifaciens 18%
Citrobacter freundii 9%
Most bacteria of concern in wastewater get there from human feces, although a
few, such as Leptospira, enter through urine. The contribution from wash water, or
"grey water," is probably relatively insignificant, except as it may contain oppor-
tunistic pathogens. Human feces contains 25-33% by weight of bacteria, most of
these dead. Although the exact viable bacteria composition of feces is dependent on
such factors as the age and nutritional habits of the individual, some gross estimates
appear in the literature. Two such estimates are summarized in Table 4. The bacteria
listed are normal fecal flora, and are only occasionally associated with disease as
opportunistic pathogens.
In the case of those persons infected with one of the pathogenic bacteria of major
concern, the fecal content of that bacterium may be quite high. Estimates are
presented in Table 5 (Feachem et al. 1978).
Since the bacteria of feces are predominantly anaerobes while the environment of
wastewater is often aerobic, and thus toxic to the anaerobes, the bacterial composi-
tion of wastewater is drastically different from that of feces. The composition also
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TABLE 4. VIABLE BACTERIA IN HUMAN FECES (number/g wet weight)
Carnow et al 1979 Feachem et al. 1978
Anaerobes
Bacteroides 109-1010 108-1010
Bifidobacterium 109-1010 109-101°
Lactobacillus 103-106 106-10°
Clostridium 103-105 105-106
Fusobacterium 103-105
Eubacterium - 108-1010
Veillonella <103
Aerobes
Enterobacteria* 106 107-109
Enterococci (fecal Streptococcus) 105 105-108
Staphylococcus <103
Bacillus, Proteus, Pseudomonas,
Spirochetes «103 -
'Enterobacteria are primarily Eschenchia colt, with some Klebsiella and Enterobacter (Carnow et al 1979)
TABLE 5. PATHOGENIC BACTERIA IN FECES OF INFECTED PERSONS
Name Number/g wet weight
Campylobacter jejuni ?
Escherichia coli (enteropathogemc strains) 108
Salmonella paratyphi (A, B, C) 106
Salmonella typhi 106
Salmonella spp. 106
Shigella sonnet, S. flexnen, S. boydii, S. dysenteriae 106
Vibrio cholerae 106
Yersmia enterocolitica, Y. pseudotuberculosis 106
varies with geographic region and season of the year, higher densities being found in
summer. According to Carnow et al. (1979) the most prominent bacteria of human
origin in raw municipal wastewater are Proteus, Enterobacteria (105/ml), fecal
Streptococcus (103-104/ml), and Clostridium (102-103/ ml). Less prominent bacteria
include Salmonella and Mycobacterium tuberculosis. The total bacterial content of
raw wastewater, as recovered on standard media at 20°C (Carnow et al. 1979), is
about 106-107 organisms/ml. The presence and levels in wastewater of any of the
pathogens listed in Tables 1 and 2 depend, of course, on the levels of infection in the
contributing population.
PREAPPLICATION TREATMENT
Although any level of bacterial inactivation could theoretically be accomplished
by disinfection with chlorine, such a practice on raw wastewater would be very costly
(because of the high BOD, and thus high chlorine consumption), could produce
carcinogenic chloromethanes, and could cause damage to the soil biota. Thus,
simpler methods of preapplication treatment should be considered, if indeed they are
necessary for the protection of public health.
An important point to keep in mind when discussing the degree of pathogen
removal or survival during various wastewater treatment unit processes is the health
significance of the number of organisms remaining. For example, if a wastewater
contains 105 pathogenic bacteria per liter, a superficially impressive 99% removal, or
10
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1% survival, will produce an effluent with 10'pathogenic bacteria per liter. This level
may still be of great public health concern, depending on how the effluent is used. As
Feachem et al. (1978) summarize the issue:
When considering treatment technologies in terms of their ability to
remove pathogens, it is necessary not to dwell on trivial differences, as
between 92.3% removal and 97.8% removal, but to look at orders of
magnitude. Conventional treatment works remove between 1 and 2 log
units of enteric bacteria and should be contrasted with technologies,
like waste stabilization ponds, which remove 5 or more log units. When
considering technologies, like stabilization ponds or thermophilic
digesters, with very high removal performance it is also misleading to
talk in terms of percentage removal. Use of this convention disguises,
for instance, the important difference between 99.99% removal and
99.999% removal.
The minimum preapplication treatment system likely to be used in land treatment
is sedimentation, or conventional primary treatment. Typical degrees of bacterial
removals have been summarized by Crites and Uiga (1979) and Sproul (1978), and
are presented in Table 6.
TABLE 6. BACTERIAL REMOVAL DURING WASTEWATER
SEDIMENTATION
Total coliforms 10%
Fecal coliforms 35%, 27-96%
Eschenchia coli 15%
Mycobacterium tuberculosis 50%
Salmonella spp. 15%
Shigella spp. 15%
As a result of the need for winter storage of wastewater in most land treatment
systems, and the possible need for low-cost further pathogen removal, wastewater
stabilization ponds are likely to be the most common preapplication treatment
system. Wastewater stabilization ponds, or "lagoons," are large shallow ponds in
which organic wastes are decomposed by the action of microorganisms, especially
bacteria. There are three types of ponds in common use, often used in a series
(Feachem et al. 1978):
1. Anaerobic pretreatment ponds, 2-4 m deep, 1-5 day retention time.
2. Facultative ponds, with oxygen supplied by algae, 1-1.5 m deep, 10-40 day
retention time.
3. Maturation ponds, 1-1.5 m deep, 5-10 day retention time.
Feachem et al. (1978) have surveyed a large body of literature on bacterial survival
in ponds, and concluded that:
1. In single anaerobic ponds E. coli removals of 46-85%after 3.5-5 days at various
temperatures have been reported.
2. In single facultative and aerobic ponds E. coli removals of 80 to over 99% after
10-37 days at various temperatures have been reported.
3. In single facultative and aerobic ponds fecal streptococci removals are similar to
or greater than E. coli.
4. Removals of 99.99% or greater have been reported for series of 3 or more ponds.
5. One or two ponds will remove 90-99% of Salmonella or other pathogenic
bacteria.
6. Complete elimination of pathogenic bacteria can be achieved with 30-40 day
retention times, particularly at high temperatures (over 25°C).
7. A series of 5-7 ponds, each with a 5 day retention time, can produce an effluent
with less than 100 fecal coliforms and fecal streptococci per 100 ml.
-------
Aerated lagoons, i.e., ponds with mechanical aerators, have been reported (Crites
and Uiga 1979) to provide removal rates of 60 to 99.99% for total coliforms and 99%
for fecal coliforms, total bacteria, Salmonella typhi, and Pseudomonas aeruginosa.
Thus, wastewater stabilization ponds can be designed to achieve practically any
degree of bacterial pathogen removal deemed necessary for the protection of public
health, including complete wastewater treatment. Such a high degree of preapplica-
tion treatment, of course, should not be necessary for most land treatment systems.
AEROSOLS
Where wastewater is applied to the land by spray equipment of some sort, e.g.,
impact sprinklers, fan sprinklers, rain guns, and fixed-aperture rocker-arm sprayers,
aerosols that travel beyond the wetted zone of application will be produced (Shaub
el al. 1978a). These are suspensions of solid or liquid particles up to about 50 /jm in
diameter, formed, for example, by the rapid evaporation of small droplets to form
droplet nuclei. Their content of microorganisms depends upon the concentration in
the wastewater and the aerosolization efficiency of the spray process, a function of
nozzle size, pressure, angle of spray trajectory, angle of spray entry to the wind,
impact devices, etc. (Schaub el al. 1978a).
Although aerosols represent a means by which pathogens may be deposited upon
fomites such as clothing and tools, the major health concern with aerosols is the
possibility of direct human infection through the respiratory route, i.e., by inhala-
tion. The exact location where aerosol particles are actually deposited upon inhala-
tion is a function of their size. Those above about 2 /urn in diameter are deposited
primarily in the upper respiratory tract (including the nose for larger particles), from
which they are carried by cilia into the oropharynx. They then may be swallowed,
and enter the gastrointestinal tract. The smaller airways and alveoli do not possess
cilia, so that pathogens deposited there would have to be combatted by local
mechanisms. Although the pattern of deposition is variable, the greatest alveolar
deposition appears to occur in the 1 -2 /jm range, decreasing to a minimum at about
0.25 yum, and increasing (due to Brownian motion) below 0.25 /_im (Sorber and
Outer 1975).
When aerosols are generated, bacteria are subject to an immediate "aerosol
shock," or "impact factor," which may reduce their level by one log within seconds
(Schaub el al. !978a). There is some evidence that this might be caused by rapid
pressure changes (Biederbeck 1979). Their survival is subsequently determined
primarily by relative humidity and solar radiation (Carnow el al. 1979, Teltsch and
Katzenelson 1978). At low relative humidities rapid desiccation occurs, resulting in
rapid die-off (Sorber and Outer 1975), although concentration of protective
materials within the droplet may occur (Schaub el al. 1978a). Solar radiation,
particularly the ultraviolet portion, is destructive to bacteria, and increases the rate
of desiccation. Teltsch and Katzenelson (1978) have found bacterial survival at night
up to ten times that during daytime in Israel. High temperature is another factor
decreasing bacterial survival While biological aerosol decay is occurring, the rate of
physical aerosol decay, or deposition, simultaneously affects the distance of dissemi-
nation of the bacteria This is influenced by wind speed, air turbulence, and local
topography, e.g., a windbreak of trees.
Any of the bacteria listed earlier as present in feces, urine, or wastewater could
appear in aerosols emanating from land treatment sites. In aerosols generated by
activated sludge aeration tanks, Kenline and Scarpino (1972) found Klebsiella,
Enterobacter, Escherichta, Citrobacter, Shigella, Arizona, Hafnia, and Serrano, but
no Salmonella (other than Arizona) or Proteus. Carnow el al. (1979), after reviewing
the literature on wastewater treatment plant aerosols, concluded that recovered
bacteria include Klebsiella, Enterobacter, Proteus, Staphvlococcus, Streptococcus,
Mvcobactenurn, and other nonpathogens. The dominance of Klebsiella, a respira-
tory pathogen, in the aerosol literature may be in error since Johnson el al. (1980)
12
-------
have recently shown that further bacteriological confirmation steps of "Klebsiella "
isolates reveal them to be nonpathogenic bacteria, true Klebsiella dying off rapidly
during the aerosolization process.
Because of the low density of aerosol bacteria normally emanating from land
treatment sites, high-volume samplers, e.g., 1 m3/ min electrostatic precipitators, are
often necessary for aerosol analysis. Likewise, because of the normally low density
of pathogenic bacteria compared with nonpathogens, most measurements of aerosol
bacteria have utilized traditional indicator bacteria, e.g., standard plate count, total
coliforms, and fecal coliforms. The measurements of Johnson el al. (1980) have
shown little correlation between densities of these indicator bacteria and densities of
the pathogens which they are intended to indicate. This results in "extreme under-
estimation of pathogen levels," since the pathogens which they studied, i.e.,
Pseudomonas, Streptococcus, and Clostndium perfringens, survived the aerosoliza-
tion process much better than did the indicator bacteria. They suggest that fecal
streptococci might be a more appropriate indicator organism because of its similar
hardiness upon impact and viability to those of pathogens. Similarly, Teltsch et al.
(1980) measured densities of coliforms, Salmonella, and the entero viruses in aerosols
and wastewater at an Israeli land treatment site, and from ". . . the ratios of
salmonellae to coliforms and enteroviruses to coliforms in the air, as compared to
these ratios in the wastewater, it was concluded that the suitability of coliforms as an
indication of airborne contamination caused by spray irrigation is questionable."
The results of some of the most important studies of aerosol bacteria production at
land treatment spray sites are summarized in Table 7. Although local environmental
conditions, e.g., wind speed, vary among and within these studies, the results give a
general idea of aerosol bacteria levels to be expected at land treatment sites.
The results suggest that the aerosol bacteria are usually detected at a maximum
distance less than 400 m from the spray site. Experiments in Israel (Katzenelsone; al.
1977) found that Escherichia coli could be detected in aerosols 10 m from the
sprinkler only when its concentration in the wastewater reached 104/ ml or more. The
Pleasanton, California data (Johnson et al. 1978) suggest that a threshold value of
103/ml might be more reasonable for wastewater bacteria. There is some evidence
(Reploh and Handloser 1957) that the type of sprinkler and spray diameter has little
effect on the distance of aerosol bacteria transport. It is generally felt, however, that
downward-directed, low-pressure sprinklers (usually on center-pivot spray rigs) pro-
duce much less aerosol than the upward-directed, high-pressure types used to obtain
the data in Table 7. The Ft. Huachuca, Arizona results indicate a much greater trans-
port distance during night than day, likewise the 400 m measurement in Germany
(Bringmann and Trolldenier 1960) occurred at night. The high nighttime transport
of aerosol bacteria is probably due to high humidity and absence of solar radiation.
Most of the aerosols represented by the data in Table 7 are probably respirable, since
Bausum et al. (1978) found that, at 30 m in Deer Creek, 75% of the particles fell in the
range of 1-5 /urn, with a median of 2.6 /am.
The human exposure to aerosol bacteria at land treatment sites can be roughly
estimated from the data at Kibbutz Tzora, Israel, where raw wastewater was
sprayed, thus yielding higher bacterial levels than those found at Deer Creek, Ft.
