United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/028 June 1987
Project Summary
Survival and Transport of
Pathogens in
Sludge-Amended Soil: A
Critical Literature Review
Charles A. Sorber and Barbara E. Moore
A study was undertaken to critically
review available information on the
survival and transport of pathogens
from municipal wastewater sludges ap-
plied to land. Unfortunately, the
amount of quantitative, comparable
data related to pathogen behavior in
sludge-amended soils is extremely lim-
ited. Most available data are restricted
to Salmonella and indicator bacteria.
In general. Salmonella showed a 90%
(T90) reduction within 3 weeks in
sludge-amended soils. In warm cli-
mates, inactivation of viruses near the
surface was quite rapid, with a median
Tgo of 3 days. However, at low tempera-
tures, T90 values of approximately 30
days were observed for viruses. Maxi-
mal parasite survival, as determined by
Ascaris ova recovery, was relatively
long near the surface, with a median Tgo
of 77 days.
Extremely limited vertical movement
of some pathogens may be anticipated
in sludge-amended soils. Although
monitoring at sludge application sites
has not revealed that sludge amend-
ment affects the bacterial quality of
groundwater, limited transport of indi-
cator bacteria to depths up to 180 cm
has been reported. Under field condi-
tions including exposure to natural
rainfall, virtually no viruses have been
detected in soil-water percolates. Avail-
able literature strongly favors the con-
tention that parasitic ova are retained
at the point sludge is introduced to the
soil. Finally, insufficient data are avail-
able for adequate modeling of patho-
gen survival and transport in sludge-
amended soils.
This Project Summary was devel-
oped by EPA's Water Engineering Re-
search Laboratory, Cincinnati, OH, to
announce 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
An integral part of almost any waste-
water treatment plant is the sludge
management system. Residual solids
are produced in nearly every unit proc-
ess associated with conventional waste-
water treatment. Approximately 6.5 mil-
lion dry tons of municipal wastewater
sludges are generated annually in the
United States. By the year 2000, the
quantity of municipal wastewater
sludge produced is projected to almost
double. Sludge management currently
accounts for approximately half of the
cost of wastewater treatment. Thus a
major goal is to reduce the costs of
sludge handling. Equally important is to
reduce to an acceptable level the risks to
public health, safety, and welfare that
arise from and are otherwise associated
with sludge disposal.
Among several disposal alternatives,
land application of sludge is increasing
in popularity. Indeed, there is every rea-
son to believe that the practice will
expand at a greater rate in the years to
come. The presence of infectious mi-
-------
croorganisms in sludges may, however,
place certain constraints on their use on
land.
The concentration of pathogens in
wastewater and thus in wastewater
sludges is influenced by a number of
factors, including the age and health of
the contributing population, population
density, sanitary habits, and the season
of the year. Microorganisms of public
health concern are generally classified
into three broad categories: bacteria,
viruses, and parasites. Parasites are
often further differentiated into
helminths and protozoans. Hundreds of
organisms fall into these categories and
may be present in domestic waste-
waters.
A wide variety of disease-causing mi-
croorganisms known to be transmitted
by the fecal-oral route may potentially
be transmitted through environmental
exposure. A more focused list of micro-
bial agents can be prepared, however,
with the application of additional crite-
ria such as demonstrable presence in
wastewaters or sludges and/or docu-
mented environmental transmission of
disease. Table 1 provides such a listing.
Although some of the organisms listed
are overt pathogens, reports of their oc-
currence in wastewater and sludges in
the United States are quite rare. How-
ever, advances in microbiological and
medical sciences may identify addi-
tional pathogenic organisms linked to
environmental disease transmission.
Wastewater treatment affects the var-
ious organism types in different ways.
