SEPA
            United States
            Environmental Protection
            Agency
            Office of Research and
            Development
            Washington DC 20460
EPA/600/6-91/001
March 1991
Preliminary Risk
Assessment for
Parasites in Municipal
Sewage Sludge
Applied to Land

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                                                             EPA/600/6-91/001
                                                             March 1991
PRELIMINARY RISK ASSESSMENT FOR PARASITES
IN MUNICIPAL SEWAGE SLUDGE APPLIED TO LAND
        Environmental Criteria  and  Assessment  Office
        Office of Health and  Environmental  Assessment
        Office of Research and  Development           ,
        U. S. Environmental Protection  Agency
        Cincinnati, OH 45268
                                                 Printed on Recycled Paper

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                                   DISCLAIMER

      This document  has been reviewed in accordance with U.S. Environmental  Protection
Agency  policy and  approved for publication.   Mention  of trade  names,  or commercial
products does not constitute endorsement  or recommendation  for use.
                                          11

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                                      PREFACE

    . v Section ,405 of the Clean  Water  Act requires  the U.S. Environmental   Protection
Agency to develop and issue regulations  that identify:  (1) uses for sludge, including disposal;
(2) specific  factors  (including costs) to be taken into account in determining  the measures
and practices applicable for each  use or disposal; and  (3) concentrations  of pollutants  that
interfere with each use or  disposal.   To  comply  with  this mandate,  the U.S. EPA has
embarked on a program to develop  four  major technical  regulations:   land application,
including  distribution  and marketing; landfilling; incineration  and  surface disposal.   The
development of these technical regulations  requires a consideration of pathogens  as  well
as chemical constituents  of sludge.  Public concern related to the reuse and  disposal of
municipal sludge often  focuses  on the issue of pathogenic  organisms.  The purpose of this
report   is to  use,  the  pathogens   methodology,  Pathogen  Risk   Assessment  for Land
Application  of Municipal  Sludge,  to  develop  a .preliminary assessment  of risk to human
health  posed by parasites  in municipal  sewage sludge applied to land as fertilizer or soil
conditioner.  The preliminary risk assessment includes a description  of the most critical data
gaps that must be filled before development of a definitive risk assessment and recommends
research priorities.
                                          in

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                          DOCUMENT  DEVELOPMENT
Cynthia Sonich-Mullin, Project  Officer
Norman  E. Kowal, Technical Project Manager
Randall J.F. Bruins
Environmental  Criteria and Assessment Office
U.S. Environmental Protection  Agency
Cincinnati, OH

Authors

Charles T. Hadden
Marialice Wilson,  Project Manager
Science Applications International  Corporation
Oak Ridge, TN
Reviewers

Thomas T. Evans
Exposure Applications  Branch
Office of Research and Development
U.S. Environmental Protection' Agency
Washington, D.C.

Walter Jakubowski
Frank  W. Schaefer, III
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Cincinnati,  OH

Milovan S. Beljin
Groundwater  Research Center
The University of Cincinnati
Cincinnati,  OH

Judith  Olsen, Editorial  Review
Environmental Criteria and Assessment Office
U.S. Environmental  Protection Agency
Cincinnati,  OH
                                        IV

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                          TABLE  OF CONTENTS


 1. EXECUTIVE SUMMARY	 .	          1

 2. INTRODUCTION	 ,	 ...   6

 3. LITERATURE  REVIEW OF PARASITES   ......................	.  12

      3.1.   SIGNIFICANCE OF INTESTINAL PARASITES  		  12

            3.1.1. Reproduction and Life Cycle . . . I	  14
            3.1.2. Transmission/Exposure  Routes   .	      15
            3.1.3. Occurrence  of Parasites in Sludge	  18
            3.1.4. Epidemiology	...'.'         18

      3.2.   SURVIVAL IN TREATMENT  PROCESSES AND DENSITY
            IN TREATED SLUDGE	   21

            3.2.1. Survival in Treatment Processes	   21
            3.2.2. Density of Parasites  in Treated  Sludge	!	',',',   27

      3.3.   VIABILITY AND'SURVIVABILITY  IN SOIL AND WATER  	".'  28

      3.4.   TRANSPORT	  .........   31

            3.4.1. Transport in Soil		   31
            3.4.2. Transport in Surface Runoff	      '  '   34
            3.4.2. transport by Wind  .	...:......]....... ]  ]'.'.'. .   35

4. PARAMETERS  FOR MODEL RUNS  	   37

      4.1.   RATIONALE FOR PARAMETER  SELECTION  	   37

      4.2.   PARAMETER  VALUES	.	   41

            4.2.1.  Main Program Parameters	 ...   41
            4.2.2.  Parameters for Subroutine  RISK 	        • • • •   ^
            4.2.3.  Subroutine GRDWTR	      	   44
            4.2.4.  Subroutine RAINS   		 '.  44

5. SITES  FOR MODEL RUNS	                46

      5.1.  SITE 1: ANDERSON COUNTY, TENNESSEE	   46

           5.1.1.  Description of Soil	     45
           5.1.2.  Narrative Climatological Summary	   45

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                 TABLE OF CONTENTS (continued)

      5.1.3. Temperature	   47
      5.1.4. Rainfall  	..,...,	 . . ^,  47
   '   5.1.5. Parameters  for Subroutine  RAINS	   48

5.2.   SITE 2: CHAVES COUNTY, NEW MEXICO  ..'..'		: . •   49

      5.2.1. Description of Soil	   49
      5.2.2. Narrative Climatological  Summary  .... . ../......	   49
      5.2.3. Temperature . . .-vv. . .= , . ij. ;,-•,•;•: •'.• • > • •''•:'-, • •  -;- • • ;	   ^9
      5.2.4. Rainfall  .	• •;•,•• .,...•...,...	   50
      5.2.5. Parameters  for Subroutine  RAINS	   50

5.3.   SITE 3: CLINTON COUNTY,' IOWA	   51

      5.3.1. Descriptipn of Soil  . ,	  . • ....... •  • • ซ • •  • • • • •   51
      5.3.2. Narrative Climatplogical .Summary  .  ., . . ... . ,..-	   51
      5.3.3. Temperature  	• • • •  • • "•':'• i-V'r'• •  v,.........  52
      5.3.4. Rainfall	.->.;>;:...;.''•  •,,;••:-•— • •'• ซ'.• •  52
      5.3.5. Parameters  for Subroutine RAINS	 .	• • •  52

5.4.   SITE 4: HIGHLANDS  COUNTY, FLORIDA  	-  53

      5.4.1. Description of Soil  ..... .-. . .*..;.  ... . .... ._../; :•'••• .......  53
      5.4.2. Narrative  Climatological Summary	 • •  • •  53
      5.4.3. Temperature	•: • • • • •••:•,•  54
      5.4'.4. Rainfall '.	.'	  54
      5.4.5. Parameters for Subroutine RAINS .  .... . . ..-• • • • • • • • • • • •••  •• •'54

5.5.  SITE 5: KERN COUNTY,  CALIFORNIA	  55

      5.5.1.  Description of Soil  	• •  55
      5.5.2.  Narrative CUmatological  Summary	  55
      5.5.3.  Temperature	  55
      5.5.4.  Rainfall  . . ;	  56
      5.5.5.  Parameters for Subroutine RAINS . . :	  56

 5.6.   SITE 6: YAKIMA COUNTY,  WASHINGTON   	  56

       5.6.1. Description of Soil	   56
       5.6.2. Narrative Climatological Summary	, . .	   57
       5.6.3. Temperature	'	   57
       5.6.4. Rainfall	.• •   57
       5.6.5. Parameters  for Subroutine RAINS	   58
                                  VI

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                   TABLE OF CONTENTS (continued)


6.  RESULTS	..............;........:	  59

     6.1.  SENSITIVITY TO VARIABLES	 .  59

     6,2.  EXPOSURE  COMPARTMENTS	'	  64

          6.2.1. ONSITE . .... ..... .	....;.... .-. . . . .- . .	     68
          6.2.2. FOOD CONSUMER (EATER)  ................         71
          6.2.3. SWIMMER		. . . .	.	  76

7.  CONCLUSIONS   			. .  go

     7.1.  SENSITIVITY ANALYSIS  	                      80
     7.2.  ONSITE EXPOSURES		 . . . .		  81
     7.3.  SEDIMENT TRANSPORT  AND SURFACE RUNOFF  ..           81
     1A.  OFFSITE EXPOSURES  .	                  82
     7.5.  WAITING PERIOD   	. .	  82

8.  RESEARCH NEEDS	  84

     8.1.  INFORMATION  NEEDS FOR PARASITES  	               84
     8.2.  MODEL DEVELOPMENT   	........	  86

9.  REFERENCES  .  . .			  89

APPENDIX. MODEL OVERVIEW  .............. . . . . . . . . .... . ......  A-l
                                vu

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                                LIST OF TABLES


No.                                    Title


2-1   Compartments Included in the Sludge Management Practices  ..........


2-2   Sludge Management  Practices and Descriptions in Land Application  Model


3-1   Computer Search Strategy	 1".	


3-2   Pathogens of Concern	


3-3   Concentration, Viability and Survivability of Parasites in Sludge   ........


4-1   Die-off Rates of Parasites  in Sludge	.,


6-1   Sensitivity Coefficients  of  Site-specific Variables	


6-2   Sensitivity to Parameters of Subroutine RAINS	•,


6-3   Probability of Infection Onsite		


6-4   Probability of Infection, Swimmer	


6-5   Maximum Probability of Infection, Site 1	


6-6   Maximum Probability of Infection, Practice  I	


6-7   Probability of Infection by Consumption of Contaminated  Crops   	


6-8   Maximum Probability of Infection of Food Consumer (Eater)    	
                                                                   i

6-9   Variation  of EATER Risk with Time  of Harvesting	


6-10  Probability of Infection by Exposure to Runoff Water (Swimmer)  	
Page


. "7"


   9


  13'


  16


  22


  39


  62


  65


  66


  67


  69


  70


  72


  73


  75


  78
                                        Vlll

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                              LIST OF FIGURES



No,                                  Title



6-1    Sensitivity Coefficient  of APRATE    .......



6-2    SWIMMER Exposure by Practice,  Site 1   . . .




6-3    SWIMMER Exposure by Site, Practice I
63



77



79
                                      IX

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                          LIST OF ABBREVIATIONS






D&M       Distribution  and marketing



dia         Diameter



g           Gram



ha          Hectare         ......             .



hr          Hour



m          Meter



MID        Minimum  infective dose



min         Minute



NOAA      National Oceanic  and Atmospheric Administration



PSRP       Processes  to significantly reduce pathogens



sec         Second



USD A      U.S. Department   of Agriculture

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                             1. EXECUTIVE  SUMMARY'
       This preliminary risk assessment  study focuses oh-the probability of -'human  infeetioii
from protozoa and helminths, usually referred  to as parasites, in municipal sludge applied
to land.  It is based on the  Pathogen Risk Assessment computer model and  methodology
described in Pathogen  Risk Assessment  for  Land Application of Municipal'''Sludge.
       This document  reports (1) the results  of a literature review designed to find the data
on parasites  required by the pathogens  methodology, and (2) the results, of numerous site-
specific computer simulations, running  the Pathogen Risk Assessment  Model with a wide
range of values for the parameters  required.  The parameters required  for parasites  are (1)
        •
density  of viable parasites  in treated sludge  destined  for land application;  (2) die-off rates
in soil, dry particulates, liquid aerosols, and  water; (3) dispersion in the environment,  i.e.,
transport  in water,  soil and air; and (4) minimum infective dose, which for parasites is
assumed to be MID = 1 since single eggs'of helminth's  and single  cysts of protozoa  havb
produced  infections in humans.  Of these parameters/''density is site-specific  and requires
a standard method for enumerating  parasites, die-off rate data are very limited, transport,
data are essentially  non-existent, and infective dose has been determined 'to  be MID = 1.
       Locations  selected   for  site-specific   application  of  the  model include Anderson
County, Tennessee;  Chaves County, New Mexico; Clinton County, Iowa; Highlands  County,
Florida; Kern County, California; and Yakima County, Washington.   The sites were chosen
to provide - diversity in  geographic  location, topography,  soil type,  rainfall  pattern and
temperature.
      .Parasites are of health  significance in land application  practices because  they tend
to become concentrated  in sludge during sewage treatment  processes and because  they can
remain  viable as  environmentally  stable protozoan cysts or helminth  ova for months  or
years under  favorable conditions.   Although epidemiological studies suggest little  risk to
human health from parasites in treated  municipal sludge  or wastewater  applied to land,
their  low minimum  infective dose and  persistence in soil mean  that  the issue cannot, be
dismissed.
       Density and  Viability of  parasites  in  sludge are  site-specific, based  on source  of
wastes, species of parasites  present, climate,  and efficacy of sludge treatment.  Densities of

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parasites have been reported  to be generally higher in sludges from southern  than  from
northern states.  However, accurate  risk assessment would require  site-specific  analysis of
density  levels by standard  methods  for enumerating  parasites  in sludges and  soil.  Parasite
densities reported in the literature  range from 100-2000 ova/kg dry wt in dried sludge and
0-30,000 cysts or ova/kg  in liquid  sludge; however, the values are highly dispersed  and
geometric  means are  in the  range of 200-2000  ova/kg dry wt.  According  to  EPA
regulations, composted sludge for distribution  and marketing  (D&M)  must have  no more
than  1  ovum/g or cyst/g volatile sludge solids.  Based on  the literature  ranges, values
                                *•                                 •         . • .   • -
suggested  for use in the Pathogen  Risk Assessment model are 5000 ova or cysts/kg  for
liquid sludge, 500 ova or cysts/kg for dried sludge and  1000 ova or cysts/kg for composted
(D&M) sludge. "The value used in the following risk assessment  was 5000 ova or cysts/kg
for all practices.
       During storage  under unfavorable conditions,  ova and  cysts may  become inactive
(non-infective) before they die.  Death may be followed by disintegration.   Although  some
of the studies  discussed include information  on infectivity, in many cases  only  viability of
eggs  and cysts was reported,  and some studies reported only occurrence,  not viability.
       Inactivation  of  parasites  appears  to  be most closely  tied  to temperature during
treatment  or  storage,  with higher  temperatures   contributing  to  increased  inactivation.
Temperatures  in the 45-55 ฐC range are likely to kill resistant parasites within a few hours.
Alternate  freezing and thawing reduce viability more rapidly and to a greater extent than
constant above-  or below-freezing temperatures.
       Field studies of parasite-contaminated   sludge applied to agricultural plots,  however,
have  not produced a direct statistical correlation  between  viable Ascaris ova concentration
and solar radiation,  relative humidity or soil temperatures.   In fact, no statistical correlation
was  found  between" parasite  egg  concentration   and chemical,  physical  or  biological
parameters.
       Data on die-off rates are very limited,  but a published  90% die-off time of 270 days
implies an exponential  rate of 10fr0'oool?4)/hour.  Published ranges for die-off are approximately
10WlOOOI)/hour  to  lO^'^Vhour at ambient  temperature.   Based  on these  ranges, suggested
values in the model  for die-off of ova and cysts are:

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       During  application/incorporation
              0 for Temp  < 20ฐC;
                    "  or 0.00041/hour for 20 .<_Temp < 40;
                    or 0.65/hour  for Temp J>_40;
       In moist soil
              0 for Temp  < 20 ฐC or for 8 hours  after irrigation;
              lO'"0-00023' or 0.000533/hour fpr 20 <.Temp  < 40;
              10<-o.ซ7> or o.7845/hour  for 40 _<_Temp ^.50;
              10(4)-12S) or 0.25/hour  for Temp  > 50;
       On crop surfaces
                    or 0.7845/hour  at all temperatures;
       In water
                     Qr o.000533/hour at all temperatures.
       Although detailed  data  on survival and transport of parasites  in soil are lacking, the
Pathogen  Risk  Assessment  Model appears  to  confirm the general  observations  in  the
literature  that parasites are persistent, justifying land-use restrictions.  Model runs implied
that restrictions  on the consumption  of below-ground  crops may be overly conservative.
       Model runs showed that within narrow limits, the probability  of human  infection by
parasites as a result of exposure to soil contaminated with sewage sludge is proportional  to
the concentration  of organisms in the sludge,  the amount of sludge applied and the amount
of contaminated  soil to which the individual is exposed, either by casual contact  or ingestion
of food grown in the  contaminated soil.  Many of the parameters of the model seemed  to
have little bearing on the probability of infection, apparently because they had  no effect on
the number  of  organisms to which  the human  receptor  was exposed  in  each exposure
compartment  or they exerted  their  effect after the  time of maximum .exposure.   The
probability of infection was sensitive to the rate of inactivation or die-off of the parasite ova
or cysts and  to the method of application.  According to the  model, human exposure  via
subsurface application of sewage  sludge would be unlikely because  it  is believed  that ova
or cysts cannot move significant distances through soil.
       The model  predicted that the most significant potential source of infection would be
exposure to runoff water and sediment  transported to an onsite pond after rainfall. Model
runs indicated that it would be prudent  to limit  access to runoff water and  sediment  from
a sludge-amended  field, either  by mulching to reduce runoff, ditching and diking to contain

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the runoff or restricting access  to any onsite ponds • receiving runoff.
       Various model runs predicted that it was unlikely that a significant number of ova
or cysts would be transported off-site either by droplet aerosols or wind-blown dusts. The
model also predicted that parasites  moving through  the  soil column into groundwatei*  was
unlikely.   Therefore, one can infer, based  on the model parameters  used, that  there  is
relatively little risk to human health from parasitic infection via inhalation  of contaminated
fugitive dust emissions  or ingestion of contaminated  groundwater.
       Using a benchmark probability of infection  of IxlO"4 as an indicator  of sufficient
protection of human health, a waiting period appeared to be unnecessary  for consumption
of aboveground  crops  contaminated  with 0.1 g soil/crop  unit.  A waiting period of  18
months appeared  to be adequate for below-ground  crops, whose  consumption  is currently
forbidden  for 5 years after sludge application.
       The current version of the Pathogen  Risk  Assessment Model does not address some
of the properties  of parasite survival in soil.  Mathematical  descriptions  of the die-off of
parasite  ova, cysts and oocysts as a function of temperature  and  moisture   are  not  yet
adequate to allow construction of algorithms for die-off rates. It may be appropriate  to add
a diurnal cycle to the model's temperature  algorithm. Other changes may be limited by the
constraint that the model should run on a personal computer.
       The following research  priorities  are recommended  to  allow  development  of a
definitive  risk assessment for parasites  in land-applied  sludge:
For Helminths:
              Standard  quantitative  methods  for examining  helminths  in sludge  and  soil
              samples;
              Data on  transport in water,  soil and aerosols;
              Die-off rates  in water, soil and aerosols;
              The relationship  of those decay rates to environmental conditions,  previous
              sludge treatment,  method  of sludge application and various  effects of crop
              cover.
For Protozoa:
              Quantitative methods  for examining protozoa  in sludge and soil samples;  and

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              Quantitative • data on occurrence  and  survivability of  protozoa  in  treated
     '         sludge.         j.  ;   .. .;•                                    ,.'   . .
If results  indicate that protozoa  survive in sludge, the following additional  research needs
become apriority:
              Data  on transport  in water,  soil and aerosols;
              Die-off rates  in water, soil and aerosols;
              The relationship  of those decay rates to environmental  conditions, previous
              sludge treatment,   method  of sludge application  and  various  effects of crop
              cover.

