&EPA
United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S1-81-006 Apr. 1981
Project Summary
Potential Health Effects from
Viable Emissions and Toxins
Associated with Wastewater
Treatment Plants and Land
Application Sites
Vimala A. Majeti and C. Scott Clark
This study presents an overview of
the literature on potential health
effects from viable emissions and
toxins associated with wastewater
treatment plants and land application
facilities to the workers and nearby
populations. The different types of
microorganisms present in waste-
water and sludge and the effective-
ness of the various treatment pro-
cesses in their removal or inactivation
is discussed briefly. The monitoring of
microorganisms and toxins in aerosols
generated at wastewater treatment
plants and land application sites, the
disadvantages in using coliform
organisms as indicators to represent
the actual levels of pathogenic micro-
organisms in aerosols, and the various
mathematical models that are used to
predict the microorganism levels in
aerosols are also reviewed. The levels
of microorganisms detected in
aerosols at wastewater treatment
plants and land application facilities
from some of the recent studies are
presented.
This Project Summary was develop-
ed by EPA's Health Effects Research
Laboratory. Cincinnati. OH. to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
A large variety of potential disease-
causing microorganisms and viruses
are present in municipal wastewaters.
Wastewater treatment plant workers
are potentially exposed to these patho-
genic microorganisms and viruses
through ingestion as well as inhalation
of the aerosolized pathogens. Residents
of nearby wastewater treatment plants
may be exposed to low densities of
these pathogenic microorganisms and
viruses that become airborne.
Land application of wastewater and
sludge is gaining renewed interest as an
alternative means to the more conven-
tionally used disposal methods, such as
ocean and surface water dumping, and
incineration. Land application repre-
sents a recycling process in which
water and plant nutrients are returned
to the soil. However, wastewater treat-
ment does not completely remove
pathogens and many become concen-
trated in the sludge.
Exposure to airborne pathogens and
toxins can affect the health of workers
at wastewater treatment plants and
land application sites, and on the popu-
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lations living in the vicinity of the
treatment plants and land application
sites. Precautions should be taken to
limit human exposure to these airborne
pathogens and toxins.
Information regarding human health
risks resulting from contact with waste-
water and sludge brought about by
occupational exposure or by residing
near wastewater treatment plants and/
or land application facilities is limited.
Several health effects studies have
been initiated in the past few years on
the health risks of pathogens in waste-
water and aerosols generated at the
wastewater treatment plants.
Discussion
Microorganisms. The major groups of
microorganisms present in municipal
wastewater and sludge are bacteria,
viruses, protozoa, and helminths. Some
of these microorganisms, the diseases
that are attributed to them, and known
reservoirs of infection are shown in
Table 1.
Toxins. The dust generated at the
wastewater treatment plants during
sludge heat-treatment operations and
at land application sites may contain
significant quantities of toxins which
may represent a potential health risk to
the workers. The toxins of concern are
endotoxins derived from bacteria and
mycotoxins produced by the fungi.
Wastewater and Sludge Treatment.
Primary treatment involves physical
processes, such as screening, grit
removal, and sedimentation in which
the microorganisms may settle out by
their density or by being adsorbed to
solids. Because of their relatively small
size, viruses are less easily removed
from wastewater than bacteria,
protozoa, or helminths. Secondary
treatment is a biological degradation
process. Activated sludge treatment,
trickling filters, aerated lagoons, and
ponding are some of the secondary
treatment processes. Chemical
treatment, filtration, adsorption, ion
exchange, and nitrogen removal are
forms of tertiary treatment processes.
Information on survival of microorgan-
isms during tertiary treatment
processes is limited. Indications are that
microorganisms are not completely
removed by tertiary treatment. Chlorin-
ation and ozonation are two of the
methods used for the disinfection of
wastewater effluents, of which chlorin-
ation is most commonly used.
Each of the above mentioned sedi-
mentation processes produces a sludge.
Stabilization of sludge by treatment
prior to land application is usually
necessary to reduce the levels of patho-
genic microorganisms and decomposi-
ble organic matter. Anaerobic digestion,
aerobic digestion, chemical treatment,
heat-drying, and composting are some of
the methods that can be used to stabil-
ize the sludge.
The existing data indicate that some
of the microorganisms survive during
wastewater and sludge treatment. Also,
the amount of endotoxins may increase
during treatment processes that result
in destruction of bacteria. Workers at
wastewater treatment plants and land
application sites will, therefore, be
potentially at risk of exposure to patho-
genic bacteria, viruses, and endotoxins.