In general, microbial segregation oc-
curs during conventional wastewater
treatment. Bacteria, viruses, and some
parasitic cysts tend to become associ-
ated with the sludge component, as do
the heavier eggs of certain parasites
such as Ascaris. Conventional sludge
treatment processes can reduce the lev-
els of sludge-associated pathogens. In
the absence of extensive treatment,
however, wastewater sludges will con-
tain measurable concentrations of these
microorganisms. Thus from a public
health standpoint, applying wastewater
sludge to land needs regulation in re-
gard to the pathogens known to be
present in these sludges.
Interim regulations relating to sludge
treatment and disposal have been de-
veloped and were published in 40 CFR
Part 257. These current regulations are
based on the expected operational per-
formance of specific unit processes and
on the absence of health effects directly
related to land application practices. Ul-
timately, however, regulations should
be founded on both a complete under-
standing of the fate and transport of
pathogens in sludge-amended soils and
on the epidemiological implications as-
sociated with the numbers of organ-
isms to which humans are subjected as
a result of these practices. To facilitate
the development of scientifically based
regulations, a critical review was made
of available information on the survival
and movement of pathogens from mu-
nicipal wastewater sludges applied to
land.
Methods
Acquisition of Literature
Extensive literature searches were
conducted, and a significant number of
documents were accumulated from a
variety of sources. The search for rele-
vant documents was carried out in four
steps: primary (database) searches,
secondary searches, author contacts,
and manual searches.
A total of 12 primary literature data-
bases were searched. This step resulted
in the acquisition of a total of 819 titles
and abstracts. After they were read and
duplication was eliminated, 95 unique
documents were identified for hard-
copy acquisition.
The secondary literature searches
were begun when the hard copies of
documents from the primary searches
were available for review. All references
in the primary documents were consid-
ered possible secondary sources. Fur-
thermore, each document from this sec-
ondary search represented possibilities
for the identification of additional litera-
ture sources.
Contacts were made with authors
identified as major contributors to the
literature obtained during the primary
and secondary searches. In addition,
personal contacts were made at a num-
ber of national meetings. These efforts
proved fruitful, as they obtained a num-
ber of obscure and unpublished docu-
ments of value to the study.
Manual searches were made of se-
lected current science and engineering
journal issues. The journals selected for
manual searches were those that
yielded documents relevant to the study
through the primary and secondary lit-
erature searches.
Guidelines for Literature
Evaluation
The literature review encountered a
broad spectrum of studies ranging from
investigations employing exogenously
added organisms to monitoring of in-
digenous organisms at field sites. The
Table 1. Organisms of Major Concern in Land Application of Municipal Wastewater and Sludges
Group Name of Organism Primary Disease Remarks
Bacteria
Viruses
Helminths
Protozoans
Legionella pneumophila
Salmonella sp.
Shigella sp.
Vibrio cholerae
Hepatitis A virus
Non-A, Non-B hepatitis
Norwalk-like agents
Rotavirus
Ascaris sp.
Giardia lamblia
Acute respiratory disease
Gastroenteritis, typhoid
and paratyphoid fever
Bacillary dysentery
Cholera
Infectious hepatitis
Hepatitis
Gastroenteritis
Gastroenteritis
Ascariasis
Giardiasis (Gastroenteritis)
Aerosol transmission documented,
but no cases linked to wastewater
exposure to date
Overt pathogens but low probability
of occurrence in wastewater in the
United States
Documented waterborne transmission
Preliminary evidence for waterborne
transmission
Documented waterborne transmission
Documented waterborne transmission
Documented waterborne transmission
-------
challenge posed by such diverse experi-
mental conditions was to qualify the
data within a common framework, re-
flecting (insofar as possible) expected
responses in natural systems. To en-
sure a relatively unbiased appraisal of
existing literature, guidelines were set
to critically evaluate both laboratory
and field studies before beginning the
review of individual reports.
