United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 2771 1
Research and Development EPA/600-'!-85/01 5 September 1 985
oEPA Health Effects of
Land Application of
Municipal Sludge
-------
EPA/600/1-85/015
September 1985
Health Effects of
Land Application of Municipal Sludge
by
Norman E. Kowal
Toxicology and Microbiology Division
Health Effects Research Laboratory
Cincinnati, OH 45268
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
-------
NOTICE
This document has been subjected to the U.S. Environmental Protection Agency's
peer and administrative review policy and approved for publication as an EPA
document. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
U.S. environment;:! Protection Agency
-------
FOREWORD
The many benefits of our modern, developing industrial society are accompanied
by certain hazards. Careful assessment of the relative risk of existing and new
man-made environmental hazards is necessary for the establishment of sound
regulatory policy. These regulations serve to enhance the quality of our environment
in order to promote the public health and welfare and the productive capacity of our
Nation's population.
The complexities of environmental problems originate in the deep interdependent
relationships between the various physical and biological segments of man's natural
and social world. Solutions to these environmental problems require an integrated
program of research and development using input from a number of disciplines. The
Health Effects Research Laboratory, Research Triangle Park, NC and Cincinnati,
OH, conducts a coordinated environmental health research program in toxicology,
epidemiology, and clinical studies using human volunteer subjects. Wide ranges of
pollutants known or suspected to cause health problems are studied. The research
focuses on air pollutants, water pollutants, toxic substances, hazardous wastes,
pesticides, and non ionizing radiation. The laboratory participates in the develop-
ment and revision of air and water quality criteria and health assessment documents
on pollutants for which regulatory actions are being considered. Direct support to
the regulatory function of the Agency is provided in the form of expert testimony and
preparation of affidavits as well as expert advice to the Administrator to assure the
adequacy of environmental regulatory decisions involving the protection of the
health and welfare of all U.S. inhabitants.
This report provides information on the health effects of land application of
municipal sludge. The results of this study suggest that the land application of sludge
can be a safe practice, provided that the proper precautions are taken.
F. G. Hueter, Ph.D.
Director
Health Effects Research Laboratory
-------
ABSTRACT
The potential health effects arising from the land application of municipal sludge
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. The pathogens include bacteria, viruses, protozoa, and
helminths; the toxic substances include organics, trace elements, and nitrates.
For each agent of concern the types and levels commonly found in municipal
wastewater and sludge 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, some general conclusions are presented.
-------
CONTENTS
Page
Foreword m
Abstract iv
Figures vii
Tables viii
1. Introduction 1
2. General Conclusions 3
Types and Levels of Agents in Wastewater and Sludge 3
Aerosols 3
Surface Soil and Plants 3
Movement in Soil and Groundwater 4
Animals 4
Infective Dose, Risk of Infection, Epidemiology 4
3. Bacteria 5
Types and Levels in Wastewater and Sludge 5
Aerosols 9
Surface Soil and Plants 10
Movement in Soil and Groundwater 12
Animals 13
Infective Dose, Risk of Infection, Epidemiology 14
4. Viruses 19
Types and Levels in Wastewater and Sludge 19
Aerosols 22
Surface Soil and Plants 22
Movement in Soil and Groundwater 23
Animals 26
Infective Dose, Risk of Infection, Epidemiology 27
5. Protozoa 29
Types and Levels in Wastewater and Sludge 29
Soil and Plants 30
Animals 31
Infective Dose, Risk of Infection, Epidemiology 31
6. Helminths 33
Types and Levels in Wastewater and Sludge 33
Soil and Plants 37
Animals 38
Infective Dose, Risk of Infection, Epidemiology 38
-------
CONTENTS
Page
7. Organics 39
Types and Levels in Wastewater and Sludge 39
Soil and Groundwater 43
Plants 49
Animals 50
8. Trace Elements 53
Types and Levels in Wastewater and Sludge 53
Soil and Plants 54
Groundwater 56
Animals 57
Cadmium 57
9. Nitrates 61
References 63
-------
FIGURES
Number Page
1 Health effects of pathogens and toxic substances 2
-------
TABLES
Number Page
1 Survival Times of Pathogens on Soils and Plants 3
2 Pathogenic Bacteria of Major Concern 5
3 Pathogenic Bacteria of Minor Concern 6
4 Viable Bacteria in Human Feces 8
5 Pathogenic Bacteria in Feces of Infected Persons 8
6 Density of Bacteria in Municipal Sludge 9
7 Survival Times of Bacteria in Soil 10
8 Survival Times of Bacteria in Crops 11
9 Infective Dose to Man of Enteric Bacteria 16
10 Human Wastewater Viruses 19
11 Levels of Enteric Viruses in U.S. Wastewaters 21
12 Survival Times of Enteric Viruses in Soil 24
13 Survival Times of Enteric Viruses on Crops 25
14 Oral Infective Dose to Man of Enteric Viruses 27
15 Types of Protozoa in Wastewater 29
16 Levels of Protozoa in Wastewater 31
17 Pathogenic Helminths of Major Concern 34
18 Animal-Pathogenic Helminths 35
19 Helminth Egg Density in Treated Municipal Sludge 37
20 Most Frequently Detected Priority Organics in Raw
Municipal Wastewater 41
21 Most Frequently Detected Priority Organics in Raw
Municipal Sludge 42
22 Common Types of Chemical Transformations in the Environment 44
23 Biodegradability of Priority Organic Compounds 46
24 Concentrations of Trace Elements in Typical Dry Digested
Municipal Sludges and Agricultural Soils, and Maximum
Cumulative Application Limits 55
25 Cadmium Concentration in Foods and Calculated Dietary Intake 58
-------
SECTION 1
INTRODUCTION
For centuries Western man has been conscious of the potential value of the
application 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 spite of von Liebig's pessimism, farmers in many areas of the world have been
applying sewage sludge to agricultural land for centuries. The practice has continued
for millennia in the Far East. Sewage sludge (or "municipal sludge") has
characteristics that make it valuable as a fertilizer and a soil conditioner it contains
fair amounts of nitrogen, phosphorus,and micronutrients, and it increases soil
friability, tilth, pore space, and water-holding capacity.
In the United States a mandate for the greater use of land application of both
municipal wastewater and sludge has been provided by the Clean Water Act of 1977
(PL 95-217), Title. II (Grants for Construction of Treatment Works), Section 2O1,
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 production of agriculture,
silviculture, or aquaculture products, or any combination thereof. . ."
The land application of wastewater (or "land treatment") has been discussed in
previous reports (Kowal 1982, 1985); the land application of sludge is the subject of
the present report.
Land application of sludge consists of the low-rate application (compared with a
purely disposal operation) to agricultural, forest, or reclaimed land of municipal
wastewater sludge which has been "stabilized" in some way, e.g., anaerobic digestion
or composting. That land application of sludge is an important and probably
growing practice in the U.S. is indicated by the results of a recent survey of 1008
publicly owned treatment works, accounting for over 2 million dry metric tons per
day of sludge (Peirce and Bailey 1982). The survey found 17% of the total sludge to be
utilized in large scale food-chain landspreading, 12% in large scale nonfood-chain
landspreading, and 21% in distribution and marketing systems (much of which
probably ends up in gardens and lawns).
With the application to land of large volumes of wastewater and sludge, it is
evident that considerable potential for adverse health effects exists. The major health
concerns with land treatment of wastewater and land application of sludge are
somewhat different. Thus, the potential exposure of humans through the routes of
aerosols and groundwater is frequently emphasized with wastewater, and through
the food chain with sludge. Nevertheless, the agents, or pollutants, of concern from a
health effects viewpoint are almost the same in wastewater and sludge. These agents
-------
can be divided into the two broad categories of pathogens and toxic substances. The
pathogens include bacteria (e.g.,Salmonella andShigella), viruses (i.e., enteroviruses,
hepatitis virus, adenoviruses, rotaviruses, and Norwalk-like agents), protozoa
(e.g.,Entamoeba andGiardia), and the helminths (or worms, e.g.,Ascaris,Trichuris,
andToxocara). The protozoa and helminths are often grouped together under the
term, "parasites," although in reality all the pathogens are parasites. The toxic
substances1 include organics, trace elements (or heavy metals, e.g., cadmium and
lead), and nitrates. Nitrates are usually not viewed as "toxic" substances, but are here
so considered because of their potential hematological 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 in Figure 1.
Agent (Pollutant)
Pathogens —
Toxic
Substances-
Bacteria
Viruses
Protozoa
Helminths
Organics
Trace Elements
Nitrates
Health Effect
-Infection, Disease
-Hypersensitivity
- Acute Toxicity
-Mutagenesis and Carcinogenesis
-Teratogenesis
-Other Chronic Effects
(cardiovascular, immunological,
hematological, neurological, etc.)
Figure 1. Health effects of pathogens and toxic substances.
For each agent of concern the types and levels commonly found in municipal
sludge 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.
(Runoff to surface water is not considered, since it is assumed that this will be
prevented in a well-managed sludge land application operation.) For the pathogens,
infective dose, risk of infection, and epidemiology are then briefly reviewed.
'The term "toxin" is often incorrectly used as a synonym A toxin is a poisonous, often protemaceous,
product of the metabolism of a living organism, e g , snake, wasp, or pathogenic bacterium Correct
synonyms for"toxic substance" include "toxicant" and "toxic" when used as a noun
-------
SECTION 2
GENERAL CONCLUSIONS
Types and Levels of Agents in Wastewater and Sludge
The types and levels in wastewater and sludge of most pathogens are fairly well
understood, with the exception of viruses. Since only a fraction of the total viruses in
wastewater and other environmental samples may actually be detected, the
development of methods to recover and detect viruses needs to be continued. The
occurrence of viruses in an environmental setting should probably be based on viral
tests rather than bacterial indicators since failures in this indicator system have been
reported.
The tremendous number of organic chemicals possibly present in sludge, together
with their myriad health effects and poorly understood behavior in the environment,
represent a potential for public health risk when the sludge is applied to agricultural
land. Among the trace elements, probably only cadmium, under ordinary
circumstances, is likely to be of health concern to humans as a result of the land
application of sludge, with the exposure being through food plants or organ meats.
Minimizing of health risks can probably be accomplished by the monitoring of
sludge composition, and the regulation of maximum concentrations and cumulative
application of toxic substances in land-applied sludge. The complexity of the
organics composition of sludges, however, might require the development and use of
biological assays to screen for toxicity (Babish et al. 1982).
Aerosols
Because of the potential exposure to aerosolized bacteria, and possibly viruses, at
land application sites, it would be prudent to limit public access to a sludge spray
source, such as an active spray gun or tank truck. Human exposure to pathogenic
protozoa or helminth eggs through aerosols is unlikely.
Surface Soil and Plants
The survival times of pathogens on soil and plants are summarized in Table 1 (after
Feachem et al. 1978). Since pathogens survive for a much longer time on soil than on
plants, recommended waiting periods before harvest are based upon probable
contamination with soil. However, what is a safe waiting period before crop harvest
for human consumption is really an unsettled issue.
Table 1. Survival Times of Pathogens on Soil and Plants
Soil Plants
Pathogen
Bacteria
Viruses
Protozoa
Helminths
Absolute
Maximum
1 year
6 months
1 0 days
7 years
Common
Maximum
2 months
3 months
2 days
2 years
Absolute
Maximum
6 months
2 months
5 days
5 months
Common
Maximum
1 month
1 month
2 days
1 month
-------
Aerial crops with little chance for contact with soil should probably not be
harvested for human consumption for at least one month after the last sludge
application; subsurface and low-growing crops for human consumption would
probably require a six-month waiting period after last application. These waiting
periods need not apply to the growth of crops for animal feed, however.
The levels of toxic organics likely to be present in soils at land application sites will
probably result in very low levels in above-ground portions of plants, but levels in
roots, tubers, and bulbs may present a health hazard.
The potential increase in cadmium levels in human food due to land application of
sludge is still an unsettled question. Present levels of total dietary intake of cadmium
for most people appear to be fairly safe. However, in view of human variability in
sensitivity and the variability in food supply, these levels probably should not be
allowed to rise greatly.
Movement in Soil and Groundwater
Properly designed sludge application sites may pose little threat of bacterial or
viral contamination of groundwater. Human exposure to pathogenic protozoa or
helminths through groundwater is unlikely. Groundwater is unlikely to represent a
significant organic or trace element threat.
There is a possibility that land application of sludge may raise the nitrate
concentration of groundwater above the drinking water standard of 10 mg/1 as N.
This can be prevented, however, by proper siting and management practice, e.g.,
matching loading rate to crop uptake.
Animals
The literature to date suggests little danger of bacterial, viral, or protozoan disease
to animals grazing at land application sites if grazing does not resume until four
weeks after last application (Yeager 1980), but the need for complete inactivation of
helminths in sludge before land application is still unsettled. The feeding of land-
application-site-grown plants to animals is unlikely to pose a health problem, but
grazing animals may accumulate significant levels of toxic organics. The issue of
accumulation of organics from the soil by plants and animals (particularly into milk),
and into the human food supply, is poorly understood.
Infective Dose, Risk of Infection, Epidemiology
Because of the possibility of contracting an infection, it would be wise for humans
to maintain a minimum amount of contact with an active land application site.
Epidemiological studies to date suggest little effect of land application on disease
incidence. However, many questions on the public health consequences of land
application of wastewater and sludge remain (Larkin 1982).
-------
SECTION 3
BACTERIA
Types and Levels in Wastewater and Sludge
The pathogenic bacteria of major concern in wastewater and sludge 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 and sludge include those by Benarde (1973), Burge and
Marsh (1978), Elliott and Ellis (1977), Kristensen and Bonde (1977), and Menzies
(1977).
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 andShigella, 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 Scientific
Working Group 1980). All produce acute diarrhea, but by different mechanisms.
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
Table 2. Pathogenic Bacteria of Major Concern
Name Nonhuman Reservoir
Campylobacter jejuni Cattle, dogs, cats, poultry
Escherichia coli (pathogenic strains)
Leptospira spp. Domestic and wild mammals, rats
Salmonella paratyphi A, B, C*
Salmonella typhi
Salmonella spp. Domestic and wild mammals, birds,
turtles
Shigella sonnei. S. flexneri,
S. boydii, S. dysenteriae
Vibrio cholerae
Yersinia enterocolitica. Wild and domestic birds and mammals
Y. pseudotuberculosis
*Correct nomenclature: Salmonella paratyphi A, S. schottmuelleri, S. hirsch-
feldi, respectively.
-------
Table 3. Pathogenic Bacteria of
Minor Concern
Aeromonas spp.
Bacillus aureus
Brucella spp.
Citrobacter spp.
Clostridium perfringens
Coxiella burnetii
Enterobacter spp.
Erysipe/othrix rhusiopathiae
Francisella tularensis
Klebsiella spp.
Legionella pneumophila
Listeria monocytogenes
Mycobacterium 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 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
transient 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 sporadically
in the U.S., where about 500 cases occur per year (Taylor et al. 1983), 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 1980, 30,004 cases were reported to the Centers for Disease
Control (CDC) (CDC 1982).
Shigella sonnei, S. flexneri, S. boydii, and S. 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 etal. 1977).In 1980,14,168 cases were reported to
CDC (MMWR 1981).
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
etal. 1980).
Yersinia enterocolitica and Y. pseudotuberculosis cause yersiniosis, an acute
gastroenteritis and / or mesenteric lymphadenitis, with diarrhea, abdominal pain, and
numerous other symptoms. Death is uncommon. Yersiniosis occurs only sporadically
in the U.S., and is 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 facultative 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 gram-negative, nonspore-forming rods (Jawetz et al. 1978). The family
Enterobacteriaceae includes the following tribes and genera (Holt 1977):
Escherichieae
Eschenchia
Edwardsiella
Citrobacter
Salmonella (including Arozona)
Klebsielleae
Klebsiella
Enterobacter
Hafnia
Serratia
Proteeae
Proteus
Yersinieae
Yersinia
Erwinieae
Erwinia
Obligate anerobic bacteria constitute 95-99% of the gut flora, but these are usually
not included in the term, "enteric bacteria" (Davis et al. 1980). 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
Citrobacter freundii 46%
Klebsiella pneumoniae 18%
Escherichia coli 14%
Enterobacter agglomerans 1 2%
E. cloacae 4%
E. hafniae 3%
Serratia liquifaciens 1 %
Fecal Coliform Species
Escherichia coli 73%
Serratia liquifaciens 1 8%
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
opportunistic 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. Three 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 any 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
composition of wastewater is drastically different from that of feces. The composition
-------
Table 4. Viable Bacteria in Human Feces (number/g wet weight)
Carnow Feachem Tomkins
et al. et al. et al.
1979 1978 1981
Anaerobes
Bacteroides 109-1010 108-1010 101°-10"
Bifidobacterium 109-10'° 109-10'° 109-1010
Lactobacillus 103-105 106-108
Clostridium 103-105 106-106 104-107
Fusobacterium 103-106
Eubacterium - 108-1010
Veillone/la <103
Aerobes or Facultative Bacteria
Enterobacteria* 106 107-109 105-109
Enterococci (fecal
Streptococcus) 106 106-108 104-1010
Staphylococcus <103
Bacillus, Proteus,
Pseudomonas,
Spirochetes «103
*Enterobacteria are primarily Escherichia coli, with some Klebsiella and
Enterobacter (Carnow et al. 1979).
Table 5. Pathogenic Bacteria in Feces of Infected Persons
Name Number/g Wet Weight
Campy lobacter jejuni ?
Escherichia co//(enteropathogenic strains) 10s
Salmonella paratyphi (A, B.C) 106
Salmonella typhi 106
Salmonella spp. 106
Shigella sonnei, S. llexneri, S. boydii, S. dysenteriae 106
Vibrio cholerae 106
Yersinia enterocolitica. Y. pseudotuberculosis 105
also varies with geographic region and season of the year, higher densities being
found in summer. According to Carnow et al. ( 1 979) the most prominent bacteria of
human origin in raw municipal wastewater are Proteus, Enterobacteria (105/ml),
fecal Streptococcus (toMO^/ml), and Clostridium (10 -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 pathogenc listed in Tables 2 and 3 depend, of course, on the levels of infection in
the contributing population.
The density of bacteria in municipal sludges is highly variable. Pedersen(1981) has
surveyed most of the available literature on density levels of microbes in sludge for
the period 1940-1980. Table 6 summarizes the results for bacteria in raw sludge.
Sludge treatment provides variable reduction of these levels; Pedersen (1981)
concluded that anaerobic digestion results in a 1-2 log reduction, aerobic digestion
less than one log, and lime stabilization more than 2 log. It must be realized that there
may be great site-specific variation about these values.
-------
Table 6. Density of Bacteria in Municipal Sludge
(geometric means, number/g dry wt) (Pedersen 1981)
Total Coliforms
Fecal Coliforms
Fecal Streptococci
Salmonella
Raw Primary
Sludge
1.2x10"
2.0 x107
8.9 x106
4.1 x102
Raw Secondary
Sludge
7.0x1 0s
8.3 x106
1 .7 x 1 06
8.8 xlO2
Raw Mixed
Sludge
1.1 x 109
1 .9 x 1 05
3.7 x 10S
29x 102
Aerosols
Where liquid sludge is applied to the land by spray equipment of some sort,
aerosols that travel beyond the zone of application will be produced. These are
suspensions of solid or liquid particles up to about 50 fjm in diameter, formed, for
example, by the rapid evaporation of small droplets. Their content of micro-
organisms depends upon the concentration in the sludge 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 et al 1978).
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
inhalation. The exact location where aerosol particles are actually deposited upon
inhalation is a function of the size, shape, and density of the particles; respiratory
anatomy; breathing pattern; dead space; disease state; etc. (Brain and Valberg 1979).
Those above about 2 fjm in aerodynamic 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. About
40% of 1 pm particles are removed (about half in the pulmonary region—respiratory
bronchiole, alveolar ducts, and alveoli) by the respiratory system at resting breathing
rates, increasing to nearly 100% for 10 fjm particles. Deposition increases (greater
than 70%) for particles smaller than 0.1 fjm, primarily in the pulmonary region (Brain
and Valberg 1979).
When aerosols are generated, bacteria are subject to an immediate "aerosol
shock," or "impact factor," which may reduce their level tenfold within seconds
(Schaub et al. 1978). 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 et 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 et al. 1978). Solar radiation,
particularly the ultraviolet portion, is destructive to bacteria, and also 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
dissemination 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 application sites. Harding et al. (1981) have
studied the production of microbial aerosols by the land application of liquid
municipal sludge at two sites using tank-truck application and two sites using
high-volume spray guns. Very low bacterial aerosol levels were found at the tank-
-------
truck sites, but elevated levels of fecal coliforms, fecal streptococci, and my co bacteria
were found at the spray sites. Levels were significantly less, however, than those
observed at wastewater spray application sites, and it was concluded that the spray
application of sludge does not represent a serious threat to health for individuals
more than 100 m downwind (Sorber et al. 1984).
Surface Soil and Plants
The surface soil, and occasionally plants, of a sludge application site may be
initially heavily laden with enteric bacteria, depending on the level of prior treatment.
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 (Gerbaetal. 1975; USEPA 1981) are:
1. Moisture content. Moist soils and periods of high rainfall increase survival
time. This has been demonstrated for Escherichia coli, Salmonella typhi, and
Mycobacterium aviitm.
2. Moisture-holding capacity. Survival time is shorter in sandy soils than in 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 encount-
ered with the endemic soil microorganisms decreases 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
unsterilized 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
useful summaries of this literature are those of Bryan (1977) and Feachem et al.
(1978). The ranges given in Table 7 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
Table 7. Survival Times of Bacteria in Soil
Coliform
Fecal coliform
Fecal streptococci
Leptospira
Mycobacterium
Salmonella paratyphi
Salmonella typhi
Streptococcus faecalis
4- 77 days
4- 55 days
8-> 70 days
< 15 days
10 days- 15 months
>259 days
1 1 - >280 days
26- 77 days
10
-------
methodology, and other factors. If kept frozen, most of these bacteria would survive
longer than indicated in Table 7, but this would not be a realistic soil situation.
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, that are potentially
infectious for man are not contaminants from human beings. For example,
Klebsiella spp., Enterobacter spp., Serratia spp., and Pseudomonas aeruginosa 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 et al. 1951a), 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 Feachem et al. (1978). The
ranges given in Table 8 are extracted from these summaries, as well as other
literature.
Table 8. Survival Times of Bacteria on Crops
Bacterium
Coliform
Escherichia coli
Mycobacterium
Salmonella typhi
Salmonella spp.
Shigella spp.