Huachuca, or Pleasanton, where treated wastewater was sprayed. Thus, an adult
male, engaged in light work, breathing at a rate of 1.2m3/hr, and exposed to 34 coli-
forms/m3 (the Kibbutz Tzora average) at 100 m downwind from a sprinkler, would
inhale approximately 41 coliforms per hour. Since the ratio of aerosolized
Salmonella to coliforms is 1:105 (Grunnet and Tramsen 1974) the rate of inhalation
of Salmonella would be about 105-fold less, an extremely low rate of bacterial expo-
sure. More recent data from Kibbutz Tzora allows a more accurate estimate of
human exposure (Teltsch et al. 1980). During a period of time in 1977-78, when the
wastewater total coliforms were 2.4*106 to 1.4*107/100 ml and Salmonella was
0-60/100 ml, the density of aerosol Salmonella at 40 m, the maximum distance
found, was 0-0.054/ m3, with a mean of 0.014/ m3. This would result in an inhalation
13
-------
TABLE 7. AEROSOL BACTERIA AT LAND TREATMENT SITES
Wastewater
type
Raw or primary
Ponded,
chlorinated
Location
(reference)
Germany (Reploh &
Handloser 1957)
Germany (Brmgmann
& Trolldenier 1960)
California (Sepp 1971)
Kibbutz Tzora,
Israel (Katzenelson
& Teltch 1976)
Deer Creek, Ohio
(Bausum et al
1978)
Distance (m)
90-160
63-400
32
10
20
60
70
100
150
200
250
300
350
400
Upwind
21-30
41-50
200
Bacteria
Coliform
Coliform
Coliform
Coliform
Fecal coliform
Coliform
"
Salmonella
Coliform
"
"
"
11
"
"
"
Std. plate count
"
"
Density (/m3)
Detected at maximum
distance
Detected at maximum
distance (night)
Detected at maximum
distance
11-496
35-86
0-480
0-501
Detected at maximum
distance
30-102
0-88
4-32
0-25
0-17
0-21
0-7
0-4
111(23-403)
485(46-1582)*
417(0-1429)*
37KO-223)*
Continued
-------
TABLE 7. Continued
Wastewater Location
type (reference) Distance (m)
Secondary, Ft. Huachuca, Upwind
nonchlorinated Arizona (Schaub
etal. 1978a) 45-49
120-152 m
Pleasanton, California Upwind
(Johnson etal 30-50
1978, 1980)
1 00-200
Bacteria
Std plate count
Cohform
Std. plate count
Klebsiella
Std plate count
Std plate count
"
Total coliform
Fecal coliform
Fecal streptococci
Pseudomonas
Klebsiella
Clostridium
perfrmgens
Mycobactenum
Std plate count
Total coliform
Fecal coliform
Fecal streptococci
Pseudomonas
Klebsiella
Clostridium
perfringens
Mycobacterium
Density (/m3)
28(12-170)
2.4(0-58)
430-1 400(day)
560-6300(night)
1-23
86-130(day)
1 70-41 0(night)
300-805
450-1 560
2 4-2.5
04
0.3-1.7
34
<5
09
08
330-880
06-1 2
<0.3
0.3-1 9
43
<5
1 1
08
'Corrected for upwind background value
-------
rate of 0.017/ hr at 40 m, higher than the previous estimate, but still an extremely low
rate of bacterial exposure (cf. the infective dose discussion below).
SURFACE SOIL AND PLANTS
The surface soil and plants of an active land treatment site are constantly heavily
laden with enteric bacteria; these are the specific locations where the actual treatment
of the wastewater and inactivation of the bacteria occur. (In some situations bacteria
may be deposited on plants in the environs of a land treatment site, due to aerosol
drift.) The survival time of bacteria in surface soil and on plants is only of concern
when decisions must be made on how long a period of time must be allowed after last
application before permitting access to people or animals, or harvesting crops.
The factors affecting bacterial survival in soil (Gerba el al. 1975, USEPA 1977)
are:
1. Moisture content. Moist soils and periods of high rainfall increase survival time.
This has been demonstrated for Escherichia coli. Salmonella tvphi, and
Mvcobacterium avium.
2. Moisture-holding capacity. Survival time is shorter in sandy soils than those
with greater water-holding capacity.
3. Temperature. Survival time is longer at lower temperatures, e.g., in winter.
4. pH. Survival times are shorter in acid soils (pH 3-5) than in neutral or alkaline
soils. Soil pH is thought to have its effect through control of the availability of
nutrients or inhibitory agents. The high level of fungi in acid soils may play a
role.
5. Sunlight. Survival time is shorter at the surface, probably due to desiccation and
high temperatures, as well as ultraviolet radiation.
6. Organic matter. Organic matter increases survival time, in part due to its
moisture-holding capacity. Regrowth of some bacteria, e.g., Salmonella, may
occur in the presence of sufficient organic matter. In highly organic soils
anaerobic conditions may increase the survival of Escherichia coli (Tate 1978).
7. Soil microorganisms. The competition, antagonism, and predation encountered
with the endemic soil microorganisms decrease survival time. Protozoa are
thought to be important predators of coliform bacteria (Tate 1978). Enteric
bacteria applied to sterilized soil survive longer than those applied to unsteri-
lized soil.
In view of the large number of environmental factors affecting bacterial survival in
soil, it is understandable that the values found in the literature vary widely. Two use-
ful summaries of this literature are those of Bryan (1977) and Feachem et al. (1978).
The ranges given in Table 8 are extracted from these summaries, as well as other
literature. "Survival" as used in this table, and throughout this report, denotes days
of detection. It should be noted that inactivation is a rate process and therefore
detection depends upon the initial level of organisms, sensitivity of detection
methodology, and other factors. If kept frozen, most of these bacteria would survive
longer than indicated in Table 8, but this would not be a realistic soil situation.
TABLE 8. SURVIVAL TIMES OF BACTERIA IN SOIL
Coliform 4-77 days
Fecal coliform 8-55 days
Fecal streptococci 8->70 days
Leptospira <1 5 days
Mycobacterium 10 days-15 months
Salmonella paratyphi >259 days
Salmonella typhi 1 -120 days
Salmonella spp. 11 ->280 days
Streptococcus faecalis 26-77 days
16
-------
The survival of bacteria on plants, particularly crops, is especially important since
these may be eaten raw by animals or humans, may contaminate hands of workers
touching them, or may contaminate equipment contacting them. Such ingestion or
contact would probably not result in an infective dose of a bacterial pathogen, but if
contaminated crops are brought into the kitchen in an unprocessed state they could
result in the regrowth of pathogenic bacteria, e.g., Salmonella, in a food material
affording suitable moisture, nutrients, and temperature (Bryan 1977). It should be
kept in mind that many bacteria on plants, as well as soil, are not contaminants from
human beings. For example, Klebsiella spp., Enterobacter spp., Serratia spp., and
Pseudomonas aerugmosa are believed to be part of the natural flora of vegetables
(Remington and Schimpff 1981).
Pathogens do not penetrate into vegetables or fruits unless their skin is broken
(Bryan 1977, Rudolfs el al. 195 la), and many of the same factors affect bacterial
survival on plants as those in soil, particularly sunlight and desiccation. The survival
times of bacteria on subsurface crops, e.g., potatoes and beets, would be similar to
those in soil. Useful summaries of the literature on the survival times of bacteria on
aerial crops are those of Bryan (1977), Sepp (1971), and Feachemer al. (1978). The
ranges given in Table 9 are extracted from these summaries, as well as other
literature.
TABLE 9. SURVIVAL TIMES OF BACTERIA ON CROPS
Bacterium Crop Survival
Coliform Tomatoes >1 month
Fodder 6-34 days
Leaf vegetables 35 days
Eschenchia coli Vegetables <3 weeks
Grass <8 days
Mycobacterium Grass 10-14 days
Lettuce >35 days
Radishes >13days
Salmonella typhi Vegetables 10-31 days
(leaves and stems)
Salmonella spp.
Shigella spp.
Vibrio cholerae
Radishes
Lettuce
Leaf vegetables
Beet leaves
Tomatoes
Cabbage
Gooseberries
Clover
Grass
Orchard crops
Tomatoes
Apples
Leaf vegetables
Fodder
Orchard crops
Vegetables
Dates
24-53 days
18-21 days
7-40 days
3 weeks
3-7 days
5 days
5 days
1 2 days
>6 weeks
>2 days
2-5 days
8 days
2-7 days
<2 days
6 days
5-7 days
<1-3 days
17
-------
On the basis of New Jersey field experiments with tomatoes irrigated with munici-
pal wastewater, Rudolfs el al. (1951 a) concluded that: (1) cracks and split stem ends
provide protected harboring places for enteric bacteria to survive for long periods,
and such portions should be cut away before consumption, (2) on normal tomatoes,
without cracks, after direct application of wastewater to the surface of the fruit the
residual coliform concentration decreases to or below that of uncontaminated
controls by the end of 35 days or less, (3) survival of Salmonella and Shigella on
tomato surfaces in the field did not exceed 7 days, even when applied with fecal
organic material, and (4) if wastewater application is stopped about one month
before the harvest, the chances for the transmission of enteric bacterial diseases will
decrease to almost nil.
On the basis of field experiments with lettuce and radish irrigated with municipal
wastewater, Larkin el al. (1978a) concluded that leafy vegetables cannot be
considered safe from Salmonella contamination until the soil can be shown to be free
of Salmonella. They also noted that, because of regrowth in soil and on leaf crops,
total coliforms and fecal streptococci bore no relationship to Salmonella levels, and
are unacceptable indicators of fecal contamination; they recommended using fecal
coliforms or Salmonella itself.
Thus, the consumption of subsurface and low-growing food crops, e.g., leafy vege-
tables and strawberries, harvested from an irrigated site within about six months of
last application, is likely to increase the risk of disease transmission, because of
contamination with soil and bacterial survival in cracks, leaf folds, leaf axils, etc.
Possible approaches to avoid this problem are (1) use of the subsurface or covered
drip irrigation method for aerial crops (Sadovski el al. 1978a, 1978b), (2) growth of
crops the harvested portion of which does not contact the soil, e.g., grains and
orchard crops, or (3) growth of crops used for animal feed only, e.g., corn (maize),
soybeans, or alfalfa. The last alternative is probably the most common and most
economic. In the situation where the harvested portion does not contact the soil nor
is within splash distance, stopping wastewater application a month prior to harvest
would be prudent.
MOVEMENT IN SOIL AND GROUNDWATER
Over 60 million people in the United States are served by public water supplies
using groundwater, and about 54 percent of the rural population and 2 percent of the
urban population obtain their water from individual wells (Duboise el al. 1979).
Thus, it is imperative that land treatment systems do not result in the transmission of
disease through groundwater. This is not to imply that groundwater in the U.S. is
now pristine. Almost half of the waterborne disease outbreaks in the U.S. between
1971 and 1977 were caused by contaminated groundwater (Craun 1979), and a recent
examination of individual groundwater supplies in a rural neighborhood of Oregon
(Lamka el al. 1980) showed more than one-third to be fecally contaminated. But,
thus far, no disease outbreaks have been attributed to wastewater land treatment
systems (Gerba and Lance 1980)
It is generally felt that the removal of bacteria at land treatment sites occurs
primarily by filtration, or straining, with most bacteria retained within about 50 cm
of the soil surface. Under optimum conditions 92-97% of coliforms have been
observed to be trapped in the first centimeter of soil (Gerba el al. 1975). Coarse sandy
or gravelly soils or fissured subsurface geology would, of course, allow the bacteria
to penetrate to great depths. Adsorption of bacteria also plays a secondary role,
being increased by the presence of clay-sized particles, high cation concentration,
and low pH. This adsorption is reversible, and the bacteria can be released and
moved down the soil profile by distilled water or any water with low conductivity,
e.g., rainfall (Sagik et al. 1978).
Once retained, the bacteria are inactivated by sunlight, oxidation, desiccation, and
predation and antagonism by the soil microbial community. Intermittent applica-
18
-------
tion and drying periods result in more rapid die-off of enteric bacteria (USEPA
1977). However, too long a drying period has been found to result in deeper penetra-
tion of bacteria in rapid-infiltration systems upon resumption of flooding (Bouwer
et al. 1974). This phenomenon is probably due to the decomposition of filtering
organic matter on the soil surface and the decrease in soil microbial activity during
extended drying. With the resumption of flooding, the filtering organic matter starts
to accumulate on the surface and the soil microbial activity increases, causing greater
bacterial removal.
Summaries of data on the soil penetration of bacteria at some of the most impor-
tant land treatment sites are presented in Table 10 for slow-rate systems, and Table
11 for rapid-infiltration systems. Overland-flow systems should result in negligible
penetration of soil by bacteria.
It is evident from Table 10 that most slow-rate sites pose little threat to the ground-
water, but that the combination of high bacterial densities and shallow water table,
resulting in seeping, such as that at the San Angelo site, should be avoided. The data
of Table 11 suggest that bacteria at rapid-infiltration sites may penetrate about 10 m
vertically and variable distances laterally. These distances are, of course, highly site-
specific, and the vertical distance may be more than 10 m, but is usually much less.