For example, attention was focused
on the appropriateness of both sam-
pling and analytical procedures for the
recovery and identification of specific
organisms. The adequacy of the experi-
mental design was evaluated with re-
gard to the number and frequency of
samples collected as well as the control
procedures used. From a regulatory and
design standpoint, the collection of sup-
porting data during the course of exper-
imentation or monitoring could provide
valuable information; thus particular at-
tention was given to ancillary data that
might affect pathogen survival or trans-
port or both. Specifically, the collection
of environmental data in the areas of
temperature, rainfall, and various soil
parameters was deemed important.
Finally, to provide a common frame-
work within which organism survival
could be addressed, simple inactivation
values representing 90% (T90) and 99%
(T99) dieaway were graphically deter-
mined. For this purpose, minimal crite-
ria were established for using published
data: initial monitoring of amended soil
must have occurred within 2 weeks of
sludge application, and a minimum of
three positive, quantitative recoveries
must have been recorded over a con-
secutive monitoring period. In addition,
there must have been no data extrapo-
lation beyond the actual sampling pe-
riod.
Results and Discussion
In considering the various studies de-
tailing the survival and transport of mi-
croorganisms in sludge-amended soils,
the limitations influencing quantitative
results in such systems must be recog-
nized. Perhaps the most important
problem in evaluating the behavior of
microbes in sludges and soils is the
methods used for organism recovery.
Though standard methods for detecting
indicator bacteria in water and waste-
water have been widely applied in soil
systems, these bacterial groups are not
normally associated with human dis-
ease. The recovery and enumeration of
bacterial pathogens, viruses, and para-
sites often require elaborate procedures
involving a high degree of technical
competence and experience. In addi-
tion, the factors affecting organism re-
covery from sludge and soil systems are
not well understood. Furthermore, the
recovery of viable bacteria, viruses, and
parasites is limited by the volume of
sample that can be analyzed, thus im-
posing, in some instances, a restrictive
sensitivity limit on organism detection.
Survival of Microorganisms in
Sludge-Amended Soils
Factors frequently cited as affecting
microbial survival in soil include soil
moisture content, temperature, pH, sun-
light, organic matter, and antagonistic
soil microflora. Microbial pathogens in-
troduced into the soil by sludge amend-
ment will be influenced by these factors.
However, the nature of the sludge-
amended soil environment may moder-
ate soil conditions in ways that could
affect the survival of microorganisms.
For example, sludge application may
dramatically increase the organic con-
tent, nutrient content, and moisture-
retention capability of sandy soils. In ad-
dition, soil pH could be influenced by
added sludge or management practices
such as lim>ng. Even soil temperature
could be affected by the surface applica-
tion of sludge. Though the interplay of
these factors in sludge-amended soil
may favor organism survival in some
cases, more rapid pathogen inactivation
may occur in other situations.
As shown in Table 2, T90 values for
Salmonella survival in sludge-amended
soil fall within the range of 3 to 61 days,
with median values of 12 and 8 days for
soil depths of 0 to 5 cm and 5 to 15 cm,
respectively. A closer review of selected
studies reveals a seasonal trend of bac-
terial inactivation. When salmonellae in
sludge-amended soils were subjected
to winter conditions, T90 values of 12 to
15, 17, and 22 to 61 days have been esti-
mated in three published field studies.
Similarly, at a temperature of 12°C,
Salmonella sp. were observed to decay
with a T90 of 8 to 11 days in a controlled
laboratory study. During summer expo-
sure, a much more rapid inactivation of
indigenous salmonellae has been ob-
served with T90 values of 4 and 6 days in
two separate field studies. Experiments
conducted during warm growing sea-
sons with laboratory-grown strains of
Salmonella have resulted in T90 values
of 6 and 10 days in an Ohio study and 14
days in a Norway study. Hence studies
with both indigenous and seeded
salmonellae are in relatively good
agreement, showing (with one excep-
tion) a 90% bacterial reduction within 3
weeks of sludge application.
