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United States
Environmental Protection
Agency
Health Effects
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S1-85/015 Aug. 1986
Project Summary
Health Effects of Land
Application of Municipal
Sludge
Norman E. Kowal
The potential health effects arising
from the land application of munici-
pal sludge are examined, and an ap-
praisal 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 in-
clude 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 munici-
pal wastewater and sludge are briefly
reviewed. A discussion of the levels, be-
havior, and survival of the agent in the
medium or route of potential human
exposure, i.e., aerosols, surface soil and
plants, subsurface soil and ground-
water, and animals, follows as appro-
priate. Infective dose, risk of infection,
and epidemiology are then briefly re-
viewed. Finally, some general conclu-
sions are presented.
This Project Summary was devel-
oped by EPA's Health Effects Research
Laboratory, Research Triangle Park, NC,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
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"
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 uncon-
cerned 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 agri-
cultural 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 condi-
tioner: it contains fair amounts of nitro-
gen, 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 Con-
struction of Treatment Works), Section
201, which states that the:
"Administrator shall encourage
waste treatment management which
results in the construction of revenue
producing facilities providing for
(1)the recycling of potential sewage
pollutants through the production of
agriculture, silviculture, or aquacul-
ture products, or any combination
thereof. . ."
The land application of wastewater
(or "land treatment") has been dis-
cussed in previous reports; the land
application of sludge is the subject of the
present report.
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Land application of sludge consists of
the low-rate application (compared with
a purely disposal operation) to agricul-
tural, forest, or reclaimed land of munic-
ipal wastewater sludge which has been
"stabilized" in some way, e.g., anaero-
bic 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 re-
cent survey of 1008 publicly owned
treatment works, accounting for over
2 million dry metric tons per day of
sludge. 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 sys-
tems (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 in-
clude bacteria (e.g., Salmonella and
Shigella), viruses (i.e., enteroviruses,
hepatitis virus, adenoviruses, ro-
taviruses, and Norwalk-like agents),
protozoa (e.g., Entamoebaand Giardia),
and the helminths (or worms, e.g., As-
caris, Trichuris, and Toxocara). The
protozoa and helminths are often
grouped together under the term,
"parasites," although in reality all the
pathogens are parasites. The toxic sub-
stances include organics, trace ele-
ments (or heavy metals, e.g., cadmium
and lead), and nitrates. Nitrates are
usually not viewed as "toxic" sub-
stances, but are here so considered be-
cause 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.
For each agent of concern the types
and levels commonly found in munici-
pal sludge are briefly reviewed. A dis-
cussion of the levels, behavior, and sur-
2
vival of the agent in the medium or
route of potential human exposure, i.e.,
aerosols, surface soil and plants, sub-
surface soil and groundwater, and ani-
mals, 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 epidemiol-
ogy are then briefly reviewed.
General Conclusions
Types and Levels of Agents in
Wastewater and Sludge
The types of 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 envi-
ronmental samples may actually be de-
tected, the development of methods to
recover and detect viruses needs to be
continued. The occurrence of viruses in
an environmental setting should proba-
bly 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 ap-
plied to agricultural land. Among the
trace elements, probably only cad-
mium, under ordinary circumstances, is
Agent (Pollutant)
likely to be of health concern to human
as a result of the land application <
sludge, with the exposure bein
through food plants or organ meat!
Minimizing of health risks can probabl
be accomplished by the monitoring c
sludge composition, and the regulatio
of maximum concentrations and curr
ulative application of toxic substances!
land-applied sludge. The complexity c
the organics composition of sludge;
however, might require the developmer
and use of biological assays to screen fc
toxicity.
Aerosols
Because of the potential exposure t<
aerosolized bacteria, and possibh
viruses, at land application sites, i
would be prudent to limit public acces:
to a sludge spray source, such as ai
active spray gun or tank truck. Humai
exposure to pathogenic protozoa o
helminth eggs through aerosols is un
likely.
Surface Soil and Plants
The survival times of pathogens or
soil and plants are summarized ir
Table 1. Since pathogens survive for •<
much longer time on soil than on plants
recommended waiting periods befon
harvest are based upon probable con
tamination with soil. However, what is i
safe waiting period before crop harves
for human consumption is really ar
unsettled issue.
Health Effect
Toxic
Substances
Bacteria
Viruses
Protozoa
Helminths
Organics
Trace Eleme
Nitrates
nts
-i
Carcinogenesis
(cardiovascular, immunological
hematological, neurological, etc.
Figure 1. Health effects of pathogens and toxic substances.
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Table 1. Survival Times of Pathogens on Soil and Plants
Soil
Plants
Pathogen
Bacteria
Viruses
Protozoa
Helminths
Absolute
Maximum
t year
6 months
10 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 con-
tact 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 appli-
cation of sludge is still an unsettled
question. Present levels of total dietary
intake of cadmium for most people ap-
pear 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 Ground-
water
Properly designed sludge application
sites may pose little threat of bacterial
or viral contamination of groundwater.
Human exposure to pathogenic proto-
zoa or helminths through groundwater
is unlikely. Groundwater is unlikely to
represent a significant organic or trace
element threat.
There is a possibility that land appli-
cation of sludge may raise the nitrate
concentration of groundwater above
the drinking water standard of 10 mg/C
as N. This can be prevented, however,
by proper siting and management prac-
tice, 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 appli-
cation sites if grazing does not resume
until four weeks after last application
but the need for complete inactivation of
helminths in sludge before land appli-
cation is still unsettled. The feeding of
land-application-site-grown plants to
animals is unlikely to pose a health
problem, but grazing animals may ac-
cumulate significant levels of toxic or-
ganics. The issue of accumulation of
organics from the soil by plants and
animals (particularly into milk), and into
the human food supply, is poorly under-
stood.
Infective Dose, Risk of Infec-
tion, Epidemiology
Because of the possibility of contract-
ing 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 sug-
gest little effect of land application on
disease incidence. However, many
questions on the public health conse-
quences of land application of waste-
water and sludge remain.
The EPA author Norman £. Kowal is with the Toxicology and Microbiology
Division of the Health Effects Research Laboratory—RTP, Cincinnati, OH
45268.
The complete report, entitled "Health Effects of Land Application of Municipal
Sludge," (Order No. PB 86-197 456/AS; Cost: $11.95. 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 author can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S1-85/015
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