To prevent the entry of enteric bacteria into groundwater, it would thus be
advisable (unless an underdrain system is installed) not to site land treatment systems
where the water table is shallow, particularly if the soil is sandy or gravelly, large
cracks or root tunnels are present, or a thin soil mantle overlies rock with solution
channels or fissures. This is especially true for rapid-infiltration systems.
Once in the groundwater the bacteria may travel long distances underground in
situations where coarse soils or solution channels are present, but normally the
filtering action of the matrix should restrict horizontal travel to only a few hundred
feet (Sorber and Outer 1975). The actual distance travelled also depends upon the
rate of movement of the groundwater and the survival time of the bacteria. The rate
of movement of groundwater is highly site-specific, but often is extremely slow. The
survival time of bacteria in groundwater would be expected to be longer than that in
surface soil because of the moisture, low temperature, nearly neutral pH, absence of
sunlight, and usual absence of antagonistic and predatory microorganisms. Ground-
water survival times found in both field and laboratory measurements have been
summarized by Gerba et al. (1975):
Cohforms 17 hours (for 50% reduction)
Escherichia coli 63 days-4.5 months
Salmonella 44 days
Shigella 24 days
Vibrio cholerae 7.2 hours
Concern has recently been expressed over the presence of endotoxin in municipal
wastewater, and the possibility of it entering groundwater at land treatment sites
(Goyal et al. 1980). Endotoxin is a lipopolysaccharide which is a natural component
of cell walls of gram-negative bacteria, including enterobacteria, and, upon entry
into the bloodstream, may cause acute nonspecific inflammation, fever, nausea, and
shock. Goyal et al. (1980) showed that 90-99% of endotoxin is removed after travel
of wastewater through 100-250 cm of loamy sand, but that the endotoxin can be
desorbed and moved by rainfall, and can be detected in the groundwater beneath
several land treatment sites. Since the concentration of endotoxin in the normal gut
would be expected to be high due to endemic bacteria, the significance of endotoxin
in groundwater is questionable. Chills, fever, and hypotension may occur if
endotoxin-contaminated water is used for hemodialysis without pretreatment, but it
would be impractical for water authorities to maintain endotoxin-free water since
blue-green algae (closely related taxonomically to gram-negative bacteria), com-
mon in the flora of lakes and rivers, also produce endotoxin (Hindman et al. 1975).
19
-------
TABLE 10. SOIL PENETRATION OF BACTERIA AT SLOW-RATE LAND TREATMENT SITES
Location
(soil and
substrate)
Taber, Alberta
(Loamy sand)
Swift Current,
Saskatchewan
(Clay loam)
San Angelo, Texas
(Sandy clay)
Dickenson, North
Dakota
(Sandy alluvium)
Roswell, New Mexico
(Silty clay loams)
Type of
applied
effluent
Aerobic
lagoon
Aerobic
lagoon
Primary
Series
lagoon
Chlorinated
secondary
Application
rate
4 5 cm/wk
2-3 times
crop re-
quirement
140 cm/yr
80 cm/yr
Bacterium
FC*
FC
TC*
FC
Salmo-
nella
FC
TC & FC
Concentration
in applied
effluent
230- 17007 ml
8400/100 ml
102-105/ml
10-10Vml
Present
9100/100 ml
Bacteria
Depth
>69 cm
>30 cm
Seepage
creeks
2 5-75 ft
(20 wells)
18-1 05 ft
(groundwater)
recovered
Concentration
None
detected
None detected
10-10Vml
10-102/ml
Present
None detected
No increase
over control
Ref.
1
2
3
4
5
*FC - fecal cohform, TC - total cohform
1 - Bell and Bole 1978
2 - Biederbeck and Bole 1979
3 - Weaver et al 1978
4 - Benham-Blair el a/ 1979
5 - Koerner and Haws 1979a
-------
TABLE 11. SOIL PENETRATION OF BACTERIA AT RAPID-INFILTRATION LAND
TREATMENT SITES
Location
(soil and
substrate)
Lodi, California
(Sandy loam)
Santee, San Diego,
California (Coarse
gravel & sand)
Flushing Meadows,
Phoenix, Arizona
(Sand & gravel)
Hollister,
California
(Gravelly sand
over clay & silt)
Vineland, New Jersey
(Sand)
Fort Devens,
Massachusetts
JSand & gravelL
Type of
applied
effluent
Undismfected
Oxidation
pond
Secondary
Primary
Primary
Primary
Application
rate Bacterium
Coliforms
Fecal
streptococci
330 ft (99 m)/yr
2 wk/3 wk dry TC*
2 day/3 day dry TC
FC*
15.4 m/yr, TC
intermittent
FC
FC
27.1 m/yr, TC
intermittent
FC
Concentration
in applied
effluent
(per 100 ml)
4500
106
106
106-106
276x106
124xl06
6.8x106
32x106
Bacteria
Depth
(meters)
1 2-2.1
3.9
61 L**
122 L
450 L
9
9
60 L
7-10
21-24
48
7-10
21-24
48
6-9
>9
183
60-100 L
60-100 L
recovered
Concentration
(per 100 ml)
<1
Detected in
one case
20
48
68
200
5
ND"*
0.23-1.1x106
<2-1,570
9
156-186x103
0-11
<1
0-300
0
3500
<200
ND
Ref.
1
1
1
2
3
4
5
6
"TC - total coliform, FC - fecal coliform, "* L - Lateral, *** ND - Not detected
1 - Gerba et al 1 975
2 - Bouwer and Rice 1978
3 - Pound el a/ 1978
4 - Koerner and Haws 1979b
5 - Satterwhite et al 1976b
6 - Satterwhite e! al 1976a
-------
ANIMALS
The major bacterial concerns with respect to animals grazing at land treatment
sites are Salmonella infections and bovine tuberculosis (Mvcobacterium bovis and
M. tuberculosis); both can be passed on to man.
That the transmission of salmonellosis to cattle grazing at land treatment sites is at
least possible was demonstrated by Taylor and Burrows (1971), who showed that
calves grazing pastures, to which 106 Salmonella dublin organisms/ml of slurry had
been applied, became infected. No infection occurred when the rate was decreased to
10J/ml, suggesting that Salmonella may only be of concern when high concentra^
tions are present. At the San Angelo, Texas, slow-rate soil treatment site, although
Salmonella was isolated from the soil and the seepage creeks, the proportion of cattle
grazing the pastures that were shedding Salmonella in their manure was not unusu-
ally high (Weaver el al. 1978). Feachem et al. (1978) concluded that there is no clear
evidence that cattle grazed at land treatment sites are more at risk from salmonellosis
than other cattle, probably because the required infectious doses are high and
Salmonella infections are transmitted among cattle in many other ways. On the basis
of Salmonella measurements in wastewater and sludge in England, Jones el al.
(1980) concluded that a four-week waiting period would prevent salmonellosis in
grazing animals.
Several investigations on tuberculosis infection of cattle grazing on wastewater-
irrigated land have been performed in Germany, with the conclusion that if applica-
tion is stopped 14 days before pasturing, there is no danger that grazing cattle will
contract bovine tuberculosis (Sepp 1971).
Other possible bacterial concerns with respect to animals grazing at land treat-
ment sites are Leptospira (causing leptospirosis), Brucella (causing brucellosis), and
Bacillus anthracis (causing anthrax). Wastewater, however, probably contains insig-
nificant numbers of these pathogens, and plays a negligible role in the transmission
of these diseases (Feachem et al. 1978).
INFECTIVE DOSE, RISK OF INFECTION, EPIDEMIOLOGY
Upon being deposited on or in a human body a pathogen may be destroyed by
purely physical factors, e.g., desiccation or decomposition. Before it can cause an
infection, and eventually disease, it must then overcome the body's natural defenses.
In the first interaction with the host, whether in the lungs, in the gastrointestinal
tract, or other site, the pathogen encounters nonspecific immunologic responses, i.e.,
inflammation and phagocytosis. Phagocytosis is carried out primarily by neutro-
phils or polymorphonuclear leukocytes in the blood, and by mononuclear phago-
cytes, i.e., the monocytes in the blood and macrophages in the tissues (e.g., alveolar
macrophages in the lungs). Later interactions with the host result in specific
immunologic responses, i.e., humoral immunity via the B-lymphocytes, and cell-
mediated immunity via the T-lymphocytes (Bellanti 1978).
With these barriers to overcome it is understandable that an infection resulting
from inoculation by a few bacterial cells is a most unlikely occurrence; usually large
numbers are necessary. Some representative oral infection dose data for enteric
bacteria, based upon numerous studies using nonuniform techniques, are presented
in Table 12 (adapted from Bryan 1977).
Although the terms, "infective dose," "minimal infectious dose,"etc., are used in
the literature, it is obvious from Table 12 that these are misnomers, and that we are
really dealing with dose-response relationships, where the dose is the number of cells
to which the human is exposed, and the response is lack of infection, infection
without illness, and infection with illness (in an increasing proportion of the test
subjects). The response is affected by many factors, making it highly variable. Some
of the most important factors are briefly discussed below.
22
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TABLE 12. INFECTIVE DOSE TO MAN OF ENTERIC BACTERIA
No
Infection Infections
or no without
Percent of volunteers
developing illness
Bacterium
Clostridium perfringens
Escherichia coli
0124:K72:H-
0148 H28
0111:B4
Several strains
Salmonella typhi
Ty2W
Zermat vi
Most strains
S. newport
S. bareilly
S. ana turn
S. meleagridis
S. derby
S. pullorum
illness
104
103
10"-106
10"-106
105-106
104-109
illness 1-25
10'° 108
108
lO'MO6 106
10s
106
10s
105
106-108
106
26-50
108
108
105-108
106
106
106
107
107
109
51-75 76-100
109 109
1010
106-109
108-10'° 10'°
10"
108-109
107-108
109-10'°
Shigella dysenteriae
S. flexneri
Streptococcus faecalis
var. liquefaciens
108
Vibrio cholerae
NaHC03-buffered 10
Unbuffered 104-10'°
103
10-102 102-10" 103 10"
102-104 103-109 106-108
109 10'°
103-108 104-106
108-10"
The site of exposure determines what types of defense mechanisms are available,
e.g., alveolar macrophages and leukocytes in the lungs, and acidity and digestive
enzymes in the stomach. The effect of acidity is clearly shown by the cholera
(Vibrio choleras) data in Table 12, where buffering reduces the infective dose by
about a thousandfold. Direct inoculation into the bloodstream results in the
fewest barriers being presented to the pathogen; Hellman et al. (1976) found 10
tuleremia organisms injected to be comparable to 10s by mouth.
Previous exposure to a given pathogen often produces varying degrees of
immunity to that pathogen, through the induction of specific immune responses.
A study in Bangladesh showed that repeated ingestion of small inocula(103-104
organisms) of Vibrio cholerae produced subclinical or mild diarrhea infection
followed by specific antibody production. For this reason the peak incidence of
endemic cholera occurs in the one to four-year old age group, and decreases with
age thereafter as immunity developes (Levine 1980).
Other host factors, such as age and general health, also affect the disease
response. Infants, elderly persons (Gardner 1980), malnourished people, those
with concomitant illness, and people taking antiinflammatory, cytotoxic, and
immunosuppressant drugs would be more susceptible to pathogens. An example
23
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of human variability (possibly genetic) is the following response of men orally
challenged with several different doses of Salmonella lyphi(Hornicketal. 1970):
Number of Percent developing
S. typhi typhoid fever
1
-------
Other epidemiological reports on the health effects of land treatment have been
more superficial. Examination of the workers on sewer farms in Berlin and
Memmingen in Germany has not shown them to have a higher rate of infectious
diseases or worm infestation than the rest of the population (Sepp 1971). At land
treatment sites near Paris, grain for cattle, beef cattle, and vegetables (e.g., beans,
onions, and celeriac) are raised (Dean 1978). The vegetables are checked for
Salmonella, with none having been found, and no disease has been traced to the
farms. During a cholera outbreak, no cholera bacteria were found on the vegetables.
At Wernbee Farm in Melbourne, Australia, there has never been a reported
epidemic or outbreak of disease among employees or residents, although no pre-
cautions other than normal hygiene practices have been taken, and the general health
of employees and residents is no different from that of the community in general
(Croxford 1978).
Although these retrospective studies are reassuring, a better measure of the health
effects of land treatment will come from well-planned prospective epidemiological
studies. Two such studies are currently underway—at Lubbock, Texas, and in Israel.
The results of these two projects may well modify the conclusions and recommenda-
tions of this report in the future
CONCLUSIONS AND RESEARCH NEEDS
The level of preapplication treatment required is highly site-specific. It may be as
little as simple sedimentation at sites with limited public access where crops are
protected by appropriate choice of crops and waiting periods, and groundwater is
protected by appropriate hydrological studies and application rate selection. In any
case, wastewater stabilization ponds or other pretreatment systems can be designed
to achieve practically any degree of bacterial pathogen removal deemed necessary
for the protection of public health.
The human exposure to aerosol bacteria at land treatment sites does not appear to
pose a high public health risk. Limiting public access to about 50 m should prevent
any problem from developing.
Aerial crops with little chance for contact with soil should not be harvested for
human consumption for at least one month after the last wastewater application;
subsurface and low-growing crops for human consumption should not be grown at a
land treatment site for at least six months after last application. Growth of crops for
animal feed, however, is probably a safe practice.