The exceptionally long survival times
often cited for Salmonella persistence
actually arise from seeded studies in
which high levels of bacteria ranging
from 106 to 1010/L were added to sludge
before land application. Under these
conditions, and assuming a maximum
T99 of 45 days, persistence times in ex-
cess of 5 months could be anticipated. If
growth or regrowth of seeded orga-
nisms occurs, this survival time could
be substantially longer. On the other
hand, indigenous salmonellae at actual
field sites have generally persisted at
low levels for less than 2 months, al-
though a few positive recoveries have
been reported as long as 3 to 5 months
after sludge application.
Most published literature documents
the behavior of indicator bacteria in
sludge-amended soils. With the excep-
tion of one study, 90% of the fecal coli-
forms could not be recovered within 6
weeks of sludge application. A 90% loss
of fecal streptococci occurred with 4
weeks. Although the number of studies
is more limited, total coliform bacteria
displayed significantly slower inactiva-
tion rates, with T90 values generally
twice those of the other bacterial indica-
tor groups (Table 2). Note, however,
that T90 values for total coliforms are
polarized, with most values ranging
from 14 to 42 days and a second group
ranging from 129 to 172 days. An evalu-
ation of the overall survival results of
these groups of bacteria reveals a di-
chotomy with the seasonal survival of
coliform bacteria as reported by two re-
search groups working in the Pacific
Northwest region of the United States.
Although the actual Tgo values were dra-
matically different, both studies ob-
served longer survival times during
warmer months than during cooler
months. Coliform regrowth is the most
likely explanation of these findings. In-
deed, regrowth of coliform bacteria in
the spring following a decrease in levels
during the winter has been reported.
These results highlight the difficulty in
evaluating bacterial inactivation when
organisms are capable of replication. In-
terpretation of data for indicator bacte-
ria is further complicated by the fact that
several bacterial species, including
unique soil microflora, may be recov-
ered by the analytical procedures used.
These bacterial populations do not nec-
essarily share the same inactivation or
regrowth characteristics.
-------
Table 2. Summary of Microorganism Survival in Sludge Applied to Soil
Die-off—T90 (days)
Die-off—T99 (days)
Bacteria
Salmonella
Fecal streptococci
Fecal coliforms
Total coliforms
Viruses
Parasites
Depth
(cm)
0- 5
5-15
0- 5
5-15
0- 5
5-15
0- 5
5-15
0- 5
5-15
0- 5
5-15
Minimum
6
3
7
72
7
4
16
9
<1
12
17
Maximum
61
22
28
30
84
49
172
70
30
56
270
Data unavailable
Median
12
8
14
20
25
13
85
17
3
30
77
Observations
10
17
9
11
19
12
6
12
9
4
11
Minimum
11
7
14
30
12
9
28
18
2
60
68
Maximum
45
45
63
60
165
90
350
40
52
100
500
Median
22
18
24
40
53
32
155
32
6
60
81
Observations
8
15
8
10
16
11
4
9
6
3
5
Data unavailable
Survival of viruses in soils is influ-
enced by many of the same parameters
described for bacteria. The effect of
temperature on the survival of viruses is
well documented: lower temperatures
favor longer survival. Furthermore, an
optimal soil moisture content favors
virus survival in soil, whereas desicca-
tion results in a more rapid loss of
viruses. Also remember that viruses (as
obligate intracellular parasites) do not
replicate outside of an appropriate host.
Thus data characterizing their survival
in sludge-amended soil are perhaps
more straightforward.
Viral T90 values have ranged from less
than 1 day under hot summer condi-
tions to 56 days in the winter. Note that
data presented in Table 2 that appear to
support extended viral survival with soil
depth actually reflect sampling to 20 cm
in one Danish study where an average
temperature of 0.5°C was observed. Un-
doutstedly, viruses can persist for ex-
tended periods in the soil environment
where cold temperatures favor their
survival. Studies completed under win-
ter conditions in both Denmark and
Ohio showed very similar inactivation
rates, with T90 values of 30 days for two
different enteric viruses. As evidenced
by available data, however, inactivation
at the soil surface can be quite rapid
when viruses are exposed to high tem-
peratures and drying conditions such as
those prevailing in the southern United
States during the summer and fall.