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                                2.  INTRODUCTION

      This preliminary  risk assessment study fqcuses^on the probability of human infection
from intestinal protozoa and helminths in municipal sludge applied to land. These two types
of microorganisms  are  usually grouped  under the heading  of "parasites" (Kowal, 1985).
S}udge,  a byproduct of sewage treatment,  is the mixture of solids and liquids remaining
after settling processes  remove solids from municipal or domestic  wastewater.  Secondary
and  tertiary  sludges contain  biomass resulting  from  microbial digestion  of the  sewage.
Being derived from human sanitary  wastes, sludge contains  microorganisms  that colonize
humans and  can cause  infection and "disease.                                           •
      This risk assessment is based on the Pathogen Risk Assessment computer model  arid
methodology described  in Pathogen   Risk Assessment  for Land Application  of Municipal
Sludge  (U.S. EPA, 1990b). The purpose of the  model is to determine the probability of
infection  of a  human  receptor  from pathogens  in the land-applied  sludge.  The model
consists  of  a series  of compartments  (Table  2-1). representing   discrete points  in  the
application  pathway.  The compartments  are the various locations, states or activities in
which sludge or sludge-associated  pathogens  exist; they vary to some  extent among practices.
Compartments  representing sources  of human exposure  are designated  with an asterisk in
Table  2-1.  In each compartment,  pathogens  increase,  decrease  or remain  the  same in
number  with time, as  specified by  "process functions" (growth, die-off or no population
changes) and "transfer functions" (movement between compartments).  Infection rather than
disease is used to measure risk in the methodology, since exposures to parasites  may  lead
to human infection that is asymptomatic  (Kowal, 1985).  The outputs produced by running
the  model  are numerical values for the  probability  of a  human  receptor  receiving an
exposure in 24 hours exceeding the  minimum infective dose (MID).  The MID is assumed
to  be one  since  single eggs of helminths  and  single cysts  of protozoa have produced
infections in humans  (Kowal,  1985).  The model will run until the day specified or until the
number of pathogens in each compartment  -decreases  to  < 1 at which point the number  is
rounded  to zero.     .'••'.
       Two categories of land application are emplbyed' in the  methodology, (1) agricultural
utilization and (2) distribution  and marketing (D&M), and the source of parasites  is either

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                        TABLE 2-1




COMPARTMENTS INCLUDED IN THE SLUDGE MANAGEMENT PRACTICES
Compartment
Name and Number

Application
Incorporation
Application/Tilling .
Emissions ,
Soil Surface
Particulates ^
Surface Runoff
Direct Contact
Subsurface Soil
Groundwater '
Irrigation Water
Soil Surface Water
Offsite Well
Aerosols
Crop Surface ,
Harvesting
(Commercial) Crop
Animal Consumption
Meat
Manure
Milk
Hide
Udder
Liquid Sludge
Management Practices
•'. ;.-3i ;.".'•..;•. •/.,ซ....' ' .,;'••'•'.; '.-:Y.: .'• .
I II
,,1 - ... • -„.-. -1
..2;-... •;.-. 2_
3* "" 3*
4 „. ..( :> 4
5* . . 5*;,
.6* x .••.;...-. (^*
7f..'. ;:;-.^7*
8* '-- t • ~~- : * l- 1 ' Q'
. • . i, , . ,., ' •' Q- •
- 9 .-> :'*::-g--
• :- ' ',''••'•
'10 ' " " 10
11 •" 11
12* 12*
, 13*.'... ,,,,.^*
14 ... 14,
15 • -• •
, -16Vv--:;-,,v-
..->; ..••..•..^-•'i7
.- •.-'r.':.-^- jjjS-1
'19
20*
•_ >ih,..."'2lf.
22
III
....",. 1,
.-:.;., - 2,.,.. ., '
3*
4. '
;,::-. :S*.'-
-.- :....-.. 6* ,
•. ' '•• ••• 7* -. ,
:,;:,;,. r,8
'- o
i .'•-'- •.•=•.">'
	 11
12*
14
15

•'•>"-•• ':--n, :
:"': '" 18*
19
. 2Q*
'.'; ' '^i,-'-
22
Dried/Composted
Sludge Management
Practices
IV V
1 1

'*",-,","
3* ' 3* '
4 , , , 4 . -.
5* 5*

7* 7*
8 - -• -8

11 11

14 14
15
16*






*Indicates exposure compartment ,f ^ V ;,; ," ^f;: •
                            :7

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 liquid or dried/composted  municipal. sewage sludge.   The  five municipal  sewage-sludge
 management  practices (Table 2-2) included in the model, are application of liquid treated
 sludge (I)  for production of commercial  crops  for human  consumption,   (II)  to grazed
 pastures, and (HI) for production  of crops processed before  animal  consumption;  and
 application  of dried or composted sludge (TV) to residential  vegetable gardens  and (V) to
 residential  lawns.  Practices III and V, while ostensibly  limited to hay fields and residential
 lawns, respectively, can be modified by selection of appropriate parameters to represent
 sludge application on golf courses,  parks,  roadsides,  etc.  Although Practice  V does  not
 include  an  onsite pond,  the  risk to  SWIMMER  can be  modeled  by  using  appropriate
 parameters  in Practice III.                                          ,
       Risk assessment  for pathogens  in land-applied  municipal  sludges requires  the
 following input data:
              Types  of pathogens  and  their  concentrations  in the  sludge,  their
              survivabilities, and their infective doses (MID = 1  for   parasites);
              The sludge  reuse/disposal   option  used  and the conditions of sludge
              application  (quantities,  frequencies, application  method);
              The fate of the pathogens  in the  environment, i.e., the die-off rate
              under different conditions including moist soil, dry particulates, droplet
              aerosols  and water;  and
              The  level of exposure  of human  receptors to the applied sludge.
       This document  reports  (1) the results of a literature  review designed to find the data.
on  parasites  required  by the pathogens  methodology,  and  (2)  the  results of numerous
computer simulations, running the Pathogen Risk Assessment  Model with a wide range  of
values for the parameters  required.   Six sites,  chosen  to provide diversity in geographic
location, topography,  soil type,  rainfall pattern and  temperature,  were selected  for site--
specific  applications  of the model:  Anderson  County, Tennessee;   Chaves  County,  New
Mexico;  Clinton  County, Iowa; Highlands County, Florida; Kern County, California;  and
Yakima  County,  Washington.  Because of the unlimited number of possible sites, the final
selections were  somewhat arbitrary, being  based  on  an  attempt  to represent  different
geographic  regions and to ensure  a variety  of weather  patterns.
       Exposure  pathways, i.e.,migration routes of parasites from or  within the  application
                                           8

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                                 TABLE 2-2

        SLUDGE MANAGEMENT PRACTICES AND DESCRIPTIONS IN
                        LAND APPLICATION MODEL
PRACTICE
          DESCRIPTION
                  Application of Liquid Treated Sludge for Production of Commercial
                  Crops for Human Consumption
 II

 III


 IV


 V
Application of Liquid Treated Sludge to Grazed Pastures

Application of  Liquid Treated  Sludge  for  Production of  Crops
Processed before Animal Consumption

Application of Dried or Composted Sludge to Residential Vegetable
Gardens

Application of Dried or Composted Sludge to Residential Lawns
 Two types of sludge are used in this model - liquid and dried/composted. The extent of
 treatment or conditioning prior to application is variable and must be determined for each
 case.

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site to a receptor, for sludge applied  to land include the following:
              Inhalation ' and ingestion of emissions from application  of sludge or
              tilling of sludge/soil;
              Inhalation and ingestion  of windblown  or mechanically  generated
              particulates;
              Swimming in a pond fed by surface water runoff;
              Direct contact with sludge-contaminated soil or crops (including grass,
              vegetables, or forage crops);
              Drinking water from an off site well;
              Inhalation and  subsequent  ingestion of aerosols from irrigation;
              Consumption  of vegetables grown in sludge-amended  soil;
              Consumption  of meat  or  milk from  cattle  grazing  on or consuming
              forage from  sludge-amended  fields.
       This methodology  assumes  that  exposure to parasites will not result in infection
unless the  organisms are actually swallowed.  Risks due to inhalation of enteric  pathogens
will be considered only because  the organisms can be subsequently  swallowed. Disease can
result through routes  of exposure other than the alimentary tract;  calculations of exposure
by direct contact in the Pathogen Risk Assessment  methodology do not distinguish among
routes of-infection.
       The following human  receptors are the  exposed individuals whose probability  of
infection by parasites is calculated  by this model:
              Onsite person  (ONSITE) who is exposed  by ingestion (includes pica
              in children) or skin penetration  of parasites following direct contact
              with  soil, vegetables,  or  forage  or  by inhalation   and  subsequent
              ingestion  of aerosols  (particulates  or  liquid);
              Offsite person  (OFFSITE)  who is exposed to  particulate  or liquid
              aerosols  carried by wind;
       •       Food consumer (EATER)  who eats  vegetable  crops, meat or milk
              produced  on sludge-amended  soil;,
              Groundwater  drinker (DRINKER)   who consumes water from a well
              near but not on the sludge application site;
                                          10

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             Pond swimmer (SWIMMER)  whose skin is penetrated  by parasites  or who
             ingests, a small amount of water while swimming in the pond that receives the
             surface runoff from the application  site.
The model  conceptualization  (U.S. EPA,  1990b) specifies  that  workers engaged  in the
transportation,  handling and  application of liquid sludge are not  included as exposed
individuals because  such activity is an occupational  exposure.
       The  U.S.  EPA (1985, 1986) has  provided extensive  information  relevant  to the
conceptual risk assessment  framework  for land application of  sludge.  These key studies
address the pathogens associated with sewage sludge, as well as  exposure pathways and the
potential risks to humans  from each of the pathways. Most of that information will not be
repeated  here.  Additional  information  about  the  computer model  and methodology is
available  in  Volumes  I and II  of Pathogen 'Risk  Assessment for  Land  Application  of
Municipal Sludge (U.S. EPA, 1990b) and in Wilson et aL (1989); a  brief overview of the
model  is included as an Appendix.
                                          11

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                    3.  LITERATURE' REVIEW  OF PARASITES

       A literature  search was performed  to find the most current information available  for
the parameters  required by  the  model for simulating  land application  of sludge.  The
parameters  required  for parasites are  (1) density of viable parasites in treated  sludge
destined  for land application;  (2)  die-off rates  in soil, dry particulates,  liquid aerosols, and
water; (3) dispersion in the  environment,  i.e., transport  in air, soil  and water;  and  (4)
infective dose, which for parasites  is assumed  to be MID = 1.
       Appropriate codes and keyword truncation  were used  to produce the most effective
search strategy for each data base.  Table 3-1 lists the computerized  data bases queried and
the keywords used. The three columns of keywords were "anded" together to produce a set
in which  at least  one keyword in each column was a descriptor  or  was contained  in a
retrieved  record.            '                 ,,	  =    .-..	           V  v
       References   in review  articles  and  in  relevant 'articles retrieved  by  the computer
search were also evaluated, 'and names  of pertinent,'authors  were searched to find recent
                                                        " -v  - *' , •      "    . ''  '    '  "- -   " ''
papers that may not have been  incorporated  into online1 databases.        ."         ,   .
                                          ,'-".'   *• "     ''•",*-'; ซ"" ' -
3.1.   SIGNIFICANCE  OF INTESTINAL PARASITES    .'           ,
       The protozoan   pathogens  cause  a  variety  of  symptoms  by  colonizing   the
gastrointestinal  tract.    Protozoan diseases  may be  debilitating  but  are - rarely  fatal -in
developed  countries.   Protozoa are  present  in sewage and..sludge as cysts and  oocysts,
dormant  structures resistant to  adverse 'environmental  conditions  (U.S. EPA, 1990b).
       The pathogenic   helminths  include  a  variety  of .worms,  some of which are only
incidental parasites of humans.  Among  them  are  pinworms, roundworms, whipworms, and
a variety  of tapeworms.   The larval  stages of helminths  often  migrate  through  the  body
before maturing in the gut and can cause serious  tissue and organ damage.   Adult forms
primarily  cause malnutrition and  anemia while residing in the gut.  Helminths  are present
in sewage and  sludge as ova.  More complete  data  on pathogenic  helminths  and protozoa
are discussed  in Kowal  (1985) and U.S. EPA  (1985,  1986).
                                           12

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                                 TABLE 3-1

                        COMPUTER SEARCH STRATEGY
     DATA BASES
                  KEYWORD  GROUPS
AGRICOLA
AGRIS
BIOSIS
CAB ABSTRACTS
CRIS/USDA
ENVIROLINE
FSTA
NTIS
POLLUTION ABSTRACTS
TOXLINE
WATER RESOURCES ABS
ZOOLOGICAL  RECORD
PARASITE.       , .  :
HELMINTH/HELMINTHES
ROUNDWORM
HOOKWORM
TAPEWORM
CESTODE/CESTODA
NEMATODE/NEMATODA
GIARDIA
CRYPTOSPORIDIUM
PROTOZOA
TAENIA
ASCARIS
ENTAMOEBA/ENTAMEBA
AMEBA/AMOEBA
ACANTHAMOEBA/
ACANTHAMEBA
SURVIVAL
DISPOSAL
TRANSPORT
FATE
VIABILITY/
VIABLE
LIFE CYCLE
MOVEMENT
DIE-OFF
SEWAGE
SOIL-'
AIR
AEROSOL
WATER
SLUDGE
                                   '  13

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3.1.1. Reproduction  and Life Cycle.  Protozoa typically reproduce asexually, by fission, but
many also have sexual cycles in which they 'form zygotes, which mature to cysts or oocysts
(Daly, 1983b).  Trophozoites  are the  active stage  of flagellate  protozoans  in the intestines
of infected  individuals, whereas sporozoites are the active stage for coccidians.  Following
a period of reproduction,  the  trophozoites  or sporozoites can become  precysts, capable .of
secreting a  tough membrane .to protect the parasite (Kowal, 1985). It is these thick-walled,
environmentally resistant,  dormant  structures  that are excreted in the feces and are found
in sewage and sludge.  These  forms are capable of causing human  infection.
       Helminths  are parasitic  worms  that typically reproduce  in  the gut: and generally
require more than  one host to complete their life cycle. They may  have simple life cycles
in which humans become  infected  by ova or  larvae produced  by the worms.  Or,  the life
cycle may be more  complex, requiring several  hosts before reaching humans. Typically, the
adult tapeworm lives in the gut of the definitive (final) host and sheds fertilized ova, either
free or contained  in proglottids,. in the  feces.   Helminth ova are  the resistant  stage found
in sludge.  The ova are eaten  by the intermediate  host and develop  into larvae, which may
form cysts within the tissues of the intermediate .host.  The definitive  host species ingests
the infected tissue, and the larva develops into an adult  in the  gut  of this host.  An example
of this life  cycle is the beef  tapeworm,  Taenia saginata.  found  in the small intestine  of
humans. It is obtained  through eating poorly cooked beef. The adult tapeworm  can attain
lengths of  ~5 m,  containing  as many  as 2000 proglottids that  pass  eggs as they move
through the lower  gastrointestinal  tract.  These ova must  be eaten  by herbivores  such as
cattle  to allow  further  development.    The larva  released from the  egg penetrates  the
intestine and  form a cysticercus  in the striated muscle.  When ingested  by humans,  the
cysticercus transforms  into a mature tapeworm (Daly, 1983a).  Rarely, humans have been
known to be infected by Taenia ova (Beaver  et al., 1984).
       Other important parasitic  helminths are tissue roundworms that can .cause  visceral
larval migrans or cutaneous larval migrans in  humans.  Larvae of the dog and cat  ascarids
Toxocara  canis and Toxocara  cati can produce visceral larval migrans  as they  migrate
through  human tissues, producing inflammatory  reactions  in organs  such  as the liver
(hepatomegaly)  and lungs  (pneumonitis).  Serious  irreversible  damage is possible if critical
areas such as the nervous system are affected.   The life cycle of these nematodes is similar
                                           14