Properly designed slow-rate land treatment systems pose little threat of bacterial
contamination of groundwater. Considerable threat exists, however, at rapid-infil-
tration sites where the water table is shallow, particularly if the soil is porous. The
survival of bacteria in groundwater, once they get there, is poorly understood, and is
an important research need
There appears to be little danger to animals gra/ing at land treatment sites, if
grazing does not resume until four weeks after last application
Although the infective doses of bacteria appear to be fairly high, it would be wise
for humans to maintain a minimum amount of contact with an active land treatment
site.
25
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SECTION 5
VIRUSES
Transmission of viruses by feces is the second most frequent means of spread of
common viral infections, the first being the respiratory route. Transmission by
urine has not been established as being of epidemiological or clinical importance,
although some viruses, e.g., cytomegalovirus and measles, are excreted through this
route. The gastrointestinal tract is an important portal of entry of viruses into the
body, again second to the respiratory tract (Evans 1976). There has been some recent
concern that land treatment may increase the population size of the tree-hole
breeding mosquito, Aedes tnseriatus, a vector of California encephalitis virus (Zaim
el al. 1979), but this would likely only be a problem in wooded and waste areas, and is
not further considered here.
TYPES AND LEVELS IN WASTEWATER
The human enteric viruses that may be present in wastewater are listed in Table 13
(Melnick et al. 1978, Holmes 1979). These are referred to as the enteric viruses and
new members are constantly being identified. Since no viruses are normal inhabi-
tants of the gastrointestinal tract and none of these have a major reservoir other than
man (with the likely exception of rotaviruses), all may be regarded as pathogens,
although most can produce asymptomatic infections.
TABLE 13. HUMAN WASTEWATER VIRUSES
Enterovi ruses
Poliovirus
Coxsackievirus A
Coxsackievirus B
Echovirus
New Enterovirus
Hepatitis A Virus
Rotavirus ("Duovirus," "Reovirus-like Agent")
Norwalk-Like Agents (Norwalk, Hawaii, Montgomery County, etc )
Adenovirus
Reovirus
Papovavirus
Astrovirus
Calicivirus
Coronavirus-Like Particles
Upon entry into the alimentary tract, if not inactivated by the hydrochloric acid,
bile acids, salts, and enzymes, enteroviruses, hepatitis A virus, rotavirus, adenovirus,
and reovirus may multiply within the gut. The multiplication and shedding of adeno-
virus and reovirus here has not been shown to be of major epidemiological impor-
tance in their transmission (Evans 1976). The rotavirus often produces diarrhea in
children, but the local multiplication of enteroviruses and (possibly) hepatitis A virus
26
-------
in cells lining the area rarely produces local symptoms, i.e., diarrhea, vomiting, and
abdominal pain. Most enterovirus infections, even with the more virulent types,
cause few or no clinical symptoms. Occasionally, after continued multiplication in
the lymphoid tissue of the pharynx and gut, viremia may occur, i.e., virus enters the
blood stream, leading to further virus proliferation in the cells of the reticulo-
endothelial system, and finally to involvement of the major target organs—the
central nervous system, myocardium, and skin for the enteroviruses, and the liver for
hepatitis A virus (Melnick et al. 1979, Evans 1976).
Polioviruses cause poliomyelitis, an acute disease which may consist simply of
fever, or progress to aseptic meningitis or flaccid paralysis (slight muscle weakness to
to complete paralysis caused by destruction of motor neurons in the spinal cord).
Polio is rare in the United States, but may be fairly common in unimmunized
populations in the rest of the world. No reliable evidence of spread by wastewater
exists (Benenson 1975).
Coxsackieviruses may cause aseptic meningitis, herpangina, epidemic myalgia,
myocarditis, pericarditis, pneumonia, rashes, common colds, congenital heart
anomalies, fever, hepatitis, and infantile diarrhea.
Echoviruses may cause aseptic meningitis, paralysis, encephalitis, fever, rashes,
common colds, epidemic myalgia, pericarditis, myocarditis, and diarrhea.
The new enteroviruses may cause pneumonia, bronchiolitis, acute hemorrhagic
conjunctivitis, aseptic meningitis, encephalitis, and hand-foot-and-mouth disease.
The prevalence of the diseases caused by the Coxsackieviruses, echoviruses, and new
enteroviruses is poorly known, but 7,075 cases were reported to the Center for
Disease Control (CDC) in the years 1971-75 (Morens et al. 1979). These entero-
viruses are practically ubiquitous in the world, and may spread rapidly in silent
(asymptomatic) or overt epidemics, especially in late summer and early fall in
temperate regions. Because of their antigenic inexperience, children are the major
target of enterovirus infections, and serve as the main vehicle for their spread. Most
of these infections are asymptomatic, and natural immunity is acquired with
increasing age. The poorer the sanitary conditions, the more rapidly immunity devel-
ops, so that 90% of children living under poor hygienic circumstances may be
immune to the prevailing enteroviruses (of the approximately 70 types known) by the
age of 5. As sanitary conditions improve, the proportion of nonimmunized in the
population increases, and infection becomes more common in older age groups,
where symptomatic disease is more likely and is more serious (Melnick et al. 1979,
Benenson 1975). Thus, decreasing the human exposure to the common enteric
viruses through the water and food route has its disadvantages, as well as advan-
tages.
Hepatitis A virus causes infectious hepatitis, which may range from an inapparent
infection (especially in children) to fulminating hepatitis with jaundice. Recovery
with no sequelae is normal. Approximately 40,000-50,000 cases are reported
annually in the U.S. About half the U.S. population has antibodies to hepatitis A
virus, and the epidemiological pattern is similar to that of enteroviruses, with child-
hood infection common and asymptomatic (Duboise et al. 1979).
Rotavirus causes acute gastroenteritis with severe diarrhea, sometimes resulting
in dehydration and death in infants. It may be the most important cause of acute
gastroenteritis in infants and young children, especially during winter (Konno et al.
1978), but also may strike older children and adults (Holmes 1979).
Norwalk-like agents include the Norwalk, Hawaii, Montgomery County, Ditch-
ling, W, and cockle viruses, and cause epidemic gastroenteritis with diarrhea,
vomiting, abdominal pain, headache, and myalgia or malaise. The illness is generally
mild and self-limited (Kapikian et al. 1979). These agents have been associated with
sporadic outbreaks in schoolchildren and adults (Holmes 1979).
Adenoviruses are primarily causes of respiratory and eye infection, transmitted by
the respiratory route, but several strains are now believed to be important causes of
sporadic gastroenteritis in young children (Richmond et al, 1979, Kapikian et al.
1979).
27
-------
Reoviruses have been isolated from the feces of patients with numerous diseases,
but no clear etiological relationship has yet been established. It may be that reovirus
infection in humans is common, but associated with either mild or no clinical mani-
festations (Rosen 1979).
Papovaviruses have been found in urine, and may be associated with progressive
multifocal leukoencephalopathy (PML), but are poorly understood (Warren 1979).
Astroviruses, caliciviruses, and coronavirus-like particles may be associated with
human gastroenteritis, producing diarrhea, but are also poorly understood (Holmes
1979, Kapikian et a/. 1979).
Viruses are not normal inhabitants of the gastrointestinal tract nor regular
components of human feces, while certain types of bacteria are. Because of this
difference, the concept of using bacteria, e.g., coliforms and fecal streptococci, as
indicators of potential viral contamination in the environment has been a very
attractive one. Unfortunately the response of viruses to wastewater treatment and
their behavior in the environment are very different from those of bacteria (Berg
el al. 1978); for example, viruses are less easily removed during passage through soil
than are bacteria (Sobsey et al. 1980). Thus, Goyal et al. (1979) provided data to
indicate that current bacteriological standards for determining the safety of shellfish-
growing waters do not reflect the occurrence of enteroviruses. Likewise, Marzouk
et al. (1979) isolated enteroviruses from 20% of Israeli groundwater samples,
including 12 samples which contained no detectable fecal bacteria. They found no
significant correlation between the presence of virus in groundwater and levels of
bacterial indicators, i.e., total bacteria, fecal coliforms, and fecal streptococci. An
expansion of the study to include potable, surface, and swimming pool waters
resulted in the same conclusion (Marzouk et al. 1980). It appears, therefore, that
estimates of virus presence or levels in the environment will have to be made on the
basis of measurements of viral indicators, e.g., vaccine poliovirus or bactenophage,
or of the viral pathogens themselves, e.g., coxsackievirus or echovirus, rather than of
indicator bacteria.
The concentration of viruses in the feces of an uninfected person is normally zero.
The concentration in the feces of an infected person has not been widely studied.
However, from the available data it has been estimated to be about 106 per gram
(Feachem et al. 1978), but may be as high as 10'° per gram in the case of rotavirus
(Bitton 1980).
Estimates of the concentration of viruses in wastewater in the United States vary
widely, but it is thought to be tower than that in many developing countries. Num-
bers tend to be higher in later summer and early fall than other times of the year
because of the increase in enteric viral infections at this time, except for vaccine
polioviruses, whose concentration tend to remain constant. The concentrations
reported in the literature may be as little as one-tenth to one-hundredth of the actual
concentrations because of the limitations of virus recovery procedures and the use of
inefficient cell-culture detection methods (Akin et al. 1978, Keswick and Gerba
1980). (The use of several cell lines usually detects more viral types than a single cell
line does, and many viruses cannot yet be detected by cell-culture methods, e.g.,
hepatitis A virus and Norwalk-like agents.) Some representative levels of enteric
viruses in raw U.S. wastewaters are summarized in Table 14. It is evident that
reported concentrations are highly variable; Akin and Hoff (1978) have concluded
that ". . . from the reports that are available from field studies and with reasonable
allowances for the known variables, it would seem extremely unlikely that the total
concentration would ever exceed 10,000 virus units per liter of raw sewage and would
most often contain less than 1,000 virus units/liter."
PREAPPLICATION TREATMENT
Chlorine, although effective as a bactericide, is a very inefficient inactivator of
wastewater viruses. Levels as high as 8 mg/1 have little effect in secondary effluent
28
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TABLE 14. LEVELS OF ENTERIC VIRUSES IN U.S. WASTEWATERS
Description
St. Petersburg
Various souces
Chicago
Honolulu
Cincinnati
Urban
Calculated U S. average
Viral units/liter
10->183
100-400
Up to 440
0-820
0-1450
Up to 6000
7000
Reference
Wellings et a/. 1978
Akin and Hoff 1978
Fannin et al. 1977
Ruiter and Fujioka 1978
Akin and Hoff 1978
Vaughn 1977
Clarke et al. 1961
(Berg 1973) because of the difficulty in maintaining the more vincidal form, free
chlorine, under acidic conditions. Although very high doses of chlorine will destroy
viruses in wastewater, cost, production of carcinogens, and toxicity make this
impractical.
Processes for virus inactivation in wastewater have been briefly reviewed by
Melnick el al. (1978). Sedimentation, or conventional primary treatment, results in
low rates of removal, most of which is associated with the settling of solids in which
the viruses are embedded or on which they are adsorbed (Lance and Gerba 1978).
Removal rates of up to 90 percent have been reported (Melnick el al. 1978), with 10
percent or less being more common (Sproul 1978, Crites and Uiga 1979).
The survival of viruses in wastewater stabilization ponds is poorly known
(Feachem et al. 1978). Some representative survival data is summarized in Table 15
(Feachem et al. 1978, K otter a/. 1978). The data suggest that long retention times, of
the order of 50 days, particularly in combination with ponds in series, might accom-
plish quite significant virus removals.
TABLE 15. ENTERIC VIRUS SURVIVAL IN WASTEWATER
STABILIZATION PONDS
Description
Model ponds
Pond fed by activated
sludge effluent
Pond
3 ponds in series
Secondary effluent pond
in Israel, summer
(water temp. 18-20°C)
Retention time (days)
38
30
2.0
7 (total)
11
35
Removal rate
0
20% of
samples positive
0-96%
>90%
96%
100%
Jeconda
ry effluent pond
in Israel, winter
(water
temp down to 8°C)
8
15
22
29
34
40
47
73
51%
81%
96%
91%
96%
97%
97%
100%
29
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AEROSOLS
Aerosols have been of concern as a potential route of transmission of disease
caused by enteric viruses because, as with bacteria, once they are inhaled they may be
carried from the respiratory tract by cilia into the oropharynx, and then swallowed
into the gastrointestinal tract. Some enteroviruses may also multiply in the respira-
tory tract itself (Evans 1976). Another reason for concern is the theoretically
possible transmission of respiratory viruses through wastewater aerosols. On the
basis of actual viral sampling of wastewater, however, Johnson et al. (1980) con-
cluded that the likelihood of finding respiratory viruses in treated wastewater is very
small.
The initial aerosol shock during the process of aerosolization may result in a half
log loss of virus level (Sorber 1976). The subsequent die-off, estimated to be about
one log every 40 seconds (Sorber 1976), is determined primarily by solar radiation,
temperature, and relative humidity (Lance and Gerba 1978). The effect of relative
humidity appears to depend upon the lipid content of viruses, lipid-containing
viruses surviving better at low humidities, and those without lipid (e.g., most of the
enteric viruses) surviving better at high humidities (Carnow et al. 1979). Sorber
(1976) has estimated that, under the least desirable meteorological conditions
studied, less than 200 meters would be required to provide a reduction of three logs in
aerosolized virus concentrations.