Among the parasites, protozoa seem
to be very sensitive to drying, and under
these conditions, survival rates are usu-
ally short. However, ova of helminths
such as Ascaris are quite resistant to en-
vironmental stress. Parasites are also
unable to replicate outside of their ap-
propriate animal or human hosts.
Only three independent research
groups have reported quantitative data
for parasite survival in sludge-amended
soil that allows estimation of inactiva-
tion rates. All but one Tgo value is based
on the addition of exogenus Ascaris or
Toxocara ova to the sludge-soil system.
As expected, T90 values for these para-
sitic forms exceeded those of all other
microbial groups, ranging from 17 to
270 days, with a median value of 77
days (Table 2). Seasonal effects on ova
survival were observed. Following sum-
mer sludge application, Ascaris ova
were inactivated with apparent T90 val-
ues of 17 days in one study. Survival
after applying sludge in the fall at the
same location was more extended, with
a T90 value of 65 days for Ascaris ova
and 77 days for Toxocara ova. From an-
other report, a T90 value of 30 days was
estimated for Ascaris in sludge sprayed
onto an untilled plot in the summer,
whereas 90% inactivation following
winter application required 80 and 90
days in separate experimental plots.
Notably, after winter sludge application
in this study, Ascaris ova survived dra-
matically longer, with a T90 of 200 days
in tilled plots planted with a cover crop
in the spring. Presumably, this ex-
tended survival time was favored by de-
creased soil temperature resulting from
crop shading and/or by higher soil
moisture resulting from irrigation and
rainfall.
Attempts were made to analyze
statistically the available quantitative
data. Unfortunately, sufficient data
were available only for temperature and
die-off. Least-squares regression analy-
ses of raw and transformed data were
performed for the die-off recorded for
salmonellae, fecal streptococci, fecal
coliforms, total coliforms, viruses, and
parasites. Only for fecal coliforms were
there sufficient data to discriminate be-
tween soil depths. In the cases of
salmonellae, viruses, and parasites, die-
off at all depths was used in the analy-
sis. Die-off at 5 to 15 cm was used in the
analysis of salmonellae, fecal strepto-
cocci, and total coliforms.
Poor correlation was observed be-
tween organism inactivation and tem-
perature for salmonellae, fecal strepto-
cocci, total coliforms, and parasites,
whereas very good correlation was ob-
served for fecal coliforms at both depths
and for viruses. Results of this analysis
for viruses appear in Figure 1 and illus-
trate some of the limitations of the avail-
able data. More often than not, the
transformed T90/T99 data correlated bet-
ter with temperature, but the difference
was not judged to be significant. Close
scrutiny of these data shows that usable
information for microorganisms such
as viruses was available only at temper-
ature extremes. Or, in other words, data
tended to be clumped at either the
warm or cold ranges, with few data in
between. This observation restricts the
value of an analysis over a range of tem-
peratures and suggests the need for
more detailed evaluation.
One approach to this evaluation was
to use nonparametric correlations that
make no assumptions about the nor-
mality of the distribution of the vari-
ables. The Kendall rank-order correla-
tion was chosen for this evaluation.
Only fecal coliform data at both the 0- to
5-cm depth and 5- to 15-cm depth were
judged to be significant at the 5% level.
Transport of Microorganisms
from Sludge-Amended Soils
In addition to survival of pathogens in
sludge-amended soils, consideration
must be given to their ability to move in
this environment, either into surface
waters through runoff or, perhaps more
important, into groundwater through
the soil profile. Though runoff may be
viewed as largely the physical transport
-------
Correlation Coefficient = 0.906
1 .