Vibrio cholerae
Crop
Tomatoes
Fodder
Leaf vegetables
Vegetables
Grass
Grass
Lettuce
Radishes
Vegetables (leaves & stems)
Radishes
Lettuce
Leaf vegetables
Beet leaves
Tomatoes
Cabbage
Gooseberries
Clover
Grass
Orchard crops
Tomatoes
Apples
Leaf vegetables
Fodder
Orchard crops
Vegetables
Dates
Survival
>1 month
6- 34 days
35 days
<3 weeks
<8 days
10-14 days
>35 days
>1 3 days
10-31 days
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
II
-------
On the basis of New Jersey field experiments with tomatoes irrigated with
municipal wastewater, Rudolfs et 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 uncontam-
inated 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 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 et 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
vegetables and strawberries, harvested from an application 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) growth of crops the
harvested portion of which does not contact the soil, e.g., grains and orchard crops,
or (2) 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 application a month prior to harvest would be prudent, although
in a typical sludge-application operation harvesting would normally occur much
longer than one month after the last (often only) application.
Movement in Soil and Groundwater
Approximately 117 million people in the United States obtain their drinking water
from groundwater, supplied by 48,000 community public water systems and
approximately 12 million individual wells; the concentration is highest in rural areas
(USEPA 1984). Thus, it is imperative that land application of sludge does 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 et al. 1980) showed more than
one-third to be fecally contaminated.
It is generally felt that the removal of bacteria at land application 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 et al. 1975). Once
retained, the bacteria are inactivated by sunlight, oxidation, desiccation, and
predation and antagonism by the soil microbial community. 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
(Sagike/a/. 1978).
12
-------
Land application of sludge may pose little bacterial threat to ground water. Liu
(1982) in Canada has found that after 4 years of heavy sludge application sewage
bacteria were incapable of moving through the soil columns tested, and over 90% of
the surviving sludge bacteria were still detained in the top 20 cm layer of soil. He
concluded that there was little possibility of bacterial contamination of groundwater
by the practice of sludge farmland application, provided that the water table was not
too high and the soil was well drained. Similar results have been found in leachate
experiments in South Africa (Nell et al. 1981).
Once in the groundwater the bacteria may travel long distances under ground 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.
Groundwater survival times found in both field and laboratory measurements have
been summarized by Gerba et al. (1975):
Coliform 17 hours (for 50% reduction)
Escherichia coli 63 days—4.5 months
Salmonella 44 days
Shigella 24 days
Vibrio cholerae 1.2 hours (for 50% reduction)
Animals
The disease hazards to farm animals from land application of sludge have been
reviewed by Argent et al. (1977) and Carrington (1978). The major bacterial concerns
with respect to animals grazing at land application sites are Salmonella infections
and bovine tuberculosis (Mycobacterium bovis and M. tuberculosis); both can be
passed on to man.
That the transmission of salmonellosis to cattle grazing at land application sites is
at least possible was demonstrated by Taylor and Burrows (1971), who showed that
calves grazing in pastures, to which 108 Salmonella dublin organisms/ml of slurry
had been applied, became infected. No infection occurred when the rate was
decreased to 103/ml, suggesting that Salmonella may only be of concern when high
concentrations are present. Feachem et al. (1978) concluded that there is no clear
evidence that cattle grazed at land wastewater 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 et
al. (1980) concluded that a four-week waiting period would prevent salmonellosis in
grazing animals.
Argent et al. (1981) applied raw sludge (11 Salmonella/100 ml) to a field at the rate
of 44.8 m3/ha, and confined 10 lambs to the field for 2 months. None of the lambs
became infected, as measured by feces, rumen, and tissue samples, and clinical
symptoms. Ayanwale et al. (1980) raised goats on corn silage grown on sludge-
amended land, and found no Salmonella infections in spite of the presence of
Salmonella in the sludge, supporting the position that the potential public health
hazard resulting from the use of sludge as fertilizer when properly treated has so far
proven not to be a threat. Nevertheless the significance of Salmonella in land-applied
sludge is an issue yet to be settled. Evidence in Switzerland from studies of carrier
rates and serotypes in cattle grazed on sludge-treated pastures has indicated a
positive association and a cycle of infection from man to sludge to animals to man.
13
-------
Experience in the Netherlands is similar, but there is no evidence of such a link in the
United Kingdom, despite the compulsory reporting of incidents there (WHO 1981).
Animal feed raised on sludge-amended land appears to be even less of a risk. Thus,
after feeding for 36 months on corn silage grown on land fertilized with Salmonella-
containing sewage sludge, a goat herd was free of clinical and subclinical Salmonella
infection (Ayanwale and Kaneene 1982).
Several investigations on tuberculosis infection of cattle grazing on wastewater-
irrigated land have been performed in Germany, with the conclusion that if
application 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
application sites are Leptospira (causing leptospirosis), Brucella (causing brucel-
losis), and Bacillus anthracis (causing anthrax). Sludge, however, probably contains
insignificant numbers of these pathogens, and plays a negligible role in the
transmission of these diseases (Feachem et al. 1978). Jones et al. (1981) examined
sludges in England for Leptospira, Mycobacterium, Escherichia, Brucella, and
Bacillus anthracis, and concluded that the application of sludge to agricultural land
should present no greater hazard than the spreading of animal manure if sensible
grazing restrictions are observed.
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 neutrophils
or polymorphonuclear leukocytes in the blood, and by mononuclear phagocytes, 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 infective dose data for enteric
bacteria, based upon numerous studies using nonuniform techniques, are presented
in Table 9 (adapted from Bryan 1977).
Although the terms, "infective dose," "minimal infectious dose," etc., are used in
the literature, it is obvious from Table 9 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.
1. 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 cholerae) data in Table 9, 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 108 by mouth.
2. Previous exposure to a given pathogen often produces varying degrees of
immunity to that pathogen, through the induction of specific immune
14
-------
Table 9. Iniective Dose to Man of Enteric Bacteria
Bacterium
Clostridium
perfringens
Escherichia coli
0124:K72:H-
0148:H28
0111 :B4
Several
strains
Salmonella typhi
Ty2W
Zermat vi
Most strains
S. new port
S. bareilly
S. anatum
S. meleagridis
S. derby
S. pullorum
Shigella
dysenteriae
S. flexneri
Streptococcus
faecalis var.
liquefaciens
Vibrio cholerae
NaHCOa-buffered
Unbuffered
No
Infection
or No
Illness
104
103
lOMO6
10M08
106-106
104-109
10"
10
10M010
Infections
Without
Illness 1-25
10'° 10s
10s
10M06 106
108
105
105
105
10M08
106
10 -102
10M04
10«
103
Percent of Volunteers Developing Illness
26-50
10"
10s
10s- 10s
106
106
106
107
107
109
10M04
1010
1Q3-10*
10MO"
51-75
109
108-109
108-1010
104
107-108
103
103-109
lOMO6
76-100
109
1010
1010
10«-109
109-1010
10*
106-108
-------
responses. A study in Bangladesh showed that repeated ingestion of small
inocula (103-104 organisms) of Vibrio cholerae produced subclinical or mild
diarrheal 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 develops (Levine 1980).
3. 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 anti-inflammatory, cytotoxic, and
immunosuppressant drugs would be more susceptible to pathogens. An
example of human variability (possibly genetic) is the following response of
men orally challenged with several different doses of Salmonella typhi
(Hornickrt al. 1970):
Number of Percent Developing
5. typhi typhoid Fever
103 0
106 28
107 50
109 95
Twenty-eight percent of the men came down with typhoid fever after 10s
organisms, while 5% were still resistant to 109 organisms, four orders of
magnitude as many.
4. The number of organisms that must be swallowed for intestinal colonization
(subclinical infection), and consequent risk of clinical disease, is affected by
treatment with antibiotics (Remington and Schimpff 1981). Due to its normal
content of anaerobic bacteria and their products, the gut can resist colonization
when an oral dose of about 108 organisms is given. Once competition is
reduced by systemic or oral antibiotics, the dose required to induce coloniza-
tion is only 10 to 100 organisms.
5. The timing of the exposure to pathogens, e.g., as a single exposure or an
exposure over a long period of time, would be expected to affect the response.
6. Finally, as illustrated by Escherichia coli and Salmonella typhi in Table 9, the
virulence, or pathogenicity, of bacteria varies among strains. Thus, three
different strains of Shigellaflexneri have been found to have infective doses of
1010 or higher, 105-10a and 180 organisms (NRC 1977).
The risk of infection is probably greatest for Salmonella spp. and Shigella spp.,
because they are the most common bacterial pathogens in municipal wastewater. The
infective dose for Salmonella is high (105-108 organisms) but this dose might be
reached on a contaminated foodstuff under conditions that allow multiplication. A
recent review of experimentally induced salmonellosis and salmonellosis outbreaks,
however, has resulted in the conclusion that the infective dose for Salmonella may
well be below 103 organisms (Blaser and Newman 1982). On the other hand the
infective dose for Shigella is low—as few as 10 to 100 organisms. "Because of this
miniscule inoculum it is rather simple for shigellae to spread by contact without
interposition of a vehicle such as food, water or milk to amplify the infectious dose"
(Keusch 1979). Consequently, it would be prudent for humans to maintain a
minimum amount of contact with an active land application site, and to rely on the
passage of time to reduce the bacterial survival, as discussed earlier, when growing
crops for human consumption.
A number of epidemiological reports have attested to the fact that transmission of
enteric disease can occur when raw wastewater is used in the cultivation of crops to be
eaten raw (Geldreich and Bordner 1971, Hoadley and Goyal 1976, and Sepp 1971).
16
-------
Salmonellosis has been traced to the consumption of wastewater-irrigated celery,
watercress, watermelon, lettuce, cabbage, endive, salad vegetables, and fruits;
shigellosis to wastewater-irrigated pastureland; and cholera to wastewater-irrigated
vegetables in Israel.
A multiyear prospective epidemiological study of the health effects of the
application of sewage sludge to agricultural land in Ohio has recently been completed
(Brown 1985). Digested municipal sludge was applied to family-operated farms at the
rate of 2-10 dry metric tons per hectare per year. Health of humans and livestock on
47 sludge-receiving farms and 46 control farms was evaluated by questionnaires,
blood samples, fecal samples, and tuberculin testing. No significant differences
between sludged and control farms were found in symptoms of respiratory, digestive,
or other disease, or exposure to Salmonella, Shigella, or Campylobacter in humans,
nor in animal health. No tuberculin conversions occurred on the sludged farms.
17
-------
SECTION 4
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).
Types and Levels in Wastewater and Sludge
The human enteric viruses that may be present in wastewater and sludge are listed
in Table 10 (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
inhabitants 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 10. Human Wastewater Viruses
Enteroviruses
Poliovirus
Coxsackievirus A
Coxsackievirus B
Echovirus
New Enteroviruses
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
adenovirus and reovirus here have not been shown to be of major epidemiological
importance in their transmission (Evans 1976). The rotavirus often produces
diarrhea in children, but the local multiplication of enteroviruses and (possibly)
hepatitis A virus in cells liningthe area rarely produces local symptoms, i.e., diarrhea,
vomiting, and abdominal pain. Most enteroviral 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 bloodstream, leading to further virus proliferation in the cells of the
19
-------
reticuloendothelial 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
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 Centers for
Disease Control (CDC) in the years 1971-75 (Morens et al. 1979). These enteroviruses
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 (i.e., lack of previous
exposure), 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 develops, 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
unimmunized 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 advantages.
Hepatitis A virus causes infectious hepatitis, which many 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 childhood 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,
Ditchling, 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 school children and adults (Holmes 1979).
Adenoviruses are primarily causes of respiratory and eye infection, transmitted by
the respiratory route, but several recently isolated types referred to as enteric
adenoviruses are now believed to be important causes of sporadic gastroenteritis in
young children (Richmond et al. 1979, Kapikian et al. 1979).
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
manifestations (Rosen 1979).
20
-------
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 al. 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 et al.
1978); for example, viruses are less easily removed by treatment processes and 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 and 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 bacteriophage, 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 1010 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 lower than that in many developing countries. Numbers
tend to be higher in late 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 tends 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 readily 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 11. It is evident that reported
concentrations are highly variable; Akin and H off (1978) have concluded that
"...from the reports that are available from field studies and with reasonable
Table 11. Levels of Enteric Viruses in U.S. Wastewaters
Description
St. Petersburg
Various sources
Chicago
Honolulu
Cincinnati
Urban
Viral Units/Liter
10->183
100-400
Up to 440
0-820
0-1450
192-1040
Reference
Wellingsefa/. 1978
Akin and Hoff 1978
Fannin era/. 1977
Ruiter and Fujioka 1 978
Akin and Hoff 1978
Sorber 1 983
21
-------
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."
Reported concentrations of enteric viruses in sludge have been summarized by
Gerba (1983). Ranges, in virus units/gram, found in the U.S. were: 2-215 for raw,
0.04-17 for anaerobically digested, and 0-260 for aerobically digested sludges.
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
respiratory tract itself (Evans 1976).
The initial aerosol shock during the process of aerosolization may result in a half
log loss of virus level (Sorber 1976). The subsequent dieoff, 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, with lipid-containing
viruses surviving better at low humidities, and those without lipids (e.g., most of the
enteric viruses) surviving better at high humidities (Carnow et al. 1979).
The concentration of viruses in aerosols at liquid sludge spray-application sites has
been examined by Harding et al. (1981; Sorber et al. 1984). On a special virus run,
1470 m3 of air was sampled and no human enteric viruses were detected from the
pooled sample. This converts to a concentration of less than 0.0016 PFU/ m3 of air at
a distance of 40 m downwind from the spray gun, and probably results from low viral
concentration in sludge (0.7 PFU/g) and viral adsorption into poorly aerosolized
solid matter. This suggests that aerosolization of viruses in liquid sludge may not
present a significant health risk.
Surface Soil and Plants
The survival time of viruses at a sludge application site 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 in the soil toward the
groundwater.
The factors affecting virus survival in soil are solar radiation, moisture,
temperature, 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, rotavirus, and
bacteriophages, Hurst et al. (1980) 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 fluctuation in soil moisture, temperatures, ionic
strength, pH, dissolved gas concentrations, nutrient concentrations, etc. These may
be caused by meteorological changes, by the action of other soil organisms, 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
22
-------
et al. (1978) have reported data that indicate virus may penetrate up to 58 feet of
sandy soil, but much less for loamy or clay soils.
Much of the recent literature on survival times of enteric viruses in soil is
summarized in Table 12. Approximately one hundred days appear 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
on evaporation rates, which causes dessication and inactivation of virus without high
temperature.
The phenomenon of virus inactivation by evaporative dewatering has heen
documented by Ward and Ashley (1977), who observed a decrease in poliovirus liter
of greater that three orders of magnitude when the solids content of sludge was
increased from 65% to 83%. This loss of infectivity was due to irreversible
inactivation of poliovirus 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. Recent studies with high concentrations of bacteriophage in
hydroponically grown corn and bean plants have shown little viral uptake in uncut
roots, more in cut roots, and viral transport to all plant parts examined, but with
survival times of limited duration. The authors concluded that the possible public
health significance associated with viral uptake through the root systems of plants
was minimal (Ward and Mahler 1982). Moreover, the rapid adsorption of virus by
soil particles under natural conditions may make them unavailable for plant
absorption, thereby suggesting that plants or plant fruits would be unlikely reservoirs
or carriers of viral pathogens. The intact surfaces of vegetables are probably
impenetrable for enteroviruses (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 sunlight,
high temperature, drying, and washing off by rainfall (USEPA 1981). Some of the
literature on survival times is summarized in Table 13 (Feachem et al. 1978). The data
are similar to those for bacteria (cf. Table 8), and likewise appear to support a
minimum one-month waiting period after last application before harvest.
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 might be
required as a minimum safe waiting period. As with bacteria, this period could be
shortened by (1) the growth of crops the harvested portion of which does not contact
the soil, or (2) the growth of crops used for animal feed only.
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
23
-------
Table 12. Survival Times of Enteric Viruses in Soil
Virus
Enterovirus
Polovirus
Poliovirus
Coxsackievirus
Poliovirus
Poliovirus
Poliovirus and
Coxsackievirus
Moisture and
Soil Temperature
Sandy or loamy podzol 10-20%, 3-1 0°C
10-20%, 18-23°C
Air dry, 18-23°C
Sand Moist
Dry
Loamy fine sand Moist, 4°C
Moist, 20°C
Clay 300 mm rainfall,
-12-26°C
-14-27°C
15-33°C
Sugarcane field Open, direct sunlight
Mature crop, moist,
shaded
Sandy loam 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
Duboiseer al. 1976
Damgaard-Larsen et al.
1977
Tierney et al. 1 977
Lau et al. 1975
Yeager and O'Brien 1 979
-------
Table 13. Survival Times of Enteric Viruses on Crops
Virus Crop
Enterovirus Tomatoes
Poliovirus Radishes
Conditions
3-8°C
18-2°C
5-1 0°C
Survival
(days)
1 0 (90%
reduction)
1 0 (99%
reduction)
20 (99%
reduction),
>60
Reference
Bagdasaryan
1964
Bagdasaryan
1964
Poliovirus
Tomatoes
Poliovirus
Parsley
Lettuce and
radishes
Indoors,
22-25°C
Indoors, 37°C
Outdoors
15-31°C
Sprayed,
summer-fall
Kott and
Fishelson
1974
<5
<2
6 (99%
reduction),
36(100%
reduction)
Larken et al.
1976
Poliovirus
Enterovirus
Lettuce and
radishes
Cabbage
Peppers
Tomatoes
Flooded,
summer
—
23
4
12
18
Tierney et al.
1977
Grigor' Eva
et al. 1 965
physical-chemical reasons for virus adsorption to soil surfaces are poorly understood,
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). For a review of virus adsorption see Gerba (1984).
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
electrostatic potential between virus and soil, which, in turn, affects the degree of
interaction 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 polioviruses
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
25
-------
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
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 occurring low molecular
weight (<50,000) humic substances (Bixby and O'Brien 1979, Scheuerman et al.
1979).
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 wastewater
land treatment 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 poliovirus, previously adsorbed in the top 5 cm of soil, can be
desorbed and eluted to a depth of 160 cm (Lance et al. 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
varies with type and strain (Landry et al. 1979).
There appears to be little reliable information on viruses getting into groundwater
beneath sludge application sites, although one would expect the threat to be low
because of virus binding to sludge solids. Studies with sludge-amended soil indicate
that viruses are not easily eluted by rainfall and are efficiently retained by sludge-soil
mixtures (Damgaard-Larsen et al. 1977, Farrah et al. 1981), even on sandy soils
(Bittonef al. 1984).
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). For example,
Vaughn et al. (1983) have recovered human enteroviruses at 18 m depth and 67 m
down gradient from a septic tank leach field in a shallow sandy aquifer. Low
temperatures prolong survival, but the factors affecting survival in groundwater are
poorly understood. 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). For a review of virus in soil and groundwater see Vaughn and Landry (1983).
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
association with man in the household. The present state of information on virus
transmission in animals and man does not appear to allow an evaluation of the effect
of land application 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.
26
-------
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 14 (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.
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
Table 14. Oral Infective Dose to Man of Enteric Viruses
Virus Subjects
Vaccine Infants
poliovirus
Dose*
0.2 PFU**
2PFU
20 PFU
10s.5
1Q7.5
Percent
Infected
0
67
100
50
100
Reference
Koprowski 1956
Gelfand et al.
1960
106.6
107.6
60 Krugman et al.
75 1961
5.5x106PFU
103
104
105
103
103
89
29
46
57
68
79
Holguin et al.
1962
Lepowef a/. 1962
Warren et al.
1964
Premature
infants
Infants
Echovirus 12 Young Adults
1
2.5
10
7-52f
24-63
55-93
17 PFU
919 PFU
30
33
67
1
10
50
1
50
Katz and Plotkin
1967
Minor et al. 1981
Schiff et al. 1984
*Tissue Culture Dose 50% (TCD50) unless indicated.
**Plaque-Forming Unit.
f95% Confidence Limits.
27
-------
be the case in the real world, 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 on the basis of oral poliovaccine studies,
nonimmunologic barriers, human immunologic responses, and probabilistic factors
(Lennette 1976).
Viruses do not regrow on foods or other environmental media, as bacteria
sometimes 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 application site, and to rely on the
viral survival data discussed earlier for limiting the hazard from crops for human
consumption grown on sludge-amended soils.
Fecally polluted vegetable-garden irrigation water in Brazil has been found to
contain polioviruses and coxsackieviruses, and has been associated with epidemics
among the consumers of the garden products (Christovao et al. 1967a, 1967b).
However, at the Muskegon, Michigan, land treatment spray irrigation site, where no
products for human consumption are grown and where much higher exposure to
aerosols would be expected than at sludge application sites, there was no increase in
clinical illness among the site workers and there was no evidence of an increased risk
of infection, for either viruses or bacteria (Linnemann et al. 1984). With a minor
exception, they did not have increased prevalence of infection by hepatitis A,
poliovirus (1, 2, 3), coxsackievirus (B2, B5), or echovirus (7, 11), as measured by
serology. The exception was a high antibody liter to coxsackievirus B5 in the spray
nozzle cleaners, a group with presumably high exposure to wastewater.
In the previously mentioned epidemiological study of sludge application to
agricultural land in Ohio (Brown 1985), no significant difference in frequency of viral
infections, as evidenced by serological examinations, was found between sludge and
control groups.
In spite of these negative epidemiological results, however, some virologists feel
that current epidemiological techniques are probably not sufficiently sensitive to
detect the low levels cf viral disease transmission that might occur from a modern
land application site (Melnick 1978, WHO 1979).
28
-------
SECTION 5
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 unlikely that they will find their way into either aerosols or groundwater
at land application 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 parasitic infection
in the U.S. is minimal (Larkin el al. 1978b). However, because of the increasing
recognition of parasitic 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 and Sludge
The most common protozoa which may be found in wastewater and sludge are
listed in Table 15. Of these, only three species are of major significance for
Table 15. Types of Protozoa in Wastewater
Name
Protozoan Class
Nonhuman Reservoir
HUMAN PATHOGENS
Entamoeba histolytica Ameba
Giardia lamblia
Balantidium coli
Toxop/asma gondi!
Dientamoeba fragilis
Isospora belli
I. hominis
HUMAN COMMENSALS
Endolimax nana
Entamoeba coli
lodamoeba butschlii
ANIMAL PATHOGENS
Eimeria spp.
Entamoeba spp.
Giardia -spp.
Isospora spp.
Flagellate
Ciliate
Sporozoan (Coccidia)
Ameba
Sporozoan (Coccidia)
Sporozoan (Coccidia)
Ameba
Ameba
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
29
-------
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. Eimeria spp.
are often identified in human fecal samples, but are considered to be spurious
parasites, entering the gastrointestinal tract from ingested fish.