Very few measurements of aerosol viruses from the spraying of wastewater have
been reported in the literature. The spraying in Israel of 3-5 day detention time
oxidation pond effluent, having a coliform density of about 106/100 ml, resulted in
the detection of poliovirus, coxsackievirus, and echovirus up to 100 m downwind
(Shuval 1978). To obtain quantitative measurements of aerosol virus concentrations
in air may require heroic efforts. Johnson el al. (1980) operated ten high-volume
samplers (1 m3/min electrostatic precipitators) for three-hour sample periods, at
50 m downwind from the source, to measure the aerosol enteroviruses produced by
the spraying of unchlorinated aerated-pond effluent in Pleasanton, California. Like-
wise, Teltsch et al. (1980) used a large-volume scrubber-cyclone sampler to extract
27+11 m' of air downwind from an irrigation line spraying raw wastewater at
Kibbutz Tzora, Israel. The results of these two studies are summarized in Table 16.
TABLE 16. AEROSOL ENTEROVIRUSES AT LAND TREATMENT SITES
Site
Pleasanton,
California
(Pond effluent)
Kibbutz Tzora,
Israel
(Raw
wastewater)
Distance
(m)
50
36-42
50
Wastewater
total
coliforms
(/I)
6.4x1 06-1 9x1 06
3 1xl07-1.5x109
1.0x10B
Wastewater
Enteroviruses
(mean)
(PFU/I)
45-330
(188)
0-650
(125)
650
Aerosol
Enteroviruses
(mean)
(/nv>)
0.011-0.017
(0.014)
0-0.082
(0.015)
0 14
70
Ox107-1.7x108
100 2.4xl07-30x108
170-13,000
(6585)
0-82,000
(16,466)
0-0.026
(0013)
0-0.10
(0.038)
30
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The results obtained from these two studies are highly variable, but it appears
reasonable to make use of the Pleasanton aerosol virus density, i.e., 0.014/m3, to
make human exposure estimates, since (1) the Pleasanton wastewater virus level is
similar to that in U.S. wastewaters in general (cf. Table 14), (2) the high Israeli waste-
water virus levels are not typical of those found in the U.S., and, in any case, a waste-
water stabilization pond would decrease these levels, and (3)theO. 14/m3 value found
at 50 m in Israel is based on only one sample, and does not appear to be represent-
ative of the other values.
From these data it can be calculated that an adult male, engaged in light work,
breathing at a rate of 1.2 m3/ hour and exposed to 0.014 PFU/m3 at 50m downwind
from a sprayer, would inhale approximately 0.13 PFU of enterovirus during an 8-
hour work day. This is probably an insignificant level of exposure. However, since
the recovery of enteric viruses from environmental samples is not perfectly efficient,
isolation of viruses increases as more cell culture types are used, and some enteric
viruses cannot yet be isolated on cell cultures, the actual exposure to enteric viruses
may be as much as ten to a hundred times the reported level (Teltsch et al. 1980).
Thus, it might be prudent to recommend a 100 m or 200 m minimum exposure
distance of the general public to a land treatment spray souce.
SURFACE SOIL AND PLANTS
As is the case with bacteria, the surface soil and plants of an active land treatment
site are constantly receiving enteric viruses. The survival time of viruses is primarily
of concern when decisions must be made on how long a period of time must be
allowed after last application before permitting access to people or animals, or
harvesting crops. Another concern is that the longer viruses survive at the surface the
greater opportunity they have for being desorbed and moving into the soil toward
the groundwater. This is not a problem with overland flow systems, which, although
68 to 85% of the enteric viruses are deposited at the surface, little virus penetrates into
the soil profile (Schaub et al. 1978b, 1980).
The factors affecting virus survival in soil are solar radiation, moisture, tempera-
ture, pH, and adsorption to soil particles. The soil microorganisms appear to have a
less important effect on virus degradation. Although it is often believed that
adsorption to inorganic surfaces prolongs the survival of viruses, there is some
evidence that adsorption may result in their physical disruption (Murray and
Laband 1979). Desiccation and higher temperatures decrease survival time (Sagik
et al. 1978). On the basis of studies with coxsackievirus, echovirus, poliovirus, rota-
virus, and bactenophages, Hurst et al. (1980b) have concluded that temperature and
adsorption to soil appear to be the most important factors affecting virus survival.
The soil is a complex medium, however, with fluctuations in soil moisture, tempera-
tures, ionic strength, pH, dissolved gas concentrations, nutrient concentrations, etc.
These may be caused by meteorological changes, by the action of other soil orga-
nisms, or by the activities of metazoans including humans (Duboise et al. 1979), and
understanding of the behavior of viruses in soil will be slow developing.
It is believed that most virus inactivation occurs in the top few centimeters of soil
where drying and radiation forces are maximal. The persistence of virus particles
that survive surface forces and enter the soil matrix is not well studied. However,
Wellings et al. (1978) has reported data that indicates virus may penetrate up to 58
feet of sandy soil.
Much of the recent literature on survival times of enteric viruses in soil is
summarized in Table 17. Approximately one hundred days appears to be the
maximum survival time of enteric viruses in soil, unless subject to very low
temperatures, which prolong survival beyond this time. Exposure to sunlight, high
temperatures, and drying greatly reduce survival times. Thus, Yeager and O'Brien
(1979) could recover no infectivity of poliovirus and coxsackievirus from dried soil
regardless of temperature, soil type, or type of liquid amendment. They suggested
that the main effect of temperature on virus survival in the field may be its influence
31
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on evaporation rates. They also suggested that enterovirus contamination of soil,
and possible migration to underlying groundwater, might be reduced or eliminated
by allowing the soil to dry between wastewater applications.
TABLE 17. SURVIVAL TIMES OF ENTERIC VIRUSES IN SOIL
Virus Soil
Enterovirus Sandy or
loamy podzol
Poliovirus Sand
Poliovirus Loamy fine
sand
Coxsackievirus Clay
Poliovirus —
Poliovirus Sugarcane
field
Poliovirus and Sandy loam
coxsackievirus
Moisture and
temperature
10-20%
3-1 0°C
10-20%
18--23°C
Air dry,
18-23°C
Moist
Dry
Moist, 4°C
Moist, 20°C
300 mm rain-
fall, -12-26°C
-14-27°C
15-33°C
Open, direct
sunlight
Mature
sugarcane
Saturated,
37°C
Saturated,
4°C
Dried, 37°C
and 4°C
Survival
(days)
70-170
25-110
15-25
91
<77
84
«90%
reduction)
84
(99.999%
reduction)
<161
89-96
<11
7-9
<60
12
>180
<3-<30
Reference
Bagdasaryan 1964
Lefler and Kott
1974
Duboise et at. 1976
Damgaard-Larsen
et at 1977
Tierney et a/. 1977
Lau et al. 1975
Yeager and O'Brien
1979
The phenomenon of virus inactivation by evaporative dewatering has been
documented by Ward and Ashley (1977), who observed a decrease in poliovirus liter
of greater than three orders of magnitude when the solids content of sludge was
increaed from 65% to 83%. Thislossofinfectivity was due to irreversible inactivation
32
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of pohovirus because viral particles were found to have released their RNA
molecules which were extensively degraded Both Ward and Ashley's (1977) and
Yeager and O'Brien's (1979) studies made use of radiolabeled viruses to correct for
virus recovery efficiency (affected by irreversible sludge and soil binding).
The absorption of enteric viruses by plants is a theoretical possibility. Murphy and
Syverton (1958) found enterovirus to be absorbed by tomato plant roots grown in
hydroponic culture under some conditions, and in some cases to be translocated to
the aerial parts. However, the rapid adsorption of virus by soil particles under
natural conditions may make them unavailable for plant absorption, thereby
indicating that plants or plant fruits would be unlikely reservoirs or carriers of viral
pathogens. The intact surfaces of vegetables are probably impenetrable for entero-
viruses (Bagdasaryan 1964).
On the surface of aerial crops virus survival would be expected to be shorter than
in soil because of the exposure to deleterious environmental effects, especially sun-
light, high temperature, drying, and washing off by rainfall (USEPA 1977). Some of
the literature on survival times is summari7ed in Table 18 (Feachem et al. 1978). The
data are similar to those for bacteria (cf. Table 9), and likewise appear to support a
one-month waiting period after last wastewater application before harvest.
TABLE 18. SURVIVAL TIMES OF ENTERIC VIRUSES ON CROPS
Virus
Crop
Conditions
Survival
(days)
Reference
Enterovirus
Tomatoes
Poliovirus
Pohovirus
Radishes
Tomatoes
3-8°C 10 Bagdasaryan 1964
(90% reduction)
18-21°C 10
(99% reduction)
5-10°C 20 Bagdasaryan 1964
(99% reduction),
>60
Indoors,
22-25°C
<12 Kott and Fishelson
1974
Indoors,
37°C
<5
Outdoors <1
Parsley 15-31°C <2
Pohovirus Lettuce and Sprayed, 6(99% Larkm et al. 1976
radishes summer-fall reduction)
36 (100%
reduction)
'oliovirus Lettuce and
radishes
Enterovirus Cabbage
Peppers
Tomatoes
Flooded,
summer
—
23
4
12
18
Tierney et al. 1 977
Grigor'Eva et al.
1965
33
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Because of the possible contamination of subsurface and low-growing crops with
soil, in which viruses have a longer survival time, about one hundred days would
probably be a safe waiting period. As with bacteria, this period could be shortened
by (1) the use of subsurface or covered drip irrigation (Sadovski etal. 1978a, 1978b),
(2) the growth of crops the harvested portion of which does not contact the soil, or (3)
the growth of crops used for animal feed only. At a site where (2) and (3) were
practiced, the Roswell, New Mexico, slow-rate land treatment site where secondary
effluent has been applied by ridge-and-furrow irrigation for 33 years, no entero-
viruses were found on or in the leaf and grain portions of corn (Koerner and Haws
I979a).
MOVEMENT IN SOIL AND GROUNDWATER
While viruses near the soil surface are rapidly inactivated due to the combined
effects of sunlight, drying, and the antagonism of aerobic soil microorganisms, those
that penetrate the aerobic zone can be expected to survive over a more prolonged
period of time. The longer they survive, the greater the chance that an event will
occur to promote their penetration into groundwater (Gerba and Lance 1980).
In contrast with bacteria, filtration plays a minor role in the removal of viruses in
soils, virus removal being almost totally dependent on adsorption. Since adsorption
is a surface phenomenon, soils with a high surface area, i.e., those with a high clay
content, would be expected to have high virus removal capabilities. Although the
physical-chemical reasons for virus adsorption to soil surfaces are poorly under-
stood, it appears that adsorption is increased by high cation exchange capacity, high
exchangeable aluminum, low pH (below 5), and increased cation concentration
(Gerba and Lance 1980). As the flowrate, or application rate, increases, virus
removal declines (Lance and Gerba 1980, Vaughn el al. 1981). Although it is
commonly believed that soluble organics compete with viruses for adsorption sites
on the soil particles, resulting in decreased virus adsorption or even elution of
already adsorbed viruses, Gerba and Lance (1978) found that adsorption of
poliovirus from primary effluent was similar to that from secondary effluent, and
that the adsorbed virus from the two sources had similar desorption properties.
These results suggest that adsorption of poliovirus and movement through the soil
are not affected by the higher organic content of primary effluent.
The degree of adsorption of viruses to soil is highly variable. Thus, Goyal and
Gerba (1979) found virus adsorption to differ greatly among virus types, virus strains
(within a type), and soils. Differences in adsorption among different strains of the
same virus type may be due to differences in the configuration of proteins in the outer
capsid of the virus, which affects the net charge on the virus. This affects the electro-
static potential between virus and soil, which, in turn, affects the degree of inter-
action between the two particles. They concluded that ". . . no one enterovirus or
coliphage can be used as the sole model for determining the adsorptive behavior of
viruses to soils and that no single soil can be used as the model for determining viral
adsorptive capacity of all soil types."
Much of the research in the past on virus behavior in soils has been done with
vaccine strains of poliovirus, because of their availability and safety, but poliovirus
adsorb better to soils than most other viruses (Gerba et al. 1980). Thus, the existing
literature may underestimate the mobility of viruses in soil.
With respect to variability among soils, the generalization can probably be made
that clayey soils are good virus adsorbers and sandy and organic soils poor virus
adsorbers. Sobsey et al. (1980) found ^95% virus removal from intermittently-
applied wastewater in unsaturated 10-cm-deep columns of sandy and organic soils.
However, considerable quantities of the retained viruses were washed out by
simulated rainfall. Under the same conditions clayey soils resulted in ^99.995% virus
removal, but none were washed out by simulated rainfall. The reason for the poor
adsorption of sandy soils is probably the low level of available surface area. The
34
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reason for the poor adsorption of organic soils, in spite of their high surface area, has
been suggested to be the complexation of virus by naturally-occuring low molecular
weight (<50,000) humic substances (Bixby and O'Brien 1979, Scheuerman et al.
1979).