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 to that  of human  Ascaris lumbricoides.  with the source of infection being  ingested soil
 containing  embryonated  ova.   Children  suffering  from  pica,  an abnormal  soil-eating
 behavior,  are  more  likely than  adults to acquire this  infection.  However, for Toxocara.
 humans are  abnormal  hosts in whom the life cycle cannot  be completed  (Daly,  1983a).
        Cutaneous  larval migrans  is a skin inflammation  most  commonly  caused by the
 hookworm Ancylostoma braziliense.  The filariform larvae penetrate the skin  and produce
 lesions  within the skin.  As  they  travel around  under  the  skin, the larvae produce  an
 irritative pruritis that leads to scratching and can result  in secondary  bacterial  infections.
 As is the case with Toxocara.  the larvae cannot complete their life cycle in a  human  host.
 Other dog hookworms  and some other nematodes can also  cause cutaneous  larval migrans
 (Daly,  1983a).                        .
 3.1.2. Transmission/Exposure   Routes.  Transmission  of parasitic infections  is usually by
 one of the following routes:  ingestion of contaminated  food or water, direct  contact with
 the parasite  form in feces, soil or water, or consumption of the undercooked  flesh of the
 host. The modes of transmission for those parasites  of concern in sewage  sludge are listed
 in Table 3-2.                       ' "                    •
       Toxoplasma  infections  are  transmitted  by  direct contact  with  cat  feces or  by
 ingestion of undercooked  meat containing  the oocyst, but the'most  hazardous  route is
 transplacental.   While typically asymptomatic  for  most infected individuals,  toxoplasmosis
 during pregnancy can seriously harm  the fetus (Hershey and  McGregor,  1987).
       The transmission  potential  for Crvptosporidium. a coccidian protozoan,  is as yet
 unknown, although  it has been the cause of several outbreaks  of waterborne' illness (Rose,
 1988; Crawford and  Vermund,  1988; Hayes  et al., 1989).   Features  of the pathogen's
 taxonomy and life cycle contribute  to  the likelihood for waterborne transmission (Current,
 1987).  Cryptosporidium  may be the cause of  much of the diarrheal  illness in  humans and
other mammals  worldwide. Infected individuals  excrete "an environmentally  stable oocyst"
in feces, and evidence of significant cross-transmission  among mammals  (wild and domestic
animals and humans) suggests the organism is ubiquitous in the environment  (Payer and
Ungar,  1986; Current, 1987; Rose, 1988).
     • Data are as yet  insufficient  to determine  the  significance of Crvptosporidium in
municipal sewage sludge destined for  land application.  However, Kayed and Rose (1987)
                                          15

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       TABLE 3-2




PATHOGENS OF CONCERN
,

Pathogen
HELMINTHS -
Ancvlostoma
duodenals
Ancyclostoma
braziliense
Ancvlostoma
caninum
Ascaris
lumbricoides

Ascaris
suum

Enterobius
vermicularis
Necator
americanus
Strongyloides
stercoralis
Toxocara canis

Toxocara cat!

Common
Name or
Class
Nematoda
Hookworm

Cat
hookworm
' Dog
hookworm
Roundworm


Swine
roundworm

Pinworm

Hookworm

Threadworm

Dog
roundworm
Cat
roundworm
Trichuris trichiura Whipwonn

HELMINTHS -
Echinococcus
granulosus
Echinococcus
multilocularis
Hvmenolepis
nana


Cestoda
Dog
tapeworm
Tapeworm

Dwarf
tapeworm


Nonhuman
Disease Reservoir
. . ,L , ,,. , „„., , . ... .lt 	 , 	 ,
Hookworm disease

Cutaneous cat, dog*
larva migrans
Cutaneous dog*
. larva migrans
Ascariasis

, ~ ^ - -
Ascariasis pig*
.. .. . .. •-.

Enterobiasis

Necatoriasis

Strongyloi- dog
diasis
Visceral dog*
larva migrans
Visceral cat* ...
larva migrans
Trichuriasis


Unilocular dog*
hydatid disease ,
Alveolar dog, fox
hydatid disease
Taeniasis rat,
mouse

Human
Infective
Stage
.,„ „,„ . 	 , , „ , „, ,,,,,„ , , „„
free-living
larva
free-living
larva
free-living
larva
embryonated
ovum

embryonated
ovum

ovum

embryonated
ovum
free-living
larva
embryonated
ovum
embryonated
ovum
ovum


ovum

ovum

ovum
(auto-
possible)

Mode of
Transmission.
. ,, = , • n , * i 	
skin penetration,
soil contact
skin penetration,
soil contact
skin penetration,
soil contact
ingestion of •
water, food,
soil
ingestion of
water, food,
soil
ingestion of ova

skin penetration,
soil contact
skin penetration,
soil contact
ingestion of
water, food, soil
ingestion of
water, food, soil
ingestion of
food

ingestion of
water, food
ingestion of
water, food
ingestion of
water, food

          16

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                                           TABLE  3-2

                         	 PATHOGENS: OF CONCERN (continued)


Pathogen


• Taenia saginata

Taenia solium

PROTOZOA.
Balantidium coir
Crvptosporidium
parvum
Dientamoeba
fragilis
Entamoeba
histolytica -"':••
Giardia lamblia
. Isospora, belli
Isospora hominis

Toxonlasma
gondii
Common
Name or-
Glass


Beef1 '
tapeworm

Pork
tapeworm
..-.', ' „ •:

Ciliate
(dysentery)
Sporozoan
(Coccidia)
Amoeba
Amoeba
* .•.' r
Flagellate
Sporozoan ,
(Coccidia)
' Sporozoan
(Coccidia)
Sporozoan
(Coccidia)

Nonhuman
Disease Reservoir


Taeniasis .-

Taeniasis,
cysticerosis


Balantidiasis pigs, other
mammals
Cryptosporidiosis cattle
Amebiasis
Amebiasis
(amebic \
dysentery)
Giardiasis mammals
	 	 .-..-. - ป --- dog, .
dog
Toxoplasmosis -cat
Human
Infective
Stage


ovum, as well
as larva in or
from inter-
mediate host
ovum,larva
in or from
intermediate
host

cyst
oocyst
unknown
cyst
cyst
oocyst
oocyst
oocyst •

Mode of
Transmission


ingestion of
water, food

ingestion of
water,- food


ingestion of
water, food
contact,
ingestion of
water, food
ingestion of
water, food
ingestion of
water, food
contact, '
ingestion of
water, food
ingestion of
water, food
ingestion of
water, food
ingestion of
water, food
Source:  Kowal, 1985; U.S. EPA, 1988; Sorber and Moore, 1986
* Definitive host; humans only incidentally infested
                                              .17

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reported Cryptosporidium oocyst concentrations  in anaerobically  digested  sludges ranging
from  1250-38,700/g  dry wt.  Madore  efal. (1987)  found that  Cryptosporidium  oocyst
removal efficiency by sewage treatment,  using activated  sludge, approached  79%. Sewage
treatment  utilizing sand  filtration  in conjunction  with activated  sludge  resulted in lower
levels of oocysts (10/L) in finished effluent than  treatment  using activated sludge treatment
only (1300 oocysts/L), suggesting  that the filtered oocysts would be found in the  sludge.
The importance of Cryptosporidium  as a waterborne pathogen  and its similarity to Giardia
suggests further  studies  are needed  to  clarify its survivability in  water and  wastewater
treatment  processes.   There is some disagreement  over whether  Cryptosporidium  or
Giardia  duodenalis  is the' more- common intestinal  parasite  and  which has  the  greater
potential for causing waterborne  disease  (Rose,  1988; Sykora  et  al., 1990).
3.1..3.  Occurrence of Parasites in Sludge. Several literature reviews have included  surveys
of parasites present in sludge at different stages of treatment, and  most discuss the diseases
associated  with these  pathogen  populations  (WHO,  1981; Kowal,  1982, 1985;  U.S. EPA,
                           *                  .       .
1986).  Several reviews have summarized > information  on parasites in sludge  applied to
land:   Kowal (1985),  Sorber and  Moore (19'86)}' Pedersen  (1981),  Reimers et  al. (1981,
1986, 1990), Yanko (1988), and U.S. EPA  (1985).  Most of that information  will not be
repeated here, although conclusions derived in  these  reviews are included in the relevant
sections  of this document.
       Table 3-2 lists the protozoa  and helminths  most commonly found in sewage sludge
and wastewater  that are significant human pathogens.  For a descriptive summary of these
parasites, their life cycles, and the symptoms of infection  in humans,  see Kowal (1985).  His
review provides information on the occurrence and viability of pathogens  in sludge and in
the environment  following application.  Information  on their levels, survival, and behavior
in soil, groundwater, surface water, aerosols  and animals  is discussed; and available data on
infective dose, risk of infection and  epidemiology of these agents are  summarized.
3.1.4.  Epidemiology.   Epidemiological  studies have  suggested little risk to human health
from  parasites in municipal sludge or wastewater  applied to land.  The low. MID for
parasites, however, and the persistence  of some  parasites,  particularly helminths,  in soil
suggests that  all  questions  of public  health  risk have not been  answered  (Kowal  and
Pahren,  1982).
                                           18

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        Yanko  (1988) studied the occurrence  of pathogens  in  498 samples  of municipal
 composts, air-dried and heat-treated  sludge products, often referred  to  as distributed  and
 marketed  (D&M) sludge.  Products sampled  weekly for one year were from a windrow
 composting  facility  and from an aerated  static pile composting  facility.   Final  sludge
 products  from 24 other municipalities were sampled bimonthly  for a year.  No protozoan
 cysts were found in the  samples, and helminth  ova,' while regularly detected,  were not
 viable. Trichuris and Ascaris were the helminth ova most commonly found, and evidence
 suggests that many of the Trichurus  ova were from non-human, sources.  Hymenolepis  and
 Toxocara  ova  were detected infrequently.  No health hazards  from parasites  were found
 associated w'ith the treated  sludge products.             ,
       With respect  to  wastewater,  Clark et al. (1981)  reported results of a prospective
 seroepidemiological  study of municipal  wastewater  workers and  controls  in Memphis,
 Cincinnati, and Chicago.  They concluded that  wastewater workers were  not subject to "any
 detectable risks due  to parasites  in wastewater."
       Amebic infections have been linked epidemiologically with vegetables fertilized  with
 night soil or irrigated  with untreated  wastewater  (Bryan, 1977; Geldreich  and Bordner,
 1971).  When raw wastewater was used to irrigate fields on Israeli kibbutzim,  however, no
 excess of enteric  diseases  was found  (Shuval and Fattal,  1980).
       The occurrence  of giardiasis is common  and may be of epidemic proportions due to
 infection  acquired by ingesting Giardia cysts in public water supplies  or in surface water
 (Meyer and Radulescu,  1979).  The potential  for waterborne  disease transmission  of
 Crvptosporidium  may equal  or  exceed that of Giardia  (Rose,  1988; Current,  1987).   In
 addition,  its transmission  by the fecal-oral  route  from host  to  host  by means  of its
 environmentally stable  oocyst and its capacity for auto-infection makes its epidemiology  of
 extreme importance  (Rose,  1988; Current,  1987).
       Dorn et al. (1985) concluded that health  risks to humans and  animals on Ohio farms
receiving  yearly applications  of municipal sewage sludge were  not significantly different
from those on control farms. Sludge was applied at relatively low rates of 2-10 dry metric
tons/hectare(ha)/year   in accordance with U.S. EPA guidelines.  The authors  caution  that
higher application rates,  higher  concentrations, of disease  organisms  in the  sludge or
increases  in treated  acreage/farm  may produce different  health  risks.  In fact, Fertig  and
                                           19

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Dorn (1985)  summarized  an  epidemiological  investigation  of an  outbreak  of Taenia
saginata  cysticercosis on an  Ohio cattle farm, concluding that  it is likely that  the infection
of the seven slaughtered cattle was associated  with application  of municipal  sewage sludge.
       Wallis  et al. (1984) concluded  that health risks were no greater from sludged  fields
than from the control  hayfield and pasture receiving no sludge application.  They recorded
decreases in numbers  of parasite eggs from 11,000 eggs/kg  dry  wt in the initial sludge
applied to a grass plot to 7000 parasite eggs/kg dry wt after 7 days.  No eggs were found
at 43, 84 or 118 days following sludge application.  Sludge injected  into' the  soil showed
reductions  from the initial 11,000 eggs/kg dry wt to almost none  within 4  weeks. Storey
and  Phillips (1985),  however,  found  that Taenia  saginata and Ascaris lumbricoides ova
could be washed  into the soil where they were  afforded  protection  from radiation and
desiccation, increasing survival with increasing  depth  in the soil profile.
       In Europe, researchers have concluded that the chief hazards  of sludge application
for agriculture are from Salmonella  spp.  and  from the ova of Taenia  saginata  and Ascaris
spp. (Block et al., 1986).  Matching the degree of pathogen reduction with restrictions  on
use of the sludged land is the method  used to eliminate risks.  Since the use of disinfected
sludge has the fewest  restrictions, pasteurization of sludge at 70 ฐC for 30 minutes  has been
developed  in Switzerland  (where it is now required) and in Germany to protect  cattle from
salmoneUosis  (Pike et al., 1988).
       Burger  (1984)  reviewed the prevalence of Taenia saginata  in humans  in Europe;  it
ranged from  a low of 0.013% in an unselected  population  in Poland  to  8.04% in clinic
patients  in Turkey.  The  prevalence of cysticercosis (the larval stage)  in  cattle ranged'from
0.13% in Cuba to 4.2% in Sudan. Insufficient data on infectivity of T. saginata eggs allow
only a recommendation  to prohibit grazing by cattle for at least 4 months following spring
application  of sludge  to pastures and longer  during cooler seasons in a moderate  climate.
                                           20

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  3.2.   SURVIVAL  IN TREATMENT  PROCESSES  AND DENSITY  IN  TREATED
  SLUDGE                                                                          ,
        The density of parasites  in municipal sludge (Table  3-3) is site-specific, being related
  to the population  served by the sewage treatment  system,  i.e.,source of the wastes, species
 , of parasites  present,  geographic area, and  season or  climate.   Density  and^ viability of
  parasite  species are  also dependent  on the type of sludge treatment.   Primary sludge has
 .received primary treatment  such as screening  and  settling;  secondary sludge is produced' by
  biological waste treatment,  or secondary  treatment;  primary  and  secondary  sludge are
  combined  to produce mixed sludge  (U.S. EPA, 1985).  Studies of municipal sludges  from
  southern  states  showed that 99%  of primary sludges  and  89% of final  sludges contained
  large numbers of viable parasite cysts and ova (Reimers  et al., 1981; Leftwich :et ,al.r!981).
  3.2.1. Survival in Treatment Processes.  Ward et al. (1984) summarized the reductions: of
 parasites  in various processes  to significantly  reduce pathogens  (PSRP) expressed as  Iog10:
,  mesophilic anaerobic ,digestion, 0.5; aerobic digestion, 0.5; composting, 2-4; air drying, 0.5-
  4; and lime stabilization,; 0.5.          ;    :  ,     .        ,                     , ,.-.
        Pedersen  (1981)    reviewed  the  literature   concerning  parasites   in  municipal
 wastewater  sludge and concluded   that digestion  does  not .effectively reduce  levels of
 parasites  in sludge, but that sludge lagooning-.could produce  a 1-log reduction  of parasitic
 ova if carried out for > 6 months  at  temperatures  > 20ฐ Cor for 3 years at temperatures
  <20ฐC.      --••.,   .  -                     ,  .     •   -           .....      :  •
  ....   •  Reimers  et al.  (1990)  found  that Ascaris  suum eggs in  lagoon-stored  sludge in
 Louisiana and Texas were inactivated after  15 months. ,  Die-off of Ascaris in municipal
 sludge appeared  to be a function of temperature  except in  petroleum-contaminated   sludge.
        Information  on  survivability of Giardia and  Crvptosporidium  in treated  sludge is
 .lacking, but-waterborne  outbreaks  of cryptosporidiosis  are possible when Crvptosporidium
 oocysts, resistant to routinely-used  disinfectants,  escape filtration (Payer  and Ungar, 1986;
 Current,  1987).  A survey of one drinking water treatment  plant  found that  a large number
 of oocysts were recovered off the filter, indicating concentration  of oocysts by filtration  and
 reduction   in  finished  water  of  as much  as 91%  (Rose,  1988).    An  outbreak  of
 cryptosporidiosis in Carrollton,  GA was linked to  oocysts in drinking water that had been
 through the disinfection  process (Hayes et al., 1989).
                                          .'21

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                                           TABLE 3-3

                     CONCENTRATION,  VIABILITY, AND SURVIVABILITY
                                  OF PARASITES IN SLUDGE	
  Pathogen
 Density in
  Treated
  Sludge
(Mean ova/
 kg dry wt)
Viability
Survivability
                                                                                Reference
HELMINTHS -Nematoda
Ancvlostoma duodenale

Ancvlostorna
  braziliense

Ancvlostoma
     jnur

 iscaris
  lumbricoides
Ascaris
suum
                         11,000
                         (digested,
                         lagooned);
                         100-2000
                         D&M
  (Ascaris spp.)
  9600 southern
  states; 2030
  Chicago; 565
  northern'
  states, in
  of final
  sludges;
  geometric
  mean of 1360
  in secondary
  sludges
   69%

   64%,
                                                           15 years
                                                       Wallis, 1984


                                                       Yanko, 1988
                    Reimers et
                    al., 1981;
                    Kowal, 1985;

                    Arther et al.,
                    1981; Reimers
                    et al., 1986
 Enterobius
  vermicularis

 Necator
  americanus

 Strongvloides
  stercoralis
                                              22

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                                             TABLE 3-3