Entamoeba histolytica causes amebiasis, or amehic dysentery, an acute enteritis,
whose symptoms may range from mild abdominal discomfort with diarrhea to
fulminating dysentery with fever, chills, and bloody or 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 lamblia 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 1.5 and 20% (Benenson 1975), and it is
transmitted by cysts contaminating water or food, and by person-to-person contact
(Osterholm et 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 et 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 1.5x 107per
day (Chang and Kabler 1956), and by an adult infected with Giardia lamblia at
2.1-7.1 x 108 per day (Jakubowski and Ericksen 1979). The concentration of
Entamoeba histolytica cysts in the feces of infected individuals has been estimated to
be 1.5 x 105/g (Feachem et al. 1978). The concentration of Giardia lamblia cysts in
the feces has been estimated to be 105/ g in infected individuals (Feachem et al. 1978),
up to 2.2 x 106/g in infected children, and up to 9.6 x 107/g in 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 presented in Table 16. The sparse
literature (Pedersen 1981) suggests that protozoan cysts will be absent, or at least
nonviable, from anaerobically digested sludge.
Soil and Plants
Protozoan cysts are sensitive to drying. Rudolfs et al. (1951b) have reported
survival times during New Jersey summer weather 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
30
-------
Table 16.
Levels of Protozoa in Wastewater
Species
Wastewater
Concentration
(cysts/I) Reference
Entamoeha
histolytica
Giardia
lamblia
Untreated
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- Jakubowski and
2.4x105 Ericksen1979
Up to 8x104 Weaver ef at, 1978
by the recent isolation of high levels of Entamoeba histolytica, E. coli, Endolimax
nana, and Giardia lamblia on 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 Entamoeha 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 unlikely that any public health risk will ensue.
Animals
Although it would be theoretically possible for protozoan diseases to be
transmitted through animals at a land application site, little relevant 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, would probably limit the risk of human illness.
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 ofEntamoeba coli,
and there is no biological reason why single cysts of Giardia would not also be
infectious (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.
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 application
site. However, a waiting period for crop harvest after application would significantly
reduce the risk of infection because of the cysts' sensitivity to drying.
A few epidemiological reports have linked the transmission of amebiasis to
vegetables irrigated with raw wastewater or fertilized with night soil (Bryan 1977,
Geldreich and Bordner 1971).
31
-------
SECTION 6
HELMINTHS
Types and Levels in Wastewater and Sludge
The pathogenic helminths whose eggs are of major concern in wastewater and
sludge are listed in Table 17. They are taxonomically divided into the nematodes, or
roundworms, 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 sludge
application sites. Some common helminths, pathogenic to domestic or wild animals,
but not to humans, are listed in Table 18 (after Reimers et al. 1981), since their eggs
are likely to be identified in wastewater and sludge. Several of the human pathogens
listed in Table 17, e.g., Toxocara spp., are actually animal parasites, rather than
human parasites, infesting man only incidentally, and not completing their life cycle
in man.
Enterobius vermicularis, the pinworm, causes itching and discomfort in the
perianal 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 for only 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 (Phills et al. 1972).
Trichuris trichiura, 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. 1981), 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. 1981). The prevalence of trichuriasis in
the U.S. was estimated to be about 2.2 million in 1972 (Warren 1974). Reimers et al.
(1981, 1984) have found Ascaris, Trichuris, and Toxocara to be the most frequently
recovered helminth eggs in municipal wastewater sludge in both southeastern and
northern United States.
33
-------
Table 17. Pathogenic Helminths of Major Concern
Pathogen Common Name
NEMATODES (Roundworms)
Enterobius Pinworm
vermicularis
Ascaris Roundworm
lumbricoides
A. suum Swine
roundworm
Trichuris trichiura Whipworm
Necator americanus Hookworm
Ancylostoma Hookworm
duodenale
A. braziliense Cat hookworm
A. caninum Dog hookworm
Strongyloides Threadworm
stercoralis
Toxocara canis Dog roundworm
T. cati Cat roundworm
CESTODES (Tapeworms)
Taenia saginata** Beef tapeworm
T. solium Pork tapeworm
Hymenolepis nana Dwarf tapeworm
Echinococcus Dog tapeworm
granulosus
E. multilocularis
Disease
Enterobiasis
Ascariasis
Ascariasis
Trichuriasis
Necatoriasis
Ancylostomiasis
Cutaneous larva
migrans
Cutaneous larva
migrans
Strongyloidiasis
Visceral larva
migrans
Visceral larva
migrans
Taeniasis
Taeniasis, Cysticerosis
Taeniasis
Unilocular hydatid
disease
Alveolar hydatid
disease
Nonhuman
Reservoir
Pig*
Cat, dog*
Dog*
Dog
Dog*
Cat*
Rat, mouse
Dog*
Dog, fox,
cat*
"Definitive host; man only incidentally infested.
*Eggs not infective for man.
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 bloodstream to the lungs, enter the alveoli,
34
-------
Table 18. Animal-Pathogenic Helminths
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
Capillaria hepatica Rat
C. gastrica Rat
C. spp. Poultry, wild birds, wild
mammals
Hymenolepis dimi nut a Rat
H. spp. Birds
Taenia pisiform is Cat
Hydatigera taeniaeformis Dog
Macracanthorhynchus Pig
hirudinaceous
*Toxascaris leonina may produce visceral larva migrans in
experimental animals, but its role in human disease is
undefined (Quinn era/. 1980).
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 anticoagulant causing
bleeding at the site of attachment) and debility, especially 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 (Warrren 1974).
Ancylostoma braziliense and A. canimtm, 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.
Strongyloides stercoralis, the threadworm, lives in the mucosa of the upper small
intestine. Eggs hatch within the intestine, and 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 autoinfection
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 canis and T. car/, 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
35
-------
Ascaris. However, since Toxocara cannot complete its life cycle, the larvae do not
migrate to the pharynx, but, instead, wander aimlessly through the tissues, producing
"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. 1981, 1984).
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
wastewater-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
livestock grazing on land application sites. The major direct hazard to man is the
possibility 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.
Hymenolepis 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%, mostly among children under 15.
Echinococcusgranutosus 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 et 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 the intensity of infection.
36
-------
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 contribution to
the system. Foster and Engelbrecht (1973) suggested a value of 66 helminth ova/1 in
untreated wastewater, and Larkin et al. (I978b) cited values of 15-27 Ascaris eggs/1
and 6.2 helminth eggs/1 in primary effluent. Since helminth eggs are denser than
water, most will settle to the bottom during a sedimentation unit process, and
primary effluent should have fairly low densities of eggs. As a consequence, sludge
may have high densities of viable helminth eggs.
Reliable published figures for the density of helminth eggs in municipal sludge
(mostly digested) are reproduced in Table 19. The data for the northern states have
not been analyzed to date, but the densities are lower than those of the southern states
(Reimers et al. 1984). The values for Chicago sludge probably reflect a lower rate of
human infection and a higher contribution from pets than the southern states.
As with protozoa, the large size of helminth eggs makes it unlikely that they will
find their way into either aerosols or groundwater at land application sites.
Table 19. Helminth Egg Density in Treated Municipal Sludge
Southern States1 Chicago2
Helminth
Ascaris spp.
Trichuris spp.
Toxocara spp.
Toxascaris leonina
Mean Ova/
kg dry wt.
9600
3300
700
—
(Viability)
(69%)
(48-64%)
(52%)
—
Mean Ova/
kg dry wt.
2030
360
1730
480
(Viability)
(64%)
(20%)
(53%)
(63%)
'Reimers et al. 1981.
2Arther et al. 1981.
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 in
which they have evolved, while protozoa have evolved through 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.
Because of the growth of crops and the presence of people at sludge application
sites, and the longevity of helminth eggs, it might be considered advisable to select a
sludge treatment method which will inactivate helminth eggs before use at these sites.
From a less conservative point of view, Fitzgerald (1979) reviewed the potential
impact on public health of parasites in soil/sludge systems, and concluded that the
proper utilization of wastewater sludge did not pose any great threat to the health of
society through actual transmission of pathogens that might be present in sludge.
37
-------
Animals
The most serious threat to cattle at land application sites is the beef tapeworm,
Taenia saginata (Feachem et al. 1978, WHO 1981). 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. \ 978, 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.
Arundel and Adolph (1980) have found no cysticercosis in cattle grazed on pasture
irrigated with effluent from lagooning, compared with a 3.3% infection rate from
trickling filter effluent, 9.0-12.5% from activated sludge effluent, and 30.0% from raw
sewage.
Because of the longevity of helminth eggs in the soil, and the fact that cattle
consume considerable quantities of soil as they graze, it might be prudent to select a
sludge treatment method which will completely remove or inactivate helminth eggs at
land application sites where cattle are allowed to graze, such as high-quality
composting or heat treatment.
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 (Mueller 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 application site, unless the sludge has been pretreated to remove or
inactivate helminths.
A few epidemiological reports have linked the transmission of Ascaris and
hookworm to the use of night soil on gardens and small farms in Europe and the
Orient (Geldreich and Bordner 1971).
38
-------
SECTION 7
ORGANICS
The potential health effects of toxic organic compounds are myriad. Systems
affected range from the dermatological to the nervous to the subcellular, and effects
produced range from rash to motor dysfunction to cancer. The degree of toxicity of
organic compounds varies widely from essentially harmless (e.g., most carbo-
hydrates) to moderately toxic (e.g.,most alcohols) to extremely toxic (e.g.,
aflatoxins).
A glance at the current edition of The Merck Index will reveal that the number of
organic compounds described thus far is almost unfathomable.Nearly any of these
may appear in wastewater, depending upon its sources.Thus, the discussion below
must be perforce rather general, and the presence of any particular toxic organic in
high concentration in sludge may require a site-specific evaluation of potential health
effects.
Types and Levels in Wastewater and Sludge
Most common organics in domestic wastewater derive from feces, urine, paper
products, food wastes, detergents, and skin excretions and contaminants (from
bathing). In medium-strength sewage (700 ppm total solids content), organics make
up about 75% of the suspended solids and about 40% of the filterable solids (colloidal
and dissolved), consisting primarily of proteins (40-60%), carbohydrates (25-50%),
and fats and oils (10%) (Metcalf and Eddy 1972). After secondary treatment, the
more refractory and high-molecular-weight organics predominate, e.g., fulvic acid,
humic acid, and hymathomelanic acid (Chang and Page 1978). In general, however,
the chemical nature of domestic wastewater remains poorly characterized.
Although most of the organics found in municipal sludge of domestic origin are
probably harmless in a land application context, it has recently been found that fecal
material commonly contains mutagens. It is widely believed that mutagens form a
large class of potential carcinogens (Weisburger and Williams 1980). Thus, there is
evidence that one of the causes of colorectal cancer is the presence of carcinogens or
co-carcinogens produced by the bacterial degradation in the gut of bile acids or
cholesterol (Thornton 1981). The mutagenicity of feces can be increased by anaerobic
incubation and by the presence of bile and bile acids (Van Tassel et al. 1982), and is
lower in vegetarians than non-vegetarians (Kuhnlein et al. 1981). High levels of
chromosome-breaking mutagenic activity have also been found in the feces of
animals—dog, otter, gull, cow, horse, sheep, chicken, and goose (Stich et al. 1980).
The chemical nature of the fecal mutagens is unknown. In the case of the latter animal
mutagens, evidence suggests that at least part of the mutagenic action is due to
hydrogen peroxide and the ensuing radicals which can be formed during oxidation of
many organic compounds (Stich et al. 1980).
Ten domestic and industrial secondary effluents in Illinois were recently examined
for mutagenicity by Johnston et al. (1982), with the results that all ten effluents
assayed showed significant mutagenicity. Mutagenic activity per unit volume of
effluent varied over a 4,500-fold range, and toxicity varied over a 120-fold range.
Selective extraction of whole effluents appeared to unmask mutagenic activity,
probably by separating mutagens and substances that interfere with the mutagen
assay. In several effluents there was evidence of several mutagenic compounds
present, and it appeared that the mutagens were predominantly nonpolar, neutral
39
-------
compounds. There was no obvious influence of disinfection by chlorination on the
effluent mutagenicity, in spite of the fact that one would expect many mutagens to be
formed by the action of chlorine on humic substances and other organics found in
wastewater.
Whether natural mutagens are of any significance in sludge, however, is doubtful,
since a recent small-scale survey has shown only municipal sludge with industrial
input to have mutagenic activity. Mutagenic activity could not be demonstrated in
purely domestic sludge (Hopke et al. 1982, 1984). However, since industrial input is
characteristic of most American cities,it is reasonable to assume that most sludges
will possess mutagenic activity. Thus Babish et al. (1983) found mutagenicity in 33 of
34 sludges from different American cities demonstrated by at least 1 of 5 tester strains
of Salmonella in the Ames test.
The major contributors of toxic organics to municipal wastewaters are usually
assumed to be industrial discharges. However, household wastewater discharge may
represent an important contributor since many consumer products in daily use
contain toxic substances. A recent study (Hathaway 1980) identified consumer
products containing toxic compounds on EPA's list of 129 "priority" pollutants,
which may eventually end up in wastewater. (It should be recognized that this list of
"priority" pollutants is, to some extent, arbitrary. Although the list has been used by
EPA and others for many purposes, there exist numerous other toxic organic
compounds which are of public health concern.) The most frequently used products
are cleaning agents and cosmetics, containing solvents and heavy metals as main
ingredients. Next are deodorizers and disinfectants, containing naphthalene, phenol,
and chlorophenols. Discarded into wastewater infrequently, but in large volumes,
are pesticides, laundry products, paint products, polishes, and preservatives.The
organic priority pollutants most frequently used and discharged into domestic
wastewater were predicted to be the following:
benzene
phenol
2,4,6-trichlorophenol
2-chlorophenol
1,2-dichlorobenzene
1,4-dichlorobenzene
1,1,1-trichloroethane
naphthalene
toluene
diethylphthalate
dimethylphthalate
trichloroethylene
aldrin
dieldrin
Because of the difficulty of analysis of complex mixtures, it has only recently been
possible to measure the actual levels of organics in wastewater using advanced
methods of extraction, gas and other chromatography, mass spectrometry, and
computer analysis. The U.S. Environmental Protection Agency has sponsored two
extensive surveys of the types and levels of priority pollutants in municipal
wastewaters, which, of course, result from both domestic and industrial discharges.
The first (DeWalle et al. 1981), supported by the Municipal Environmental Research
Laboratory in Cincinnati, covered 25 cities located throughout the United States,
and the second (Burns and Roe 1982), supported by the Effluent Guidelines Division
in Washington, D.C., covered 40 cities.
In the 25-city survey (DeWalle et al. 1981) most of the 24-hour composite samples
of raw wastewaters contained less than 1 mg/1 of priority organics,and the numbers
of compounds detected clustered between 20 and 50. In the 40-city survey (Burns and
40
-------
Roe 1982) six days of 24-hour sampling was completed. Comparison with other
available data sets has shown the 40-city survey to be generally representative of
municipal sludges (Fricke et al. 1985). The priority organics detected in at least 50%
of the samples analyzed in either survey are listed, together with their concentrations,
in Table 20. Comparison of the results of the two surveys with the list of organic
priority pollutants most likely to be discharged into domestic wastewater, reveals
considerable overlap, and gives one some confidence that these two studies have
Table 20. Most Frequently Detected Priority Organics in Raw
Municipal Wastewater
DeWalle ef a/. 1981
Burns
and Roe 1982
Detection Concentration Detection Concentration
Frequency Range Frequency Range
Compound (%) (fjg/\) (%) (A
-------
yielded a reasonable characterization of the priority organics in municipal
wastewater, at least of those identifiable by modern methods.
The priority organics in raw municipal sludge detected in at least 10% of the
samples analyzed in the 40-city survey (Burns and Roe 1982) are listed, together with
their concentrations, in Table 21. Note that, of the 30 compounds listed, 21 also
appear in Table 20. The broad range of concentrations detected among the samples
suggests that sludge applied to land should be regularly monitored for toxic organics.
This measure is emphasized by the occasional discharge of toxic substances into
municipal wastewater systems with resulting medical effects in treatment plant
workers, such as the recent hexachlorocyclopentadiene episode in Louisville,
Kentucky (Kominsky et al. 1980).
Table 21. Most Frequently Detected Priority Organics
in Raw Municipal Sludge (Burns and Roe
1982)
Compound
Bis(2-ethylhexyl)phthalate
Toluene
Dichloromethane
Ethylbenzene
Benzene
1 ,2-Trans-dichloroethylene
Trichloroethylene
Pyrene
Phenanthrene
Phenol
Anthracene
Di-n-butylphthalate
Fluoranthene
Butylbenzylphthalate
Tetrachloroethylene
1,1 -Dichloroethane
Naphthalene
Chrysene
1 ,2-Benzanthracene
Trichloromethane (Chloroform)
1 ,1 ,1 -Trichloroethane
1 ,4-Dichlorobenzene
1 ,2-Dichlorobenzene
1 ,1 ,2,2-Tetrachloroethane
Pentachlorophenol
Chlorobenzene
1 ,2,4-Trichlorobenzene
3,4-Benzofluoranthene
Di-n-octylphthalate
1 ,2-Dichloroethane
Detection
Frequency
(%)
95
94
73
63
61
60
54
53
53
50
48
45
44
43
40
34
34
31
27
24
19
17
16
15
14
13
13
11
10
10
Concentration
Range
-------
Soil and Groundwater
Organic compounds in sludge may be volatilized, immobilized by adsorption, or
transported through the soil column, possibly to reach the groundwater. At normal
application rates and management techniques, however, leaching or soil migration of
organics from a municipal sludge land application site is probably insignificant
(Overcash 1983). Adsorbed organics may be subsequently chemically or photo-
chemically degraded, microbially decomposed, or desorbed. A considerable body of
research has been performed on the behavior of pesticides in soil. This research has
shown that the affinity of soil components for pesticides, and presumably for
organics in general, decreases in the following order (Chang and Page 1978):
Organic Matter
Vermiculite
Montmorillonite
Illite
Chlorite
Kaolinite
Iron and aluminum oxides also adsorb organics. Adsorption of organic pesticides
tends to increase with the concentration of functional groups such as amine, amide,
carboxyl, and phenol. Both laboratory and field experiments suggest that, because of
adsorption by soil particles, most pesticide residues remain in surface soils during
land treatment (Chang and Page 1978).
It has recently been shown that for polynuclear aromatic hydrocarbons adsorption
increases with increasing organic carbon content of the soils and increasing effective
chain length of the molecule (Means et al. 1980). The behavior of polychlorinated
biphenyls (PCBs) in soil has been comprehensively reviewed by Griffin and Chian
(1980), who concluded that PCBs are strongly adsorbed by soil, and that the nature
of the surface, the soil organic matter content, and the chlorine content and/or
hydrophobicity of the individual PCB isomers are factors affecting adsorption.
Adsorption increases with increasing organic matter content of the soil, with
increasing chlorine content, and with increasing hydrophobicity. One study of PCB
percolation through soil columns showed that less than 0.05% of one isomer was
leached in the worst case. Fairbanks and O'Connor (1984) have recently shown that
PCBs remain tightly adsorbed to sludge-amended soil, with minimal transport by
soil water.
Once organics are immobilized by adsorption on the surfaces of soil particles,
microbial decomposition, or biodegradation, is probably the major mechanism of
their breakdown. Although there are several abiotic mechanisms for chemical
change, nonenzymatic reactions rarely result in appreciable changes in chemical
structure, and it is biodegradation that brings about major alterations and
mineralization of organics (Alexander 1981). The chief agents of this metabolism are
the indigenous heterotrophic bacteria and fungi.
It is, of course, possible that high levels of toxic organics in sludge could have a
severe inhibitory effect on the soil microflora. However, such levels are much greater
than one would expect to find with the land application of municipal sludge
(Overcash 1983).
The potential of microbial decomposition for removal of organics is demonstrated
by the experience at two rapid infiltration and one overland flow wastewater land
treatment sites. At Flushing Meadows in Arizona secondary effluent has resulted in
no accumulation of organic carbon in the soil after ten years of operation and 754 m
of total infiltration (Bouwer and Rice 1978). Secondly, the Lake George Village
Sewage Treatment Plant in New York has been applying unchlorinated secondary
effluent to natural delta sand beds by rapid infiltration since 1939 (Aulenbach and
Clesceri 1978). After about forty years of daily infiltration rates of 0.08 to 0.30 m/day,
43
-------
there were no indications that the soil's capacity to treat the applied effluent was
approaching exhaustion. The greatest removal of constituents occurred in the top 10
m of the sand beds. At a prototype overland flowland treatment system, at the U.S.
Army Cold Regions Research and Engineering Laboratory in New Hampshire,
greater than 94% removal of each of 13 trace organics by volatilization and
adsorption was observed (Jenkins et al. 1983), with removal efficiencies decreasing as
application rates increased and temperature decreased. With the possible exception
of PCB, biodegradation resulted in the absence of contaminant buildup in the surface
soil.
Although complete mineralization and detoxication of organic compounds is
common, many compounds are acted on biologically in soils without the
microorganisms being able to use them as their sources of nutrient or energy. The
microorganisms are probably utilizing another substrate while performing the
transformations known as "cometabolism" (Alexander 1981). Cometabolism may
lead to detoxication, the formation of new toxic substances, or the synthesis of
persistent products. There is evidence that cometabolism may be particularly
common for toxic organics in very low concentrations in the environment (Rubin et
al. 1982, Subba-Rao et al. 1982).
The metabolism of few chemicals has been studied in microbial cultures,and even
fewer in natural ecosystems. Why certain intermediate compounds in a metabolic
sequence accumulate outside or inside the active organism is not known, and it is
extremely difficult to predict the chemical fate of toxic organics in the environment.
The prediction of biodegradability from chemical structure, although theoretically
possible, has thus far proven problematic. Alexander (1981) has described several
common types of reactions that may occur, and these are listed in Table 22. It used to
be thought that every organic compound could be completely decomposed by
microorganisms. Thus a recent evaluation (Kobayashi and Rittmann 1982) indicated
that the use of properly selected populations of microorganisms, and the maintenance
of appropriate controlled environmental conditions, could be an important means of
improving biological treatment of organic wastes, and that members of almost every
class of synthetic compound can be degraded by some microorganism. However,
field evidence has resulted in the conclusion that some synthetic organics are
decomposed slowly, if at all, and may persist for long periods in the environment.
Alexander (1981) has summarized the possible reasons for this, concluding primarily
that various synthetic compounds, e.g., polymers and halogenated aromatics, are too
far from the mainstream of catabolic pathways to be substrates for any microbial
species.