Upon the application of wastewater to land most of the viruses are adsorbed in the
top few centimeters of the soil profile. In packed column studies with Flushing
Meadows, Arizona, soil, 90-99% of applied polioviruses was retained in the top 5-10
cm at infiltration rates of 15-55 cm/day. Removal appeared to be independent of
the concentration of the virus and was the same in both primary and secondary
effluent, but was less at flow rates exceeding 1.2 m/day. Tests with echovirus 1 and
echovirus 29 showed somewhat different adsorption patterns from that of polio-
virus, but all three viruses has approximately a 99% removal in the top 40 cm of soil
(Gerba and Lance 1980). Hurst and Gerba (1979), using the same soil in the field,
found enterovirus concentrations above 2.5 cm depth to be ten times those at 2.5-25
cm, confirming the laboratory column studies. Application of poliovirus-seeded
sewage effluent (1 cm/hr) to in situ soil cores in Long Island resulted in 77% of the
viruses adsorbed by the first 5cm of soil, 11% by 5-10 cm, 8% by 10-25 cm, and the
remainder (4%) by 25-50 cm (Landry et al. 1980).
After being adsorbed to the soil, viruses may remain infective and, under certain
conditions, may be desorbed and migrate down the soil profile. Thus, at a land treat-
ment site in Florida, viruses were not detected in 3 m and 6 m wells until periods of
heavy rainfall occurred (Wellings et al. 1975). Subsequent laboratory studies have
shown that pohovirus, previously adsorbed in the top 5 cm of soil, can be desorbed
and eluted to a depth of 160 cm (Lance et at. 1976). The degree of desorption and
migration is inversely related to the specific conductance of the percolated water
(Duboise et al. 1976). Viruses desorbed near the surface will usually readsorb further
down the soil profile (Landry et al. 1980), but might gradually migrate downward in
a chromatographic effect in response to cycles of rainfall. Lance et al. (1976) have
found that drying for one day between viral application and flooding with deionized
water prevented desorption (or enhanced inactivation). The importance of drying is
emphasized by the fact that poliovirus may retain its ability to migrate through the
soil for 84 days if the soil is kept moist (Duboise et al. 1976). As is the case with soil
adsorption of viruses, the degree of desorption of enteroviruses vanes with type and
strain (Landry et al. 1979).
As a result of the migration of viruses down the soil profile, they have been
detected in the groundwater beneath several rapid-infiltration land treatment sites.
These events are summarized in Table 19 (modified from Gerba and Lance 1980).
The two Florida land treatment sites showed viruses only after periods of heavy rain-
fall. Vaughn et al. (1978) noted that none of the enteroviruses isolated at the two New
York sites were polioviruses, supporting the observation that poliovirus is an
especially strong soil adsorber. No viruses were found in the groundwater at a third
New York land treatment site, where the infiltration basins were 24 m above the
water table. The Hawaiian groundwater contamination was attributed to underlying
soil fissures and fractures, which channeled the percolating waters at the land treat-
ment site (Hori et al. 1970). Most of these land treatment sites were underlain by very
coarse soils, i.e., sandy and / or gravelly, which would be expected to have a high rate
of water percolation. Since coarse-textured soils and a high rate of effluent applica-
tion are characteristic of rapid-infiltration sites, it would appear that rapid-infiltra-
tion land treatment sites have a high potential for the contamination of groundwater
with enteric viruses.
In contrast to the above, in the Flushing Meadows, Arizona, rapid-infiltration
land treatment site, although viruses were present in the secondary effluent used to
flood the basins, no viruses were detected in wells 6 m deep and 3 m away
horizontally (Gilberts al. 1976). At this site, basins in loamy sand underlaid at about
1 m with coarse sand and gravel are intermittently flooded at an average application
rate of about 90 m/ year. The excellent virus removal and prevention of groundwater
35
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TABLE 19. GROUNDWATER PENETRATION OF VIRUSES AT
RAPID-INFILTRATION LAND TREATMENT SITES
Location
St. Petersburg, Florida
Cypress Dome, Florida
Fort Devens, Massachusetts
Vineland, New Jersey
East Meadow, New York
Holbrook, New York
Oahu, Hawaii
Depth
(m)
6
3
183
16.8
11 3
6 1
Groundwater
Horizontal
distance
(m) Reference
— Wellmgs et al. 1975
7 Wellmgs et al. 1974
183 Schaub and Sorber 1977
250 Koerner and Haws 1979b
3 Vaughn et al. 1978
457 Vaughn et al. 1978
— Hon et al. 1 970
contamination has been attributed to the low rainfall in the region, the fine loamy
sand, and the practice of intermittent flooding of the soil (Gerba and Lance 1980).
It might be advisable, therefore, to site rapid-infiltration systems only on fine
sandy soils, avoiding coarse gravelly or organic ones, and to apply the effluent
intermittently, allowing the soil to dry between applications. The drying should help
to inactivate both viruses and bacteria, and has recently been recommended by Hurst
et al. (1980a) to prevent virus contamination of ground water. If, for climatic reasons,
drying between applications is impossible, as would be the case for much of eastern
U.S., many viruses would survive to the next application, at which time they could be
desorbed and migrate to the groundwater. To obviate this problem it would be
prudent to utilize wastewater stabilization ponds or some other form of pretreatment
which would decrease virus levels in the effluent. Serious consideration also should
be given to performing standard soil column tests (e.g., those described by Lance and
Gerba 1980) to assess virus retention at potential rapid-infiltration sites (Bitton
1980).
As is the case with bacteria, slow-rate land treatment sites probably pose little
threat of viral contamination of groundwater. This is because of the finer-textured
soils, the low rate of application, and the usual drying between applications. Thus,
test wells at a Roswell, New Mexico, site had no viruses after 33 years of application
of secondary effluent (Koerner and Haws 1979a).
Once enteric viruses get into groundwater, they can survive for long periods of
time, 2 to 188 days having been reported in the literature (Akin et al. 1971), and
probably migrate for long distances (Keswick and Gerba 1980). Low temperatures
prolong survival, but the factors affecting survival in groundwater are poorly under-
stood. It might be possible, for example, that entry of viruses into the groundwater
would be tolerable if sufficient underground detention time could be provided before
movement of the groundwater to wells or streams (Lance and Gerba 1978). Until
these factors are well-understood, it would be prudent to assume that groundwater
underlying coarse sandy or gravelly soils, and in the vicinity of rapid-infiltration land
treatment sites, or septic tank-leaching field systems, is contaminated with viruses.
Groundwater drawn from such sources for use as potable water supplies should be
disinfected; this advice is consistent with that of the World Health Organization
Scientific Group on Human Viruses in Water, Wastewater and Soil (WHO 1979).
The conclusion to this section on viruses in soil and groundwater at land treat-
ment sites can be taken from the recent review by Gerba and Lance (1980):
Although the presence of viruses in groundwater has been demon-
strated, it would appear that with proper site selection and management
the presence of viruses could be minimized or eliminated. The key is to
define the processes involved in the survival and transport of pathogens
in groundwater. With proper design, land treatment could be used as an
36
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effective method for reducing the number of pathogens in wastewater.
With the proper soil type, viruses and bacteria can be reduced to levels
as effective as chlorination as currently practiced, after the travel of
wastewater through only a few centimeters of soil.
ANIMALS
Human polioviruses, coxsackieviruses, echoviruses, and reoviruses have been
recovered from, or found to produce infection in, at least six species of animals —
dogs, cats, swine, cattle, horses, and goats (Metcalf 1976). Dogs and cats were found
to be involved in a majority of instances, probably because of their intimate associa-
tion with man in the household. The present state of information on virus trans-
mission in animals and man does not appear to allow an evaluation of the effect of
land treatment on animal infections or the role of animals as reservoirs of human
disease (Metcalf 1976).
Polley (1979) noted that, under experimental conditions, rotaviruses of human
origin have infected pigs, calves, and lambs, but concluded that in Canada their
transmission to livestock via effluent irrigation was a slight and unproven risk.
INFECTIVE DOSE, RISK OF INFECTION, EPIDEMIOLOGY
In contrast with bacteria, where large numbers of cells are usually necessary to
produce an infection, a few virus particles are currently thought to be able to produce
an infection under favorable conditions. The most important studies on the oral
infective dose of enteric viruses in humans are summarized in Table 20 (modified
from National Research Council 1977). The results are highly variable, and may
reflect differences in experimental conditions as well as states of the hosts. The recent
data do suggest, however, that the infective dose of enteroviruses to man is low,
possibly of the order of 10 virus particles or less. The same factors discussed earlier,
that affect bacteria also affect the virus dose-response relationship.
Since a potential route of exposure to viruses at land treatment sites is aerosols, it
is of great importance to compare the infective dose through the respiratory route
with that through the ingestion route. Couch el al. (1965) and Gerone et al. (1966)
reported the human inhalation infective dose of coxsackievirus A21 to be SJ18
TCDso, which is comparable with the oral infective dose of the enteroviruses.
Theoretically, a single virus particle is capable of establishing infection both in a
cell in culture and in a mammalian host (Westwood and Sattar 1976). If this were to
be the case, extreme care should be taken to avoid human exposure to enteric viruses
through aerosols or crops grown on land treatment sites. On the other hand, the
concept that a single virus particle often constitutes an infective dose in the real
world has been argued against (Lennette 1976) on the basis of the oral poliovaccine
studies, nonimmunologic barriers, human immunologic responses, and probabilistic
factors.
Viruses do not regrow on foods or other environmental media, as bacteria some-
times do. Therefore, the risk of infection is completely dependent upon being
exposed to an infective dose (which may be very low) in the material applied. In any
event, as is the case with bacteria, it would seem prudent for humans to maintain a
minimum amount of contact with an active land treatment site, and to rely on the
viral survival data discussed earlier for limiting the hazard from crops grown for
human consumption on wastewater-amended soils.
Fecally-polluted vegetable-garden irrigation water in Brazil has been found to
contain polioviruses and coxsackieviruses, and has been associated with earlier
epidemics (Christovao et al. 1967a, 1967b), but current epidemiological techniques
are probably not sufficiently sensitive to detect the low levels of viral disease trans-
mission that might occur from a modern land treatment site (Melnick 1978, WHO
1979).
37
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TABLE 20. ORAL INFECTIVE DOSE TO MAN OF ENTERIC VIRUSES
Virus Subjects
Vaccine Infants
poliovirus
Dose*
0.2 PFU**
2 PFU
20 PFU
105.5
107.5
106.6
107-6
Percent
infected
0
67
100
50
100
60
75
Reference
Koprowski
Gelfand et
1956
al. 1960
Krugman et al 1961
5.5*106
•Tissue Culture Dose 50% (TCD50) unless indicated
""Plaque-Forming Unit
t9S% Confidence Limits
89
Holgiun et al. 1962
103-5
104.5
1Q5. 5
103.5
1Q5.5
Premature 1
infants 2.5
10
Infants 7-52f
24-63
55-93
Echovirus 12 Young 10 PFU
adults 100 PFU
29
46
57
68
79
30
33
67
1
10
50
18
67
Lepow et al. 1 962
Warren et al. 1 964
Katz and Plotkm 1967
Miner et al. 1981
Schiff et al. (personal
communication) 1980
CONCLUSIONS AND RESEARCH NEEDS
Since only one-tenth to one-hundredth of the total viruses in wastewater and other
environmental samples may actually be detected, the development of methods to
recover and detect viruses continues to be a research need.
As in the case with bacteria, the level of preapplication treatment required is highly
site-specific, but may be minimal where crops and groundwater are protected. Where
protection of ground water cannot be assured, wastewater stabilization ponds should
be considered, but the survival of viruses in these ponds is an important research
need.
Because of the potential exposure to aerosol viruses at land treatment sites, it
would be prudent to limit public access to 100-200 m from a spray source.
Aerial crops with little chance for contact with soil should not be harvested for
human consumption for at least one month after the last wastewater application; for
subsurface and low-growing crops about one hundred days would probably be a safe
waiting period. An important research need is the effect of drying of the soil between
wastewater applications on the survival of surface-soil viruses.
As with bacteria, properly designed slow-rate land treatment systems pose little
threat of viral contamination of groundwater. Considerable threat exists, however,
38
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at rapid-infiltration sites, and appropriate management or preapplication treatment
techniques should be instituted; until then, groundwater drawn for use as potable
water supplies should be disinfected. The factors controlling the migration of viruses
in soils and the survival of viruses in groundwater are poorly understood, and are
significant research needs.
The role of animals at land treatment sites in transmitting human viral disease is
poorly known, and is a research need.
Since the infective doses of viruses are low, it would be wise for humans to main-
tain a minimum amount of contact with an active land treatment site. The compari-
son of the respiratory infective dose of enteric viruses with the oral infective dose is a
significant research need.
39
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SECTION 6
PROTOZOA
The protozoa and helminths (or worms) are often grouped together under the
term, "parasites," although in reality all the pathogens are biologically parasites.
Because of the large size of protozoan cysts and helminth eggs, compared with
bacteria and viruses, it is extremely unlikely that they will find their way into either
aerosols or groundwater at land treatment sites, and, thus, these routes of exposure
are not further considered in this report. Little attention has been given to the
presence of parasites in wastewater, and their potential for contaminating food crops
in the United States, probably because of the popular impression that the prevalence
of parasite infection in the U.S. is minimal (Larkin et al. 1978b). However, because
of the increasing recognition of parasite infections in the U.S., the return of military
personnel and travelers from abroad, the level of recent immigration and food
imports from countries with a high parasitic disease prevalence, and the existence of
resistant stages of the organisms, a consideration of parasites is warranted.