Correlation Coefficient = 0.542
10 20
Temp., °C
10 20
Temp., °C
30
Correlation Coefficient -0.913
Correlation Coefficient = 0.987
10 20
Temp., °C
10 20
Temp., °C
Figure 1. Least squares regression plots for temperature and virus survival at all depths.
of microorganisms associated with par-
ticulate material, vertical microbial
transport is more complex.
Exceedingly few studies have ad-
dressed the presence of microorga-
nisms in runoff from sludge-amended
soils. No significant bacterial or viral im-
pact has been observed on surface
water at actual sludge application sites.
However, as long as viable bacteria
were present in sludge-amended soil,
they were recovered at elevated levels
from runoff intercepted at the lower end
of sludge-amended test fields. Simi-
larly, parasitic ova have been recovered
from irrigation return flow at a sludge
application site. Obviously, sludge ap-
plication methods that minimize the dis-
placement of sludge in surface runoff
should be used if microorganism trans-
port in runoff is to be avoided.
Removal of bacteria from wastewater
percolating through a soil is due to both
mechanical action (i.e., straining or
sieving at the soil surface) and adsorp-
tion to soil particles. Similarly, the phe-
nomenon of adsorption as a mecha-
nism for retaining viruses in soil
systems has been demonstrated. Re-
lease and movement of these microor-
ganisms would be expected, since
physical adsorption to particulates is a
reversible phenomenon and, in part,
ion-dependent.
The transport of protozoa and
helminths in soils appears to be more
limited than for bacteria or viruses. This
may be the result of the considerable
size differences between viruses, bacte-
ria, and parasites. For example, proto-
zoa are up to 20 times larger than bacte-
ria and up to 2,000 times larger than
enteroviruses. Ascaris eggs are even
larger. Clearly, mechanical straining
may be the most important factor gov-
erning the transport of these parasites.
Relatively few studies conducted at
sludge application sites have looked for
vertical transport of microorganisms.
Limited monitoring has shown no
demonstrable impact of sludge applica-
tion on fecal coliform levels in ground-
water. However, coliform bacteria have
been detected sporadically at shallow
depths of 100 and 180 cm beneath
sludge-amended sites in the northwest-
ern United States. In contrast, viruses
have been recovered from relatively
deep wells (8.5 and 18 m) at one sludge
disposal site in Florida, whereas the re-
sults of groundwater monitoring at a
second location in Florida were nega-
tive for viruses. Comparison of such re-
sults at operational field sites is often
impeded, however, by the fragmentary
nature of available data. Few studies
have conducted integrated, long-term
monitoring for viruses in which sludge,
sludge-amended soil, and groundwater
sampling were coordinated. Available
literature strongly favors the contention
that parasitic ova are retained at the
point of sludge introduction. Ground-
water monitoring for parasites has not
been conducted and seems unneces-
sary given the relative size of most para-
sitic forms and their observed retention
in the upper soil profiles.
Notwithstanding these limited field
data, laboratory studies have demon-
strated some transport of bacteria and
viruses through sludge-amended soils.
A single study has demonstrated move-
ment of Yersinia, fecal coliforms, and
fecal streptococci through 46 cm of soil,
although maximal levels represented
less than 0.1% of the bacteria present in
the sludge. Note that experimental con-
ditions in this study were chosen to rep-
resent a worst-case situation in which a
total of 46 cm of rainfall was applied
over a 3-week period.
Several laboratories have studied the
vertical movement of viruses in model
soil columns or cores. Studies in which
lysimeters or cores amended with
virally contaminated sludge have been
exposed to natural rainfall have con-
firmed results obtained by groundwater
monitoring at most sludge application
sites. Specifically, in two separate stud-
ies, very few viruses were detected in
soil water percolates intercepted at
depths of 54 and 125 cm. Under certain
laboratory test conditions, however,
viruses applied with sludges have been
transported through soil depths ranging
from 13 cm in one study to 46 cm in a
second study. When compared with the
movement of free viruses, sludge-
bound virions are much more effec-
tively retained, apparently within the
sludge-soil matrix at the point of appli-
cation.