Table 22. Common Types of Chemical Transformations in the
Environment
Dehalogenation Nitro metabolism
Deamination Oxime metabolism
Decarboxylation Nitrite/amide metabolism
Methyl oxidation Cleavage reactions (many types)
Hydroxylation and ketone formation Nondegradative reactions:
/3 oxidation Methylation
Epoxide formation Ether formation
Nitrogen oxidation N-Acylation
Sulfur oxidation Nitration
=Sto=0 N-Nitrosation
Sulfoxide reduction Dimerization
Reduction of triple bond Nitrogen heterocycle formation
Reduction of double bond Oligomer and polymer formation
Hydration of double bond
44
-------
A general idea of the relative degree of biodegradation of toxic organics to be
expected in soil may be gained from Tabak et al.'s (1981)studies on organic priority
pollutants. They collected data on the biodegradability and rate of microbial
acclimation of 96 compounds (5 and 10 mg/l)in a static culture flask screening
procedure, using domestic wastewater inoculum and synthetic medium. Microbial
acclimation, or adaptation, was measured by making three weekly subcultures;
percentage biodegradation was measured after seven days incubation in the dark at
25°C. Their overall results are summarized in Table 23. Significant biodegradation
was found for phenolic compounds, phthalate esters, naphthalenes, and nitrogenous
organics; variable results were found for monocyclic aromatics, polycyclic aromatics,
polychlorinated biphenyls, halogenated ethers, and halogenated aliphatics; and no
significant biodegradation was found for organochlorine pesticides.
Extrapolation of the above results to the behavior of toxic organics in the soil must
be done with two provisos: (1) biodegradation in soil may be somewhat different
from that in the aquatic medium used for the tests, and(2) the lower concentration of
the organics at the land application site may not elicit microbial activity or enzyme
induction. Nevertheless, a comparison of the results with the compounds to be
expected in wastewater, as listed in Table 20, is instructive. Among the top ten
compounds in the table, nine have significant degradation, and one has slow to
moderate degradation with significant volatilization. Among the next ten com-
pounds, eight have significant degradation, two of which are followed by toxicity.
Only two compounds are not significantly degraded, the pesticides heptachlor and
lindane.
Other than for pesticides, the literature on the microbial decomposition of toxic
organics in soil is sparse. The degradation of petroleum hydrocarbons, a mixture of
aliphatic, aromatic, and asphaltic compounds, has been reviewed by Atlas (1980,
1981). Factors which appear to be important in encouraging high decomposition rate
of petroleum hydrocarbons are high temperature, low concentrations, high soil
fertility, and an aerobic environment. There is little evidence for significant
downward leaching of oil. Experiments with the high-rate application of high
petroleum hydrocarbon sludge to land have shown a 77% degradation rate near the
surface after one year, most of the degraded compounds being n-alkanes (Lin 1980),
and it was concluded that sludge land disposal would not result in petroleum
hydrocarbon buildup in the soil. In studies of organic substances in wastewaters used
for irrigation, Dodolina et al. (1976) found acetaldehyde, crotonaldehyde, benz-
aldehyde, cyclohexanone, cyclohexanol, and dichloroethane to disappear from soil
within ten days. The biodegradation in soil of polychlorinated biphenyls was
reviewed by Griffin and Chian (1980) who concluded that they are degradable, but
that resistance increases as isomers have higher chlorination. Polybrominated
biphenyls, on the other hand, have shown little biodegradation after one year in soil
(Jacobs et al. 1978).
It has recently been found that it might be possible for carcinogenic and
teratogenic nitrosamines to be formed from secondary and tertiary amines at
wastewater land treatment sites. Thus, Thomas and Alexander (1981) have shown
that dimethylamine and trimethylamine can be formed in municipal wastewater from
naturally-occurring precursors. Dimethylamine may then go on to be microbially
nitrosated, forming N-nitrosodimethylamine, a process which can occur under
conditions resembling land treatment of wastewater(Green et al. 1981). Whether this
can actually occur under field conditions, resulting in a threat to groundwater, is
unknown. The issue may be moot, however, since Mumma et al. (1984) have found
nitrosamines already present in 14x>f 15 municipal sludges analyzed. In any case,
Dressel (1976) has demonstrated that nitrosamines are rapidly degraded in soil.
Similarly, mutagens, as detected by the Ames test, in municipal sludge applied to soil
at the rate of 112 dry t sludge/ ha and mixed, could no longer be detected after 4 weeks
(Angle and Baudler 1984).
45
-------
Table 23. Biodegradability of Priority Organic Compounds (after Tabak et al. 1981 )*
Test Compound
Phenols
Phenol
2-chloro phenol
2,4-Dichloro phenol
2,4,6-Trichloro phenol
Pentachloro phenol
2,4-Dimethyl phenol
Phthalate Esters
Dimethyl phthalate
Diethyl phthalate
Di-n-butyl phthalate
Naphthalenes
Naphthalene
2-Chloro naphthalene
Acenaphthene
Acenaphthylene
Monocyclic Aromatics
Benzene
Chlorobenzene
1 ,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dichlorobenzene
1 ,2,4-Trichlorobenzene
Polycyclic Aromatics (PAHs)
Anthracene
Phenanthrene
Fluorene
Fluoranthene
Performance
Summary
D
D
D
D
A
D
D
D
D
D
D
D
D
D
D-A
T
T
T
T
A
D
A
A-N
Test Compound
p-Chloro-m-cresol
2-Nitro phenol
4-Nitro phenol
2,4-Dinitro phenol
4,6-Dinitro-o-cresol
Bis-(2-ethyl hexyl) phthalate
Di-n-octyl phthalate
Butyl benzyl phthalate
Hexachlorobenzene
Nitrobenzene
Ethylbenzene
Toluene
2,4-Dinitrotoluene
2,6-Dinitrotoluene
1,2-Benzanthracene
Pyrene
Chrysene
Performance
Summary
D
D
D
D
N
A
A
D
N
D
D-N
D
T
T
N
D-N
A-N
-------
Table 23. (Continued)
Test Compound
Performance
Summary
Test Compound
Performance
Summary
Polychlorinated Biphenyls (PCBs)
Aroclor-1016
Ar odor-1221
Aroclor-1232
Aroclor-1242
Halogenated Ethers
Bis-(2-chloroethyl) ether
2-Chloroethyl vinyl ether
4-Chlorodiphenyl ether
Nitrogenous Organics
Nitrosamines
N-Nitroso-di-N-propylamine
N-Nitrosodiphenylamine
Substituted benzenes
Isophorone
1,2-Diphenylhydrazine
Halogenated A liphatics
Chloroethanes
1,1 -Dichloroethane
1,2-Dichloroethane
1,1,1 -Trichloroethane
1,1,2-Trichloroethane
1,1,2,2-Tetrachloroethane
Hexachloroethane
Halomethanes
Methylene chloride
Bromochloromethane
Carbon tetrachloride
N
D
D
N
D
D
N
N
D-A
D
T
A
B
B
C
N
D
D
D
D
Aroclor-1248
Aroclor 1254
Aroclor-1260
4-Bromodiphenyl ether
Bis-(2-chloroethoxy)methane
Bis-(2-chloroisopropyl) ether
Acrylonitrile
Acrolein
Chloroethylenes
1,1 -Dichloroethytene
1,2-Dichloroethylene-cis
1,2-Dichloroethylene-trans
Trichloroethylene
Tetrachloroethylene
Chloropropanes
1,2-Dichloropropane
Chloropropylenes
1,3-Dichloropropylene
Chlorobutadienes
N
N
N
N
N
D
D
D
A
B
B
A
A
-------
Table 23. (Continued)
Test Compound
Performance
Summary
Test Compound
Performance
Summary
Chloroform
Dichlorobromomethane
Bromoform
Chlorodibromomethane
Trichlorofluoromethane
Organochlorine Pesticides
Aldrin
Dieldrin
Chlordane
DDT p,p'
DDE p,p'
ODD p,p'
Endosulfan-alpha
Endosulfan-beta
Endosulfan sulfate
Endrin
A
A
A
N
N
N
N
N
N
N
N
N
N
N
N
Hexachloro-1,3-butadiene
Chloropentadienes
Hexachlorocyclopentadiene
Heptachlor
Heptachlor epoxide
Hexachlorocyclohexane
orBHC-alpha
Hexachlorocyclohexane
0BHC-beta
Hexachlorocyclohexane
<5BHC-delta
Hexachlorocyclohexane
xBHC-gamma (lindane)
D
D
N
N
N
N
N
N
*D—significant degradation with rapid adaptation; A—significant degradation with gradual adaptation; T—significant degradation
with gradual adaptation followed by a deadaptive process (toxicity); B—slow to moderate biodegradative activity, concomitant with
significant rate of volatilization; C—very slow biodegradative activity, with long adaptation period needed; N—not significantly
degraded under the conditions of test method.
-------
In view of multitudinous variety of organic compounds in existence, it is difficult
to generalize about their biodegradation in soil. It appears, however, that most
organics do become microbially decomposed in the soil, at least to some extent. This
is especially true of naturally-occurring compounds, or those resembling them,
because of the eons of evolution that have developed microbial enzyme systems to do
the job. The more structurally complex the molecule is, e.g., condensed rings or dense
branching, and more halogenated it is, the more difficult is biodegradation. Overcash
(1983) has concluded that very few organic compounds can be said to be non-
degradable in soil systems, in particular two classes: synthetic polymers manufac-
tured for stability, and very insoluble large molecules, e.g., 5-10 chlorinated
biphenyls.
Although few organics are likely to reach the groundwater at a sludge application
site, those that do may be subject to some of the same removal processes that affect
them at the surface, particularly adsorption and microbial decomposition, although
certainly at much lower rates. These two processes, which largely govern the
movement and fate of organics in the subsurface environment, have been reviewed by
McCarty et al. (1980, 1981).The degree of adsorption of an organic compound in
groundwater is to a great extent dependent upon its hydrophobicity, especially when
the aquifer organic content is above about 0.1%. Thus, only compounds with
octanol/water partition coefficients less than 103 are likely to readily move through
the subsurface environment. Of course, these are the very compounds most likely to
reach the groundwater, the more hydrophobic compounds having been adsorbed to
the soil above. Likewise, it is probable that most microbial decomposition would
have occurred before the organics reach the groundwater, although there is evidence
that diverse microbial populations of sulfate reducers, methanogens, and heter-
otrophs exist and are metabolically active in aquifers, and that biodegradation of
some organic pollutants occurs in groundwater (Gerba and McNabb 1981).
Nevertheless, it is difficult to avoid the conclusion that once toxic organics get into
the groundwater they may remain there for a long time.
Plants
At the low concentrations found in the soil at municipal sludge land application
sites, very few organic compounds are likely to be toxic to plants (Overcash 1983). In
a review of data on over 130,000 chemicals, Kenaga(1981) found only 0.17% of the
chemicals killed seeds or seedlings at concentrations of 0.1-0.99 ppm. Crop plants,
however, although not injured themselves, may accumulate organics that may be
toxic to the animals to which they are fed or to humans who use them as food, either
directly or through animal products. The issue is complicated by the fact that
significant levels of toxic organics, e.g., polycyclic aromatic hydrocarbons (Borneff
et al. 1968), may be synthesized by the plants themselves. Moreover, plant
composition of biologically active compounds, e.g., natural mutagens, may be
affected by growth on sludge-amended soil (Miller et al. 1983).
Among the organics, the pesticides appear to be the most notorious accumulators
in crop plants. Thus, heptachlor, dieldrin, and chlordane are absorbed at low levels
from the soil (Braude et al. 1978). Most herbicides, of course, are readily taken up and
translocated within plants, but there is no reason to think that herbicides would
present more of a problem at land application sites than they do at ordinary
agricultural sites.
In contrast with pesticides, most organic compounds are only poorly absorbed and
translocated by plants, with much of the "absorption" probably accounted for by
root adsorption, often through vapor transport. Vapor transport from the soil may
even result in shoot adsorption (Chancy 1984). Soil organic matter adsorbs lipophilic
compounds, decreasing their availability to plants. Thus, sludge itself helps to retain
toxic organics in the soil, and keeps them accessible to biodegradation.
49
-------
Numerous studies of organics uptake by plants have shown that many organics can
indeed be absorbed, but usually only at high soil levels and with little translocation to
the upper parts of the plants.
Trace levels of polychlorinatd biphenyls (PCBs) from municipal sludge applied to
an old field has resulted in no detectable PCBs in plant samples (Davis et al. 1981).
Higher levels (50-100 ppm dry soil) resulted in 3-50% of the soil concentration in
carrots (Iwata et al., 1974), with concentration increasing with lesser-chlorinated
biphenyls. Since 97% of the PCB was found in the carrot peel, very little translocation
occurred in the plant tissue. The lower-chlorinated PCBs are much more volatile and
biodegradable, and thus are less likely to be common in sludge; the higher-
chlorinated PCBs are less absorbed by plants (Fries and Marrow 1981). As a
consequence, PCB exposure through plants is probably minimal. For example, Lee
et al. (1980) were unable to detect PCBs in carrots grown in land to which 0.93 ppm
PCBs domestic sludge was applied at 2241/ha, and Naylor and Mondy (1984) have
obtained similar results with potatoes. On the basis of greenhouse and field studies of
polybrominated biphenyls (PBBs), it has been concluded that little, if any, PBB will
be translocated from contaminated soil to plant tops, and although some root crops
from highly contaminated soil might contain traces of PBB, much of this PBB could
probably be removed by peeling (Chou et al. 1978).
Irrigation of vegetables in test plots with contaminated wastewaters has shown no
accumulation of polycyclic aromatic hydrocarbons, especially benzo(a)pyrene
(Il'nitskii et al. 1974). 4-Chloroaniline and 3,4-dichloroaniline can be absorbed by
.omato plants, oats, barley, and wheat, but 90-95% remains in the roots (Fuchsbichler
et al. 1978); in carrots, however, the chloroanilines are translocated to the upper parts
of the plants in significant quantities. In a study of aldehydes and other organics at
agricultural land treatment sites Dodelina et al. (1976) found no uptake of
acetaldehyde, crotonaldehyde, and benzaldehyde in the aboveground portions of
potatoes and corn. Cyclohexanone and cyclohexanol could be found in corn plants
four days after irrigation, but not later. Dichloroethane was taken up by beets and
cereals, but was metabolized and absent within about two weeks after irrigation.
At the operating land treatment site in Muskegon, corn crop samples for 1980 did
not contain detectable levels of any of the chemicals tested, and it was concluded that
plant uptake of irrigated organic chemicals does not occur to any measurable extent
(Demirjian et al. 1981). Thus, it is probably reasonable to assume that the health risk
from toxic organics in plants is slight, provided that high levels in sludge are
prevented by monitoring.
Animals
The low levels of toxic organics to be expected in the above ground portions of
plants growing at land application sites probably pose little hazard to animals feeding
upon them. Under certain site-specific conditions, however, high concentrations of
particular organics in the sludge may cause problems. For example, PCBs in cabbage
grown on sludge-amended soil have probably caused degenerative changes in liver
and thyroid of sheep (Kienholz 1980, Haschek 1979).
Hansen et al. (1976) studied young swine fed for 56 days on corn grown on
sludge-fertilized land. It was essentially a negative study: electroencephalograms,
electrocardiograms, clinical chemistry, and histopathology were all normal.
However, they observed elevated levels of hepatic microsomal mixed function
oxidase (MFO) activity in the swine fed sludge-fertilized corn. Associated with this
were non-statistically significant increased liver weights. Other liver enzymes
(alkaline phosphatase and lactate dehydrogenase) were normal. This increased MFO
activity may be caused by toxic organics, metals, or be of no significance, but the
authors concluded that further study should be performed before such grain can be
recommended as the major dietary component for animals over long periods.
50
-------
Similar results were found by Telford et al. (1982), who examined sheep fed silage
corn grown on soil amended with municipal sludge at a high rate (224 t/ha). The
sheep had significantly higher hepatic microsomal p-nitroanisole-O-demethylase
activity than controls, but no mutagenic responses for animal feed or feces, and no
histopathological effects. In contrast, the same research group (Lisk et al. 1982)
found no hepatic microsomal MFO response in swine fed corn grown on high-rate
sludge-amended soil. Liver: body weight ratios, corn, feces, and urine mutagenicity,
and histopathology were also unremarkable, suggesting absence or low levels of
organic toxicants in the corn. Sludge-amended-soil-grown cabbage, beets, green
beans, and squash have been fed to rats for 12 weeks, resulting in no effects on weight
gain, alphafetoprotein (a marker for hepatic preneoplastic transformation), liver
weight, hepatic MFO (aminopyrene-N-demethylase and p-nitroanisole-O-de-
methylase), or liver cell ultrastructure (Boyd et al. 1982). Mutagenicity, however, was
found in the sludge-grown beans and in the urine of rats fed sludge-grown beets.
Sludge-grown cabbage has also been shown to have mutagenic activity (Miller et al.
1983).
Forages grown on soils containing PCBs have PCB residues of about one-tenth or
lower that of the soil during the first crop year (Chaney 1984). Delaying grazing for 30
days after surface sludge application and supplying alternative feeds during periods
of low forage availability reduce sludge ingestion so that 10 ppm PCBs could be
allowed in sludge surface-applied at 101 ha"1 yr~1. Subsurface injection could further
reduce exposure.
A more serious route of exposure by animals to toxic organics is the soil itself.
Most grazing animals ingest a certain amount of soil together with their food plants.
Thus, dairy cows may ingest 100-500 kg of soil per year, with an average of about
200-300 kg/yr; expressed in other terms, dairy cows may consume soil up to 14% of
dry matter intake when available forage is low and no supplemental feed is used
(Kienholz 1980, Fries 1980). Lipophilic organics present in the soil may concentrate
in animal fat. For example, feeding experiments with PCBs indicate that the steady-
state milk fat concentrations are about five times the diet concentrations, which
could result in milk fat levels of 0.7 ppm for each 1 ppm of PCBs in surface soil (Fries
1980). Body fat levels would be expected to be similar. Based upon FDA tolerances of
1.5 mg PCB/ kg milk fat, Fries (1982) has concluded that PCBs should not exceed 2.0
mg/kg dry sludge if dairy cows are allowed to graze sludge-amended pastures. In a
study of the pasture application of wastewater sludge with a high textile industry
component, deHaan (1977) found 1.2 ppm of dieldrin (almost 19 times the acceptable
level in The Netherlands) in the milk of grazing cows.
Studies at New Mexico State University (Smith 1982), involving direct feeding of
sludges to rats, sheep, and cattle, indicate no hazard from toxicants, based on uptake,
MFO activity, and histopathology.
Turning to humans, Baker et al. (1980) described the metabolic consequences of
exposure to high levels of PCBs from contaminated wastewater sludge used as a soil
amendment in Bloomington, Indiana. No skin or systemic symptoms were noted,
and of the hematologic, hepatic, and renal functions measured, only serum
triglyceride levels increased, suggesting altered lipid metabolism. Serum PCB levels
were normal. Naylor and Loehr (1982) have recently performed a detailed
toxicological analysis of the potential human health risks of the consumption of
sludge-contaminated soils and crops associated with organic priority pollutants.
They concluded that land application of sludge is not likely to result in the ingestion
of amounts of organic priority pollutants exceeding the acceptable daily intake.
The long-term effects of chronic ingestion of these same organics, many of which
are animal carcinogens, have been examined by Connor (1984). In his analysis
Connor calculated the lifetime risk of cancer from the predicted doses of known
carcinogens. The predicted doses were based upon the sludge pollutant con-
centrations and application rates summarized by Naylor and Loehr (1982), but
included ingestion resulting from uptake of organics by plants and animals as well as
51
-------
direct consumption. Connor concluded that toxic organics are not likely to present a
significant health risk, with the possible exception of polycyclic aromatic hydro-
carbons (PAHs), and that it would be prudent to develop management techniques to
decrease PAH concentrations in sludge.
52
-------
SECTION 8
TRACE ELEMENTS
Types and Levels in Wastewater and Sludge
The trace elements (including the "heavy metals") in wastewater of public health
concern, i.e., those for which primary drinking water standards (USEPA 1977) exist
(but excluding silver since its effect is largely cosmetic), are:
Primary Drinking Water
Standard (mg/1)
Arsenic (As) 0.05
Barium (Ba) 1.0
Cadmium (Cd) 0.010
Chromium (Cr) 0.05
Lead (Pb) 0.05
Mercury (Hg) 0.002
Selenium (Se) 0.01
Of these, cadmium, lead, and mercury are usually regarded as of most concern, and
barium of minor concern. Chromium and selenium are essential elements in man;
arsenic and cadmium have been shown to be essential to experimental animals and,
thus, may be essential to man as well (National Research Council 1980). Secondary
drinking water standards (USEPA 1979), i.e., those related to aesthetic quality, also
exist for copper, iron, manganese, and zinc. These latter elements, as well as all other
trace elements, are toxic if ingested or inhaled at high levels for long periods
(Underwood 1977), but this fact does not warrant considering them in the land
application context, where low levels are expected.
Arsenic is popularly known as an acute poison, but chronic human exposure to
low doses, as might be expected for all trace elements as a result of land application,
may cause weakness, prostration, muscular aching, skin and mucosal changes,
peripheral neuropathy, and linear pigmentations in the fingernails. Chronic arsenic
intoxication may result in headache, drowsiness, confusion, and convulsions
(Underwood 1977). Epidemiological evidence has implicated arsenic as a human
carcinogen, but there is little evidence that arsenic compounds are carcinogenic in
experimental animals (Sunderman 1977). Even with high concentrations in soil,
however, plants rarely take up enough of the element to constitute a risk to human
health (Underwood 1977, Council for Agricultural Science and Technology 1976).
Barium has a low degree of toxicity by the oral route. Because of its effect of
intensely stimulating smooth, striated, and cardiac muscle in acute exposures,
however, it may have cardiovascular effects in low doses, but this has not thus far
been demonstrated (Brenniman et al. 1979).
Cadmium is widely regarded as the trace element of most concern from a human
health effects viewpoint in the land application of sludge. Cadmium has a very long
biological half-life in humans, with its concentration in the liver and kidneys
continually increasing to the sixth decade of life (Kowal et al. 1979). The critical
health effect of chronic environmental exposure via ingestion is proximal renal
tubular damage due to accumulation of cadmium in the kidney. The "initial
consequence of this damage is the loss of low molecular weight serum proteins in the
53
-------
urine, followed by loss of other proteins, glucose, amino acids, and phosphate, i.e.,
the Fanconi syndrome. This kidney damage is often irreversible and constitutes a
significant adverse health effect. There is evidence that the absorption and/or
toxicity of cadmium are antagonized by zinc, selenium, iron, and calcium (Sandstead
1977). The carcinogenicity of cadmium is controversial; the epidemiological evidence
is tenuous, and the experimental evidence is conflicting (Ryan et al. 1982). The
human health effects of cadmium have been recently reviewed by Hallenbeck (1984)
and Bernard and Lauwerys (1984).