TYPES AND LEVELS IN WASTEWATER
The most common protozoa which may be found in wastewater are listed in Table
21. Of these, only three species are of major significance for transmission of disease
to humans through wastewater: Entamoeba histolytica, Giardia lamblia, and
Balantidium coli. Toxoplasma gondii also causes significant human disease, but the
wastewater route is probably not of importance. Eimena spp. are often identified in
human fecal samples, but are considered to be spurious parasites, entering the
gastrointestinal tract from ingested fish.
TABLE 21. TYPES OF PROTOZOA IN WASTEWATER
Name
Protozoan class
Nonhuman reservoir
Human Pathogens
Entamoeba histolytica
Giardia Iambi/a
Balantidium coli
Toxoplasma gondii
Dientamoeba fragilis
Isospora belli
I. hommis
Human Commensals
Endolimax nana
Entamoeba coli
lodamoeba butschlii
Animal pathogens
Eimeria spp.
Entamoeba spp.
Giardia spp.
Isospora spp.
Ameba
Flagellate
Ciliate
Sporozoan (Coccidia)
Ameba
Sporozoan (Coccidia)
Sporozoan (Coccidia)
Ameba
Sporozoan (Coccidia)
Ameba
Flagellate
Sporozoan (Coccidia)
Domestic and wild mammals
Beavers, dogs, sheep
Pigs, other mammals
Cats
Fish, birds, mammals
Rodents, etc.
Dogs, cats, wild mammals
Dogs, cats
40
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Entamoeba histolytica causes amebiasis, or amebic dysentery, an acute enteritis,
whose symptoms may range from mild abdominal discomfort with diarrhea to
fulminating dysentery with fever, chills, and bloody and mucoid diarrhea. Most
infections are asymptomatic, but in severe cases dissemination may occur, producing
liver, lung, or brain abscesses, and death may result. Amebiasis is rare in the U.S.
(Krogstad et al. 1978), and is transmitted by cysts contaminating water or food.
Giardia lambha causes giardiasis, an often asymptomatic infection of the small
intestine, which may be associated with chronic diarrhea, malabsorption of fats,
steatorrhea, abdominal cramps, bloating, fatigue, and weight loss. The carrier rate in
different areas of the U.S. may range between l.Sand 20%(Benenson 1975), and it is
transmitted by cysts contaminating water or food, and by person-to-person contact
(Osterholm el al. 1981).
Balantidium coli causes balantidiasis, a disease of the colon, characterized by
diarrhea or dysentery. Infections are often asymptomatic, and the incidence of
disease in man is very low (Benenson 1975). Balantidiasis is transmitted by cysts
contaminating water, particularly from swine.
Toxoplasma gondii causes toxoplasmosis, a systemic disease which rarely gives
rise to clinical illness, but which can damage the fetus if infection, and subsequent
congenital transmission, occurs during pregnancy. Approximately 50% of the
population of the U.S. is thought to be infected (Krick and Remington 1978), but the
infection is probably transmitted by oocysts in cat feces or the consumption of cyst-
contaminated, inadequately-cooked meat of infected animals (Teutsch el al. 1979),
rather than through wastewater.
The active stage of protozoans in the intestinal tract of infected individuals is the
trophozoite. The trophozoites, after a period of reproduction, may round up to form
precysts, which secrete tough membranes to become environmentally-resistant cysts,
in which form they are excreted in the feces (Brown 1969). The number of cysts
excreted by a carrier of Entamoeba histolytica has been estimated to be 1.5* 107 per
day (Chang and Kabler 1956), and by an adult infected with Giardia lamblia at
2.1-7.1*108 per day (Jakubowski and Ericksen 1979). The concentration of
Entamoeba hist oh-tic a cysts in the feces of infected individuals has been estimated to
be 1.5*105/g (Feachem et al. 1978). The concentration of Giardia lamblia cyslsin the
feces has been estimated to be I05/g in infected individuals (Feache met al. 1978), up
to 2,2x106/g in infected children, and up t o 9.6* 107/gin asymptomatic adult carriers
(Akin et al. 1978).
The types and levels of protozoan cysts actually present in wastewater depend on
the levels of disease in the contributing human population, and the degree of animal
contribution to the system. Some estimates are present in Table 22.
TABLE 22. LEVELS OF PROTOZOA IN WASTEWATER
Species
Wastewater type
Concentration
[cysts/1) Reference
Entamoeba Untreated
histolytica
Giardia
lamblia
Municipal effluent
During epidemic
(50% carrier rate)
Raw sewage
(1-25% prevalence)
Raw sewage
4.0 Foster and Engelbrecht
1973
2 2 Kott and Kott 1967
5000 Chang and Kabler 1956
9 6x103-2.4x1Q5 Jakubowski and Ericksen
1979
Up to 8x10" Weaver et al. 1978
41
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PREAPPLICATION TREATMENT
Entamoeba histolytica and Giardia are very chlorine resistant, Entamoeba being
one of the most chlorine-resistant pathogens known (Hoff 1979). Sedimentation, or
conventional primary treatment, appears to result in poor removals of protozoan
cysts from wastewater, as indicated by data on Entamoeba histolytica. Thus, Cram
(1943) reported lack of removal, Foster and Engelbrecht (1973) 15% removal, Sproul
(1978) 0 to incomplete removal, and Crites and Uiga (1979) 10-50% removal. These
authors reported very poor secondary treatment removals as well.
Wastewater stabilization ponds may accomplish much better removals of
protozoan cysts. Thus, 100% reduction of protozoan cysts from the effluent was
accomplished by a series of 3 ponds, with a 7-day retention time, in India (Arceivala
el al. 1970), and of Giardia cysts by a storage lagoon in Texas (Weaver et al. 1978).
However, it is likely that this treatment resulted in significant concentration of the
cysts in sludge rather than complete inactivation. Entamoeba cysts have been found
to survive several months in water at 0°C, 3 days at 30°C, 30 minutes at 45°C, and 5
minutes at 50°C (Freeman 1979). Giardia cysts can survive up to about 77 days in
water at 8°C, 5-24 days at 21°C, and 4 days or less at 37°C (Bingham et al. 1979).
SOIL AND PLANTS
Protozoan cysts are highly sensitive to drying. Rudolfs el al. (195 Ib) have reported
survival times for Entamoeba histolytica of 18-24 hours in dry soil and 42-72 hours
in moist soil. Somewhat longer times, i.e., 8-10 days, have been reported by Beaver
and Deschamps (1949) in damp loam and sand at 28-34°C.
Because of their exposure to the air, protozoan cysts deposited on plant surfaces
would also be expected to die off rapidly. The fact that cysts can survive long enough
to get into the human food supply under poor management conditions is confirmed
by the recent isolation of high levels of Entamoeba histolytica, E. coli, Endolimax
nana, and Giardia lamblta on the wastewater-irrigated fruits and vegetables in
Mexico City's marketplaces (Tay et al. 1980). Rudolfs et al. (1951b) found
contaminated tomatoes and lettuce to be free from viable Entamoeba cysts within 3
days, and the survival rate to be unaffected by the presence of organic matter in the
form of fecal suspensions. They concluded that field-grown crops"... consumed raw
and subject to contamination with cysts of E. histolytica are considered safe in the
temperate zone one week after contamination has stopped and after two weeks in
wetter tropical regions."
Therefore, if the recommendations, based on bacteria, for harvesting human food
crops are followed, it is extremely unlikely than any public health risk will ensue.
ANIMALS
Although it would be theoretically possible for protozoan diseases to be trans-
mitted through animals at a land treatment site, little relevent information on the
subject appears to exist. However, in view of the survival times discussed above, the
four week waiting period before the resumption of grazing, recommended on the
basis of bacteria, should prevent any problem from developing.
INFECTIVE DOSE, RISK OF INFECTION, EPIDEMIOLOGY
Human infections with Giardia lamblia and the nonpathogenic Entamoeba coli
have been produced with ten cysts administered in a gelatin capsule (Rendtorff
1954a, 1954b). Infections have been produced with single cysts of Entamoeba coli,
and there is no biological reason why single cysts of Giardia would not also be infec-
tious (Rendtorff 1979). This is probably true for E. histolytica as well (Beaver et al.
1956). The pathogenicity of protozoa is highly variable among strains, and human
responses likewise are variable. Thus, many infections are asymptomatic.
42
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Because of the low infective doses of protozoan cysts, it would be prudent for
humans to maintain a minimum amount of contact with an active land treatment
site. However, if the recommended waiting periods for crop harvest are followed, the
risk of infection should be minimal, because of the cysts' sensitivity to drying.
A few epidemiological reports have linked the transmission of amebiasis to vege-
tables irrigated with raw wastewater or fertilized with night soil (Bryan 1977,
Geldreich and Bordner 1971).
CONCLUSIONS AND RESEARCH NEEDS
The required level of preapplication treatment is site-specific, and wastewater
stabilization ponds can probably accomplish a significant degree of removal of
protozoan cysts. The effectiveness of ponds in the treatment for protozoa is a signifi-
cant research need, however.
Human exposure to pathogenic protozoa through aerosols or groundwater is
extremely unlikely, and, if crops are not harvested nor animals allowed to graze until
two weeks after the last wastewater application, exposure through these routes will
be minimized.
Because of the low infective doses of protozoan cysts, it would be wise for humans
to maintain a minimum amount of contact with an active land treatment site.
43
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SECTION 7
HELMINTHS
TYPES AND LEVELS IN WASTEWATER
The pathogenic helminths whose eggs are of major concern in wastewater are
listed in Table 23. They are taxonomically divided into the nematodes, or round-
worms, and cestodes, or tapeworms. The trematodes, or flukes, are not included
since they require aquatic conditions and intermediate hosts, usually snails, to
complete their life cycles, and thus are unlikely to be of concern at land treatment
sites. Some common helminths, pathogenic to domestic or wild animals, but not to
humans, are listed in Table 24 (after Reimers el al. 1980), since their eggs are likely to
be identified in wastewater. Several of the human pathogens listed in Table 23, e.g.,
Toxocara spp., are actually animal parasites, rather than human parasites, infesting
man only incidentally, and not completing their life cycle in man.
TABLE 23. PATHOGENIC HELMINTHS OF MAJOR CONCERN
IN WASTEWATER
Pathogen
Common name
Disease
Nonhuman
reservoir
NEMATODES (Roundworms)
Enterobius
vermicularis
Ascaris
lumbncoides
A. suum
Tnchuris
trichiura
Necator
americanus
Ancylostoma
duodenale
A. braziliense
A. canmum
Strongyloides
stercoralis
Toxocara cam's
T. cati
Pinworm
Roundworm
Swine roundworm
Whipworm
Hookworm
Hookworm
Cat hookworm
Dog hookworm
Threadworm
Dog roundworm
Cat roundworm
Enterobiasis
Ascariasis
Ascanasis
Trichuriasis
Necatonasis
Ancylostomiasis
Cutaneous larva migrans
Cutaneous larva migrans
Strongyloidiasis
Visceral larva migrans
Visceral larva migrans
Pig*
Cat, dog*
Dog*
Dog
Dog*
Cat*
CESTODES (Tapeworms)
Taenia
saginata**
T so/ium
Hymenolepis
nana
Echmococcus
granulosus
E. multilocularis
Beef tapeworm Taeniasis
Pork tapeworm Taeniasis, Cysticercosis
Dwarf tapeworm Taeniasis
Dog tapeworm
Unilocular hydatid disease
Alveolar hydatid disease
Rat, mouse
Dog*
Dog, fox, cat*
'Definitive host, man only incidentally infested
**Eggs not infective for man
44
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TABLE 24. ANIMAL-PATHOGENIC HELMINTHS IN WASTEWATER
Pathogen Definitive host
Trichuris suis Pig
T. vulpis Dog
Toxascaris leonina* Dog, cat
Ascaridia galli Poultry
Heterakis gallinae Poultry
Trichosomoides crassicauda Rat
Anatrichosoma buccalis Opossum
Cruzia americana Opossum
Capillana hepatica Rat
C. gastrica Rat
C. spp. Poultry, wild birds, wild mammals
Hymenolepis diminuta Rat
H. spp. Birds
Taenia pisiformis Cat
Hydatigera taeniaeformis Dog
Macracanthorhynchus hirudinaceous Pig
*Toxascans leonina may produce visceral larva migrans in experimental animals, but its role in human disease is
undefined (Quinn el a/ 19801
Enterobius vermicularis, the pinworm, causes itching and discomfort in the
penanal area, particularly at night when the female lays her eggs on the skin. A 1972
estimate of the prevalence of pinworm infections in the U.S. was 42 million (Warren
1974). Although it is by far the most common helminth infection, the eggs are not
usually found in feces, are spread by direct transfer, and live only for a few days.
Ascaris lumbricoides, the large roundworm, produces numerous eggs, which
require 1-3 weeks for embryonation. After the embryonated eggs are ingested, they
hatch in the intestine, enter the intestinal wall, migrate through the circulatory
system to the lungs, enter the alveoli, and migrate up to the pharynx. During their
passage through the lungs they may produce ascaris pneumonitis, or Loeffler's
syndrome, consisting of coughing, chest pain, shortness of breath, fever, and
eosinophilia, which can be especially severe in children. The larval worms are then
swallowed, to complete their maturation in the small intestine, where small numbers
of worms usually produce no symptoms. Large numbers of worms may cause
digestive and nutritional disturbances, abdominal pain, vomiting, restlessness, and
disturbed sleep, or, occasionally, intestinal obstruction. Death due to migration of
adult worms into the liver, gallbladder, peritoneal cavity, or appendix occurs
infrequently. The prevalence of ascariasis in the U.S. was estimated to be about 4
million in 1972 (Warren 1974).