                       CONCENTRATION, VIABILITY,  AND SURVIVABILITY
                               OF PARASITES IN SLUDGE  (continued)
   Pathogen
   Density in
    Treated
    Sludge
  (Mean ova/
   kg dry wt)
Viability
Survivability
                                                                                   Reference
 Toxocara canis
 Toxocara cati
 Trichuris trichiura
 (Toxcocara
 spp.) 700
 southern
 states; 1730
 Chicago; 370
 northern
 states, in
 of final
 sludges;
 geometric
 mean of 280
 in secondary
 sludges

 265 northern
 states, in 22%
 of final
 sludges; max
 of 7700 and
 geometric
mean of < 10
hi secondary
sludges
HELMINTHS - Cestoda
Echinococcus
  granulosus

Echinococcus
  multilocularis

Hvmenolepis
  nana
                                                   52%


                                                   53%


                                                   55%
                                                             6 years
                                                             (in soil)
                                   Reimers  et
                                   al., 1981;

                                   Arther et al.,
                                   1981; Reimers
                                   et al., 1986
                                  Seattle Metro, '
                                  1983;
                                  Reimers et al.,
                                  1981,1986
                                                 23

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                                             TABLE  3-3

                      CONCENTRATION,  VIABILITY, AND SURVIVABILITY
                              OF PARASITES  IN SLUDGE  (continued)
  Pathogen
  Density in
   Treated
   Sludge
(Mean cysts/
  kg dry wt)
Viability
Survivability
                                                                                   B.eference
PROTOZOA
Bnlantidium
  cpli

Crvptosporidium
  narvum
Dientamoeba
  fragilis

Entamoeba
  histolvtica
None detected
in D&M  sludge
1250-38,700
oocysts/g dry vyt
in anaerobically
digested sludge;
range of 140-4000
oocysts/L in
treated sewage
effluence (activated
sludge)
                        70-30,000
                        cysts/L; max
                        44 cysts/L in
                        treatment
                        plant effluent;
                        avg concn
                        387-1723
                        cysts/L in
                        liquid sludge
               Max: 10- days (on
               (on soil);
               common max:
               2 days (soil)
               > 140 days in
               water (laboratory
               study)
                     Yanko, 1988;
                     Kowal, 1985
                                      18-24 hours
                                      (dry soil);
                                      42-72 hours
                                      (moist soil);
                                      8-10 days
                                      (damp loam
                                     ,  and sand);
                                      153 days
                                      (water)

                                      1 year in
                                      liquefied feces
                                      stored at 4ฐC;
                                      < 24 hours (air-
                                      dried at 4ฐC or
                                      21 ฐC);  <24hours
                                      (artificial sea
                                      water at 4 ฐ C)
                     Kayed and Rose, 1987;
                     Current,  1987;
                     Madore et al., 1987
                                    Rudolfs et
                                    al.,, 1951;
                                    Beaver and
                                    Deschamps,
                                    1949;
                                    Mitchell,
                                    1972
                                    Sykora, 1990;
                                    Craft, 1982;
                                    Jarroll et al.,
                                    1984
     ara
  hominis

Toxoplasma
  gondii
                                      (Tbxoplasma
                                      spp.)
                                      334-410 days
                                    Frenkel et
                                    al., 1975
Source:  Jakubowski, 1990; Kowal, 1985; U.S. EPA, 1988;Sorber and Moore, 1986
                                                   24

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        Sykora et al. (1990) determined the occurrence  of Giardia cysts following wastewater
 treatment  in eleven cities across the  United  States.  Occurrence in sludges, determined  by
 direct count (centrifugation), ranged  from 70-30,000 cysts/L.  Giardia cysts were present in
 all raw sewage samples, but only half the wastewater treatment plant effluents contained
 cysts, with maximum  counts of 44 cysts/L.  Higher cyst concentrations  in raw wastewater
 during the colder months may be due to factors such as  higher rates  of infection, increased
 survival of cysts and lower settling rates  at lower temperatures  (Jakubowski  et al., 1990).
 McHarry (1984) detected  Giardia  in effluent from sewage treatment  plants in Illinois to be
 ~1 cyst/L.  Giardia  cysts were found  to be infective to rats  after one  year's storage in
 liquefied  feces at 4ฐC (Craft, 1982).
        Schwartzbrod  et  al.  (1989)  compared  the  effects of  wastewater  treatments  on
 helminth  eggs; activated  sludge, lagoon treatment and sand filtration reduced  the level of
 helminth  eggs by 77.7%, 100%  and 98.8%, respectively,  in the final effluent destined  to be
 used for crop irrigation. This finding confirms the typical results: concentration  of parasites
 in  sludge and relatively low density or  absence in wastewater  effluent.  However,  the
 authors note  that the contaminated  sludge poses a problem.  In addition,  they point  out
 that they did not determine the viability  and infectivity  of the eggs.
       Leftwich et  al. (1981)  evaluated  domestic  wastewater  treatment  processes  with
 respect to  their  ability  to  inactivate  parasites.    They  considered removal processes,
 stabilization  processes, and decontamination  or inactivation processes.  In general, aerobic
 and anaerobic processes are lethal to parasite  eggs if carried  out at  >55ฐC. Likewise,
 composting  is effective for inactivating eggs if all matter  reaches  60 ฐC for at least 2 hours.
 Drying beds  are  most effective  if moisture is reduced  to <5%.
       Pike and associates  (1988)  determined that  complete  destruction  of viable Ascaris
 ova was possible only by digestion at 49ฐC or by heating  for 15 minutes at 55ฐC. Recovery
 of viable ova from  anaerobically digested  sludge was significantly affected by temperature
 of digestion-63%  at 35 ฐC but only 0.6%  at 49ฐCปbut not by retention period. Digestion
 alone reduced viability of the recovered  ova only slightly. Heating alone  also had  little
effect at temperatures  below 51 ฐC for 1 hour, but heating to 55 ฐC for 15 minutes resulted
in no viable ova being recovered.  When heat treatment  reduced viability  of Ascaris  suum
incompletely,  subsequent  digestion at 35,ฐC further reduced  viability.
                                          25

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       The results of Pike et al. (1988) closely parallel those of Arther et  al. (1981), who
found  that  ova  of four genera  of parasites  survived anaerobic  sludge  digestion and
                                t
lagooning by a  Chicago sanitary  district  treatment  plant:  Ascaris spp.,  Toxocara  spp.,
Toxascaris leonina  and Trichuris  spp. (see  Table 3-3). , Viabilities  following  treatment
ranged from 20-64%.
       Black et al. (1982) studied the  effects of mesothermic anaerobic or aerobic sludge
digestion on survivability and viability, of eggs from Ascaris suum. Toxocara  cam's. Trichuris
yulpis, Trichuris  suis and Hymenolepis diminuta.  Anaerobic digestion destroyed  23 % of
Ascaris eggs, and the  aerobic  digestion destruction  was  38%.  Trichuris  'eggs were not
destroyed by anaerobic  digestion, but  11 %  of the eggs were destroyed by aerobic digestion.
Toxocara eggs were destroyed by  neither  method.   The viability of those  Ascaris and
Toxocara eggs surviving digestion  was not affected,  but aerobic digestion  decreased the
viabilities of Trichuris  eggs.
       Mbela et  al.  (1990) assessed temperature  effects on Ascaris ova viability following
aerobic  and  anaerobic digestion  of  municipal  sludges.    Both  aerobic  and  anaerobic
digestion processes fail to inactivate Ascaris eggs in the 25-35 ฐC temperature  range (Reyes
et al, 1963; Reimers et al.,  1987).  They concluded  that high temperature  is a  significant
factor in the inactivation of pathogens.  Increasing detention  times from 10 to 31  days while
maintaining  constant  temperature   increased  Ascaris  inactivation  from 7% to  16%  by
anaerobic digestion.  Aerobic digestion at 35 ฐC and 45 ฐC, with a 10-day detention  period,
decreased  viability  by  57%  and 82%, respectively.  Temperatures  of 45-55 ฐC achieved
complete inactivation   of Ascaris ova  within two days.  Liming and caustic  stabilization
increased inactivation;  temperatures  > 35 ฐC for sludge digestion coupled with  < 1000 mg
lime/g sludge solids completely destroyed  Ascaris eggs.
       O'Donnell et al.  (1984) performed  controlled  laboratory  studies  of lagooning of
sludge.  Results  indicated  that viability and infectivity of  eggs were  related  to  storage
temperature,   with eggs stored at a higher  temperature  (25 ฐC) becoming nbnviable in 10-
16 months whereas  those eggs held at 4ฐC were viable and infective at 25 months.
       Storey (1987) also concluded that temperature  was the major controlling factor in
the survival of Taenia  saginata eggs during. simulated  sewage treatment processes.  Eggs
survived treatment  at  55 ฐC  for only a few hours, and eggs treated at 35 ฐC were killed
                                           26

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 faster than those at 20ฐ C.                                    -    ;'                .
 3.2.2.  Density of Parasites in Treated Sludge.  Since densities of parasites  in sludge vary
 by source and treatment method, there is no true  representative  parasite  concentration  for
 any given PSRP treatment or source of sludge destined for land application.   For the most
 accurate  risk assessment, parasite density should be tested  by a standard method for a-given.
 source  of. sludge,  i.e., a  given treatment  plant  and  treatment   method.   Reimers and
 associates (1990) and Little et al. (1988) have developed methods for enumerating  parasites
 in  sludges  and  soil, but widely-accepted  standard  methods  would  make comparisons  of
 results  across studies more meaningful.   .
        Densities  of helminth  ova in positive  samples of distributed  and  marketed  sludge
 ranged  from  0.1-2 ova/g dry wt (100-2000 ova/kg dry wt) (Yanko, 1988).
        Pedersen (1981) critically reviewed the original literature detailing  quantitatively the
 density levels of pathogenic  organisms in municipal wastewater  sludge and septage.  He
 evaluated  conventional  municipal  sludge stabilization and dewatering  processes  for their
 effectiveness  in reducing those density levels.  U.S. EPA  (1985), summarizing the results of
 Pedersen  (1981), warns of several qualifications  relative to data quality: laboratory studies
 may  not  adequately  mimic operations   at  full-scale treatment  plants;  seeded  pathogen
 behavior  may not represent that of naturally occurring  organisms; operating  conditions
 during  data  collection   and pathogen  numbers  reported  are uncertain;   and  there  is
 inconsistency  relative to die-off rates during sludge  stabilization.
       Reimers et al. (1981, 1986, 1990)  investigated parasite  density in southern sludges,
 northern  sludges, and lagooned  sludges,  respectively, and  the  effectiveness  of disinfection
 techniques  on their inactivation.  Levels of viable helminth  ova were typically somewhat
 lower in  northern  sludges  than  in southern  sludges  for some  species,  and densities  of T.
 trichiura  varied Inversely with population  size served by the  treatment  facility (Reimers  et
 al., 1981, 1986).                                                   ...
       Reimers  and  associates  (1986)  conducted   a  study  of  parasites   in  municipal
 wastewater  sludges  from treatment  plants in four  northern  states.   In  approximately  90%
of the sludge  samples,  they found resistant stages  of twenty  types  of parasites.  The  most
common were Ascaris spp..Trichuris trichiura. Trichuris vulpis and  Toxocara spp., with one
or more of these parasites detected in 89% of the samples examined.  The geometric mean
                                           27

-------
density of eggs was determined  for each of these four parasites in sludge samples  destined
for disposal:  565, 265, 270 and 370 eggs/kg dry wt, respectively  (see Table  3-3).  Ascaris
eggs occurred in  final sludges at higher densities than the eggs of the other three parasites.
Although  the authors gave no confidence  limits, they stated that  there  were no significant
differences between  geometric  mean  densities of total  eggs in aerobic  and anaerobic
sludges (3000 and 2150 for Ascaris. 460 and 600 for T. trichiura. 345 and 485 for T. yulpjs,
1410 and  1155 for Toxocara.  respectively). However, there were fewer viable Ascaris and
Toxocara  eggs in anaerobic  sludges (1720 and 740, respectively)  than in aerobic sludges
(4090 and 1320, respectively).  The authors  suggested  this effect may be a result of the
higher temperature  (35-40 ฐC) typical  of anaerobic  digestion  than the  typical ambient
temperature  of  aerobic digestion.   Viability  of these  four parasites   was determined  in
samples of undigested,  digester and postdigestion sludge and also for the total of all three
sludge types.  The ratio of geometric means  of  viable  eggs  to total eggs (viable arid
nonviable) in the total of all three sludge types is  710/1000 eggs/kg dry  wt of sludge for
Ascaris.  400/440 for Trichuris trichiura.  370/400  for  Trichuris  vulpis.  and  670/880 for
Toxocara (see Table 3-3). The ratio of viable to total eggs in all sludge- samples  from the
four northern  states is  1400/1900  eggs/kg dry wt of sludge for Ascaris. 200/380 for T.
trichiura.  260/290  for T. vulpis. and  1100/1400 for Toxocara  (see Table  3-3).  A similar
comparison  of sludge  samples  from five southern  states  showed  a  significantly higher
density of all parasites  except Toxocara. with ratios of geometric  means  of viable to total
eggs of 2500/2800  eggs/kg  dry wt of sludge for Ascaris. 880/910  for T. trichiura. 430/470
for T. vulpis. and 680/790 for Toxocara.
       Sykora et al. (1990) determined  the density of  Giardia cysts following wastewater
treatment  in eleven cities and  found the  highest average  concentration  (1723 cysts/L, or
 ~ 1723 cysts/kg wet wt) was from Pennsylvania samples of sludge that  were  dewatered but
not digested; the lowest average concentration was 387 cysts/L (or  -387 cysts/kg wet wt)
in samples from  the Illinois plant.  Giardia cysts were detected in the wastewater treatment
plant effluents, with maximum counts of  44 cysts/L.

3.3.   VIABILITY AND SURVTVAfflLITY  IN SOIL AND WATER
       Microorganisms are inactivated in soil at rates that vary with the  type of organism,
                                           28

-------
  the degree of predation  by other microorganisms,  the  amount  of sunlight, and the physical
  and  chemical composition  of the  soil, including  moisture content,  pH and  temperature'
  (Gerba  et al., 1975; Kowal, 1985).  Moist, cold soils contribute  to increased survival time
  of protozoan cysts and helminth ova; therefore, soils  with a higher percentage  of organic
  matter,  which have a greater  water-holding  capacity, may be more conducive  to pathogen
  survival. Protozoan  cysts are extremely sensitive  to drying.  Likewise,  helminth eggs and
  larvae are  susceptible to die-off when  exposed to desiccation  and  sunlight,  but in cool,
  moist soil they may remain infective for several years  (Kowal, 1985).
        Storey and Phillips (1985) found that  the survival of H saeinata and A. lumbricoides
  ova, introduced into the upper 1 cm of soil, increased at increasing depth of the soil profile.
  The ova survived longer at  the lower levels of the  soil  profile.  At levels below 12 cm, the
  number  of H saginata  eggs surviving at 200 days was only slightly reduced from  the  initial
  number  at the beginning of the  experiment.                           .   :
        Reimers  et al.  (1986) noted  that field studies  adequately  describing parasite egg .
 survival following land application  are lacking.  These  authors  indicated  that once applied
 to land,  viable  helminth eggs may develop  into  the  infective stage.   The limited data
 available  suggest that  the more  resistant eggs (e.g., Ascaris) may survive for years.
        With helminths  having the longest survival times of the  microorganisms  of concern,
 ova of Toxocara  and Ascaris have been  shown  to persist in soil or on pasture  for several
 years.  Ascaris has  been called  the most  hardy and resistant  of all  excreted pathogens
 (Feachem et al., 1983) with survival times in soil of up to 10-12 years  (Brudastov  et al.,
 1970; Oganov  et al.,  1975).  In  addition,  many  sewage treatment  methods  serve to'
 concentrate  Ascaris eggs in the sludge.  Lack of accurate  and consistent  quantitative  data
 on the survival of parasites  under land application  conditions prompted  the U.S. EPA to
 investigate  Ascaris  ova  survival following  land  application   of municipal  wastewater
 treatment  plant sludge (Jakubowski,  1988).  Despite problems associated with field studies,
 results indicated  that infective Ascaris eggs survived throughout  the 3-year duration of the
 study. Sludge applied to the  surface grass plots produced inactivation  of Ascaris ova more
rapidly than  either subsurface or tilled  applications.
       Leftwich et al. (1988b) studied parasite survival in anaerobically  digested sludge,
spiked with Ascarij eggs, applied  to agricultural plots in  Ohio, Texas and  Louisiana.  They
                                          29

