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-

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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.

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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

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            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

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    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
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POSTAGE & FEES PAID
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Penalty for Private Use $300
EPA/600/S2-87/028

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