Aerosols. Some of the microorgan-
isms present in wastewater and sludge,
especially bacteria and viruses, can
become airborne. Major sources of the
aerosols are the aeration basin of the
activated sludge treatment units, trick-
ling filters, and land application sites
that use spray irrigation. Aerosols are
paniculate materials in either solid or
liquid form and may also include gases
and vapors that are adsorbed or con-
tained in airborne particles or liquid
droplets. Inhalation is a possible route of
infection because the viruses and most
pathogenic bacteria are in the respir-
able size range. The health hazard
posed by aerosolized particles depends
on their ability to deposit in the lungs.
Airborne microorganisms are usually
collected for sampling by the Andersen
air sampler, all glass impinger, or high
volume air sampler Viruses in aerosols
are less well studied than bacteria,
mainly due to technical limitations in
sampling and in obtaining accurate
measurement of viruses in air. Large
volumes of air must be sampled for virus
monitoring in aerosols due to the low
levels of viruses present in wastewater
and wastewater aerosols.
Coliform bacteria and coliphage
viruses are generally used as indicators
of fecal contamination in water, since
they are considered to reflect pathogen
levels. Coliform organisms do not sur-
vive wastewater aerosolization as well
as other microorganisms. Therefore,
they have limited usefulness as
indicators of pathogens in aerosols. The
use of cohform organisms as indicators
would tend to underestimate the
potential effect on workers as well as
nearby populations. One of the limita-
tions to the accurate monitoring of
endotoxin levels in environmental
samples is the lack of a sensitive and
specific assay for endotoxins.
Wastewater application methods play
an important role in the emission of
aerosols at land application sites where
spray or sprinkler irrigation is believed
to generate the maximum amount of
aerosols. Microbial concentration in
aerosols would depend on the degree of
treatment received by the wastewater
or the sludge; concentration decreasing
as the treatment process increases.
Available data indicate that microorgan-
isms in aerosols generated at spray
irrigation sites may remain viable and
be dispersed for several hundred meters
from the spray source.
Some of the variables that affect the
survival and dispersion of microorgan-
isms in aerosols are die-off, deposition,
and diffusion. These in turn are affected
by the following environmental factors;
relative humidity, wind velocity, sun-
light, temperature, and actual field
conditions compared to controlled
conditions in the laboratory.
Several theoretical mathematical dis-
persion models for predicting the
microorganism levels in aerosols have
been developed in recent years. A valid
model is used to estimate airborne t
pathogen levels at any location down- "
wind of a source of microbial aerosols,
which could also be used to predict
pathogenic microoganism exposure.
However, it should be pointed out that |
the exact health risks cannot be deter- "
mined until the threshold levels for
aerosolized pathogens resulting in
health effects are established. Compari-
son of the threshold levels with the
predicted and actual airborne values of
microorganisms would permit the
determination of the health risks
associated with aerosols at a given
facility, and would be invaluable in
planning future treatment sites. Further
predicted concentrations and their pre-
dicted associated risks could be used to
help set standards for emissions at
treatment facilities, if needed. To date,
dispersion models have limited useful-
ness in the prediction of aerosol con-
centrations of microorganisms. Further
research is needed to test and improve
present models or to develop new ones.
Because of the lack of a standard
method for viral monitoring, the com-
parison of data from two or more
laboratories must take into considera-
tion differences in sample handling,
concentration, and method of measure- m
ment. Due to the difficulties involved in ^
routinely detecting airborne viruses at
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Table 1. Major Organisms of Health Concern That May be Present in Sewage from U.S. Communities
Organisms
Disease
Reservoir(s)
I. BACTERIA
Salmonellae
(Appro*. 1700 types)
Shigellae (4 spp.j
Escherichia coli
(enteropathogenic types)
II. ENTERIC VIRUSES
Enteroviruses
(67 types)
Rot a virus
Parvovirus-like agents
(at least 2 types)
Hepatitis A virus
Adenoviruses
(31 types)
III. PROTOZOAN
Balantidium coli
Entamoeba histolytica
Giardia lamblia
IV. HELMINTHS
Nematodes (Roundworms)
Ascans lumbncoides
Ancylostoma duodenale
Necator amencanus
Ancylostoma braziliense (cat hookworm)
Ancylostoma canmum (dog hookworm)
Enterobius vermicularis (pinworm)
Strongyloides stercoralis (threadworm)
Toxocara cati (cat roundworm)
Toxocara cams (dog roundworm)
Trichuris trichiura (whipworm)
Typhoid fever
Salmonellosis
Shigellosis
(bacillary dysentary)
Gastroenteritis
Gastroenteritis, heart
anomalies, meningitis,
others
Gastroenteritis
Gastroenteritis
Infectious hepatitis
Respiratory disease,
conjunctivities, other
Balantidiasis
Amebiasis
Giardiasis
Ascariasis
A ncylostomiasis
Necatoriasis
Cutaneous larva migrans
Cutaneous larva migrans
Enterobiasis
Strongyloidiasis
Visceral larva migrans
Visceral larva migrans
Trichuriasis
Man, domestic and
Wild animals and birds
Man
Man, domestic animals
Man, Possibly lower
animals
Man, domestic animals
Man
Man, other primates
Man
Man, swine
Man
Man, domestic and
wild animals?