-------
found that the concentration  of Ascans ova decreased  >90% on untilled,  grassed plots, a
fact  possibly  attributable   to  biological activity, and lower,  freezing  soil temperatures.
Incorporation   into  soil  increased   survival of  the parasites.   Although  a  laboratory
experiment  showed  that  survival  was greatly  reduced  at extremely  low  soil moisture
(Leftwich et  al., 1988a),  under  field conditions no statistical  correlation  was obtained
between soil  moisture  and survival.  The authors were unable to draw a  direct statistical
correlation  between viable Ascaris  ova concentration and solar radiation, relative humidity
or soil temperatures.   In fact, no  statistical correlation  was  found between  parasite  egg
concentration   and chemical,  physical or biological parameters.
        Grenfell  et al. (1986) also conclude that  quantitative  analysis of field data fails to
show that mortality  of infective  larvae of Ostertagia  ostertagi  and CoQEejla  oncophora,
parasitic  gastrointestinal  nematddes of cattle, varies with climatic parameters,  despite  that
generally widespread view in the literature.
        Repeated  freezing and thawing of soil samples spiked with Ascaris  ova reduced egg
viability  more  rapidly and  to  a  greater  extent  than  did  constant  room  temperature
 (controls) or below-freezing  temperatures  (Leftwich et al., 1988a).  Viable Ascaris eggs in
 anaerobic  digested sludge and in  sediment were  reduced by 100% within  6 weeks  when
 spiked in soils of 4%, 10% and 20% moisture and subjected to freeze-thaw conditions.  The
 lower  the  soil moisture,  the  greater was the  reduction  in percentage  viable Ascaris ova,
 regardless  of temperature.                                                              ,
        Burger (1984) found  that Taenia saginata eggs survived differentially  depending on
 the season of contamination  of the  site.  The shortest  survival time, 4-8  days, occurred in
 summer when egg-contaminated soil was exposed  to the sun (Soviet Union).  The longest
 survival time was 365 days (Kenya)  when eggs were applied to open pasture (infectivity
 unknown).    Burger concludes  that the  time  interval  between  sludge application  and
 introduction   of cattle  to the pasture should be  at least four  months during seasons of
 pasture  growth and longer during  the cooler seasons in the northern European  Community.
        In a study of the development and  survival of Trichuris suis ova on pasture plots in
  southern England,  Burden  and Hammet  (1979)  found that ova required  62-90 weeks to
  develop to the infective stage (embryonation).   The  rate was dependent on temperature,
  assuming  adequate  moisture  and  oxygen. There was little  if any development during the
                                             30

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 winter. Most susceptible to adverse environmental conditions  were the early developmental
 stages.   The highest  percentage  of ova perished  in the plots contaminated  during the
 summer drought of 1975 when  maximum air temperatures were above  20ฐC.  Following
 development  to the infective stage, ova survived at least two years.
       Burden et al.  (1976) studied  the closely-related  Trichuris  trichiura  and  found a
 relatively  rapid death  rate  of ova in  soil  in southeast  England.   During  an 18-month
 observation period, 80% of the  eggs died.
       Data  on survival of parasites  in water is  very  limited.   Entamoeba   histolytica
 survived 153  days in distilled-water at  temperatures  ranging  from 12-22ฐ C and the same
 length of  time in natural waters, but  with  a decrease  of  30%  for  each 'lOฐC rise in
 temperature  (Mitchell, 1972). These data are  generally confirmed byGrenfell et al. (1986),
 who found that the optimal survival rate for Ostertagia ostertagi  in water is in the  range of
 0-15ฐC with higher die-off rates above and below  this range.
       There  is abundant  evidence that Crvptosporidium  bocysts and Giardia cysts persist
 in water.   Crvptosporidium  oocysts have been identified  in surface water  (Madore et al.,
 1987; Crawford and Vermund, 1988) and in a filtered, treated public water supply (Hayes
 et al.,  1989).  Giardia  cysts survive  relatively  long  periods  in  water,  particularly  at
 temperatures  below 20ฐC; above 20ฐC, cyst inactivation is rather rapid (Jakubowski, 1990).
 Evidence  suggests  that Giardia  cysts in water survive best at 4-8 ฐC (Jakubowski, 1990).
 Jarroll et al. (1984) reported  that  cysts did not survive when Giardia were exposed for 24
 hours to artificial  sea  water  at 4ฐC or to air-drying at 4ฐC or 21 ฐC.
       Extremes in temperature  can  reduce  oocyst viability.   Tzipori (1983) reported  that
 freeze-drying  destroyed infectivity of Crvptosporidium oocysts  as did 30-minute exposure to
 temperatures   below  freezing and above 65 ฐC.   Laboratory  studies  have shown  that
 Cryptosporidium  oocysts stored  in containers  that  exclude air  can  remain viable for 8-9
 months,  but  excystation  seems  to occur soon  after  exposure  to  air  (Tzipori,  1983).
 Quantitative  data  on die-off rates  in water or soil were not found.

3.4.    TRANSPORT
3.4.1.  Transport in Soil. It is assumed  in the  model that pathogens are distributed in the
upper soil  layer by incorporation  and tilling.  However,  materials  in the soil can  also be
                                          31

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transported  by water moving through the soil.  This movement occurs through pores, spaces
between  the particles or grains of soil.  Soil pores are generally  classified as macropores
(>62/zm) or micropores;  because water is bound  tightly to the surface  of the grains and
nearly fills  micropores,  the  bulk  of water  movement  is in macropores.   Downward bulk
transport  of water may occur as a result of gravity.; Bulk water movement occurs only when
the amount of water in the soil exceeds the  field capacity. In this case,  the path  of the
water is tortuous because -pores are not_arranged  in straight channels.  There may also be
upward and horizontal  movement  as a result  of capillarity.
       Particulate matter suspended  in soil water can be transported  as the water moves.
Particulates entering soil pores may  become  lodged because  they  are  too large  to move
through the pores or because of electrostatic binding to soil particles. Thus bulk transport
of particulates occurs more readily in macropores, cracks and channels  than in micropores.
Capillarity  is less  likely to transport  large  particulate  matter  for  significant  distances
because it occurs mainly in  the micropores, which are too  small  for large particles.
       Protozoan cysts (~5-25jum dia) and helminth ova (~ 15-80nm dia) are large enough'
that they  exhibit very little migration  through soil (U.S. EPA, 1985).  They do not move
vertically  into groundwater because  of the physical barrier provided by the soil, unless there
are vertical cracks or fissures.  In the Seattle Metro study (1983), no appreciable  downward
movement of Ascaris ova occurred after. 15 days,  nor were Ascaris  or hookworm eggs  or
Entamoeba  histolytica cysts able  to pass through  24 inches of sand.
       Sorber and Moore  (1986) conclude  in  their critical  literature  review that "there are
essentially  no data  available  in the  published  literature  that would  permit  estimating
transport  rates for pathogens from sludge-amended  soils."  They go on to indicate that the
size of protozoan cysts and helminth ova appears to prevent the vertical migration of these
parasites  from  sludge-amended  soil,  but no  studies designed  to resolve this issue were
found in their review of the literature.  However,  Storey and Phillips (1985) measured the
rate of transport of T. saginata  ( — 30 p,m  dia) and A. lumbricoides  (~50/.tm dia)  ova  in
laboratory  soil  columns.   The  mean distances  traveled  in 72  hours  by the smaller  T\
saginata  eggs and the larger A. lumbricoides  eggs were 2.21 cm and 1.78 cm, respectively,
with a drip rate of 0.25 mL/minute, and 2.54cm and 2.14cm, respectively, with a  drip rate
of 0.5 mL/minute.    The soil  columns  were  1 cm in  diameter  (0.79 cm2  in area),  so the
                                           32

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 amount of water percolating through  them at 0.25 ml/min was 0.25/0.79  = 0.316 cm/min,
 or 1367 cm in 72 hr.  Therefore the relative rate of migration of T. saginata- was 2.21/1367
 = • 1,62x10ฐ, and the  relative  rate of migration  of A.  lumbricoides  was 1.78/1367  =
 1.30x10ฐ.  From these  ratios, a rough calculation  could be  made  of the  time  required  to
 transport parasite  ova through soil. Even if the relative rate of migration were as high as
 0.01 and all rain water were to pass through the soil layer containing the ova,  the time
 required  to move the ova  100 cm  would be greater  than '65 years if the annual  rainfall
 averaged 60 inches.
        Results from the current  literature search  confirm the  dearth of data  with respect
 to the  pathogens, listed  in Table  3-2. However, there have  been a few recent reports  on
 other parasites  that  may be useful as representatives  of the  group.
        Krecek and Murrell  (1988) observed  that larvae of Ostertagia ostertagi  migrated  at
 least 15 cm down into the soil, moved laterally around a barrier and subsequently returned
 to the  surface  grass  within 5 weeks  after  the  beginning of the  experiment.   The total
 distance covered was >30cm.  Bovine fecal pats  containing 200,000 eggs were placed  on
 pasture whose base soil was composed of 72% sand, 20%  silt and 8% clay/ This capability
 for  vertical soil  migration and return  to  surface herbage   raises  the issue  of the
 epidemiological  significance of soil sequestration during periods of environmental  stress as
 a  reservoir  of Ostertagia.  The authors made no determinations  of total  numbers  of larvae
 re-emerging onto grass.  Krecek  and Murrell  (1988)  also reviewed  other  studies of larval
 migration in soil and  found results to be inconsistent:  free-living third-stage  larvae did
 migrate but authors differed in their conclusions about  the epidemiological  importance  of
 such  migration.
       Free-living larval forms may move through the  surface  soil, but these movements are
 usually  active rather  than a result of passive transport.  Larval migration in soil tends  to
 keep  the pathogens near or above the surface, where they are more likely to encounter  a
 suitable host.
       Altaif and Yakoob (1987)  studied the survival of Haemonchus  contortus  infective
 larvae on soil and pasture  in Iraq for a period of.12 months.   The authors  found  little
evidence of migration of infective  larvae in the soil; the majority of larvae of this parasitic
gastrointestinal   nematode of sheep and goats was  discovered in the herbage.     •
                                           33

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       Grenfell  et al. (1986) analyzed  the survival and  migration  rates  of the  infective
stages of Ostertagia ostertagi and Cooperia  oncophora.  parasitic  gastrointestinal  nematodes
of cattle.   They  determined,  by  use of a  mathematical  model  of larval  demography,
maximum-likelihood  estimates of mortality rates of larvae  as 0.0284/day in feces and on
herbage as 0.0087/day.  Average migration  rate from  feces to herbage  in the temperate
climate of northern  Europe  was estimated  as 0.00884/day.  The life-span of the 3rd-stage
larvae  (L3) may be 1-2 years.
       Burden and Hammet  (1979) recovered Trichuris  suis ova from contaminated  pasture
plots at all depths  sampled-0-10  cm, 10-20 cm, and 20-30  cm~for the 30-month duration
of the  test.  The samples demonstrated  that  T. suis ova did not leach  rapidly through the
chalky/flinty  soil at Compton in southern England but that  they remained  available to pigs
grazing the plots up to 30 months later.  In some of the samples, the majority of ova were
located in the 20-30 cm fraction,  presumably  because the ova were washed down the cracks
and fissures that were common on the  plots following  periods  of hot,  dry weather.
3.4.2.  Transport in Surface Runoff.  Whenever  the amount  of water  applied  to the land
surface is greater than can  be absorbed by  the soil or soil cover, water  will pool on the
surface or run  off to a lower point  on the  surface.   Microorganisms,  along with other
particulates  in the soil, can  be suspended in this surface  water  and transported  as surface
runoff. In the Pathogen  Risk Assessment Model, it is assumed that runoff occurs only after
rainfall, because it is required that irrigation be limited to prevent runoff 1  In addition, it
is assumed that both runoff from offsite onto the site and runoff from the site to an offsite
location  are prevented by ditching, diking  or other means.  Therefore,  runoff is limited  to
that  occurring  in the  specified field area.
       In the  computer  model, pathogens  in runoff water  are considered separately  from
those associated  with suspended  sediments. The concentration  of pathogens in runoff water
depends   on  how readily  they are separated  from the soil  particles  and how well  they
remain in suspension.  Viral particles  may be tightly bound to soil particles and thus be
difficult  to  suspend  in runoff water, but  suspended viruses do not readily settle out  of
suspension because they are so small.  In contrast, parasite ova, cysts  and oocysts are less
tightly bound by soil particles, but their large size makes them settle out  of suspension
rapidly.
                                           34

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       It is assumed  that organisms  in the top 1 cm of soil are available for suspension in
runoff water after a rainfall.  The fraction  of total rainfall occurring as runoff is calculated
by Subroutine RAINS, and the fraction of organisms  in the soil surface that are suspended
in runoff water is given in the model by the variable  SUSPND  [P(45)].  Although  there
have been several studies on  suspension of soil-associated  viruses  and bacteria,  there are
few data describing  the suspension of parasites in runoff water. In the model it is assumed
that  the fraction of parasites  suspended  is 0.01 in Practice I, in which the soil surface has
little cover, and 0 in Practices II and in, in which the soil has a  continuous  grass surface.
3.4.3.  Transport by Wind. The ability of protozoan  cysts and Cryptosporidium oocysts to
survive in aerosols  has  not been determined.   However, Lawande  and associates  (1979)
recovered  soil amebae, transmitted by the dust-laden air during the  harmattan  period,  from
the nasal passages of children in Nigeria.  Of the 50 children evaluated,  24% had positive
cultures  for the soil amebae.   The pathogenic  strains of Naegleria  fowleri recovered  from
two children were viable and  infective, killing mice in five days.
       Rivera  et  al.  (1987)  have also  isolated  airborne,  free-living amebae  from the
atmosphere  of Mexico City.   The  authors suggest that the ability  of the  cyst-forming
amebae to exist and remain viable in the atmosphere  can, under  favorable environmental
conditions, contribute to dispersion and invasion  of water supplies, food, or healthy people.
       Airborne transport  of dry larvae or  eggs of nematodes  has  been modeled by Carroll
and  Viglierchio  (1981) using simplified Gaussian  plume models.   They measured  the
sedimentation  velocities  of dry  larval, egg and  cyst forms of a  number  of parasites and
found  that  most fell between 0.1 and  0.6 m/sec, indicating  that they  would  be  more
erodible than dry soil particles.  Their results indicated that, given the presence of eggs or
larvae  on a loose,  dry soil surface  and  with sufficient wind velocity (11  m/sec,  particles
lofted  to a height of 30 m by  tilling), eggs could be carried up to'0.6 km and larval forms
1-3 km as a result of tilling. The authors concluded that nearly all dust suspended by wind
vortices (dust devils) would be deposited  within 4 km, but a few individual  organisms  could
be transported  as far as 40 km away.
       The authors'  calculations indicated that the maximum concentration  (pathogens/m 3)
of larval forms  at a distance   of 80  m during cultivation at a windspeed  of 2 m/sec was
approximately 4% of the release rate (in pathogens/sec).   The  U.S. EPA model for tilling
                                           35

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emissions (U.S. EPA,  1983) yields  a release  rate  of  approximately  1.0(5 kg  soil/hr, or
approximately 0.3g/sec.  At a sludge application  rate of 10T/ha, a concentration  of 5000
pathogens/kg,  and dispersal  of the  pathogens  in  2x10*  kg surface  soil/ha  (Naylor  and
Loehr, 1982), the concentration  of pathogens  in soil would be 0.025 pathogens/g.  Thus the
concentration  of pathogens  transported 80 m by wind in the case described  above would be
0.04x0.3x0.025=3x10"" pathogens/m  3.  This figure  implies  a low  risk  of  infection by
windblown pathogens as a result of tilling and  subsequent  air transport.
                                          36

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                       4. PARAMETERS  FOR  MODEL RUNS   .

4.1.   RATIONALE  FOR PARAMETER  SELECTION
       The assessment  of human  health risk from pathogenic parasites as a result of land
application of sewage  sludge requires a realistic description  of the fate and transport of the
pathogens.   Information  in the  published  literature  confirms that protozoan  cysts and
parasite ova  survive during  the sewage treatment process, but quantitative  data on survival
of protozoa  in sludge are  scarce.  There appear  to be  few quantitative  measures  of
movement or  die-off  rates of ova or cysts in soil  or  their inclusion  in  aerosols.  Most
researchers assume  that, ova and cysts are too large to migrate in soil or into groundwater.
That assumption  was maintained  in this analysis.  Some researchers  conclude that  ova and
cysts are  unlikely to be  included  in  droplet  aerosols.   In this analysis,  however, it was
assumed that ova and cysts would be included in any droplet aerosols  formed  by spray
application,  as well  as in any paniculate  aerosols formed as a result of disturbance of the
soil by wind  or cultivation.  Although  the droplet aerosol model includes  droplets  smaller
than ova and  cysts, no  modifications  were  made  to exclude these  particles  from  the
infectiveness  calculation.  Therefore, estimates of the infectiveness  of  very small droplets
may be unrealistically  high.
       Various estimates  have been made for the rates of inactivation  of parasite ova and
protozoan  cysts.  These forms  of the pathogens  are more  resistant  to environmental
conditions  than  the unencysted,   larval or  adult  forms, which  do not  survive  sewage
treatment.  Therefore,  ova  and cysts are considered  to be more significant with regard  to
exposure  risk  from  sewage sludge.   However,  the survival  properties of ova and cysts
depend  on the specific organism in question, as well as on the conditions to which they are
exposed.   Therefore,   a single  mathematical  description  of  die-off will at best  only
approximate  the  behavior of all parasites.  Default values in  the model for die-off of ova
and cysts are those found in the initial version of the model (U.S. EPA, 1980). They are:

       During application/incorporation
             0 for Temp < 20ฐC;
              1(r.ooo,7s>  or o.00041/hour for 20 _< Temp  < 40;
              10(-ฐ'456) or 0.65/hour for Temp >i40;
                                          37

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       In moist soil
              0 for Temp  < 20 ฐC or for 8 hours after irrigation;
              10punai) Qr o.000533/hour for 20 _< Temp < 40;
              10W667)  or  0.7845/hour  for 40 ^Temp  jC 50;
              10WM  or  0.25/hour for Temp > 50;    ,.
       On crop surfaces
              KjtMtQ  or  o.7845/hour  at  all temperatures;
       In water
                     Of o.000533/hour at all temperatures.
       A  90% die-off time  of 270 days  for Ascaris ova in  soil reported by Sorber and
Moore  (1986) implies  an exponential  rate of lO*'"270*24' -or  lO^'^/hour  (fractional  rate
0.00035/hour); this value is near  the  model's default value.  In the model  analysis a value
of 10<4>>cool)/hour  was used as a lower limit for die-off rate in  moist soil.
       O'Donnell et al. (1984) reported  a decrease in the number of recoverable  Ascaris
ova treated  in sludge and  stored  in soil.  The decrease occurred at rates of approximately
lO^Ymonth  for  aerobically   treated   sludge  and   approximately   10C"ฐ'3Y month   for
anaerobically  treated  sludge;   viability of the ova recovered  dropped at a rate  of - 10"
Oi003)/month for aerobically treated  sludge and lO^'^Vmonth for anaerobically treated sludge,
giving composite rates  for Ascaris of lO^'^/month  (lO'^^^Vhour)  for aerobically treated
sludge and  lO'^/month  (10(-aooฐ45)/hour)  for anaerobically treated  sludge. The value for
aerobically  treated  sludge agrees  well with the default value. A value of 10l"ฐ-(1005)/hour was
used  as an  upper limit for the  model  analysis.   Recovery and viability of Toxocara.
Trichuris  and Hymenolepis ova appeared  not to be greater than for Ascaris (O'Donnell  et
al.,1984).
       Published data  on die-off rates for parasites  in sludge are summarized  in Table 4-1.
For maximum utility, rates should be  determined  for all of the organisms listed. However,
quantitative data are not available for most of them.
                                           38

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Stronevloides
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Toxocara cati
                                                       39

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                                                         40

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4.2.    PARAMETER  VALUES
       Prior to the site-specific simulations, an initial  sensitivity  analysis was performed.