Chromium is much more toxic in its hexavalent form than its trivalent form, its
predominant state in wastewater and soil. Chronic oral exposure in experimental
animals has been associated with growth depression, and liver and kidney damage
(Underwood 1977). Hexavalent chromium causes respiratory cancer upon chronic
exposure to chromate dust (Sunderman 1977). Most crops absorb relatively little
chromium from the soil (Council for Agricultural Science and Technology 1976).
Lead chronic toxicity is characterized by neurological defects, renal tubular
dysfunction, and anemia. Damage to the central nervous system is common,
especially in children, who have low lead tolerance, resulting in physical brain
damage, behavioral problems, intellectual impairment, and hyperactivity. At soil pH
above 5.5 and high labile phosphorus content, common conditions at a land
treatment site, little movement of lead from the soil into plant tops and seed would be
expected (Council for Agricultural Science and Technology 1976, Stewart 1979).
Mercury in low levels can result in neurological symptoms such as tremors,
vertigo, irritability, and depression, as well as salivation, stomatitis, and diarrhea.
Mercury can enter plants through the roots, and appears to be readily translocated
throughout the plant (Council for Agricultural Science and Technology 1976),
although there is some contrary evidence (Stewart 1979).
Selenium exposure in its chronic form is associated with dental caries, jaundice,
skin irruptions, chronic arthritis, deformed finger and toenails, and subcutaneous
edema. It has also been found to have an inhibitory effect against several types of
cancer (Fishbein 1977). Selenium is readily taken up by plants and passed onto
animals, and has caused toxicity in livestock in high-selenium soils (Council for
Agricultural Science and Technology 1976, Underwood 1977).
The concentrations of trace elements (after Chancy 1984) in typical dry digested
municipal sludges and in typical agricultural soils are presented in Table 24. Also
included in the table are the limits for the maximum cumulative application of trace
elements in sludge to agricultural land, which have been recommended by various
governmental agencies for the protection of public health and the prevention of
phytotoxicity. [For a concise discussion of phytotoxicity from land application of
sludge, see Logan and Chancy (1983).]
Soil and Plants
The availability of trace elements for uptake by plants (and thus entry into the
human food chain) and transport to groundwater is controlled by chelation to
organic matter, adsorption, and precipitation. Adsorption occurs on organic matter,
hydrous oxides of iron and manganese, clays, and other soil minerals. Precipitation
reactions include the formation of poorly soluble oxides, hydroxides, carbonates,
phosphates, sulfides, etc., for the cations (the metals), and formation of anions for
arsenic and selenium. Mercury, of course, may leave the soil through volatilization.
As a result of these processes only small amounts of the trace elements remain free in
the soil solution, from which they are available for absorption by plant roots. These
processes are strongly affected by soil pH, cation levels decreasing and anion levels
increasing in the soil solution with increasing pH (Chaney 1984). Repeated annual
cropland sludge application does not appear to affect the form of many trace
elements in the soil, e.g., cadmium and lead remain predominantly in the carbonate
form, and chromium in the sulfide residue form (Chang et al. 1984a).
54
-------
Table 24. Concentrations of Trace Elements (After Chaney 1984) in Typical Dry Digested Municipal Sludges and
Agricultural Soils, and Maximum Cumulative Application Limits
Agricultural Soil Cumulative Limits
Element
Arsenic
Barium
Cadmium
Chromium
Lead
Mercury
Selenium
Sludge
Minimum
(ppm)
1.1
1504
1
10
13
0.6
1.7
Sludge
Maximum
(ppm)
230
4,000"
3,410
99,000
26,000
56
17.2
Sludge
Median
(ppm)
10
1 ,500"
10
500
500
6
5
(ppm)
64
500*
0.1
25
25
0.034
0.24
(kg/ha}>
12
1,000
0.2
50
50
0.06
0.4
USA2
(kg/ha)
--
--
5/10/205
--
800
--
--
UK3
(kg/ha)
10
--
5
1,000
1,000
2
5
'Assuming tillage depth of 15 cm (thus soil volume of 1500 mVha), and soil bulk density of 1330 kg/m3 (Page 1974).
2USEPA, USFDA, and USDA 1981.
National Water Council 1977.
"Page 1974.
5For soils with cation exchange capacities of <5,5-15, and>15 meq/1 OOg, respectively, and soil pH >6.5. If soil pH <6.5, first figure
holds.
-------
The uptake of trace elements by plants has been reviewed by Logan and Chaney
(1983). Important factors affecting uptake rate include: trace element properties, soil
properties, the immediate environment (especially pH) of the roots, plant crop
species, and plant crop cultivar (variety or strain). As an example of species effects,
leafy vegetables, especially Swiss chard, are much better cadmium accumulators than
most other plants. Cultivars of maize (corn) and wheat have been shown to have very
different rates of cadmium accumulation.
The problem of cadmium uptake from sludge by crop plants, and the significance
of its buildup in the soil, has been studied and argued about for many years. The
current state of knowledge appears to allow the following generalizations to be made:
(1) Low-cadmium sludges result in low plant uptake, and high-cadmium sludges
result in high uptake. (2) While high cadmium land application rates using high-
cadmium sludges result in high uptake, the same high cadmium application rates
using low-cadmium sludges result in low uptake. (3) In soil to which sludge is
amended annually, cadmium adsorption increases, and thus plant uptake (with
reference to total soil cadmium) decreases with time (Chaney 1984, Logan and
Chaney 1983). Uptake decreases very rapidly after sludge applications are terminated
(Hinesly et al. 1984). Another potentially dangerous toxic trace element in municipal
sludge, lead, has been shown to have low availability when applied to land, and no
appreciable migration to the reproductive and reserve organs of vegetables (Berthet
et al. 1984, Naylor and Mondy 1984).
After a trace element enters the root cells, translocation to shoots, and thus into
above-ground human-food plant organs (leaves, fruits, seeds), depends upon the
properties of the specific element and plant. Involved in the process are membrane
surfaces, organic chelators, and cells specialized for pumping materials into the
xylem, through which it reaches the shoot. Chromium, lead, and mercury are
strongly held in the root cells, so that very little is translocated to the shoots of crop
plants. On the other hand, cadmium and selenium are weakly chelated, and thus
easily translocated (Logan and Chaney 1983).
These generalizations are supported by recent analyses of corn silage grown on
sludge-amended soils (Bray et al. 1985). Silage was produced for three years on land
amended by municipal sludge each year at high rates (15-90 metric tons/hectare).
The silage contained elevated levels of cadmium and zinc, but not of any of the other
12 elements tested, including arsenic, chromium, lead, mercury, and selenium.
Cadmium, therefore, under ordinary circumstances is the only trace element likely
to be of human health concern as a result of the application of municipal sludge to
agricultural land. This is because of the potentially high concentrations in sludge and
high sludge concentrations compared with normal soil concentrations (Table 24),
cadmium's relative ease of absorption into and translocation through plants, its low
level of phytotoxicity, and cadmium's human toxic effects.
Groundwater
At sludge application sites, trace elements are probably immobilized near the soil
surface, especially at high pH. In sludge-applied soils, Chang et al. (1984b) have
found over 90% of the deposited trace elements (e.g., cadmium, chromium, and lead)
to accumulate in the 0-15 cm soil depth, with little movement occurring below 30 cm.
Leachate from sludge-applied land in South Africa regularly had cadmium
concentrations below the drinking water standard of 10 /ug/1 (Nell et al. 1981).
Dowdy and Volk (1983) feel that the potential for groundwater contamination by
sludge-borne trace elements is extremely limited. Trace element movement will be
most likely with large applications to a sandy, acid, low organic-matter soil that
receives high precipitation or irrigation, but even under these conditions the extent of
movement will be limited.
56
-------
Animals
Just as in the case of organics, animals can be exposed to trace elements through
sludge residuals adhering to plants, sludge on the soil surface or mixed into the soil,
or trace elements absorbed and translocated by plants. All three routes would
operate on grazing land, but only the third when animals are fed sludge-amended-
soil-grown feed.
Studies of the accumulation of trace elements in cattle grazed on sludge-amended
pastures have revealed raised levels in liver and kidney, but not in muscle tissue
(Bertrande/a/. 198 la, Baxter ef al. 1983). Sheep grazing on sludge-amended pasture
have been found to have non-statistically-significant higher tissue levels of cadmium,
but no toxic effects (Hogue et al. 1984). Bertrand et al. (1981 b) observed no increases
when cattle were fed sludge amended-soil-grown forage sorghum, nor did increases
occur in mice or guinea pigs fed lettuce and Swiss chard grown on sludge-amended
soil (Chaney 1984). Other studies, however, have shown significant increases in
kidney and liver, but not muscle, cadmium in animals fed sludge-fertilized crops, e.g.,
swine and corn (Hansen and Hinesly 1979, Lisk et al. 1982), pheasants and corn
(Hinesly et al. 1984), goats and corn silage (Bray et al. 1985), rats and beets (Boyd et
al. 1982), and guinea pigs and cabbage (Babish et al. 1979); the latter two studies used
extremely high cadmium and sludge application rates.
Trace element levels and disease conditions of cattle grazing on land reclaimed by
Chicago sludge have been observed by Fitzgerald (1978) for four years; it was
concluded that little risk to man or animals is associated with land application of
anaerobically digested wastewater sludge. Experience at Werribee Farm in
Melbourne, Australia, where cattle are grazed on wastewater-irrigated pastures, has
shown higher organ levels of cadmium and chromium than in Farm cattle graced on
non-irrigated pastures, but comparable to non-Farm cattle (Croxford 1978). Organ
levels of lead, however, did not increase, in spite of increases in both soil and pasture
plants.
Since trace elements accumulate in very small quantities in animal muscle tissue,
there is probably little concern about non-visceral meats in the marketplace. Liver
and kidneys of animals do, however, accumulate high levels of cadmium, just as they
do in man, so that these meats may be of concern to those people consuming large
quantities of them.
Cadmium
It seems reasonable to conclude that cadmium is the only trace element likely to be
of health concern to humans as a result of land application of sludge, with the
exposure being through food plants or organ meats. Groundwater is unlikely to
represent an exposure threat. Although the risk from sludge application is real, it
should be kept in mind that, on a regional scale, agricultural land usually receives
more cadmium from wind deposition and phosphate fertilizers than from municipal
sludge (Davis 1984).
The significance of this concern with cadmium getting into the human food chain
depends upon the cadmium levels presently existing in human food, the total dietary
intake of cadmium, and the potential increase in cadmium levels in human food due
to land application. [Drinking water and ambient air contribute relatively little to
total daily cadmium intake (Pahren et al. 1979).]
The cadmium levels presently existing in human food can be estimated, at least for
the United States, by data from the U.S. Food and Drug Administration's
Compliance Program ("market-basket survey"). These levels, together with the
calculated normal dietary intake and vegetarian dietary intake of cadmium, are
summarized in Table 25. It should be noted that root and leafy vegetables have the
highest concentrations of cadmium. More accurate estimates of cadmium (and other
trace element) concentrations in crops grown in the United States, together with
57
-------
Table 25. Cadmium Concentration in Foods and Calculated Dietary
Intake (from Ryan et al. 1982)
Normal Diet" Vegetarian Diet0
Food Classes ppb Cd* g/day jug Cd/day g/day >yg Cd/day
Dairy products 5.7 549 3.1 584 3.3
Meat, fish, poultry 15.3 204 3.1
Grain & cereal 23.2 331 7.7 203 4.7
products
Potatoes 48.0 138 6.6 43 2.1
Leafy vegetables 40.5 42 1.7 252 10.2
Legume vegetables 6.2 51 0.3 166 1.0
Root vegetables 32.3 25 0.8
Garden fruits 14.7 69 1.0
Fruits 3.0 173 0.5 284 0.8
Oily fats, 15.3 56 0.9 107 1.6
shortenings
Sugars & adjuncts 10.0 65 0.7 110 1.1
Beverages 3.0 534 1.6 600 1.8
Total Intake 2,237 28.0 2,349 26.6
"From FDA Compliance Program Evaluation 1974 Total Diet Studies.
"Adjusted on a caloric basis from the FDA 1974 Total Diet Studies to represent
the normal diet which compares with the adult lacto-ovo-vegetarian diet.
cLoma Linda lacto-ovo-vegetarian diet. Based on response of 183 southern
Californians in a food frequency questionnaire by the Department of
Biostatistics and Epidemiology, Loma Lii da University School of Health, 1978.
Leafy vegetables class includes root vegetable and garden fruit classes from
normal diet.
concentrations in the soils in which they are growing, will be available from a survey
jointly supported by the USEPA, USFDA, and USDA. In this survey, 6,000 crop
samples and 18,000 soil samples are being analyzed over a four-year period, and the
results should be available in the near future. Initial results suggest that the USFDA
levels are too high (Wolnik et at. 1983).
The present total dietary intake of cadmium was estimated in Table 25 to be about
28 //g/day. Other estimates based on the market-basket method have resulted in
higher values: 30.9-36.9 j/g/day in 15- to 20-year-old U.S. males, by the USFDA
(1980), and 52 /ug/day in Canadians (Kirkpatrick and Coffin 1977).
A more direct, and potentially more accurate, method of estimating dietary intake
of cadmium is by measuring the cadmium content of human feces. This method is
feasible because the absorption of cadmium from the gut is low (rarely more than
10%, and usually 4-6%) and the excretion of cadmium into the gut is also very low. It
is more accurate because cadmium is generally about ten times more concentrated in
feces than food, and because feces reflect actual food intake rather than predicted. A
recent study, using existing fecal cadmium data collected in Chicago and Dallas, and
estimating daily feces production, resulted in a final estimate of the average daily
intake of cadmium in food for U.S. inhabitants of 13-16>ug/day (Kowal et al. 1979).
(Since the ingestion rate of the teenage male is often used in discussions of cadmium
intake, values of 24/ug/day, 19//g/day, and 18//g/day for 10-to 19-year-old males
from Chicago 1974, Chicago 1976, and Dallas, respectively, were estimated.) A more
recent study in California, using both measured cadmium concentration and
measured feces production, has resulted in a value of 23.7 /ug/day for 40- to 60-year
olds (Willard 1984).
58
-------
These estimates of the average daily intake of cadmium in food can be compared
with other estimates by the fecal analysis method, where the daily feces production of
each individual was measured. In Sweden, rates of 16 /ug/ day in nonsmokers and 19
/ug/ day in smokers (former and present) have been reported (see Kowal et al. 1979 for
references). Nine /ug/day fecal cadmium has been measured in Sweden, compared
with a value of 10 /ug/ day measured by the total diet collection method. In Germany,
31 /ug/day has been measured, compared with 48 /ug/day measured by the market-
basket method. In Japan, where cadmium levels in food are higher because of
industrial pollution, the fecal analysis method has resulted in several estimates
ranging from 24 /ug/day to 84 /ug/day.
The issue of cadmium in tobacco is particularly significant since tobacco is a
cadmium accumulator. For example, it has been recently found that growing
tobacco on soils amended with municipal sludges at very high rates (224 t/ha) can
result in a 30-fold increase in the cadmium content of cigarette smoke (Gutenmann et
al. 1982). Since th<" absorption of cadmium from the lungs is much greater than from
the gut, it is evident that tobacco should not be grown on sludge-amended land.
"It has generally been concluded that ingestion of 200 to 350 mg Cd/day
over a 50-year exposure period is a reasonable estimate for individuals
(excluding smokers and occupationally exposed) within the population to
reach the critical renal concentration (200 mg Cd/g wet weight in the renal
cortex) associated with the initiation of proteinuria. This ingestion limit
assumes background exposure levels of air and no exposure from smoking. If
these exposures are increased, then the suggested ingestion limit must be
correspondingly reduced. Smoking one pack of cigarettes/day will reduce the
limit by about 25 /ug/day. Again these exposures are assumed to occur over a
50-year exposure period and, in the case of cigarettes, since many smokers start
as teenagers, this addition would be relevant for much (30 to 35 years) of the
50-year exposure period. Therefore, smokers must be considered as being at
increased risk." (Ryan et al. 1982).
Thus, present levels of total dietary intake of cadmium for most people appear to
be fairly safe. H owever, in view of human variability in sensitivity and the variability
in food supply, these levels probably should not be allowed to rise greatly.
It is of interest to note that increased consumption by individuals of those leafy and
root vegetable crops highest in cadmium, and of organ meats as well, would increase
the dietary iron intake. Since iron-sufficient humans absorb only about 2.3% of
dietary cadmium, compared to an average absorption of 4.6% in the generally
iron-deficient American population (Flanagan et al. 1978, McLellane/a/. 1978), the
increased iron intake would tend to correct for the increased cadmium intake
(Chancy 1980). The increased zinc and calcium intake would have similar effects.
The potential increase in cadmium levels in human food due to land application of
sludge is still an unsettled question (see Ryan et al. 1982). It is clear, however, that
increased cadmium in the soil results in increased cadmium in the plants grown in
that soil, the degree of increase being a function of cadmium amendment, plant
species and cultivar, soil pH, organic matter, and time since application, but
especially sludge cadmium concentration, with low-cadmium sludges resulting in
minimal cadmium uptakes (Logan and Chaney 1983). A detailed discussion of the
food-chain impact of cadmium in sludge may be found in Hansen and Chaney (1984).
Some are optimistic. Thus, Davis and Coker (1980) made an extensive review of
cadmium in agriculture, particularly the potential transfer of cadmium from
wastewater sludge into the human food chain. It was concluded that when sludge is
applied to farmland in accordance with current practice, the hazard attributable to
possible effects of the cadmium in the sludge on crops, animals, or the human food
chain, is negligible.
59
-------
This view is borne out by the results of the Seven Markets Garden study in England
(Sherlock 1983). The dietary cadmium content of gardeners and their families,
growing cash crops on land which had received massive applications of sewage sludge
during previous decades, was measured. In spite of mean soil cadmium concentra-
tions of 1.5-14.1 ppm, there was little difference in cadmium intake from the national
average. Davis et al. (1983) have performed an analysis of the relationship between
cadmium in sludge-treated soil and potential human dietary intake of cadmium.
They concluded that a soil concentration of 6.0-12.0 ppm in calcareous soils (pH 7-8)
is compatible with the WHO maximum acceptable dietary intake of cadmium of 70
/Kg/day for an average consumer taking all his crops from sludge-treated soil. This
estimate is similar to the current cumulative cadmium limits of 5-20 kg/ ha, since 6-12
ppm is equivalent to 10-22 kg/ha. Wheat and, to a lesser extent, potatoes were found
to have a dominating influence on dietary cadmium; this is similar to the situation
with the American diet (see Table 25). Naylor and M ondy (1984) have recently found
potatoes grown in a well managed, sludge-treated soil at pH 4.9 to not have excessive
cadmium uptake.
In a recent review, Davis (1984) has concluded that a cumulative cadmium limit of
5 kg/ ha, equivalent to about 3.5 mg Cd / kg soil, results in adequate protection to the
food chain where sludge is used on agricultural land. There would be no need for a
limit to protect public health where the land is used to grow animal feed.
The degree of risk to man in general, of course, is dependent upon the amount of
food supply affected and the diet selection of the individual.
-------
SECTION 9
NITRATES
Nitrogenous wastes are important constituents of municipal wastewaters,
consisting of (1) proteins and other nitrogenous organics from feces, food wastes,
etc., (2) urea from urine, and (3) their breakdown products. Raw domestic
wastewater has concentrations of about 8-35 mg/1 organic nitrogen, 12-50 mg/1
ammonium (plus ammonia), and, thus, 20-85 mg/1 total nitrogen, all expressed as N
(Metcalf and Eddy 1972). Nitrites and nitrates are normally present only in trace
amounts in fresh wastewater. Municipal sludges contain <0.1-17.6 percent dry
weight (median of 3.3) of total nitrogen, most of it organic (USEPA 1983).
Bacteria rapidly decompose most forms of organic nitrogen to ammonium (or
ammonia) in wastewater or soil. Under aerobic conditions ammonium is oxidized by
bacteria (Nitrosomonas) to nitrite, and the nitrite rapidly oxidized by bacteria
(Nitrobacter) to nitrate; the two-step process is called "nitrification." Under
anaerobic conditions, and in the presence of organic matter, bacteria can use nitrate
as a source of oxygen, and convert nitrate to molecular nitrogen, which escapes to the
atmosphere; this is called "denitrification." Both aquatic and terrestrial plants can
use ammonium and nitrate as a nitrogen source, and this is usually the primary
immediate economic benefit of sludge application to agricultural land, in addition to
its function as a phosphorus source and soil conditioner.
Inorganic nitrogen is normally quite innocuous from a human health point of
view, although high ammonia levels can present an aesthetic problem. The major
health concern is that infants, less than about three months of age and consuming
large quantities of high-nitrate drinking water through prepared formula, have a high
risk of developing methemoglobinemia. The incompletely developed capacity to
secrete gastric acid in the infant allows the gastric pH to rise sufficiently to encourage
the growth of bacteria which reduce nitrate to nitrite in the upper gastrointestinal
tract. The nitrite is absorbed into the bloodstream, and oxidizes the ferrous iron in
hemoglobin to the ferric state, yielding methemoglobin, a form incapable of carrying
oxygen. Fetal hemoglobin (Hb F), 50-89% of total hemoglobin at birth, is
particularly susceptible to this transformation. Methemoglobin is normally present
in the erythrocytes of adults, at a concentration of about 1% of total hemoglobin,
being formed by numerous agents, but kept to a low level by the methemoglobin
reductase enzyme system. This enzyme system is normally not completely developed
in young infants. At a methemoglobin concentration of about 5-10% of total
hemoglobin the body's oxygen deficit results in clinically-detectable cyanosis. As a
result of epidemiological and clinical studies (Shuval and Gruener 1977, Craun et al.
1981, Fraser and Chilvers 1981) a primary drinking water standard of 10 mg/1 of
nitrate-nitrogen (i.e., nitrate expressed as N) has been established (USEPA 1977) to
prevent this condition from developing.
Besides methemoglobinemia, there is also some concern about nitrates resulting in
the formation of carcinogenic N-nitroso compounds in the gut, but this phenomenon
probably involves higher concentrations than the 10 mg/1 water standard (Fraser et
al. 1980, Fraser and Chilvers 1981).
The relevance of land application, of course, centers on the possibility of highly
soluble nitrates reaching groundwater which may be used as a potable water supply.