Man, swine?
Man
Man
Cat
Dog
Man
Man, dog
Carnivores
Carnivores
Man
3
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Table 1. (continued)
Cestodes (Tapeworms)
Taenia saginata (beef tapeworm)
Taenia solium (pork tapeworm)
Hymenolepis nana (dwarf tapeworm)
Echinococcus granulosis (dog tapeworm)
Echinococcus multilocularis
Taeniasis
Taeniasis
Taeniasis
Unilocular Echinococcosis
Alveolar hydatid disease
Man
Man
Man, rat
Dog
Dog, carnivore
wastewater treatment plants and spray
irrigation facilities, it is presently not
possible to validate atmospheric dis-
persion models for their prediction. For
bacteria, the models appear to have
some usefulness, but have not been
perfected enough to replace the field
monitoring.
Health Effects. Pathogenic micro-
organisms generated at wastewater
treatment plants and land application
sites can be transmitted via inhalation,
skin contact, and ingestion. Infection
may result in disease, depending on the
degree of exposure as well as other
factors, such as pathogen density,
minimum infective dose, virulence of
the organism, and susceptibility of the
exposed individual. Under special cir-
cumstances an infection can develop
from a single virus, protozoan, or
helminth. The minimum infective dose
for bacteria ranges from 100to 100 mil-
lion, depending on species. Information
is not available on minimum infective
dose of airborne microorganism levels
for the inhalation route.
A number of epidemiological studies
have recently been performed on
workers at wastewater treatment plants
and spray irrigation facilities, and on
populations living adjacent to these
sites who would generally be exposed to
lower levels of the pathogens. Data on
health effects from the existing epidem-
iological studies do not show any corre-
lation between the airborne pathogenic
microorganism levels at wastewater
treatment plants and incidence of
disease in treatment plant workers or in
nearby populations. However, the worst
case of exposure of either the workers
or the nearby populations has probably
not yet been investigated. No adverse
health effects have been reported in
workers or in nearby populations at
wastewater spray application facilities.
4
The data on health effects from the
existing epidemiological studies con-
cludes that exposure to pathogenic
microorganisms in wastewater
aerosols is not a unique wayof initiating
enteric infections. The existence of the
other possible pathways of infection
could make the detection of a waste-
water facility effect more difficult, if
indeed one exists. There is, however, a
potential for contamination of food
crops grown on wastewater or sludge
treated lands. This should be taken into
consideration when formulating guide-
lines or recommendations.
Aerosol Control. A number of tech-
niques have been investigated to
control or suppress aerosols and/or the
levels of microorganisms in aerosols.
Vegetative barriers have been imple-
mented for aerosol suppression result-
ing in a 50% reduction of microorgan-
isms in aerosols. Strategically-placed
vegetation could effectively reduce
aerosols generated at wastewater
treatment plants and at spray irrigation
facilities. Buffer/safety zones are areas
between the wastewater treatment
plant or the edge of the wetted area of
the spray irrigation site and adjacent land
uses that ensures adequate protection
of populations from potential health
hazards or aesthetic insult of exposure
to pathogenic microoganisms in
aerosols. These zones also protect
water supplies from contamination with
pathogenic microorganisms present in
wastewater and sludge used for land
application. Disinfection of wastewater
prior to spray application has been
shown to reduce the levels of airborne
microorganisms to nondetectable
levels. Proper spray equipment design
and the use of subsurface injection navel
also been shown to effectively reduce
the generation of aerosols. Covering
aeration basins will effectively suppress
aerosols as well as control odors. These
measures could serve to control th
exposure of nearby populations, and in
some cases, but to a lesser extent, that
of the workers. Data from viral and
bacterial monitoring of wastewater and
aerosols indicate that buffer or safety
zones may not be necessary between
wastewater treatment plants or spray
application facilities and the surround-
ing population centers.
Vimala A. Majeti and C. Scott Clark are with the Department of Environmental
Health, University of Cincinnati Medical Center, Cincinnati, OH 45267.
Herbert R. Pahren is the EPA Project Officer (see below).
The complete report, entitled "Potential Health Effects from Viable Emissions
and Toxins Associated with Wastewater Treatment Plants and Land Applica-
tion Sites," (Order No. PB 81 - 145 260; Cost: $9.50, subject to change} will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
> US GOVERNMENT PRINTING OFFICE 1981-757-012/7077
I
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