Ascaris suum, the swine roundworm, may produce Loeffler's syndrome, but
probably does not complete its life cycle in man (Phillis el al. 1972).
Trichuris mchiura, the human whipworm, lives in the large intestine with the
anterior portion of its body threaded superficially through the mucosa. Eggs are
passed in the feces, and develop to the infective stage after about four weeks in the
soil (Reimers et al. 1980), and direct infections of the cecum and proximal colon
result from the ingestion of infective eggs. Light infections are often asymptomatic,
but heavy infections may cause intermittent abdominal pain, bloody stools,
diarrhea, anemia, loss of weight, or rectal prolapse in very heavy infections. Human
infections with T. suis, the swine whipworm, and T. vulpis, the dog whipworm, have
been reported, but are uncommon (Reimers et al. 1980). The prevalence of
trichuriasis in the U.S. was estimated to be about 2.2 million in 1972 (Warren 1974).
Reimers et al. (1980) have found Ascaris, Trichuris, and Toxocara to be the most
frequently recovered helminth eggs in municipal wastewater sludge in southeastern
United States.
45
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Necator americanus and Ancylostoma duodenale, the human hookworms, live in
the small intestine attached to the intestinal wall. Eggs are passed in the feces, and
develop to the infective stage in 7-10 days in warm, moist soil. Larvae penetrate bare
skin, usually of the foot (although Ancylostoma may also be acquired by the oral
route), pass through the lymphatics and and blood stream to the lungs, enter the
alveoli, migrate up the pharynx, are swallowed, and reach the small intestine. During
lung migration, a pneumonitis, similar to that produced by Ascaris, may occur
(Benenson 1975). Light infections usually result in few clinical effects, but heavy
infections may result in iron-deficiency anemia (because of the secreted anti-
coagulant causing bleeding at the site of attachment) and debility, especially in
children and pregnant women. The prevalence of hookworm in the U.S. (usually due
to Necator) was estimated to be about 700,000 in 1972 (Warren 1974).
Ancylostoma hrazilien.se and A. caninum, the cat and dog hookworm, do not live
in the human intestinal tract. Larvae from eggs in cat and dog feces penetrate bare
skin, particularly feet and legs on beaches, and burrow aimlessly intracutaneously,
producing "cutaneous larva migrans" or "creeping eruption." After several weeks or
months the larva dies without completing its life cycle.
Strongvloides stercoralis, the threadworm, lives in the mucosa of the upper small
intestine. Eggs hatch within the intestine, and the reinfection may occur, but usually
noninfective larvae pass out in the feces. The larva in the soil may develop into an
infective stage or a free-living adult, which can produce infective larvae. The infective
larvae penetrate the skin, usually of the foot, and complete their life cycle similarly to
hookworms. Intestinal symptoms include abdominal pain, nausea, weight loss,
vomiting, diarrhea, weakness, and constipation. Massive infection and autoinfec-
tion may lead to wasting and death in patients receiving immunosuppressive
medication (Benenson 1975). The prevalence of strongyloidiasis in the U.S. was
estimated to be about 400,000 in 1972 (Warren 1974). Dog feces is another source of
threadworm larvae.
Toxocara cams and T. cali, the dog and cat roundworms, do not live in the human
intestinal tract. When eggs from animal feces are ingested by man, particularly
children, the larvae hatch in the intestine and enter the intestinal wall, similarly to
Ascaris. However, since Toxocara cannot complete its life cycle, the larvae do not
migrate to the pharynx, but, instead, wander aimlessly through the tissues, pro-
ducing "visceral larva migrans," until they die in several months to a year. The
disease may cause fever, appetite loss, cough, asthmatic episodes, abdominal
discomfort, muscle aches, or neurological symptoms, and may be particularly
serious if the liver, lungs, eyes (often resulting in blindness), brain, heart, or kidneys
become involved (Fiennes 1978). The infection rate of T. canis is more than 50% in
puppies and about 20% in older dogs in the U.S. (Gunby 1979), and Toxocara is one
of the most common helminth eggs in wastewater sludge (Reimers et al. 1980).
Taenia saginata and T. solium, the beef and pork tapeworms, live in the intestinal
tract, where they may cause nervousness, insomnia, anorexia, loss of weight,
abdominal pain, and digestive disturbances, or be asymptomatic. The infection
arises from eating incompletely cooked meat (of the intermediate host) containing
the larval stage of the tapeworm, the cysticercus, however, rather than from a waste-
water-contaminated material. Man serves as the definitive host, harboring the self-
fertile adult. The eggs (contained in proglottids) are passed in the feces, ingested by
cattle and pigs (the intermediate hosts), hatch, and the larvae migrate into tissues,
where they develop to the cysticercus stage. The hazard, then, is principally to live-
stock grazing on land-treatment sites. The major direct hazard to man is the possi-
bility of him acting as the intermediate host. While Taenia saginata eggs are not
infective for man, those of T. solium are infective for man, in which they can produce
cysticerci. Cysticercosis can present serious symptoms when the larvae localize in the
ear, eye, central nervous system, or heart. Taeniasis with Taenia solium is rare in the
U.S., and with T. saginata is only occasionally found. However, human infections
with these tapeworms are fairly common in some other areas of the world.
46
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Hvmenolepis nana, the dwarf tapeworm, lives in the human intestinal tract,
where it may be asymptomatic or produce the same symptoms as Taenia. Infective
eggs are released, and internal autoinfection may occur, or, more usually, eggs may
be passed in the feces. No intermediate host is required, and, upon ingestion, eggs
develop into adults in the intestinal tract. The prevalence of infection in southern
U.S. is 0.3 to 2.9 percent, mostly among children under 15.
Echinococcus granulosus and E. multilocularis, two dog tapeworms, do not live in
the human intestinal tract. Dogs and other carnivores are their definitive hosts. Eggs
in animal feces are usually ingested by an herbivore, in which they hatch into larval
forms, which migrate into tissues, where they develop into hydatid cysts. When the
herbivore is eaten by a carnivore the cysts develop into adult tapeworms in the
carnivore's intestinal tract. If man ingests an egg, he can play the role of the
herbivore, just as in cysticercosis. A hydatid cyst can develop in the liver, lungs, or
other organs, where serious symptoms can be produced as the cyst grows in size or
ruptures. The disease is rare in the U.S., but has been reported from the western
states, Alaska, and Canada, particularly where dogs are used to herd grazing
animals, and where dogs are fed animal offal.
Since no helminths are normal inhabitants of the human gastrointestinal tract,
i.e., commensals, there are no normal levels of helminth eggs in feces. Levels
suggested by Feachem el al. (1978) for eggs in the feces of infected humans (eggs/ g)
are:
Enterobius 0
Ascaris 10,000
Trichuris 1,000
Necator and Ancylostoma 800
Strongyloides 10
Taenia 10,000
Hymenolepis ?
Obviously, these values will depend on intensity of infection.
The presence and levels in wastewater of any of these helminth eggs, or of those
from animal feces (Ancylostoma, Toxocara, and Echinococcus), depend on the
levels of disease in the contributing population, and the degree of animal contribu-
tion to the system. Foster and Engelbrecht (1973) suggested a value of 66 helminth
ova/1 in untreated wastewater, and Larkine/a/. (1978b) cited values of 15-27 Ascaris
eggs/1 and 6.2 helminth eggs/1 in primary effluent.
PREAPPLICATION TREATMENT
Since helminth eggs are denser than water, ordinary sedimentation, or conven-
tional primary treatment, is a fairly efficient method of removal. German sanitary
engineers have found one to two hours of sedimentation detention time to be
sufficient to remove most helminth eggs (Sepp 1971). Newton el al. (1949) showed
98% removal of Taenia saginata eggs by 2-hour sedimentation in the laboratory, but
lower removal under field conditions.
Conventional secondary treatment, i.e., activated sludge or trickling filter, results
in very poor helminth egg removal rates (Sproul 1978).
Wastewater stabilization ponds accomplish excellent degrees of helminth egg
removal, as indicated in Table 25 (after Feachem el al. 1978). Feachem et al. (1978)
have concluded that complete removal of helminth eggs occurs in all cases of well-
designed multicelled stabilization ponds with an overall retention time of more
than 20 days. Stabilization ponds with variable retention times at a land treatment
site in San Angelo, Texas, resulted in complete removal of helminths (Weaver et al.
1978).
It should be kept in mind that the sludge or pond sediment resulting from these
processes will have high densities of viable helminth eggs, and will require proper
treatment before utilization.
47
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TABLE 25. HELMINTH EGG SURVIVAL IN WASTEWATER
STABILIZATION PONDS
Organism
Helminths
Helminths
Enterobius
Enterobius
A scar is
Trichuris
Ancy/ostoma duodenale
Ancylostoma
Hymenolepis
Retention time or
pond description
7 days, 3 ponds
4 ponds
38 days
6 days, 3 ponds
6 days, 3 ponds
6 days, 3 ponds
38 days
6 days, 3 ponds
6 days, 3 ponds
Removal
rate
100%
1 00%
1 00%
100%
100%
100%
100%
90%
1 00%
Reference
Arceivala et a/, 1970
Koltypm 1969
Hodgson 1964
Lakshminarayana and
Abdulappa 1972
Lakshminarayana and
Abdulappa 1972
Lakshminarayana and
Abdulappa 1972
Hodgson 1964
Lakshminarayana and
Abdulappa 1972
Lakshminarayana and
Abdulappa 1972
SOIL AND PLANTS
Helminth eggs and larvae, in contrast to protozoan cysts, live for long periods of
time when applied to the land, probably because soil is the transmission medium for
which they have evolved, while protozoa have evolved toward water transmission.
Thus, under favorable conditions of moisture, temperature, and sunlight, Ascaris,
Trichuris, and Toxocara can remain viable and infective for several years (Little
1980). Hookworms can survive up to 6 months (Feachem et al. 1978), and Taenia a
few days to seven months (Babayeva 1966); other helminths survive for shorter
periods.
Because of desiccation and exposure to sunlight, helminth eggs deposited on plant
surfaces die off more rapidly. Thus, Rudolfs et al. (1951c) found Ascaris eggs, the
longest-lived helminth egg, sprayed on tomatoes and lettuce, to be completely
degenerated after 27-35 days.
At rapid-infiltration land treatment sites there should be little risk to public health
from helminths, as long as the site is dedicated to rapid infiltration. However,
because of the growth of crops and presence of people at slow-rate and overland-flow
sites, and the longevity of helminth eggs, it would be advisable to select a preapphca-
tion treatment method, e.g., stabilization ponds, which will completely remove
helminth eggs at these land treatment sites.
ANIMALS
The most serious threat to cattle at land treatment sites is the beef tapeworm,
Taenia saginata (Feachem et al. 1978). The increased incidence of cysticercosis in
cattle results in economic losses (because of condemnation of carcasses), as well as
increased incidence of disease in man. The application of wastewater sludge to
pastures has resulted in outbreaks of cysticercosis in grazing cattle in England
(Macpherson et al. 1978, 1979), but wastewater land treatment sites at San Angelo,
Texas (Weaver et al. 1978), and Melbourne, Australia (Croxford 1978, McPherson
1978), have resulted in no increase of cysticercosis in grazing cattle.
Nevertheless, because of the longevity of helminth eggs in the soil, and the fact
that cattle consume considerable quantities of soil as they graze, it would be prudent
to select a pretreatment method which will completely remove helminth eggs at land
treatment sites where cattle are allowed to graze. Arundel and Adolph (1980) have
48
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suggested that stabilization ponds remove Taenia saginata quite efficiently. They
found no cysticercosis in cattle grazed on pasture irrigated with effluent from
lagooning, compared with a 3.3% infection rate from tricking filter effluent, 9.0-
12.5% from activated sludge effluent, and 30.0% from raw sewage.
INFECTIVE DOSE, RISK OF INFECTION, EPIDEMIOLOGY
Single eggs of helminths are infectious to man, although, since the symptoms
of helminth infections are dose-related, many light infections are asymptomatic.
However, Ascaris infection may sensitize individuals so that the passage of a single
larval stage through the lungs may result in allergic symptoms, i.e., asthma and
urticaria (Muller 1953).
Because of the low infective doses of helminth eggs, and their longevity, it would
be prudent for humans to maintain a minimum amount of contact with an active or
inactive land treatment site, unless the wastewater has been pretreated to remove
helminths.
A few epidemiological reports have linked the transmission of Ascaris and hook-
worm to the use of night soil on gardens and small farms in Europe and the Orient
(Geldreich and Bordner 1971).
CONCLUSIONS AND RESEARCH NEEDS
The required level of preapplication treatment for rapid-infiltration systems is
site-specific, but slow-rate and overland-flow systems should have complete removal
of helminth eggs. This would probably be most easily done by wastewater stabiliza-
tion ponds.
Human exposure to helminths through aerosols or groundwater is extremely
unlikely, and, if wastewater is properly pretreated, exposure through crops and
animals will be minimized.
It would be wise for humans to maintain a minimum amount of contact with an
active or inactive land treatment site, unless the wastewater has been pretreated to
remove helminths.
49
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