In the case of land application of sludge, there would probably be minimal threat if
the sludge were applied at nitrogen rates not exceeding fertilizer nitrogen
recommendations for the crop grown, but higher rates or application outside of
61
-------
seasons of nitrogen uptake might result in a hazard. Data from a liquid sludge
application study (Duncomb et al. 1982) suggest that the ratio of nitrogen application
to crop removal should not exceed approximately 2 to prevent nitrate buildup below
the rooting zone of crops.
It should be kept in mind that land application sites are not the only source of
nitrate in groundwater. Many groundwaters are naturally high in nitrates, e.g., that
in the vicinity of San Angelo, Texas (Hossner et al. 1978), and in urban areas on-site
absorption fields and lawn fertilizers have been shown to be sources of nitrates in
groundwater (Porter 1980).
62
-------
REFERENCES
Akin, E.W., and J.C. Hoff. 1978. Human Viruses in the Aquatic Environment: A
Status Report with Emphasis on the EPA Research Program. Report to Congress.
EPA-570/9-78-006. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Akin, E.W., W.H. Benton, and W.F. Hill. 1971. Enteric viruses in ground and
surface waters: A review of their occurrence and survival. In: "Virus and Water
Quality: Occurrence and Control" (V. Snoeyink and V. Griffin, eds.), 59-74.
University of Illinois, Urbana-Champaign, Illinois.
Akin, E.W., W. Jakubowski, J.B. Lucas, and H.R. Pahren. 1978. Health hazards
associated with wastewater effluents and sludge: Microbiological considerations.
In: "Proceedings of the Conference on Risk Assessment and Health Effects of
Land Application of Municipal Wastewater and Sludges" (B.P. Sagik and C.A.
Sorber, eds.), 9-26. University of Texas at San Antonio, San Antonio, Texas.
Alexander, M. 1981. Biodegradation of chemicals of environmental concern. Science
211:132-138.
Angle, J.S., and D.M. Baudler. 1984. Persistence and degradation of mutagens in
sludge-amended soil. J. Environ. Qual. 13:143-146.
Argent, V.A., J.C. Bell, and M. Emslie-Smith. 1977. Animal disease hazards of
sludge disposal to land: Occurrence of pathogenic organisms. Water Pollut.
Control 76:511-516.
Argent, V.A., J.C. Bell, and D. Edgar. 1981. Animal disease hazards of sewage-
sludge disposal to land: Effects of sludge treatment on Salmonellae. Water Pollut.
Control 80:537-540.
Arther, R.G., P.R. Fitzgerald, and J.C. Fox. 1981. Parasite ova in anaerobically
digested sludge. J. Water Poll. Control Fed. 53:1334-1338.
Arundel, J.H., and A.J. Adolph. 1980. Preliminary observations on the removal of
Taenia saginata eggs from sewage using various treatment processes. Austral. Vet.
J. 56:492-495.
Atlas, R.M. 1980. Microbial aspects of oil spills. ASM News 46:495-499.
Atlas, R.M. 1981. Microbial degradation of petroleum hydrocarbons: An environ-
mental perspective. Microbiol. Rev. 45:180-209.
Aulenbach, D.B., and N.L. Clesceri. 1978. The Lake George Village (N.Y.) land
application system. In: "State of Knowledge in Land Treatment of Wastewater"
(H.L. McKim, ed.), Vol. 2, 27-35. U.S. Army Corps of Engineers, CRREL,
Hanover, New Hampshire.
Ayanwale, L.F., and J.M.B. Kaneene. 1982. Further investigation of salmonella
infection in goats fed corn silage grown on land fertilized with sewage sludge. J.
Anim. Prod. Res. 2:63-67.
Ayanwale, L.F., J.M.B. Kaneene, D.M. Sherman, and R.A. Robinson. 1980.
Investigation of Salmonella infection in goats fed corn silage grown on land
fertilized with sewage sludge. Appl. Environ. Microbiol. 40:285-286.
Babayeva, R.I. 1966. Survival of beef tapeworm oncospheres on the surface of the
soil in Samarkand. Med. Parazitiol. Parazit. Bolezn. 35:557-560.
Babish, J.G., B. Johnson, B.O. Brooks, and D.J. Lisk. 1982. Acute toxicity of
organic extracts of municipal sewage sludge in mice. Bull. Environ. Contam.
Toxicol. 29:379-384.
Babish, J.G., B.E. Johnson, and D.J. Lisk. 1983. Mutagenicity of municipal sewage
sludges of American cities. Environ. Sci. Technol. 17:272-277
Babish, J.G., G.S. Stoewsand, A.K. Furr, T.F. Parkinson, C.A. Bache, W.H.
Gutenmann, P.C. Wszolek, and D.J. Lisk. 1979. Elemental and polychlorinated
63
-------
biphenyl content of tissues and intestinal aryl hydrocarbon hydroxylase activity of
guinea pigs fed cabbage grown on municipal sewage sludge. J. Agric. Food Chem.
27:399-402.
Bagdasaryan, G.A. 1964. Survival of viruses of the enterovirus group (poliomyelitis,
ECHO, coxsackie) in soil and on vegetables. J. Hyg. Epidemiol. Microbiol.
Immunol. 8:497-505.
Baker, E.L., P.J. Landrigan, C.J. Glueck, M.M. Zack, J. A. Liddle, V.W. Burse, W.J.
Housworth, and L.L. Needham. 1980. Metabolic consequences of exposure to
polychlorinated biphenyls (PCB) in sewage sludge. Amer. J. Epidemiol. 112:553-
563.
Baxter, J.C., D.E. Johnson, and E.W. Kienholz. 1983. Heavy metals and persistent
organics content in cattle exposed to sewage sludge. J. Environ. Qual. 12:316-319.
Beaver, P.C., and G. Deschamps. 1949. The viability of E. histolytica cysts in soil.
Amer. J. Trop. Med. 29:189-191. (Cited in Feachem et al. 1978).
Beaver, P.C., R.C. Jung, H.J. Sherman, R.T. Read, and T.A. Robinson. 1956.
Experimental Entamoeba histolytica infections in man. Amer. J. Trop. Med. &
Hyg. 5:1000-1009.
Bellanti, J.A. 1978. Immunology II. W.B. Saunders Co., Philadelphia, Pennsylvania.
Benarde, M.A. 1973. Land disposal and sewage effluent: Appraisal of health effects
of pathogenic organisms. J. Amer. Water Works Assoc. 65:432-440.
Benenson, A.S., ed. 1975. Control of Communicable Diseases in Man. American
Public Health Association, Washington, D.C.
Berg, G., D.R. Dahling, G.A. Brown, and D. Berman. 1978. Validity of fecal
coliforms. total coliforms, and fecal streptococci as indicators of viruses in
chlorinated primary sewage effluents. Appl. Environ. Microbiol. 36:880-884.
Bernard, A., and R. Lauwerys. 1984. Cadmium in human population. Experientia
40:143-152.
Berthet, B., C. Amiard-Triquet, C. Metayer, and J.C. Amiard. 1984. Etude des voies
de transfer! du plomb de 1'environnement aux vegetaux cultives: Application a
1'utilisation agricole de boues de station d'epuration. Water Air Soil Poll.
21:447-460.
Bertrand, J.E., M.C. Lutrick, G.T. Edds, and R.L. West. 1981a. Metal residues in
tissue, animal performance and carcass quality with beef steers grazing Pensacola
Bahiagrass pastures treated with liquid digested sludge. J. Animal Sci. 53:146-153.
Bertrand, J.E., M.C. Lutrick, G.T. Edds, and R.L. West. 1981b. Animal
performance, carcass quality, and tissue residues with beef steers fed forage
sorghum silages grown on soil treated with liquid digested sludge. Proc. Soil Crop
Sci. Soc. Florida 40:111-114.
Biederbeck, V.O. 1979. Reduction of fecal indicator bacteria in sewage effluent when
pumping for crop irrigation. J. Environ. Sci. Health 814:475-493.
Bitton, G. 1980. Introduction to Environmental Virology. John Wiley & Sons, New
York.
Bitton, G., O.C. Pancorbo, and S. R. Farrah. 1984. Viral transport and survival after
land application of sewage sludge. Appl. Environ. Microbiol. 47:905-909.
Bixby, R.L., and D.J. O'Brien. 1979. Influence of fulvic acid on bacteriophage
adsorption and complexation in soil. Appl. Environ. Microbiol. 38:840-845.
Blake, P. A., D.T. Allegra, J.D. Synder, T.J. Barrett, L. McFarland, C.T. Caraway,
J.C. Feeley, J.P. Craig, J.V. Lee, N.D. Puhr, and R.A. Feldman. 1980. Cholera
—A possible endemic focus in the United States. New Eng. J. Med. 302:305-309.
Blaser, M.J., and L.S. Newman. 1982. A review of human salmonellosis: I. Infective
dose. Rev. Inf. Dis. 4:1096-1106.
Borneff, J., F. Selenka, H. Kunte, and A. Maximos. 1968. Experimental studies on
the formation of polycyclic aromatic hydrocarbons in plants. Environ. Res.
2:22-29.
64
-------
Bouwer, H., and R.C. Rice. 1978. The Flushing Meadows project. In: "State of
Knowledge in Land Treatment of Wastewater" (H.L. McKim, ed.), Vol. 1, 213-
220. U.S. Army Corps of Engineers, CRREL, Hanover, New Hampshire.
Boyd, J.N., G.S. Stoewsand, J.G. Babish, J.N. Telford, and D.J. Lisk. 1982. Safety
evaluation of vegetables cultured on municipal sewage sludge-amended soil. Arch.
Environ. Contam. Toxicol. 11:399-405.
Brain, J.D., and P. A. Valberg. 1979. Deposition of aerosol in the respiratory tract.
Amer. Rev. Resp. Dis. 120:1325-1373.
Braude, G.L., R.B. Read, and C.F. Jelinek. 1978. Use of wastewater on land—Food
chain concerns. In: "State of Knowledge in Land Treatment" (M.L. McKim, ed.),
Vol. 1,59-65. U.S. Army Corps of Engineers, CRREL, Hanover, New Hampshire.
Bray, B.J., R.H. Dowdy, R.D. Goodrich, and D.E. Pamp. 1985. Trace metal
accumulations in tissues of goats fed silage produced on sewage sludge-amended
soil. J. Environ. Qual. 14:114-118.
Brenniman, G.R., W.H. Kojola, P.S. Levy, B.W. Carnow, T. Namakata, and E.G.
Breck. 1979. Health Effects of Human Exposure to Barium in Drinking Water.
EPA-600/1-79-003. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Brown, H.W. 1969. Basic Clinical Parasitology. Appleton-Century-Crofts New
York.
Brown, R.E. 1985. A Demonstration of Acceptable Systems of Land Disposal of
Sewage Sludge. EPA/600/2-85/062. U.S. Environmental Protection Agency,
Cincinnati, Ohio.
Bryan, F.L. 1977. Diseases transmitted by foods contaminated by wastewater. J.
Food Protection 40:45-56.
Burge, W.D., and P.B. Marsh. 1978. Infectious disease hazards of landspreading
sewage wastes. J. Environ. Qual. 7:1-9.
Burns and Roe Industrial Services Corporation. 1982. Fate of Priority Pollutants in
Publicly Owned Treatment Works. EPA-440/1-82-303. U.S. Environmental
Protection Agency, Washington, D.C.
Butler, T., A.A.F. Mahmoud, and K.S. Warren. 1977. Algorithms in the diagnosis
and management of exotic diseases. XXVII. Shigellosis. J. Infect. Dis. 136:465-468.
Carnow, B., R. Northrop, R. Wadden, S. Rosenberg, J. Holden, A. Neal, L. Sheaff,
P. Scheff, and S. Meyer. 1979. Health Effects of Aerosols Emitted from an
Activated Sludge Plant. EPA-600/1-79-019. U.S. Environmental Protection
Agency, Cincinnati, Ohio.
Carrington, E.G. 1978. The Contribution of Sewage Sludges to the Dissemination of
Pathogenic Micro-Organisms in the Environment. Tech. Rept. 71, Medmenham
Lab., Marlow, Bucks, England.
CDC. 1982. Salmonella Surveillance Annual Summary, 1980. Centers for Disease
Control, Atlanta, Georgia.
Chaney, R.L. 1980. Health risks associated with toxic metals in municipal sludge. In:
"Sludge—Health Risks of Land Application" (G. Bitton, B.L. Damron, G.T.
Edds, and J.M. Davidson, eds.), 59-83. Ann Arbor Science Publ., Ann Arbor,
Michigan.
Chaney, R.L. 1984. Potential effects of sludge-borne heavy metals and toxic organics
on soils, plants, and animals, and related regulatory guidelines. In: "Proc. Pan
American Health Organization Workshop on the International Transportation,
Utilization, or Disposal of Sewage Sludge," in press.
Chang, A.C., and A.L. Page. 1978. Toxic chemicals associated with land treatment
of wastewater. In: "State of Knowledge in Land Treatment of Wastewater" (H.L.
McKim, ed.), Vol. 1, 47-57. U.S. Army Corps of Engineers, CRREL, Hanover,
New Hampshire.
Chang, A.C., A.L. Page, J.E. Warneke, and E. Grgurevic. 1984a. Sequential
extraction of soil heavy metals following a sludge application. J. Environ. Qual.
13:33-38.
65
-------
Chang, A.C., J.E. Warneke, A.L. Page, and L.J. Lund. 1984b. Accumulation of
heavy metals in sewage sludge-treated soils. J. Environ. Qual. 13:87-91.
Chang, S.L.,and P.W. Kabler. 1956. Detection of cysts of Endamoebahistolytica in
tap water by the use of the membrane filter. Amer. J. Hyg. 64:J70-180.
Chou, S.F., L.W. Jacobs, D. Penner, and J.M. Tiedje. 1978. Absenceof plant uptake
and translocation of polybrominated biphenyls (PBBs). Environ. Health Perspect.
23:9-12.
Christovao, D.d.A., S.T. laria, and J.A.N. Candeias. 1967a. Sanitary conditions of
irrigation water from vegetable gardens of the city of Sao Paulo. I. Determination
of the degree of faecal pollution through the M.P.N. of coliforms and of E. coli.
Revta Saude Publ. 1:3-11. (Cited in Geldreich and Bordner 1971).
Christovao, D.d.A., J.A.N. Candeias, and S.T. laria. 1967b. Sanitary conditions of
the irrigation water from vegetable gardens of the city of Sao Paulo. II. Isolation of
enteroviruses. Revta Saude Publ. 1:12-17. (Cited in Geldreich and Bordner 1971).
Connor, M.S. 1984. Monitoring sludge-amended agricultural soils. Bio Cycle
25(1):47-51.
Council for Agricultural Science and Technology. 1976. Application of Sewage
Sludge to Cropland: Appraisal of Potential Hazards of the Heavy Metals to Plants
and Animals. EPA-430/9-76-013. U.S. Environmental Protection Agency,
Washington, D.C.
Craun, G.F. 1979. Waterborne disease —A status report emphasizing outbreaks in
ground-water systems. Ground Water 17:183.
Craun, G.F., D.G. Greathouse, and D.H. Gunderson. 1981. Methaemoglobin levels
in young children consuming high nitrate well water in the United States. Int. J.
Epidem. 10:309-317.
Croxford, A.H. 1978. Melbourne, Australia, Wastewater System —Case Study.
Amer. Soc. Agric. Eng., 1978 Winter Meeting, Chicago, Illinois. Paper No.
78-2576.
Damgaard-Larsen, S., K.O. Jensen, E. Lund, and B. Nissen. 1977. Survival and
movement of enterovirus in connection with land disposal of sludges. Water
Research 11:503-508.
Davis, B.D., R. Dulbecco, H.N. Eisen, and H.S. Ginsberg. 1980. Microbiology.
Harper and Row, Hagerstown, Maryland.
Davis, R.D. 1984. Cadmium in sludges used as fertilizer. Experientia 40: 117-126.
Davis, R.D.,andE.G. Coker. 1980. Cadmium in Agriculture with Special Reference
to the Utilization of Sewage Sludge on Land. TR139, Water Research Centre,
Stevenage Laboratory, Herts, Great Britain.
Davis, R.D., J.M. Stark, and C.H. Carlton-Smith. 1983. Cadmium in sludge-treated
soil in relation to potential human dietary intake of cadmium. In: "Environmental
Effects of Organic and Inorganic Contaminants in Sewage Sludge" (R.D. Davis,
G. Hucker, and P. L'Hermite, eds.), 137-146. D. Reidel Publ. Co., Dordrecht,
Holland.
Davis, T.S., J.L. Pyle, J.H. Skillings, and N.D. Danielson. 1981. Uptake of
polychlorobiphenyls present in trace amounts from dried municipal sewage sludge
through an old field ecosystem. Bull. Environ. Contam. Toxicol. 27:689-694.
de Haan, F.A.M. 1977. The effects of long term accumulation of heavy metals and
selected compounds in municipal wastewater on soil. In: "Wastewater Renovation
and Reuse" (P.M. D'ltri, ed.), 283-319. Marcel Dekker, New York.
Demirjian, A., R.R. Rediske, and T.R. Westman. 1981. The Fate of Organic
Pollutants in a Wastewater Land Treatment System Using Lagoon Impoundment
and Spray Irrigation. Progress Report to U.S. Environmental Protection Agency
for Grant No. CR-806873. Muskegon County Wastewater Management System
and Department of Public Works, Muskegon, Michigan.
DeWalle, F.B., E.S.K. Chian, et al. 1981. Presence of Priority Pollutants in Sewage
and Their Removal In Sewage Treatment Plants. Draft Report Submitted to U.S.
66
-------
Environmental Protection Agency for Grant No. R-806102. U.S. Environmental
Protection Agency, Cincinnati, Ohio.
Dodolina, V.T., L.Y. Kutepov, and B.F. Zhirnov. 1976. Permissible quantities of
organic substances in waste waters used for irrigation. Vestn. S-kh. Nauki
(Moscow) 6:110-113.
Dowdy, R.H., and V.V. Volk. 1983. Movement of heavy metals in soils. In:
"Chemical Mobility and Reactivity in Soil Systems" (D.W. Nelson et al., ed.), Soil
Sci. Soc. Amer., Madison, Wisconsin.
Dressel, J. 1976. Relationship between nitrate, nitrite, and nitrosamines in plants and
soil as intensive nitrogen fertilization. Qual. Plant. Plant Foods Hum. Nutr.
25:381-390.
Duboise, S.M., B.E. Moore, and B.P. Sagik. 1976. Poliovirus survival and
movement in a sandy forest soil. Appl. Environ. Microbiol. 31:536-543.
Duboise, S.M., B.E. Moore, C.A. Sorber, and B.P. Sagik. 1979. Viruses in soil
systems. CRC Crit. Rev. Microbiol. 7:245-285.
Duncomb, D.R., W.E. Larson, C.E. Clapp, R.H. Dowdy, D.R. Linden, and W.K.
Johnson. 1982. Effect of liquid wastewater sludge application on crop yield and
water quality. J. Water Poll. Control Fed. 54:1185-1193.
Elliott, L.F., and J.R. Ellis. 1977. Bacterial and viral pathogens associated with land
application of organic wastes. J. Environ. Qual. 6:245-251.
Evans, A.S. 1976. Epidemiological concepts and methods. In: "Viral Infections of
Humans: Epidemiology and Control" (A.S. Evans, ed.), 1-32, Plenum Publ.
Corp., New York.
Fairbanks, B.C., and G.A. O'Connor. 1984. Effect of sewage sludge on the
adsorption of polychlorinated biphenyls by three New Mexico soils. J. Environ.
Qual. 13:297-300.
Fannin, K.F., S.C. Vana, and J.D. Fenters. 1977. Evaluation of Indigenous Plaque
Forming Units at Four Stages of Secondary Wastewater Treatment Using
Primary Monkey Kidney and Buffalo Green Monkey Kidney Cells. ITT Research
Institute Report No. IITRI-48019. (Cited in Akin and Hoff 1978).
Farrah, S.R., G. Bitton, E.M. Hoffmann, O. Lanni, O.C. Pancorbo, M.C. Lutrick,
and J.E. Bertrand. 1981. Survival of enteroviruses and coliform bacteria in a
sludge lagoon. Appl. Environ. Microbiol. 41:459-465.
Feachem, R.G., D.J. Bradley, H. Garelick, and D.D. Mara. 1978. Health Aspects of
Excreta and Sullage Management. The World Bank, Washington, D.C. [cf.: R.G.
Feachem, D.J. Bradley, H. Garelick, and D.D. Mara. 1983. Sanitation and
Disease: Health Aspects of Excreta and Wastewater Management. World Bank
Studies in Water Supply and Sanitation, No. 3. John Wiley & Sons, New York.]
Fiennes, R.N.T.—W.—1978. Zoonoses and the Origins and Ecology of Human
Disease. Academic Press, New York.
Fishbein, L. 1977. Toxicology of selenium and tellurium. In: "Toxicology of Trace
Metals"(R. A. Goyer and M.A. Mehlman, eds.), 191-240. John Wiley & Sons, New
York.
Fitzgerald, P.R. 1978. Toxicology of heavy metals in sludges applied to the land.
Proc. 5th Natl. Conf. on Accept. Sludge Disp. Techn., 106. Information Transfer,
Inc., Rockville, Maryland.
Fitzgerald, P.R. 1979. Potential impact on the public health due to parasites in
soil/sludge systems. Proc. 8th Natl. Conf. Municipal Sludge Management, 214.
Information Transfer, Inc., Silver Springs, Maryland.
Flanagan, P.R., J.S. McLellan, J. Haist, M.G. Cherian, M.J. Chamberlain, and L.S.
Valberg. 1978. Increased dietary cadmium absorption in mice and human subjects
with iron deficiency. Gastroenterology 74:841-846.
Foster, D.H., and R.S. Engelbrecht. 1973. Microbial hazards in disposing of
wastewater on soil. In: "Recycling Treated Municipal Wastewater and Sludge
through Forest and Cropland" (W.E. Sopper and L.T. Kardos, ed.), 247-270.
Pennsylvania State University Press, University Park, Pennsylvania.
67
-------
Fraser, P., and C. Chilvers. 1981. Health aspects of nitrate in drinking water. Sci.
Total Environ. 18:103-116.
Fraser, P., C. Chilvers, V. Beral, and M.J. Hill. 1980. Nitrate and human cancer: A
review of the evidence. Int. J. Epidem. 9:3-11.
Fricke, C., C. Clarkson, E. Lomnitz, and T. O'Farrell. 1985. Comparing priority
pollutants in municipal sludges. Bio. Cycle 26:35-37.
Fries, G.F. 1980. An assessment of potential residues in animal products from
application of sewage sludge containing polychlorinated biphenyls to agricultural
land. In: "Sludge—Health Risks of Land Application" (G. Bitton, B.L. Damron,
G.T. Edds, and J.M. Davidson, eds.), 348-349. Ann Arbor Science Publishers,
Inc., Ann Arbor, Michigan.