In. this analysis, several  parameters  were  systematically varied to simulate  a variety of

possible conditions, application  methods and agricultural practices. The parameters  varied

included those of the main program, Subroutine RISK and Subroutine RAINS. The  ranges

of values and rationale for their selection are discussed below.

4.2.1.  Main Program Parameters.  The main program  parameters varied for this analysis

are listed below (default  values are in bold-face type):
 VARIABLE
 #   NAME

 1  ASCRS
 2  APRATE



 4  TREG



 6  APMETH



 13  TRAIN



 17  IRMETH


 18  DILIRR
VALUES
200
5000
11000
l.OxlO4
2.5xl04
0
-1
 0
+ 1

Site-specific
0
1

0
1
DEFINITION
VALUES
AND   RATIONALE    FOR
Concentration  of organisms in sludge (number/kg
dry wt).  Values as high as 11,000/kg have been
reported  (Wallis et aL, 1984),  and values less
than the  default have been reported.

Rate   of   application    of  sludge   (kg/ha).
Demonstrate   the   effect   of  increased   sludge
concentration  in soil.

Waiting  period  before  harvesting   (months).
Make  parasites   available   immediately   for
exposure  as a worst case.

Application  method  (flag).   Demonstrate   the
relative  effects of  spray application,  surface
application,  and subsurface application.

Flag for rainfall subroutine menu. Rainfall is the
most significant factor in surface runoff/sediment
transport  to the onsite pond.

Irrigation method (flag).  Compare  the effects of
spray irrigation and  ditch  irrigation.

Fraction  of irrigation water that is contaminated.
Demonstrate  the effect of irrigation with sludge
as compared  to uncontaminated  water.
                                         41

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VARIABLE
#  NAME

30  COVER
31  AEREFF
45  SUSPND
66  CROP
67  TCULT
68  TCROP
69  THARV
VALUES
0
0.9
IxlO'3
2x10 "2
0.01
0.001
DEFINITION
VALUES
AND   RATIONALE    FOR
59  DTCTMT       0
                    1
60  DTCTMK       0
                    1
-1
 0
+1

0
_2
240
300
Percent of ground surface covered by vegetation.
Compare  surface runoff/sediment  transport  for
bare  soil and  soil  with  vegetation  (will  be
matched  with  values in Subroutine RAINS).

Efficiency of aerosol formation.  'Compare default
value  to  an   unrealistically  high  value  to
determine  whether  the  model is  sensitive  to
off site aerosols.

Fraction  of  soil  surface  organisms suspended in
soil surface  water.  Vary  to  determine  whether
model is sensitive  to  resuspension from surface
soil into  soil surface water.     !

Fraction  of pathogens ingested by animals that is
transferred to  meat.   No transfer of parasites to
meat  [P(59)=0], or invasion  of edible tissue by
every infective ovum  or cyst  [P(59) = l].

Fraction  of pathogens ingested by animals thai: is
transferred to  milk.   No-transfer  of parasites to
milk  [P(60)=0], or  invasion of  milk by  every
infective cyst [P(60) = l].

Type of crop (flag). Type of crop is important in
exposure during  consumption of crop.
Cultivation time  (hr) or  flag.   Include  regular
cultivation  to  determine   whether  model  is
sensitive to generation  of particulate aerosols.

Time crop surface is present  (hr).  Establish early
appearance   of  crop   surface   to  facilitate
demonstration   of  sensitivity  of exposure   to
presence of crop.  ,

Harvest time (hr).  Establish early harvesting  of
crop to facilitate  demonstration  of sensitivity ,of
exposure to presence of crop.
                                        42

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       The variable  DTCTMT  [P(59)] is used to  describe the transfer  of parasites  from
contaminated  soil or feed to meat.  This  process accounts for ingestion .of infective ova or.
larvae  by livestock, with subsequent migration of larvae to edible  tissues.  Upon ingestion
of meat  containing cysts, infection  of the food consumer (EATER)  would occur.  In all
other exposure pathways, it is assumed that the EATER ingests infective  ova or larvae.
4.2.2.Parameters for Subroutine RISK.  Parameters varied for Subroutine  RISK are listed
below  (default values are in bold-face type):
 PARAMETER
 #   NAME

 5  DRECTC
VALUE
                                         DEFINITION    AND
                                         CHOICE  OF VALUES
RATIONALE    FOR
 6  DRECTS
 34 - XDIST
0.1
0.02
0.1
0.02
0.2
200
100
                                         Ingestion  of crop  surface  (g/day).  Determine
                                         effect of reducing ingestion  of contaminated  crop
                                         surface during  routine daily work in the  field.

                                         Ingestion  of or direct contact  with soil (g/day).
                                         Determine   effects   of  reducing  ingestion  of
                                         contaminated  soil during routine daily work and
                                         of including transdermal invasion from  soil on
                                         the skin surface.

                                         Distance   (m)  downwind   of  receptor  from
                                         particulate source.  Determine  effects of reducing
                                         distance to receptor  of offsite aerosol to Verify
                                         initial   indications    that   offsite  exposure  is
                                         negligible.

       DRECTS  (Variable  6) is intended  to represent infection  by  direct  contact with

contaminated  soil or  crop  surfaces.  This exposure pathway  includes both  transdermal

invasion  by parasites  and inadvertent  ingestion of infective forms.  The default  value (0.1

g/day) was chosen to be conservative  in comparison  to U.S. EPA estimates  of ingestion of

dust and soil  by adults (0.02 g/day; U.S. EPA,  1983). Typical rates  of  soil ingestion by

children  are higher, with a 95th percentile  value of 0.4-0.6g/day (Binder et al., 1986). The

U.S. EPA suggests a daily intake of 0.2 g/day for children under 5 for assessment of risk

from  toxic chemicals  (U.S. EPA,  1990a).  However, children  (and  adults)  with pica, a

behavior characterized  by intentional  ingestion "of soil or other mineral  substances, may

ingest  much larger amounts of soil. For example,  Calabrese (1988) reports  ingestion of 5-

8 g soil/day  by one subject.  For these  persons, the risk of infection  from contaminated  soil
                                          43

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is much greater  than for the  general population.   To model  risk of infection to persons
exhibiting pica, any chosen value can be used for DRECTS  during the  input phase of the
model  run.  Exposure by ingestion of or direct  contact with contaminated   soil or crop
surfaces is summed with aerosol exposures to calculate  the probability of infection ONSITE.
4.2.3. Subroutine  GRDWTR.  Because it  was assumed  that  parasite  ova and protozoan
cysts are not transported  into  groundwater,  this subroutine was not used in the model test
runs. However, since protozoan cysts are small (5-25 /LOU), their migration through porous
soil may not be completely prevented.  If the user wished to  model subsurface transport in
groundwater, appropriate  values for parasites  would be entered  during  the input phase of
a  model run using the bacteria or virus option  of the  model. ' However,  data  on  such
parameters  as retardation coefficient and hydrodynamic dispersion coefficient have not been
found.                              ........
4.2.4. Subroutine RAINS. The Modified Universal Soil Loss  Equation, which is the  basis
for Subroutine  RAINS,  depends   on  soil  type,  topography  and  land-use  practices,  so
parameters  for Subroutine RAINS  are influenced  strongly by the choice of site.  A variety
of locations  representing  different  soil types, topography and climate were selected as test
sites for model 'runs.  Values for the parameters in Subroutine  RAINS were  chosen "to be
appropriate  for soil type, topography and meteorological patterns for the chosen  locations.
Although the model is limited  in its ability to represent the rainfall pattern of any location
because  of its restriction to no more than ten rainfall events,  these events were included as
early in the model  run as possible to  ensure  that   the effects  of rainfall on surface
runoff/sediment  transport were maximized.
                                          44

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       Subroutine  RAINS  is described  in  more detail  in U.S. EPA  (1990b).  Parameters
used by Subroutine RAINS include  the following:        .              .  ,
      ...-"•            ' .        ' •-•'  " .~-\~ , ..  •        ...     ,        "        •    i
PARAMETER
#
2 .
3
4,
5
6
?'.
8
9
10
11
NAME
PDUR
PTOT
BTLAG
CN
AMC
STAD
USLEK
USLEL
USLES
USLEC
DEFINITION
                    Event-specific duration  of rainfall (hours)         ,
                    Event-specific amount of rainfall (cm)
                    Basin time lag.  Depends on site-specific properties.
                    Curve number.  Depends on site-specific properties.
                    Antecedent  moisture  conditions (dry, intermediate1 or wet)
                    Event-specific storm advancement coefficient
                    USLE  K factor  (soilcredibility)
                    USLE  L factor  (from length of slope)
                    USLE  S factor (from steepness of slope)
                    USLE  C factor  (coyer management)
Values  used^for these variables in the model runs are given in Section 5 along with the site
descriptions.              ,    ,,.  .  ,.,.,
      . Since Practices IV and V do not include  an onsite pond to receive  surface water
runoff,  parameters  for Subroutine  RAINS are given only for Practices I, H and III.
                                           45

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                            5.  SITES FOR MODEL  RUNS

       Six  sites  were  chosen   to  provide  a  variety  of soil  types,  topography  arid

 meteorological  patterns.   Other  than Anderson  County, TN, for  which more detailed

 meteorological data were available to the authors, specific sites were chosen arbitrarily with

 the  goal  of geographic diversity.  Data  on soil  properties  were taken  from U.S. Soil

 Conservation  Service soil surveys, which have been  developed for each county  in the United

 States.   Meteorological data were taken from the National   Oceanic and  Atmospheric

 Administration Local Climatological Pata Annual Summaries for 1981 (NOAA,  1981). The

 sites chosen for the model runs are described  below.
5.1.   SITE 1: ANDERSON  COUNTY, TENNESSEE

       Values of site-specific variables  were chosen to  reflect.conditions at an agricultural
location  in  the Clinch River Valley of East  Tennessee.

5.1.1. Description of Soil. The soil chosen for the model run is the Claiborne series, which

comprises fine-loamy, siliceous, mesic  Typic Paleudults.  It is further described as follows
(USDA,  1981a):

             The Claiborne series consists of deep,  well drained soils that  formed
       in sediment deposited by water  or in residuum of dolomite.  These soils are
       on ridgetops,  on hillsides, and at the base of slopes. The  slope range is 5 to
       45 percent, but in most areas the gradient is  12 to 30 percent....   :
             The soliim is more than 60 inches  thick.  Depth to dolomite bedrock
       is more than  72 inches.  The  soil  is  strongly acid  or  very strongly acid
       throughout except for the surface layer  where limed.  The content of coarse
       chert fragments  ranges  form  5 to  25 percent in each horizon.   These
       fragments  commonly increase in size and abundance  with increasing  depth.

Claiborne soils are of hydrologic group B, characterized  by moderately low runoff potential,
moderate infiltration  rates and  moderate rates of water transmission.

       For this analysis, it was assumed that  sites with slopes greater than 10% (6ฐ) would
not be used because  of the likelihood of excessive runoff.

5.1.2. Narrative Climatological  Summary.  The following climatological  summary for Oak
Ridge, Anderson  County, TN, was taken from NOAA  (1981):

       Oak  Ridge is located in a broad  valley between  the Cumberland  Mountains,
       which lie to the northwest of the area* and  the  Great  Smoky Mountains,  to
       the southeast.  These mountain ranges are oriented northeast-southwest  and
       the valley  between is corrugated  by broken  ridges 300 to 500 feet high and

                                          46                            :        •

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       oriented  parallel  to  the  main valley.   The  local  climate is noticeably
       influenced by topography.  Prevailing winds are  usually either up-valley, from
       west to southwest,  of down-valley, from east to  northeast.  During periods of
    ;   light winds daytime winds are usually southwesterly,  nighttime winds usually
       northeasterly.  Wind velocities are somewhat decreased by the mountains  and
       ridges. Tornadoes  rarely occur in the  valley between the Cumberlands  and
       the Great  Smokies. In winter the Cumberland Mountains  have a moderating
       influence on the local  climate by retarding the flow of cold air from the north
       and west.

       The  coldest month is  normally January  but differences  between  the  mean
       temperatures  of the three winter months of December, January, and February
       are comparatively small. The lowest mean monthly temperature  of the winter
       has  occurred  in each  of  the  months  December,  January,  or  February in
       different  years.   The lowest  temperature  recorded  during the' year  has
       occurred in each of the months November, December, January,  or February
       in various  years. July is usually the hottest month but differences  between  the
       mean temperatures  of the summary months of June, July, and August  are also
       relatively small.  The highest mean monthly  temperature may occur in either
       of the months  June, July, or August and  the highest temperature of the year
       has occurred in the months of June, July, August, and  September in different
 :      years.  Mean  temperatures  of the spring and  fall months progress  orderly
       from  cooler  to warmer  and  warmer to^  cooler,  respectively, without  a
       secondary  maximum or minimum.   Temperatures of 100ฐ [38 ฐC] or Higher
       are  unusual, having occurred  during less than  one-half of the  years of the
       period of record, and  temperatures  of zero  or below  are rare.  The  average
       number  of days between the last freeze of spring and the first freeze of fall
       is approximately 200.  The average daily temperature  range is about 22ฐ
       [ 12 ฐC] with the greatest average range in spring and  fall and the smallest in
       winter.  Summery nights are seldom oppressively hot  and  humid. Low level
       temperature  inversions occur during  approximately 57 percent of the hourly
       observations.   Fall  is usually the season with the greatest number of hours of
       low level inversion with the number decreasing  progressively through spring
       and winter to  a summertime  minimum but seasonal  differences  are  small.

5.1.3.  Temperature.  The monthly average temperatures  at this location ranged  between

a low of 2.8ฐ C and a high of 24.8ฐ C.

5.1.4.  Rainfall.  An hourly rainfall record for April and May, 1989, was obtained from the

Atmospheric Turbulence  and Diffusion Laboratory, National  Oceanic  and Atmospheric.

Administration, Oak Ridge, TN.  Profiles of the  first ten rain events beginning April l,the

time the model run is initiated, were constructed  from this record.  Profiles consisted  of the

duration of the event (PDUR), the total amount  of precipitation  in the  event  (PTOT) .and

the storm advancement coefficient (STAD),  which was determined by inspection of the
                                         47

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 hourly precipitation.  The resulting  parameters  were as follows:
Event
No.
1
2
3
4
5
6
7
8
9
10
START
flirt
77
174
726
826
924
1180
1340
1549
1590
1650
PDUR PTOT
flirt
5
8
11
7
4
5
12
2
9
14
STAD
(cm)
1.60
1.52
1.55
3.30
1.50
2.31
4.06
1.63
2.52
3.48

0.65
0.36
0.12
0.27
0.56
0.19
0.52
0.46
0.52
0.45
5.1.5. Parameters  for Subroutine  RAINS.   Parameters  for  Subroutine  RAINS  were
modified to describe local rainfall and soil conditions for Anderson  County, TN.  Values
were calculated  as described in Appendix B of U.S. EPA (1990b).  The values used in the
model run were based on a field  with dimensions 500 m by 200 m, sloping at an angle of
6ฐ  (10.5%).  It  was assumed  for Practice I that  before a crop Was present, the cover
management factor  was not modified, whereas after the crop was present, a canopy cover
of 30%, a canopy height of 0.5 m and a relative root network factor of 30% were provided;
for Practices n and III, the canopy cover was taken to be 90%, the canopy height was taken
to be  less than 0.5 m and a  relative  root network factor of 90%  was iassumed.   The
resulting values were:
Parameter
No. Name
4
5
6

8
9
10
11

BTLAG
CN
AMC

USLEK
USLEL
USLES
USLEC

PRACTICE NUMBER
I II ! TIT
0.2
78
3 (TCROP)
0.32
4.76
1.25
0.45 (TCROP)
0.31
64

,
0.32
4.76
1.25
0.02

0.31
64
2
I
0.32
4.76
1.25
0.02

       The initial value (0.02) for USLEC in Practices  II and III was subsequently shown
to cause errors which halted operation  of the program, so in subsequent runs and for all
other sites that parameter  value was changed to 0.05.
                                         48

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  5.2.    SITE 2: CHAVES COUNTY, NEW MEXICO

         Values  for site-specific variables for Site 2 were chosen to represent  an agricultural
  area  near Roswell,  a city in southeast New Mexico.

'  5.2.1.  Description of Soil.  The  soil chosen for the model run is the Pecos Series, which

  comprises fine, mixed,  thermic  Torrertic  Haplustolls.   It is further described  as  follows
  (USDA,  1980):

         The Pecos series are deep, moderately  well drained,  very slowly permeable
         soils on flood plains.  The  soils formed in calcareous, saline, stratified, clayey
         alluvium. Slope  is 0 to 1  percent.