Conclusions
1. The number of quantitative, com-
parable data describing pathogen
survival or transport in sludge-
amended soils are extremely small.
Survival data are available only for
Salmonella sp., selected enteric
viruses, and Ascaris ova, and studies
on pathogen transport are limited to
Yersinia sp. and certain viruses.
2. Where adequate quantitative data
exist, these observations can be
made:
• Inactivation of indicator bacteria
as described by median T90 values
was greater than that observed for
Salmonella.
• Viral inactivation appears to be
faster than Salmonella inactivation
near the soil surface. However, all
but one study used to estimate viral
die-off were conducted in rather
narrow temperature ranges, thus
-------
highlighting a potential bias in the
application of these values.
• Inactivation of parasites near the
soil surface is relatively slow, per-
haps as much as 5 times slower
than Salmonella inactivation and
more than 13 times slower than
virus inactivation.
3. Exceedingly long survival times
somtimes cited for Salmonella arise
from studies in which high levels of
added organisms (106 - 1010/L) were
present.
4. The only strong evidence for bacte-
rial regrowth in sludge-amended
soils is related to organisms of the
coliform indicator group.
5. Of the physical and meteorological
parameters considered, only temper-
ature could be correlated with mi-
croorganism survival.
6. Inadequate data exist to assess criti-
cally the vertical transport of patho-
gens from sludge-amended soils.
However, several general observa-
tions can be made:
• Data collected at all but one opera-
tional field site have not demon-
strated a deterioration of ground-
water quality related to sludge
application.
• Selected studies have documented
limited bacterial movement to
depths of 180 cm beneath sludge-
amended soil.
• Limited laboratory studies suggest
that viral retention is enhanced in
sludge-amended soils compared
with effluent-irrigated soils.
• The size of parasites appears to pre-
clude their vertical movement from
sludge-amended soils, but studies
designed to address this question
were not found.
7. Exceedingly few studies have ad-
dressed the issue of microorganisms
in runoff from sludge-amended soils.
However, there is a high probability
that uncontrolled runoff wil contain
pathogens as long as viable orga-
nisms are present in sludge-
amended soils.
8. Insufficient data are available for ad-
equate modelling of pathogen sur-
vival or transport in sludge-amended
soils. Not only are microbial results
limited, but prevailing environmen-
tal and soil conditions have not been
adequately documented in many
published reports.
Recommendations
The following specific recommenda-
tions are designed to obtain the data
required to formulate a more complete
understanding of the survival and/or
transport of pathogens in sludge-
amended soils:
1. Studies specifically designed to
develop such comprehensive data
should be conducted.
2. These studies should be restricted
to representative pathogens such
as Salmonella, selected human
enteric viruses, and parasites in-
digenous to municipal wastewater
sludges.
3. Though it would be desirable to
conduct such studies under field
conditions with indigenous orga-
nisms, this approach may be lim-
ited by the levels of pathogens in
sludges coupled with the relative
insensitivity of currently used de-
tection methods and the existence
of a wide variety of uncontrolled
environmental variables.
4. The use of selected seeded orga-
nisms in sludges under closely
controlled laboratory conditions
may be the most reasonable ap-
proach.
5. Laboratory experimentation must
be carefully designed to simulate a
range of temperature, moisture,
sludge loading conditions, and soil
types found nationwide.
The full report was submitted in fulfill-
ment of Cooperative Agreement No.
CR811918-01-0 by The University of
Texas under the sponsorship of the U.S.
Environmental Protection Agency.
Charles A. Sorber and Barbara E. Moore are with the University of Texas at
Austin, Austin. TX78712.
Albert D. Venosa is the EPA Project Officer (see below).
The complete report entitled "Survival and Transport of Pathogens in Sludge-
Amended Soil: A Critical Literature Review." (Order No. PB 87-180 337/
AS; Cost: $18.95, 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 Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-87/028
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