Fries, G.F. 1982. Potential polychlorinated biphenyl residues in animal products
from application of contaminated sewage sludge to land. J. Environ. Qual.
11:14-20.
Fries, G. F., and G.S. Marrow. 1981. Chlorobiphenyl movement from soil to soybean
plants. J. Agr. Food Chem. 29:757-759.
Fuchsbichler, G., A. Suss P. Wallnofer. 1978. Uptake of 4-chloro-and 3,4-
dichloroaniline by cultivated plants. Zeitschrift fiir Pflanzenkrankheiten und
Pflanzenschutz 85:298-307.
Gardner, I.D. 1980. The effect of aging on susceptibility to infection. Rev. Inf. Dis.
2:801-810.
Geldreich, E.E., and R.H. Bordner. 1971. Fecal contamination of fruits and
vegetables during cultivation and processing for market: A review. J. Milk Food
Tech. 34:184-195.
Gelfand, H.M., D.R. LeBlanc, A.H. Holguin, and J.P. Fox. 1960. Preliminary
report on susceptibility of newborn infants to infection with poliovirus strains of
attenuated virus vaccine. In: "Second International Conference on Live Poliovirus
Vaccines," 308-314. Scientific Publication No. 50, Pan American Health
Organization, Washington, D.C. (Cited in NRC 1977).
Gerba, C.P. 1983. Pathogens. In: "Utilization of Municipal Wastewater and Sludge
on Land"(A.L. Page, T.L. Gleason, J.E. Smith, I.K. Iskandar, and L.E. Sommers,
eds.), 147-! 87. University of California, Riverside, California.
Gerba, C.P. 1984. Applied and theoretical aspects of virus adsorption to surfaces.
Adv. Appl. Microbiol. 30:133-166.
Gerba, C.P., and J.C. Lance. 1980. Pathogen removal from wastewater during
groundwater recharge. In: "Wastewater Reuse for Groundwater Recharge" (T.
Asano and P.V. Roberts, eds.), 137-144. Office of Water Recycling, California
State Water Resources Control Board.
Gerba, C.P., and J.F. McNabb. 1981. Microbial aspects of groundwater pollution.
ASM News 47:326-329.
Gerba, C.P., C. Wallis, and J.L. Melnick. 1975. Fate of wastewater bacteria and
viruses in soil. J. Irrig. Drain. Div., ASCE 101:157-174.
Gerba, C.P., S.M. Goyal, C.J. Hurst, and R.L. LaBelle. 1980. Type and strain
dependence of enterovirus adsorption to activated sludge, soils and estuarine
sediments. Water Res. 14:1197-1198.
Goyal, S.M., and C.P. Gerba. 1979. Comparative adsorption of human entero-
viruses, simian rotavirus, and selected bacteriophages to soils. Appl. Environ.
Microbiol. 38:241-247.
Goyal, S.M., C.P. Gerba, and J.L. Melnick. 1979. Human enteroviruses in oysters
and their overlying waters. Appl. Environ. Microbiol. 37:572-581.
Greene, S., M. Alexander, and D. Leggett. 1981. Formation of N-nitrosodi-
methylamine during treatment of municipal waste water by simulated land
application. J. Environ. Qual. 10:416-421.
Griffin, R. A, and E.S.K. Chian. 1980. Attenuation of Water-Soluble Polychlorinated
Biphenyls by Earth Materials. EPA-600/2-80-027. U.S. Environmental Protection
Agency, Cincinnati, Ohio.
68
-------
Grigor'Eva, L.V., T.G. Gorodetskii, T.G. Omel'Yanets, and L.A. Bogdanenko. 1965.
Hyg. San. 30:357. (Cited in Larkin et al. 1978b).
Gunby, P. 1979. Rising number of man's best friends ups human toxocariasis
incidence. J. Amer. Med. Assoc. 242:1343-1344.
Gutenmann, W.H., C.A. Bache, D.J. Lisk, D. Hoffmann, J.D. Adams, and D.C.
Elfving. 1982. Cadmium and nickel in smoke of cigarettes prepared from tobacco
cultured on municipal sludge-amended soil. J. Toxicol. Environ. Health
10:423-431.
Hallenbeck, W.H. 1984. Human health effects of exposure to cadmium. Experientia
40:136-142.
Hansen, L.G., and R.L. Chaney. 1984. Environmental and food chain effects of the
agricultural use of sewage sludges. In: "Reviews in Environmental Toxicology I"
(E. Hodgson, ed.), 103-172. Elsevier Sci. Publ., New York.
Hansen, L.G., J.L. Corner, C.S. Byerly, R.P. Tarara, and T.D. Hinesly. 1976.
Effects of sewage sludge-fertilized corn fed to growing swine. Amer. J. Vet. Res.
37:711-714.
Hansen, L.G., and T.D. Hinesly. 1979. Cadmium from soil amended with sewage
sludge: Effects and residues in swine. Environ. Health Perspect. 28: 51-57.
Harding, H.J., R.E. Thomas, D.E. Johnson, and C.A. Sorber. 1981. Aerosols
Generated by Liquid Sludge Application to Land. EPA-600/1-81-028. U.S.
Environmental Protection Agency, Cincinnati, Ohio.
Haschek, W.M., A.K. Furr, T.F. Parkinson, C.L. Heffron, J.T. Reid, C.A. Bache,
P.C. Wszolek, W.H. Gutenmann, and D.J. Lisk. 1979. Element and poly-
chlorinated biphenyl deposition and effects in sheep fed cabbage grown on
municipal sewage sludge. Cornell Vet. 69:302-314.
Hathaway, S.W. 1980. Sources of Toxic Compounds in Household Wastewater.
EPA-600/2-80-128. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Hellman, A., A.G. Wedum, and W.E. Barkley. 1976. Assessment of risk in the cancer
virus laboratory. Unpublished report. National Cancer Institute.
Hinesly, T.D., L.G. Hansen, and G.K. Dotson. 1984. Effects of Using Sewage Sludge
on Agricultural and Disturbed Lands. EPA-600/2-83-113. U.S. Environmental
Protection Agency, Cincinnati, Ohio.
Hoadley, A.W., and S.M. Goyal. 1976. Public health implications of the application
of wastewaters to land. In: "Land Treatment and Disposal of Municipal and
Industrial Wastewater" (R.L. Sanks and T. Asano, eds.), 101-132. Ann Arbor
Science, Ann Arbor, Michigan.
Hogue, D.E., J.J. Parrish, R.H. Foote, J.R. Stouffer, J.L. Anderson, G.S.
Stoewsand, J.N. Telford, C.A. Bache, W.H. Gutenmann, and D.J. Lisk. 1984.
Toxicological studies with male sheep grazing on municipal sludge-amended soil.
J. Toxicol. Environ. Health 14:153-161.
Holguin, A.H., J.S. Reeves, and H.M. Gelfand. 1962. Immunization of infants with
the Sabin and poliovirus vaccine. Amer. J. Pub. Health 52:600-610.
Holmes, I.H. 1979. Viral gastroenteritis. Progr. Med. Virol. 25:1-36.
Holt, J.G., ed. 1977. The Shorter Sergey's Manual of Determinative Bacteriology.
Williams & Wilkins, Baltimore, Maryland.
Hopke, P.K., M.J. Plewa, J.B. Johnston, D. Weaver, S.G. Wood, R. A. Larson, and
T. Hinesly. 1982. Multitechnique screening of Chicago municipal sewage sludge
for mutagenic activity. Environ. Sci. Tech. 16:140-147.
Hopke, P.K., M.J. Plewa, P.L. Stapleton, and D.L. Weaver. 1984. Comparison of
the mutagenicity of sewage sludges. Environ. Sci. Tech. 18:909-916.
Hornick, R.B., S.E. Greisman, T.E. Woodward, H.L. DuPont, A.T. Dawkins, and
M.J. Snyder. 1970. Typhoid fever: Pathogenesis and immunologic control. New
Eng. J. Med. 283:686-691.
Hossner, L.R., et al. 1978. Sewage Disposal on Agricultural Soils: Chemical and
Microbiological Implications. Volume I. Chemical Implications. EPA-600/2-78-
131 a. U.S. Environmental Protection Agency, Ada, Oklahoma.
69
-------
Hurst, C.J., C.B. Gerba, and I. Cech. 1980. Effects of environmental variables and
soil characteristics on virus survival in soil. Appl. Environ. Microbiol. 40:1067-
1079.
Il'nitskii, A.P., L.G. Solenova, and V.V. Ignatova. 1974. Sanitary and oncological
assessment of agricultural use of sewage containing carcinogenic hydrocarbons.
Kazanskii Med. Zh. 2:80-81. ORNL-tr-2959.
Iwata, Y., F. A. Gunther, and W.E. Westlake. 1974. Uptake of a PCB (Aroclor 1254)
from soil by carrots under field conditions. Bull. Environ. Contam. Toxicol.
11:523-528.
Jacobs, L.W., S.F. Chou, and J.M. Tiedje. 1978. Field concentrations and
persistence of polybrominated biphenyls in soils and solubility of PBB in natural
waters. Environ. Health Perspect. 23:1-8.
Jakubowski, W., andT.H. Ericksen. 1979. M ethods for detection of Giardia cysts in
water supplies. In: "Waterborne Transmission of Giardiasis" (W. Jakubowski and
J.C. Hoff, eds.), 193-210. EPA-600/9-79-001. U.S. Environmental Protection
Agency, Cincinnati, Ohio.
Jawetz, E., J.L. Melnick, andE.A. Adelberg. 1978. Review of Medical Microbiology.
Lange Medical Publ., Los Altos, California.
Jenkins, T.F., D.C. Leggett, L.V. Parker, J.L. Oliphant, C.J. Martel, B.T. Foley, and
C.J. Diener. 1983. Assessment of the Treatability of Toxic Organics by Overland
Flow. Report 83-3. U.S. Army Corps of Engineers, CRREL, Hanover, New
Hampshire.
Jewell, W.J., and B.L. Seabrook. 1979. A History of Land Application as a
Treatment Alternative. EPA-430/9-79-012. U.S. Environmental Protection
Agency, Washington, D.C.
Johnston, J.B., R. A. Larson, J. A. Grunau, D. Ellis, and C. Jone. 1982. Identification
of Organic Pollutants and Mutagens in Industrial and Municipal Effluents. Final
Report Submitted to the Illinois Environmental Protection Agency. Project FW-
38. The Institute for Environmental Studies, University of Illinois at Urbana-
Champaign, Urbana, Illinois.
Jones, P.W., L.M. Rennison, V.H. Lewin, and D.L. Redhead. 1980. The occurrence
and significance to animal health of salmonellas in sewage and sewage sludges. J.
Hyg. 84:47-62.
Jones, P.W., L.M. Rennison, P.R.J. Matthews, P. Collins, and A. Brown. 1981. The
occurrence and significance to animal health of Leptospira, Mycobacterium.
Escherichia coli, Bruce/la abortus and Bacillus anthracis in sewage and sewage
sludges. J. Hyg. 86:129-137.
Kapikian, A.Z., R.H. Yolken, H.B. Greenberg, R.G. Wyatt, A.R. Kalica, R.M.
Chanock, and H.W. Kim. 1979. Gastroenteritis viruses. In: "Diagnostic Proce-
dures for Viral, Rickettsial and Chlamydial Infections" (E.H. Lennette and N.J.
Schmidt, eds.), 927-995. American Public Health Association, Washington, D.C.
Katz, M.,andS.A. Plotkin. 1967. Minimal infective dose of attenuated poliovirus for
man. Amer. J. Pub. Health 57:1837-1840.
Kenaga, E.E. 1981. Comparative toxicity of 131,596 chemicals to plant seeds.
Ecotoxicol. Environ. Safety 5:469-475.
Keswick, B.H., and C.P. Gerba. 1980. Viruses in groundwater. Environ. Sci. Tech.
14:1290-1297.
Keusch, G.T. 1979. Shigella infections. Clinics in Gastroenterology 8:645-662.
Kienholz, E.W. 1980. Effects of toxic chemicals present in sewage sludge on animal
health. In: "Sludge —Health Risks of Land Application" (G. Bitton, B.L.
Damron, G.T. Edds, and J.M. Davidson, eds.), 153-171. Ann Arbor Science
Publishers, Inc., Ann Arbor, Michigan.
Kirkpatrick, D.C., and D.E. Coffin. 1977. Trace metal content of a representative
Canadian diet in 1972. Can. J. Pub. Health 68:162-164.
Kobayashi, H., and B.E. Rittmann. 1982. Microbial removal of hazardous organic
compounds. Environ. Sci. Tech. 16:170A-184A.
70
-------
Kominsky, J.R., C.L. Wisseman, and D.L. Morse. 1980. Hexachlorocylopentadiene
contamination of a municipal wastewater treatment plant. Amer. Ind. Hyg. Assoc.
J. 41:552-556.
Konno, T., H. Suzuki, A. Imai, T. Kutsuzawa, N. Ishida, N. Katsushima, M.
Sakamoto, S. Kitaoka, R. Tsuboi, and, M. Adachi. 1978. A long-term survey of
rotavirus infection in Japanese children with acute gastroenteritis. J. Infect. Dis.
138:569-576.
Koprowski, H. 1956. Immunization against poliomyelitis with living attenuated
virus. Amer. J. Trop. Med. Hyg. 5:440-452.
Kott, H., and L. Fishelson. 1974. Survival of enteroviruses on vegetables irrigated
with chlorinated oxidation pond effluents. Israel J. Tech. 12:290-297. (Cited in
Feachem el al. 1978).
Kott, H., and Y. Kott. 1967. Detection and viability of Endamoeba histolytica cysts
in sewage effluents. Water and Sewage Works 114:177-180.
Kowal, N.E., D.E. Johnson, D.F. Kraemer, and H.R. Pahren. 1979. Normal levels of
cadmium in diet, urine, blood, and tissues of inhabitants of the United States. J.
Toxicol. Environ. Health 5:995-1014.
Kowal, N.E. 1982. Health Effects of Land Treatment: Microbiological. EPA-600/1-
82-007. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Kowal, N.E. 1985. Health Effects of Land Treatment: Toxicological. EPA-600/1-84-
030. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Krick, J.A., and J.S. Remington. 1978. Current concepts in parasitology:
Toxoplasmosis in the adult—An overview. New Eng. J. Med. 298:550-553.
Kristensen, K.K., and G.J. Bonde. 1977. The current status of bacterial and other
pathogenic organisms in municipal wastewater and their potential health hazards
with regard to agricultural irrigation. In: "Wastewater Renovation and Reuse"
(P.M. D'ltri, ed.), 387-419. Marcel Dekker, New York.
Krogstad, D.J., H.C. Spencer, and G.R. Healy. 1978. Current concepts in
parasitology: Amebiasis. New Eng. J. Med. 298:262-265.
Krugman, S., J. Warren, M.S. Eiger, P.H. Herman, R.M. Michaels, and A.B. Sabin.
1961. Immunization with live attenuated poliovirus vaccine. Amer. J. Dis. Child.
101:23-29.
Kuhnlein, U., D. Bergstrom, and H. Kuhnlein. 1981. Mutagens in feces from
vegetarians and non-vegetarians. Mut. Res. 85:1-12.
Lamka, K.G., M.W. LeChevallier, and R.J. Seidler. 1980. Bacterial contamination
of drinking water supplies in a modern rural neighborhood. Appl. Environ.
Microbiol. 39:734-738.
Lance, J.C., and C.P. Gerba. 1978. Pretreatment requirements before land
application of municipal wastewater. In: "State of Knowledge in Land Treatment
of Wastewater" (H.L. McKim, ed.), Vol. 1, 293-304. U.S. Army Corps of
Engineers, CRREL, Hanover, New Hampshire.
Lance, J.C., C.P. Gerba, and J.L. Melnick. 1976. Virus movement in soil columns
flooded with secondary sewage effluent. Appl. Environ. Microbiol. 32:520-526.
Landry, E.F., J.M. Vaughn, M.Z. Thomas, andC.A. Beckwith. 1979. Adsorption of
enteroviruses to soil cores and their subsequent elution by artificial rainwater.
Appl. Environ. Microbiol. 38:680-687.
Landry, E.F., J.M. Vaughn, and W.F. Penello. 1980. Poliovirus retention in 75-cm
soil cores after sewage and rainwater application. Appl. Environ. Microbiol.
40:1032-1038.
Larkin, E.P. 1982. Viruses in wastewater sludges and in effluents used for irrigation.
Environ. International 7:29-33.
Larkin, E.P., J.T. Tierney, and R. Sullivan. 1976. Persistence of poliovirus 1 in soil
and on vegetables irrigated with sewage wastes: Potential problems. In: "Virus
Aspects of Applying Municipal Waste to Land" (L.B. Baldwin, J.M. Davidson,
and J.F. Gerber, eds.), 119-130. University of Florida, Gainesville, Florida.
71
-------
Larkin, E.P., J.T. Tierney, J. Lovett. D. Van Donsel, and D.W. Francis. 1978a. Land
application of sewage wastes: Potential for contamination of foodstuffs and
agricultural soils by viruses and bacterial pathogens. In: "Risk Assessment and
Health Effects of Land Application of Municipal Wastewaters
and Sludges" (B.P. Sagik and C.A. Snrber, eds.), 102-115. University of Texas at
San Antonio, San Antonio, Texas.
Larkin, E.P., J.T. Tierney, J. Lovett, D. Van Donsel, D.W. Francis, and G.J.
Jackson. 1978b. Land application of sewage wastes: Potential for contamination
of foodstuffs and agricultural soils by viruses, bacterial pathogens and parasites.
In: "State of Knowledge in Land Treatment of Wastewater" (H.L. McKim, ed.),
Vol. 2, 215-223. U.S. Army Corps of Engineers, CRREL, Hanover, New
Hampshire.
Lau, L.S., ei al. 1975. Water recycling of sewage effluent by irrigation: Afield study
on Oahu. Technical report No. 94. Water Resources Research Center, University
of Hawaii, Honolulu.
Lee, C.Y., W.F. Shipe, L.W. Naylor, C.A. Bache, P.C. Wszolek, W.H. Gutenmann,
and D.J. Lisk. 1980. The effect of a domestic sewage sludge amendment to soil on
heavy metals, vitamins, and flavor in vegetables. Nutr. Rep. Int. 21:733-738.
Lefler, E.,and Y. Kott. 1974. Virus retention and survival in sand. In: "Virus Survival
in Water and Wastewater Systems" (J.F. Malina and B.P. Sagik, eds.), 84-94.
Center for Research in Water Resources, Austin, Texas.
Lennette, E.H. 1976. Problems posed to man by viruses in municipal wastes. In:
"Virus Aspects of Applying Municipal Waste to Land" (L.B. Baldwin, J.M.
Davidson, and J.F. Gerber, eds.), 1-7. University of Florida, Gainesville, Florida.
Lepow, M.L., R.J. Warren, V.G. Ingram, S.C. Dougherty, and F.C. Robbins. 19"62.
Sabin type I oral poliomyelitis vaccine: Effect of dose upon response of newborn
infants. Amer. J. Dis. Child. 104:67-71.
Levine, M.M.I 980. Cholera in Louisiana: Old problem, new light. New Eng. J. Med.
302:345-347.
Lin, D. 1980. Fate of petroleum hydrocarbons in sewage sludge after land disposal.
Bull. Environ. Contam. Toxicol. 25:616-622.
Linnemann, C.C.. R. Jaffa, P.S. Gartside, P.V. Scarpino, and C.S. Clark. 1984. Risk
of infection associated with a wastewater spray irrigation system used for farming.
J. Occ. Med. 26:41-44.
Lisk, D.J., R.D. Boyd, J.N. Telford, J.G. Babish, G.S. Stoewsand, C.A. Bache, and
W.H. Gutenmann. 1982. Toxicological studies with swine fed corn grown on
municipal sewage sludge-amended soil. J. Animal Sci. 55:613-619.
Little, M.D. 1980. Agents of health significance: Parasites. In: "Sludge—Health
Risks of Land Application" (G. Bitton, B.L. Damron, G.T. Edds, and J.M.
Davidson, eds.), 47-58, Ann Arbor Science Publishers, Ann Arbor, Michigan.
Liu, D. 1982. The effect of sewage sludge land disposal on the microbiological quality
of groundwater. Water Res. 16:957-961.
Logan, T.J., and R.L. Chancy. 1983. Utilization of municipal wastewater and sludge
on land—metals. In: "Utilization of Municipal Wastewater and Sludge on Land."
(A.L. Page, T.L. Gleason, J.E. Smith, l.K. Iskandar, and L.E. Sommers, eds.),
235-323. University of California, Riverside, California.
Macpherson, R., et al. 1978. Bovine cysticercosis storm following the application of
human slurry. Vet. Record 101:156-157. (Cited in Policy 1979.)
Macpherson, R., G.B.B. Mitchell, and C.B. McCance. 1979. Bovine cysticercosis
storm following the application of human slurry. Meat Hygienist 21:32.
Martone, W.J., and A.F. Kaufmann. 1980. Leptospirosis in humans in the United.
States, 1974-1978. J. Inf. Dis. 140:1020-1022.
Marzouk, Y., S.M. Goyal, and C.P. Gerba. 1979. Prevalence of enteroviruses in
ground water of Israel. Ground Water 17:487-491.
Marzouk, Y., S.M. Goyal, and C.P. Gerba. 1980. Relationship of viruses and
indicator bacteria in water and wastewater of Israel. Water Res. 14:1585-1590.
72
-------
McCarty, P.L., M. Reinhard, and B.E. Rittmann. 1981. Trace organics in
groundwater. Environ. Sci. and Tech. 15:40-51.
McCarty, P.L., B.E. Rittmann, and M. Reinhard. 1980. Processes affecting the
movement the fate of trace organics in the subsurface environment. In:
"Wastewater Reuse for Groundwater Recharge" (T. Asano and P.V. Roberts,
eds.), 93-117. Office of Water Recycling, California State Water Resources
Control Board, Sacramento, California.
McLellan, J.S., P.R. Flanagan, M.J. Chamberlain, and L.S. Valberg. 1978.
Measurement of dietary cadmium absorption in humans. J. Toxicol. Environ.
Health 4:131-138.
McPherson, J.B. 1978. Renovation of waste water by land treatment at Melbourne
Board of Works Farm, Werribee, Victoria, Australia. In: "State of Knowledge in
Land Treatment of Wastewater" (H.L. McKim, ed.), Vol. 1, 201-212. U.S. Army
Corps of Engineers, CRREL, Hanover, New Hampshire.