         Typically, the surface layer is reddish brown silty clay loam about  12 inches
         thick. The upper  10 inches of the substratum is reddish brown clay, the next
         20 inches is reddish brown silty clay and silty clay loam, and  the lower part
         to a depth of 60 inches  or  more is brown loam and fine sandy loam.  Salinity
        is moderate.   Available water  capacity is high.

 Pecos soils are of hydrologic group D, characterized  by having a very slow infiltration rate
 (high runoff potential) when thoroughly wet. They consist chiefly of clays that have a high
 shrink-swell potential,  soils  that  have a permanent  high water  table,  soils  that have  a
 claypan  or clay layer at or near  the  surface,  and   soils  that  are  shallow  over  nearly
 impervious material.   These  soils have a very slow rate of water transmission.
 5.2.2. Narrative Climatological Summary (NOAA, 1981).

       The climate at Roswell conforms to the basic trend of the four seasons, but
       shows certain deviations related to geography.   A location south and  west of
       the  main part of major weather activity affords a degree of climatic seclusion.
       There are also  topographic effects that are inclined to alter the course of the
       weather  in this area. Higher landmasses  almost  surround the valley location,
       with a long, gradual descent from points  southwest  through west and north'.
       The topography acts to modify air masses, especially  the cold outbreaks  in
       wintertime.  Downslope warming of air,  as well as air interchange  within a
       tempering  environment,  often prevents  sharp  cooling.   Moreover,  the
       elevation of 3,600 feet in common  with the geographic situation, discourages
       a significant part  of the heat  and humidity that originates  in the  south  in
       summer.  In winter, subfreezing at night is tempered by considerable  warming
       during the day. Zero  [ฐF] or lower temperatures  occur as a rule a time or
       two each winter.  Subzero  cold spells are of short duration.   Winter is the
       season of least  precipitation.       ,    '

 5.2.3. Temperature.   The  monthly average temperatures at this location ranged between
 a low of 4.2ฐ C and a high of 26.2ฐ C.
                                           49

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 5.2.4.  Rainfall.  Times, duration  and total rainfall for each  rainfall event were constructed
 from the rainfall record for 1980 at the location  (NOAA, 1981). The record provided the
 date and amount  of the largest rainfall during a 24-hour period each month, as well as the
 total amount of rainfall  each month.  The largest rainfall  (greater than  the  subroutine's
 lower limit  of 1 cm)  was always used, and the  remaining  rainfall  during  the period  was
 divided into events placed  at arbitrary  times.   The  storm advancement  coefficient  was
 chosen  to reflect  the nature of rainfall  in  the  region;  the  low number  used  reflects  a
 preponderance  of thunderstorms' and sudden  showers, whereas larger numbers were used
 for some other  sites  to  reflect  a more gradual  buildup  of the  rainstorm.  The  resulting
. parameters  were as follows:                 .
Event
No.
1
2
3
4
5
6
7
8
9
10
START
fhf)
328
784
966
1280
1830
2174
2366
2800
3328
3518
PDUR
flirt
5
' 8
6
3
8
10
10
5
10
.6
PTOT
(cml
1.17
4.5
4.55
1.5
3.05
7.75
12.47
3.45
4.19
3.0
 5.2.5. Parameters  for Subroutine  RAINS.   Parameters   for  Subroutine  RAINS  were
 modified  to describe local rainfall and soil conditions.  The slope value used in the model
 run  was 1 degree (1.7%). The resulting values  were:
Parameter
No. Name
4
5
7
8
9
10
11

BTLAG
CN
STAD
USLEK
USLEL
USLES
USLEC

PRA<
I
0.32
89
0.25 "
0.32
2.54
0.16
0.45(TCROP)
CTICE NUME
II
0.38
84
0.25
0.32
2.54
0.16
0.05

tER
III
0.38
84
0.25
0.32
2.54
0.16
0.05

                                            50

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5.3.   SITE 3: CLINTON COUNTY,  IOWA

       Values for site-specific variables for site 3 were chosen to represent  an agricultural
area in eastern Iowa in a county that borders on the Mississippi River.

5.3.1.  Description  of Soil.  The soil chosen for the model run is the Fayette Series, which

comprises  fine-silty,  mixed, mesic type  Hapludalfs.   It  is further described  as  follows
(USDA, 1981b):

       The  Fayette series consists  of well drained,  moderately permeable  soils on
       loess-covered  uplands.  These soils formed in loess  that  is more  than 40
       inches thick. Slope ranges from 2 to 40 percent.

       The solum ranges from 40 to 60 inches In thickness. There are no carbonates
       to a  depth  of 40 inches to 60  inches.

Fayette soils are  of hydrologic group B, characterized  by moderately low runoff potential,
moderate  infiltration  rates,  and moderate  rates of water transmission.

5.3.2.  Narrative  Climatological Summary.   Because  a  meteorological  report  for Clinton

County was not included in NOAA (1981), the Climatological  summary and data reported
for nearby  Dubuque,  IA, (NOAA,  1981)  were used:
       The principal feature  of the climate in Dubuque is its variety.  Standing, as
       it does, at the  crossroads of the various air, masses that cross the continent,
       the Dubuque area is  subject to weather ranging from that of the  cold, dry,
       arctic air masses  in the winter with readings as  low as 32ฐ below [-36ฐC],
       when the ground  is snow covered, to the hot, dry weather,;of the air masses
       from the  desert southwest  in  the  summer  when the  temperatures  reach as
       high  as 110ฐ [43 ฐC].  More often the area  is covered by mild Pacific  air that
       has lost considerable  moisture  in crossing  the  mountains  far to the west, or
       by cool, dry  Canadian  air, or by warm, moist air from the Gulf regions.  Most
       of the year the latter  three types of air masses dominate  Dubuque weather,
       with  the invasions of  Gulf air  rarely occurring  in the winter.

       The  seasons- vary widely  from year  to   year at: Dubuque; for  example,
       successive  invasions of cold air from the  north may just reach  this  far one
       winter and bring  a  long, cold winter with snow-covered  ground from mid-
       November  until  March, and  many  days  of sub-zero  temperatures,  while
       another season the cold air  may not reach  quite  this far arid the winter can  ,
       be  mild with  bare  ground  most of the season,  and  only  a few sub-zero
       readings.  The  summers, too, may vary from hot and humid with considerable
       thunderstorm activity when the  Gulf  air prevails, to relatively  cool, dry
       weather when  air  of northerly  origin dominates the season.
                                          51

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5.3.3.  Temperature.  The monthly average temperatures at this location  ranged  between
a low of-7.5ฐ C and a high of 23.2ฐ C.
5.3.4.  Rainfall.  Times, duration  and total rainfall for each  rainfall event were constructed
from the rainfall record for 1980 (NOAA,  1981).  The  resulting rainfall parameters  were
as follows:
Event
No.
1
2
3
4
5
6
7
8
9
10
START
fhrt
180
231 .
396
636
970
1264
1791
1834
1934
2080
PDUR PTOT
flirt
8
6
8
6
6
-.8
, 10
10
6
4
(cm)
2.84
1,0
1.6
1.2 .
1.0
1.27 .
6.12
4.56
3.0
2.5
5.3.5. Parameters  for Subroutine  RAINS.   Parameters  for Subroutine  RAINS  were
modified  to describe soil conditions for Clinton County, IA, and rainfall  for Dubuque, IA,
the nearest  reporting station. The slope value used in the model  run  was-4.6ฐ (8%). The
resulting  values were:
Parameter
No. Name
4
5
6

7
8
9
10
11

BTLAG
CN
AMC

STAD
USLEK
• USLEL
USLES
USLEC

PRACTICE NUMBER
I II III
0.17
78
3 (TCROP)
0.375
0.37
4.76
0.85
0.45(TCROP)
0.26
61
2 ' . . •

0.375 .
0.37
' 4.76
0.85
0.05

0.26
61
: 2

0.375
0.37
4.76
0.85
0,05
, -
                                          52

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5.4.   SITE 4: HIGHLANDS  COUNTY, FLORIDA  ;

       Values for site-specific variables  for Site 4 were chosen  to represent  a sandy soil in

central Florida,  These soils can be productive for agriculture but can be improved greatly
by amendment.            :'•./'•..•'

5.4.1. Description  of Soil. The soil chosen for the model run is the Archbold Series, which

comprises  hyperthermic,  uncoated  Typic Quartzipsomments.    It is further described  as
follows (USDA, 1989):      ,    •         .

       The Archbold series consists of nearly level to gently sloping, moderately well
       drained, droughty soils that formed in marine and eolian deposits. These soils
       are  on moderately  high  ridges in the  ridge part of the  county.  The slopes
       range from 0 to 5 percent.

       Typically, the surface  layer is gray sand about  4 inches thick.  The underlying
       material  to a depth of 80 inches  or more is white sand.

       The soil reaction is slightly acid to extremely acid.  The texture is sand or fine
       sand.  The content of silt plus clay in the 10- to 40rinch control section is less
       than  2 percent.

Archbold  soils are  of hydrologic group  A, characterized ,by having a high infiltration  rate
(low runoff potential)  when  thoroughly  wet.  They consist mainly of deep, well drained  to
excessively  drained  sands or  gravelly  sands.   These  soils have  a high  rate  of water
transmission.

5.4.2. Narrative Climatological Summary.  Because   meteorological information  was not

given in NOAA, 1981 for Highlands  County, the summary and data  for nearby Orlando, FL,
were  used.         ., ,         ,    . ,                                      •,, .

       Orlando,  by virtue of. its location  in the central  section  of  the  Florida
       peninsula (which is abounding with lakes), is almost surrounded by .water and,
       therefore,  relative  humidities remain high here the  year round,  with values
       hovering  near 90 percent  at night and dipping to 40 to 50 percent  in the
       afternoon  (sometimes, to 20 percent  in the winter).

       The rainy season extends from June  through September  (sometimes, through
       October  when  tropical   storms  are near).    During  this period,  scattered
       afternoon thundershowers  are an almost daily occurrence, and these  bring  a
       drop  in temperature to make the  climate. bearable  (although,  most summers,
       temperatures  above 95ฐ.[35ฐC]  are rather  rare).   Too, a breeze is usually
       present,  and  this also contributes  towards general comfort.
                                          53

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5.4.3.  Temperature.  The monthly average temperatures  at this location ranged  between
a low of 15.8ฐ C and a high of 28.0ฐ C,
5.4.4.- Rainfall.  Times, duration and total rainfall for each rainfall event were constructed
from the rainfall record for 1980 at Orlando  (NOAA,  1981).  The resulting parameters
were as follows:
Event
No.
1
2
3
4
5
6
7
8
9
10
START
flirt
1043
1166
1667
1789
1958
2536
2918
3301
3547
4025
PDU
fhtf
7
8
10
9
. 6
10
6
6
7
10
PTOT
(cm)
2.1
3.12
11.17
5.7
3.0
3.17
2,0
1.6
2.44
9.93
       In model runs from Practice I, Subroutine  RAINS  returned  a floating-point error
during computations for rainfall event 9. This error  did not occur for Practices II and III,
so it was probably related  to both the number of organisms and the long time over which
the subroutine operated.   In order to complete the model  run, it was necessary  to delete
rainfall events 9 and 10 for Practice  I.
5.4.5. Parameters  for Subroutine  RAINS.   Parameters  for Subroutine  RAINS were
modified to describe  local rainfall  reported  for Orlando,  FL, and  soil conditions  for
Highlands  County,  FL.  The  slope  value  used  in the model  run was  1.2ฐ (2%).  The
resulting values were:
Parameter
No. Name
4
5
7
8
9
10
11

BTLAG
CN
STAD
USLEK
liSLEL
USLES
USLEC

PRACTICE NUMBER
I II III
0.45
67
0.2
0.1
2.54
0.26
0.45 (
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'5.5.   SITE 5: KERN COUNTY, CALIFORNIA

        Values for site-specific  variables for Site  5 were chosen  to represent "a'soil near
 'Bakersfield,  CA, which is located  in southern California.'     '           '"''"'''"''" "'v'

 5.5.1.  Description  of Soil.  The soil  chosen for the model  run is the Arvin series, which
 comprises  coarse-loamy,  mixed,  nonacid,  thermic  Mollic Xerofluvents.'  ' It is further
 described as follows (USDA, 198Ic):

        The  Arvin series  consist of very deep,  well drkined  soils  on alluvial fan,
        stream flood  plains, and  stream  terraces:  - These;  soils  formed  in mixed
     .   alluvium  derived from granitic rock.  Slope ranges from 2 to 9 percent.

        Clay content  ranges  from 5 to 18 percent  in the control  section.  Organic
        matter content  is 0.9 percent  or less.   Reaction Is,slightly acid  to mildly
        alkaline throughout.                               '.;.'.

 Arvin soils are of hydrologic group B,  characterized by moderately low  runoff  potential,
 moderate infiltration rates  and  moderate  rates  of  water transmission.
 5.5.2.  Narrative  Climatological Summary (NOAA, 1981).

        Bakersfield,  situated  in  the extreme south  end of/ the; great, San Joaquin
        Valley, is partially surrounded  by a horseshoe-shaped  rim  of mountains  with
        an open  side  to the  northwest  and  the  crest at an  average  distance of  40
        miles.   •  ••-•    ,-       .-•. •••      -   .-,- ... -  -,.-••.  -..;•:;  ;.:   I ;,;..-.  '.ป;•. .•-...:..••„•',: -•.-

        The Sierra Nevadas  to the northeast  shut out most of the  cold air  that flows
        southward over the continent during winter. They also catch  and store snow,-.;   .
      .  which provides irrigation  water  for use during the dicy months,,  .The..Tehachapi }
        Mountains, forming the southern  boundary,  act as aii obstruction  to  northwest
        wind, causing heavier precipitation on the windward slopes,;high wind velocity .
        over  the ridges and, at times, prevailing  cloudiness  in  the south end  of the
       valley after sMes have cleared  elsewhere.  To the west  are the coast  ranges,;
       and the ocean shore lies at a distance of 75 to 100 miles.     ,     -,,,,1 • •  ;•„;    ;

       Because of the nature of the surrounding  topography,  there are large climatic
       variations  within relatively  short distances.  These zones of variation  may be
       classified   as  Valley,  Mountain,  and  Desert .areas..  The, .overall, .climate,
       however,  is warm  and semi-arid.  There  is  only  one wet  season during the
       year, as 90 percent  of all precipitation  falls from October thorough  April,
       inclusive.  Snow in the valley  is infrequent,  with only  a trace: occurring  in
       about  one year out of seven.  Thunderstorms  also seldom occur in?the valley.

 5.5.3. Temperature.   The monthly average  temperatures at this  location  ranged  between
 a low of 8.5ฐ C  and a high of 28.8ฐ C.               ,             '.-"-a::   •  -. ••
                                           55

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5.5.4.  Rainfall.  Times, duration  and total rainfall for each rainfall event were constructed
from the rainfall record for 1980 at the location (NOAA,  1981).  The resulting parameters
were as follows:
Event
No.
1
2
3
4
5
6
7
8
9
10
START
flirt
16
4378
7256
. 7530
8016
8320
8606
8782
13164
16022
PDUR PTOT
fhrt
8
10
9
6
6
5
8
8
10
9
(cm)
1.0
,1.78
1.47
1.07
1.0
1.0
1.63
1.0
1.78
1.47
5.5.5. Parameters  for  Subroutine  RAINS.   Parameters  for  Subroutine   RAINS  were
modified to describe local rainfall and soil conditions.  The slope value used in the model
run was  1.7ฐ (3%).  The resulting values were:
Parameter
No. Name
4
5
6

8
9
10
11

BTLAG
CN
AMC

USLEK
USLEL
USLES
USLEC

PRACTICE NUMBER
I II III
0.3
78
3 (TCROP)
0.32
2.54
0.26
0.45 (TCROP)
0.45
61
2

0.32
2.54
0.26
0.05

0.45
61
; 2

0.32
2.54
0.26
0.05

5.6.   SITE 6: YAKIMA COUNTY, WASHINGTON
       Values  for site-specific  variables for Site 6 were chosen to represent  a soil near
Yakima, WA, which is located  in south-central  Washington  along the Yakima River. This
is a region of fairly low rainfall, but which  is successfully farmed by irrigcition.
5.6.1.  Description of Soil. The soil chosen for the model run is the Kittitas Series, which
comprises fine-silty, mixed  (calcareous),  mesic Fluvaquentic  Haplaquolls.   It is further
described as follows (USDA,  1985):
                                          56

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       The  Kittitas series consists  of very deep, somewhat poorly drained soils on
       flood plains.  These  soils formed in mixed alluvium.  Slopes range  from 0 to
       2 percent.                                                        ,

Kittitas soils are  of  hydrologic group  C, characterized  by a slow infiltration rate when

thoroughly  wet.  They  consist chiefly of soils having  a layer that impedes the downward

movement of water or  soils of moderately fine texture or fine texture.  These soils have a
slow rate  of water transmission.

5.6.2. Narrative Climatological Summary (NQAA,  1981).

       Yakima is located in a small east-west valley in  the upper (northwestern)  part
       of the irrigated Yakima Valley.  Local topography is complex with  a number
       of minor valleys and ridges giving a local relief of as much as 500 feet. This
       complex  topography  results  in marked variations in air drainage, winds, and
       minimum temperatures  within short distances.