Means, J.C., S.G. Wood, J.J. Hassett, and W.L. Banwart. 1980. Sorption of
polynuclear aromatic hydrocarbons by sediments and soils. Environ. Sci. Tech.
14:1524-1528.
Melnick, J.L. 1978. Are conventional methods of epidemiology appropriate for risk
assessment of virus contamination of water? In: "Proceedings of the Conference on
Risk Assessment and Health Effects of Land Application of Municipal Wastewater
and Sludges"(B.P. Sagik and C. A. Sorber, eds.), 61-75. University of Texas at San
Antonio, Texas.
Melnick, J.L., C.P. Gerba, and C. Wallis. 1978. Viruses in water. Bull. World Health
Org. 56:499-508.
Melnick, J.L., H. A. Wenner, and C. A. Phillips. 1979. Enteroviruses. In: "Diagnostic
Procedures for Viral, Rickettsial and Chlamydial Infections" (E.H. Lennette and
N.J. Schmidt, eds.), 471-534. American Public Health Association, Washington,
D.C.
Menzies, J.D. 1977. Pathogen considerations for land application of human and
domestic animal wastes. In: "Soils for Management of Organic Wastes and Waste
Waters" (L.F. Elliott and F.J. Stevenson, eds.), 574-585. Soil Science Society of
America, Madison, Wisconsin.
Metcalf, T.G. 1976. Prospects for virus infections in man and animals from domestic
waste land disposal practices. In: "Virus Aspects of Applying Municipal Waste to
Land"(L.B. Baldwin, J.M. Davidson, and J.F. Gerber, eds.), 97-117. University of
Florida, Gainesville, Florida.
Metcalf and Eddy, Inc. 1972. Wastewater Engineering: Collection, Treatment,
Disposal. McGraw-Hill Book Co., New York.
Miller, K.W., J.N. Boyd, J.G. Babish, D.J. Lisk, and G.S. Stoewsand. 1983.
Alteration of glucosinolate content, pattern, and mutagenicity of cabbage
(Brassica oleracea) grown on municipal sewage sludge-amended soil. J. Food
Safety 5:131-143.
Minor, T.E., C.I. Allen, A.A. Tsiatis, D.B. Nelson, and D.J. D'Alessio. 1981. Human
infective dose determinations for oral poliovirus Type 1 vaccine in infants. J. Clin.
Microbiol. 13:388-389.
MMWR. 1979. Campylobacterenteritis in a household—Colorado. Morbidity and
Mortality Weekly Report 28:273-274.
MMWR. 1981. Shigellosis—United States, 1980. Morbidity and Mortality Weekly
Report 30:462-463.
Morens, D.M., R.M. Zweighaft, and J.M. Bryan. 1979. Non-polio enterovirus
disease in the United States, 1971-1975. Int. J. Epidem. 8:49-54.
Miller, G. 1953. Investigations on the lifespan of Ascaris eggs in garden soil.
Zentralbl. Bakteriol. 159:377-379.
Mumma, R.O., D.C. Raupach, J.P. Waldman, S.S.C. Tong, M.L. Jacobs, J.G.
Babish, J.H. Hotchkiss, P.C. Wszolek, W.H. Gutenmann, C. A. Bache, and D.J.
73
-------
Lisk. 1984. National survey of elements and other constituents in municipal
sewage sludges. Arch. Environ. Contam. Toxicol. 13:75-83.
Murphy, W.H., and J.T. Syverton. 1958. Absorption and translocation of
mammalian viruses by plants. II. Recovery and distribution of viruses in plants.
Virology 6:623-636.
Murray, J.P., and S.J. Laband. 1979. Degradation of poliovirus by absorption on
inorganic surfaces. Appl. Environ. Microbiol. 37:480-486.
National Research Council. 1977. Drinking Water and Health. National Academy of
Sciences, Washington, D.C.
National Research Council. 1980. Recommended Dietary Allowances. Ninth revised
edition. National Academy of Sciences, Washington, D.C.
National Water Council. 1977. Report of the Working Party on the Disposal of
Sewage Sludge to Land. National Water Council, London.
Naylor, L.M., and R.C. Loehr. 1982. Priority pollutants in municipal sewage sludge.
Biocycle 23(4): 18-22, 23(6):37-42.
Naylor, L.M., and N.I. Mondy. 1984. Metals and PCB's in potatoes grown in sludge
amended soils. Amer. Soc. Agric. Engin. Technical Paper No. NAR 84-211. St.
Joseph, Michigan.
Nell, J.H., J.F.P. Engelbrecht, L.S. Smith, and E.M. Nupen. 1981. Health aspects of
sludge disposal: South African experience. Water Sci. Tech. 13:153-170.
Osterholm, M.T., J.C. Forfang, T.L. Ristinen, A.G. Dean, J.W. Washburn, J.R.
Codes, R.A. Rude, and J.G. McCullough. 1981. An outbreak of foodborne
giardiasis. New Eng. J. Med. 304:24-28.
Overcash, M.R. 1983. Land treatment of municipal effluent and sludge: Specific
organic compounds. In: "Utilization of Municipal Wastewater and Sludge on
Land" (A.L. Page, T.L. Gleason, J.E. Smith, I.K.. Iskandar, and L.E. Sommers,
eds.), 199-227. University of California, Riverside.
Page, A.L. 1974. Fate and Effects of Trace Elements in Sewage Sludge When
Applied to Agricultural Lands: A Literature Review Study. EPA-670/2-74-005.
U.S. Environmental Protection Agency, Cincinnati, Ohio.
Pahren, H.R., J.B. Lucas, J.A. Ryan, and G.K. Dotson. 1979. Health risks
associated with land application of municipal sludge. J. Water Poll. Control Fed.
51:2588-2601.
Pedersen, D.C. 1981. Density Levels of Pathogenic Organisms in Municipal
Wastewater Sludge—A Literature Review. EPA-600/2-81-170. U.S. Environ-
mental Protection Agency, Cincinnati, Ohio.
Peirce, J.J.,andS. Bailey. 1982. Current municipal sludge utilization and disposal. J.
Environ. Engin. Div., Proc. Amer. Soc. Civil Engineers 108:1070-1073.
Phills, J.A., A.J. Harrold, G.V. Whiteman, and L. Perelmutter. 1972. Pulmonary
infiltrates, asthma eosinophilia due to Ascaris suum infestation in man. New Eng.
J. Med. 286:965-970.
Polley, L. 1979. Health concerns—Risks to livestock. In: "Seminar Papers on
Effluent Irrigation under Prairie Conditions." Environment Canada, Environ-
mental Protection Service, Regina, Saskatchewan.
Porter, K..S. 1980. An evaluation of sources of nitrogen as causes of ground-water
contamination in Nassau County, Long Island. Ground Water 18:617-625.
Quinn, R., H.V. Smith, R.G. Bruce, and R.W.A. Girdwood. 1980. Studies on the
incidence of Toxocara and Toxascaris spp. ova in the environment. I. A
comparison of flotation procedures for recovering Toxocara spp. ova from soil. J.
Hyg. 84:83-89.
Reimers, R.S., M.D. Little, A.J. Englande, D.B. Leftwich, D.D. Bowman, and R.F.
Wilkinson. 1981. Investigation of Parasites in Southern Sludges and Disinfection
by Standard Sludge Treatment Processes. EPA-600/2-81-166. U.S. Environ-
mental Protection Agency, Cincinnati, Ohio.
74
-------
Reimers, R.S., M.D. Little, A.J. Englande, D.B. McDonell, D.D. Bowman, and
J.M. Hughes. 1984. Investigation of Parasites in Sludges and Disinfection
Techniques. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Remington, J.S., and S.C. Schimpff. 1981. Please don't eat the salads. New Eng. J.
Med. 304:433-435.
Rendtorff, R.C. 1954a. The experimental transmission of human intestinal
protozoan parasites. I. Endamoeba coli cysts given in capsules. Amer. J. Hyg.
59:196-208.
Rendtorff, R.C. 1954b. The experimental transmission of human intestinal
protozoan parasites. II. Giardia lamblia cysts given in capsules. Amer. J. Hyg.
59:209-220.
Rendtorff, R.C. 1979. The experimental transmission of Giardia lamblia among
volunteer subjects. In: "Waterborne Transmission of Giardiasis" (W. Jakubowski
and J.C. Hoff, eds.), 64-81. EPA-600/9-79-001. U.S. Environmental Protection
Agency, Cincinnati, Ohio.
Richmond, S.J., E.G. Caul, S.M. Dunn, C.R. Ashley, S.K.R. Clarke, and N.R.
Seymour. 1979. An outbreak of gastroenteritis in young children caused by
adenoviruses. Lancet 1:1178-1180.
Rosen, L. 1979. Reoviruses. In: "Diagnostic Procedures for Viral, Rickettsial and
Chlamydial Infections" (E.H. Lennette and N.J. Schmidt, eds.), 577-584.
American Public Health Association, Washington, D.C.
Rubin, H.E., R.V. Subba-Rao, and M. Alexander. 1982. Rates of mineralization of
trace concentrations of aromatic compounds in lake water and sewage samples.
Appl. Environ. Microbiol. 43:1133-1138.
Rudolfs, W., L.L. Falk, and R.A. Ragotzkie. 1951a. Contamination of vegetables
grown in polluted soil. I. Bacterial contamination. Sewage Ind. Wastes 23:253-268.
Rudolfs, W., L.L. Falk, and R.A. Ragotzkie. 1951b. Contamination of vegetables
grown in polluted soil. II. Field and laboratory studies on Endamoeba cysts.
Sewage Ind. Wastes 23:478-485.
Rudolfs, W., L.L. Falk, and R.A. Ragotzkie. 1951c. Contamination of vegetables
grown in polluted soil. III. Field studies on Ascaris eggs. Sewage Ind. Wastes
23:656-660.
Ruiter, G.G., and R.S. Fujioka. 1978. Human enteric viruses in sewage and their
discharge into the ocean. Water, Air, and Soil Poll. 10:95-103.
Ryan, J.A,, H.R. Pahren, and J.B. Lucas. 1982. Controlling cadmium in the human
food chain: A review and rationale based on health effects. Environ. Res.
28:251-302.
Sagik, B.P., B.E. Moore, and C.A. Sorber. 1978. Infectious disease potential of the
land application of wastewater. In: "State of Knowledge in Land Treatment of
Wastewater"(H.L. McKim, ed.), Vol. 1, 35-46. U.S. Army Corps of Engineers,
CRREL, Hanover, New Hampshire.
Sandstead, H.H. 1977. Nutrient interactions with toxic elements. In: "Toxicology of
Trace Elements" (R.A. Goyer and M.A. Mehlman, eds.), 241-256. John Wiley &
Sons, New York.
Schaub, S.A., J.P. Glennon, and H.T. Bausum. 1978. Monitoring of microbiological
aerosols at wastewater sprinkler irrigation sites. In: "State of Knowledge of Land
Treatment of Wastewater" (H.L. McKim, ed.), Vol. 1, 377-388. U.S. Army Corps
of Engineers, CRREL, Hanover, New Hampshire.
Scheuerman, P.R., G. Bitton, A.R. Overman, and G.E. Gifford. 1979. Transport of
viruses through organic soils and sediments. J. Environ. Eng. Div., A.S.C.E.
105:629-640.
Schiff, G.M., G.M. Stefanovic, E.G. Young, D.S. Sander, J.K. Pennekamp, and
R.L. Ward. 1984. Studies of echovirus-12 in volunteers: Determination of minimal
infections dose and the effect of previous infection on infectious dose. J. Infect.
Dis. 150:858-866.
75
-------
Sepp, E. 1971. The Use of Sewage for Irrigation: A Literature Review. Revised
Edition. Bureau of Sanitary Engineering, Dept. Publ. Health, State of California.
Sherlock, J.C. 1983. The intake by man of cadmium from sludged land. In:
"Environmental Effects of Organic and Inorganic Contaminants in Sewage
Sludge"(R-D. Davis, G. Mucker, and P. L'Hermite, eds.), 113-120. D. Reidel Pub.
Co., Dordrecht, Holland.
Shuval, H.I.,andN.Gruener. 1977. Health Effects of Nitrates in Water. EPA-600/1-
77-030. U.S. Environmental Protection Agency, Cincinnati, Ohio.
Smith, G.S. 1982. Health risks of organics in land application. Discussion. J.
Environ. Eng. Div., A.S.C.E. 108:227-228.
Sobsey, M.D., C.H. Dean, M.E. Knuckels, and R.A. Wagner. 1980. Interactions and
survival of enteric viruses in soil materials. Appl. Environ. Microbiol. 40:92-101.
Sorber, C. A. 1976. Viruses in aerosolized wastewater. In: "Virus Aspects of Applying
Municipal Waste to Land"(L.B. Baldwin, J.M. Davidson, and J.F. Gerber, eds.),
83-86. University of Florida, Gainesville, Florida.
Sorber, C.A. 1983. Removal of viruses from wastewater and effluent by treatment
processes. In: "Viral Pollution of the Environment" (G. Berg, ed.), 39-52. CRC
Press, Boca Raton, Florida.
Sorber, C.A., and K..J. Outer. 1975. Health and hygiene aspects of spray irrigation.
Amer. J. Pub. Health 65:47-52.
Sorber, C.A., B.E. Moore, D.E. Johnson, H.J. Harding, and R.E. Thomas. 1984.
Microbiological aerosols from the application of liquid sludge to land. J. Water
Poll. Control Fed. 56:830-836.
Stewart, J.W.B. 1979. Soil chemistry—Heavy metal accumulation and transfer in
effluent irrigated soils. In: "Seminar Papers on Effluent Irrigation under Prairie
Conditions." Environment Canada, Environmental Protection Service, Regina,
Saskatchewan.
Stich, H.F., W. Stich, and A.B. Acton. 1980. Mutagenicity of fecal extracts from
carnivorous and herbivorous animals. Mut. Res. 78:105-112.
Subba-Rao, R.V., H.E. Rubin, and M. Alexander. 1982. Kinetics and extent of
mineralization of organic chemicals at trace levels in freshwater and sewage. Appl.
Environ. Microbiol. 43:1139-1150.
Sunderman, F.W. 1977. Metal carcinogenesis. In: "Toxicology of Trace Elements"
(R.A. Goyer and M.A. Mehlman, eds.), 257-295. John Wiley & Sons, New York.
Tabak, M.H., S.A. Quave, C.I. Mashni, and E.F. Barth. 1981. Biodegradability
studies with organic priority pollutant compounds. J. Water Poll. Control Fed.
53:1503-1518.
Tate, R.L. 1978. Cultural and environmental factors affecting the longevity of
Escherichia coli in histosols. Appl. Environ. Microbiol. 35:925-929.
Tay, J., I. De Haro, P.M. Salazar, and M. De L. Castro. 1980. Search of cysts and
eggs of human intestinal parasites in vegetables and fruits. International
Symposium on Renovation of Wastewater for Reuse in Agricultural and
Industrial Systems, Morelos, Mexico, 15-19 Dec. 1980.
Taylor, D.N., R.A. Pollard, and P. A. Blake. 1983. Typhoid in the United States and
the risk to the international traveler. J. Infect. Dis. 148:599-602.
Taylor, T.J., and M.R. Burrows. 1971. The survival of Escherichia coli and
Salmonella dublin in slurry on pasture and the infectivity of S. dublin for grazing
calves. Brit. Vet. J. 127:536-543.
Telford, J.N., M.L. Thonney, D.E. Hogue, J.R. Stouffer, C.A. Bache, W.H.
Gutenmann, D.J. Lisk, J.G. Babish, and G.S. Stoewsand. 1982. Toxicological
studies in growing sheep fed silage corn cultured on municipal sludge-amended
acid subsoil. J. Toxicol. Environ. Health 10:73-85.
Teltsch, B., and E. Katzenelson. 1978. Airborne enteric bacteria and viruses from
spray irrigation with wastewater. Appl. Environ. Microbiol. 35: 290-296.
76
-------
Teutsch, S.M., D.D. Juranek, A. Sulzer, J.P. Dubey, and R.K. Sikes. 1979.
Epidemic toxoplasmosis associated with infected cats. New Eng. J. Med.
300:695-699.
Thomas, J.M., and M. Alexander. 1981. Microbial formation of secondary and
tertiary amines in municipal sewage. Appl. Environ. Microbiol. 42:461-463.
Thornton, J.R. 1981. High colonic pH promotes colorectal cancer. Lancet
1:1081-1083.
Tierney, J.T., R. Sullivan, and E.P. Larkin. 1977. Persistence of poliovirus I in soil
and on vegetables grown in soil previously flooded with inoculated sewage sludge
or effluent. Appl. Environ. Microbiol. 33: 109-113.
Tomkins, A.M., A.K. Bradley, S. Oswald, and B.S. Drasar. 1981. Diet and the faecal
microflora of infants, children and adults in rural Nigeria and urban U.K. J. Hyg.
86:285-293.
Underwood, E.J. 1977. Trace Elements in Human and Animal Nutrition. 4th ed.
Academic Press, New York.
USEPA. 1977. National Interim Primary Drinking Water Regulations. EPA-570/
9-76-003. U.S. Environmental Protection Agency, Washington, D.C.
USEPA. 1979. National Secondary Drinking Water Regulations. Federal Register
44(140):42195-42202.
USEPA. 1981. Process Design Manual for Land Treatment of Municipal
Wastewater. EPA-625/1-81-013. U.S. Environmental Protection Agency. Cin-
cinnati, Ohio.
USEPA. 1983. Process Design Manual for Land Application of Municipal Sludge.
EPA-625/1-83-016. U.S. Environmental Protection Agency, Cincinnati, Ohio.
USEPA. 1984. Groundwater Protection Strategy. Office of Groundwater, U.S.
Environmental Protection Agency, Washington, D.C.
USEPA, USFD A, and USD A. 1981. Land Application of Municipal Sewage Sludge
for the Production of Fruits and Vegetables: A Statement of Federal Policy and
Guidance. Joint Policy Statement, SW-905. U.S. Environmental Protection
Agency, Washington, D.C.
USFDA. 1980. Compliance Program Report of Findings, FY78 Total Diet Studies,
Adult (7305.003). Bureau of Foods, U.S. Food and Drug Administration,
Washington, D.C.
Van Tassell, R.L., O.K. MacDonald, and T.D. Wilkins. 1982. Stimulation of
mutagen production in human feces by bile and bile acids. Mut. Res. 103:233-239.
Vaughn, J.M., and E.F. Landry. 1983. Viruses in soils and groundwaters. In: "Viral
Pollution of the Environment" (G. Berg, ed.), 163-210. CRC Press, Boca Raton,
Florida.
Vaughn, J.M., E.F. Landry, and M.Z. Thomas. 1983. Entrainment of viruses from
septic tank leach fields through a shallow, sandy soil aquifer. Appl. Environ.
Microbiol. 45:1474-1480.
Ward, R.L., and C.S. Ashley, 1977. Inactivation of enteric viruses in wastewater
sludge through dewatering by evaporation. Appl. Environ.Microbiol. 34:564-570.
Ward, R.L.,andR.J. Mahler. 1982. Uptake of bacteriophagef2 through plant roots.
Appl. Environ. Micriobiol. 43:1098-1103.
Warren, J. 1979. Miscellaneous viruses. In: "Diagnostic Procedures for Viral,
Rickettsial and Chlamydial Infections" (E.H. Lennette and N.J. Schmidt, eds.),
997-1019. American Public Health Association, Washington, D.C.
Warren, K..S. 1974. Helminthic diseases endemic in the United States. Amer. J.Trop.
Med. Hyg. 23:723-730.
Warren, R.J., M.L. Lepow, G.E. Bartsch, and F.C. Robbins. 1964. The relationship
of maternal antibody, breast feeding and age to the susceptibility of newborn
infants to infection with attenuated poliovirus. Pediatrics 34:4-13.
Weaver, R.W., et al. 1978. Sewage Disposal on Agricultural Soils: Chemical and
Microbiological Implications. Volume II. Microbiological Implications. EPA-
600/2-78-131b. U.S. Environmental Protection Agency, Ada, Oklahoma.
77
-------
Weisburger, J.H., and G.M. Williams. 1980. Chemical carcinogens. In: "Casarett
and Doull's Toxicology"(J. Doull, C.D. Klassen, and N.O. Amdur, eds.), 84-138.
Macmillan Pub. Co., New York.
Wellings, P.M., A.L. Lewis, C.W. Mountain, and L.V. Pierce. 1975. Demonstration
of virus in groundwater after effluent discharge onto soil. *Appl. Microbiol.
29:751-757.
Wellings, P.M., A.L. Lewis, and C.W. Mountain. 1978. Assessment of health risks
associated with land disposal of municipal effluents and sludge. In: "Risk
Assessment and Health Effects of Land Application of Municipal Wastewater and
Sludges" (B. P. SagikandC.A. Sorber, eds.), 168-176. University of Texas at San
Antonio, San Antonio, Texas.
Westwood, J.C.N., and S. A. Sattar. 1976. The minimal infective dose. In: "Viruses in
Water" (G. Berg, H.L. Bodily, E.H. Lennette, J.L. Melnick, and T.G. Metcalf,
eds.), 61-69. American Public Health Association, Washington, D.C.
WHO. 1979. Human Viruses in Water, Wastewater and Soil. WHO Technical
Report Series 639. World Health Organization, Geneva.
WHO. 1981. The risk to health of microbes in sewage sludge applied to soil. EURO
Reports and Studies 54. World Health Organization, Copenhagen, Denmark.
WHO Scientific Working Group. 198O. Escherichia coli diarrhoea. Bull. World
Health Org. 58:23-36.
Willard, R.E. 1984. Assessment of Cadmium Exposure and Toxicity Risk in an
American Vegetarian Population. Final Report for Grant R-806006. U.S.
Environmental Protection Agency, Cincinnati, Ohio.
Wolnik, K.A., F.L. Fricke, S.G. Capar, G.L. Braude, M.W. Meyer, R.D. Satzger,
and E. Bonnin. 1983. Elements in major raw agricultural crops in the United
States. I. Cadmium and lead in lettuce, peanuts, potatoes, soybeans, sweet corn,
and wheat. J. Agric. Food Chem. 31:1240-1244.
Yeager, J.G. 1980. Risk to animal health from pathogens in municipal sludge. In:
"Sludge—Health Risks of Land Application" (G. Bitton, B.L. Damron, G.T.
Edds, and J.M. Davidson, eds.), 173-199. Ann Arbor Science Publishers, Ann
Arbor, Michigan.
Yeager, J.G., and R.T. O'Brien. 1979. Enterovirus inactivation in soil. Appl.
Environ. Microbiol. 38:694-701.
78
•fr U. S. GOVERNMENT PRINTING OFFICE:1985/559-l 11/20685
------- |