       The  climate  of the  Yakima Valley  is relatively  mild  and  dry.   It has
       characteristics  of both maritime  and continental  climates, modified  by the
       Cascade  and the Rocky Mountains, respectively. Summers  are dry and  rather
       hot,  and  winters cool  with  only light snowfall.  The  maritime influence  is
       strongest in winter when the prevailing westerlies are the strongest  and most
       steady.  The Selkirk and Rocky  Mountains in British Columbia and  Idaho
       shield the area from most of the very cold air masses that  sweep down from
       Canada into the  Great  Plains and eastern  United  States.  Sometimes a  strong
       polar high  pressure  area over western  Canada  will occur  at the same time
       that  a low  pressure  area covers the southwestern United  States.   On these
       occasions, the  cold arctic air will pour through  the passes and down the river
       valleys of British Columbia, bringing very cold temperatures  to Yakima. That
       this happens infrequently  is shown by the occurrence of temperatures of 0
       degrees  [F] or below on only 4 days a winter on the average.  On about 21
       days  during the winter the temperature  will fail to rise to the freezing  point.
       In  January  and February 1950, there  were 4 consecutive days colder  than  -
       20ฐ [-29ฐC], including  -25ฐ  [-32ฐC] on February 1. However,  over one-half
       of  the winters  remain above 0 degrees  [F (-18  ฐC)].
5.6.3.  Temperature.  The monthly average temperatures at this location  ranged between

a low of-1.5ฐ C and a high of 22.3ฐ C.

5.6.4.  Rainfall.  Times, duration  and total rainfall for each  rainfall event were constructed

from the rainfall  record for 1980 at the location (NOAA, 1981).  The resulting parameters
were:
                                          57

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Event
No.
1 '
2
3
4
5
6
7
8
9
10
START
fhrV
1628
4290
4506
5490
5722
5966
7002
7212
7498
7816
PDUR PTOT
flirt
6
8
10
6
6
6
10
8
8
8
(cm)
1.0
1.25
2.06
1.14
1.0
1.0"
2.65
1.5
1.2
1.0
5.6.5. Parameters  for Subroutine  RAINS.   Parameters  for Subroutine  RAINS were

modified to describe local rainfall and soil conditions.  The slope value used in the model

run was 0.6ฐ (1%).  The resulting values were:
      Parameter
      No.    Name'
PRACTICE  -NUMBER
       II
III
4
5
8
9
10
11

BTLAG
CN
USLEK
USLEL
USLES
USLEC

0.4
85
0.43
2.54
0.12
0.45(
-------
                                     6.  RESULTS

6.1.    SENSHTVITY  TO VARIABLES
       Limitations in mathematical processes and in the computer's operating  system result
in calculated  probabilities of infection  that, strictly speaking, are approximations rather than
accurate  evaluations of risk.  For example, the probability of infection  is calculated  as 1.0
minus  the probability  of not being infected, which is an exponential  function of exposure.
The population of a compartment  may be zero either because operations in the model have
not yet  transferred  a population  into  that compartment  or because the  program  has
rounded  off a population of < 1 to zero.  If the calculated exposure is zero, the probability
of not being infected  is calculated as 1.0,  and the  resulting risk is reported as 0.  It  is
unlikely  that there  are  actually  zero  pathogens in most compartments;  the  user has the
option of specifying the  number of pathogens in each compartment during the input phase
of the model run.
       A preliminary assessment was  made  using site-specific data for Site 1.  Seventy-five
model runs  were  made  to  assess  the  effects  on  Practices I-III  of variations  in the
parameters chosen (see  Section 4.1 above).   Several of the parameters  were  also tested  in
Practices IV and V.  In all  model runs, the  probability  of infection  for OFFSITE  and
DRINKER  was calculated  as zero. For  the  subsurface injection  option, the probability  of
infection was calculated  as zero in all exposure compartments,  because with this application
option the parasites are assumed  to be deposited below any zone in  which exposure could
occur.   ONSITE   exposure  occurs  as  a   result  of  inhalation  of  dust  generated  by
incorporation of sludge  or tilling the soil, or by direct contact, with infected  soil (U.S. EPA,
1990b).   Because  pathogens are transferred  gradually  to  the  soil compartment  during
incorporation  in  Practices  I through III,  the maxiinum exposure  by  direct  contact  is
calculated  as occurring when  all of the sludge has been incorporated.   During incorporation,
hourly exposures  are less  than  after incorporation   has been completed,  so the  highest
exposure occurs on the  day  following incorporation.   In every  model run for  Practice  I
(which requires  24 hours for the sludge to dry before the  field is  tilled), the  maximum
probability of infection  ONSITE  occurred at day 3; whereas  for Practices II and  III (which
do not require the 24-hour wait), the maximum probability of infection ONSITE occurred
                                           59

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on day 2.  For Practices IV and  V, the maximum probability occurred on day 1; in these
practices,  application  and incorporation result in more extensive direct contact than in the
agricultural practices.  Using default values for the main program variables, the maximum
daily probability of infection ONSITE was 0.0191 in Practice land  0.0027 for Practices II
and III.   Using the  same  value for  ASCRS > in Practices  IV and  V yielded maximum
probabilities  of infection of 1.42xlO~3 and 8.67X10"4, respectively. However,  the statutory
requirements for D&M  sludge allow .a maximum of 1 parasite ovum or cyst per g volatile
sludge solids (U.S. EPA, 1989). Using the similar value of 1000/kg dry weight for ASCRS,
the maximum probability of infection  would be 2.85x10"* for Practice IV and 1.73x10"" for
Practice V. On the basis of this result, a probability of infection  of IxlO"4 will be  used as
a benchmark level for acceptable risk in  discussions below.
       A preliminary  sensitivity analysis of the model was carried out (U.S.  EPA,  1990b)
to determine the relative sensitivity of model output to variations in input parameters.  In
this analysis, the  values .of selected parameters  were varied  singly, and the calculated
numbers  of organisms in various compartments  were compared.  For many parameters,
there  was no effect on  the number  of pathogens in the direct contact compartment or in
the onsite pond (the model  was not sensitive to these parameters).   The model was shown
to be sensitive  to  variations in application rate  and size of field, which are related to the
number  of organisms  applied;  method  of application,  which  determines   the  surface
availability of pathogens; and rate of inactivation of the organisms,  which determines  the
number of pathogens surviving.  In  the  preliminary  risk  assessment  for parasites,  the
sensitivity  of probability  of infection  to  variations  in input parameters  was analyzed  as
described  in the document- Pathogen Risk Assessment for Land Application  of Municipal
Sludge. Volume  I: Methodology  and Computer   Model  (U.S. EPA, ;1990b).   In this,
methodology, the  change in .the  input variable of interest is divided by its baseline value
(dB/JJ), and the resulting change in the output of interest  is divided  by the baseline  result
(dC/C).  A ratio is then taken  of the quotients,  S=(dC/C)/(d5/6).   For example, when the
value of Variable  1, ASCRS,  was changed from  5000 to 200, the maximum probability of
infection ONSITE was reduced from 0.01907 to  0.00077.  Thus d&/R was -4800/5000 and
dC/C was -0.0183/0.01907. The sensitivity coefficient S  was -0.96/-0.96 = 1.00.  In  most
cases, the sensitivity coefficient was 0 for one or both relevant exposure compartments; that
                                          60

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isy there -was no effect of changing the value of the variable.   Table 6-1 summarizes  the
results when there was a response  to a change in the value of a variable' in Practice I, using
site-specific data  for Site 1.
       These results indicate-that at low exposure  levels, the probability  of infection varies
directly (S = 1) with  the concentration  of organisms  in the   sludge (ASCRS)  and  soil
(APRATE)  and with amount  of soil ingested  or contacted directly (DRECTS).   However,
further investigation  of  the relationship  between APRATE and probability of infection
showed that as APRATE is changed farther from  the default value, S diverges from 1. To
illustrate   this  divergence,  values of S  were  calculated ' for ONSITE,  EATER   and
SWIMMER at various values of APRATE and plotted as a function of APRATE (Figure
6-1).
       The value  of S varied much  more for SWIMMER  than  for ONSITE  when  the
exponential decay rates  were  varied.  "This difference  occurs because of the nature of the
Poisson distribution  used to calculate risk of infection:  as the  average exposure increases,
the fraction of individuals exposed to more than, one infective dose increases, yielding a less
than proportional  increase  in infection  rate.   In  addition,  the  highest ONSITE  exposure
occurs at day 2 or 3, whereas the highest SWIMMER exposure occurs at  day 70; therefore, •
varying the die-off rate affects the SWIMMER exposure more  than the ONSITE exposure.
Because  the onsite-pond pathogen  densities  vary  according to rainfall events, the relative
concentrations  of the peaks  in concentration change as die-off rate  changes.  Thus, in some
cases  (but not all)  changes  in die-off rate  change  the day  on  which the  maximum
probability of infection occurred.               '     •
       Overall, the sensitivity analyses of Practices II and III gave results similar > to those
for Practice  I.   Practices TV and V do not include an  onsite  pond,  so-there are  no
SWIMMER exposures in these compartments.  As with the other practices,- there were only
small variations in S for ONSITE exposures as input  variables were changed.
       These  results  indicated  that analysis of input  variables other than SUSPND  and
DECAY  would not be productive.  Therefore, in subsequent  modeling runs, only SUSPND
and  DECAY  were changed.
       Variables  in Subroutine RAINS were also tested. Tn this test, a single rainfall event
was modeled  for simplicity.  The largest  rainfall used for Site  1, 12.47cm total  rainfall at
                                          61

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                     TABLE 6-1
SENSITIVITY COEFFICIENTS OF SITE-SPECIFIC VARIABLES
Variable
Baseline
1 ASCRS
1 ASCRS
2 APRATE
45 SUSPND
R6 DRECTS
R6 DRECTS
DECAY
DECAY
Value

200
l.lxlO4
2.5X104
0.001
0.02
0.20
-0.0005
-0.0001
Probability of Infection
ONSITE SWIMMER
0.01907
0.00077
0.0416
0.0470

0.00384
0.0378
0.01819
0.01915
0.1388
0.0060
0.2802
0.3.45
0.1656


0.0868
0.1655
Sensitivity
ONSITE

1.0
0.978
0.976

1.0
0.98,
-0.0717
-0.0096
i
Coefficient
SWIMMER

0.997
0.849
0.941
-0.21


-0.330
-0.439
                        62

-------
O 8
El
    SI
    ง
              J	L
                                                                  oq
                                                                  co
                               o
                              g
                                                                        n
o      o      d
                                                                6
                                    AXIAU1SN3S


                                       63

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a duration  of 10 hr,  was arbitrarily  placed at  Hour  240.  Other  variables  for the base
rainfall were BTLAG  = 0.32, CN =89, AMC = 2, STAD = 0.25,USLEK  = 0.32,USLEL
= 2.54.USLES  =  1.25,USLEC  = 0.05 AND  USLEP  = 1.0.  Because a number of the
variables (BTLAG, CN, USLEL and  USLES) are interdependent,  their minimum and
maximum values were combined into two model runs.  Other parameters   were varied
independently,  as indicated  in Table  6-2.   None  of the  changes  in parameters  for
Subroutine  RAINS  had an effect on ONSITE exposure,  and effects on the food consumer
(EATER)   were  minimal, except for  changes in  SUSPND  [P(45)].   Effects  on  the
SWIMMER were variable and  somewhat contradictory.  Specifying a good soil and a 1%
slope (RAIN4L)  slightly increased  the EATER  exposure  and reduced transport  to  the
onsite pond.  Conversely, increasing the erodibility of the soil  by specifying; a poor soil and
increasing the slope to 7% (RAIN4H)  slightly increased both the EATER and SWIMMER
exposures.  Specifying a moist soil (RAIN6H)  or poor  ground  cover, (RAIN 11H) markedly
increased the  SWIMMER exposure.                                    i
Both of these conditions would be expected  to increase the amount of runoff water relative
to transported  sediment.  In contrast, increasing the  resuspension factor SUSPND [P(45)],
which describes the transfer  of pathogens from soil to runoff water, greatly decreased both
the EATER and the SWIMMER exposures. This result implies that sediment  transport is
more important than runoff water as a transfer  route to  the pond. In summary, increasing
the amount of runoff water increased  exposure, but increasing the fraction of soil pathogens
suspended in runoff water decreased  exposure.  The  reason  for this apparent  inconsistency
is not clear.

6.2.  EXPOSURE COMPARTMENTS
      The results of  model runs under the various  conditions  are summarized in Tables
6-3 and 6-4, which give the probability of infection under  these conditions, at all six sites.
Default  conditions are compared  to changes in SUSPND [P(45)] and die-off rates (LOW
and  HIGH).   No SWIMMER  exposures occurred  in Practices IV and  V  because it is
assumed  that there is no onsite pond  collecting runoff from the site.
      In these model runs,  site-specific values  were used for  Subroutine RAINS (Section
5),  and  default, values were used for the main program variables, with the exception  of
                                         64

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                   TABLE 6-2
SENSITIVITY TO PARAMETERS  OF SUBROUTINE RAINS
FILE
NAME
RAINBASE
RAIN4L



RAIN4H



RAIN6L
RAIN6H
RAIN7L
RAIN7H
RAIN8L
RAIN8H
RAINBASE
RAIN11H
RAIN12L
RAINBASE
RAINSPL
RAINSPH
.VARIABLE
NAME VALUE

BTLAG
CN
USLEL
USLES
BTLAG
CN
USLEL
USLES
AMC
AMC
STAD
STAD
USLEK
USLEK
USLEC
USLEC
USLEP
USLEP
SUSPND
SUSPND

1.2
40
2.54
0.12
0.2
90
4.76
0.7
1
3
0.2
0.5
0.1
0.5
0.05
0.5
0.25
1.0
0
0.1
PROBABILITY OF INFECTION
ONSITE EATER SWIMMER
. 0.019
0.019


/
0.019



0.019
0.019
0.019
0.019
0.019
0.019
0.019
0.019
0.019
0.019
0.019
0.019
5.73xlO'5
6.07xlO-5



5.84X10'3



,5.80xlO'5 .
5.66xlO'5
5.73xlO'5
5.73xlO'3
5.73xlO-5
5.73xlO'5
5.73xlO'5
5.72xlO'3
5.73xlO'5
5.73xlO'3
6.53xlO'5
L66xlO-5
0.274
0.190



0.288



0.202
0.312
0.275
0.273
0.271
0.278 .
0.274
0.319
0.271
. 0.274
0.287
0.176
                       65

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            TABLE 6-3




PROBABILITY OF INFECTION, ONSITE
SITE PRACTICE
1 I
n
m
IV
V
2 I
II
in
IV
V
3 I
II
III

IV
V
4 I
n
in
IV
V
5 I
n
in
IV
' V
6 I "
n
in
IV
V
DEFAULT
1.907xl02
2.665xl03
2.665xl03
1.424xl03
8.667x10"-
1.907xl02 . ,,
2.665xl03
2.665xl03
1.424xl03
8.667x10"
1.907xl02
2.665xl03
2.665xl03

1.424xl03
8.667x10"
1.907xl02
2.616xl03
2.616xl03 [
1.424xl03
8.667x10"
1.907xl02
2.664xl03
2.664xl03 .
1.424xl03
8.667x10"
' 1.907xl02
2.665xl03
2.665xl03
1.424xl03
8.667x10"
'SUSPND
1.907x10*
2.665xl03
,2.665xl03, ,
l^^xlO3
8.667x10"
.. -L907X102
2.665xl03
2.665xl03
1.424xig3
8.667x10"
1.907xig2
2.665xl03
2.665xl03
* • i , ".
1.424X1O3
8.667x10"
1.907xl02 ,
2.649xl03
2.649xl03
1.424xl03
8.667x10"
1.907xl02
2.662xl03
2.662xio3
, 1.424X103
. 8.667x10"
M.907xl02
2.665xl03
• 2.665xl03
1.424xl03
8.667x10"
DIE-OFF LOW
1.915xl02
2.671xl03
2.671xl03 -
6.170X103
6.190xl03
1.915xl02
2.671xl03
2.67 IxlO3
6.170xl03
'6.190xl03
1.915xl02
2.671xl03
2.671xl03

6.170xl03
6.190xl03
1.915xlO2
2.66 IxlO3
2.661xl03
6.170xl03
6.19Qxl03
1.915xlO2
2.671xl03
2.671xl03
6.170xl03
6.190xl03
1.915xl02
2.671xl03
2.671xl03
6.170xl03
6.190xl03
DIE-OFF HIGH
1.819xl02
2.592xlO3
2.592:xig3
5.934xig3
6.030xl03
1.819xl02
2.592xl03
2.592xl03
5.934xl03
6.030xl03
1.819xl02
2.592xl03
2.592xl03

5.934xl03
6.030xl03
1.819xl02
2.592xl03
2.592xl03
5.934xl03
6.030xl03
1.819xlO2
2.592xl03 '
2.592xl03
5.934xl03
6.030xl03
1.819xl02
2.592xl03
2.592xl03
5.934xl03
6.030:id03
66 ,

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           :•      TABLE 6^4,           ,  ,




MAXIMUM PROBABILITY 'OF INFECTION, SWIMMER
SITE PRACTICE
1 I
ป
II
III
2 I
II
III
3 I
II
III
4 I
II
III
5 " I '
II
III
6 I
II
III
DEFAULT
1.388x10'
9.013x10"
9.691x10"
2.669x10'
2.433xia2
6.240xia3
1.617x10'
i.o9ixia2
i.isoxia2
7.357xia2
3,383x10"
3.767X1Q4
3.358x10"
2.930xl05
2.932xia5
4.540x10"
2.800xia4
2.803x10"
SUSPND
1.656xiar
9.008xi(T4'
9.686X104
3.572x10''
5.250xlQ3
5.448xia3
1.981x10'
L090xlCr2 ;
1.179xia2
9.279xia2
3.380X104
1.425X104
5.386xia4
2.928xia3
2.931xia5
5.396xiaV
2.797xl(J5 '
2. 80 Ix 10s
DIE-OFF .LOW
1.655x10'
1.102xl03
1.183xl03
3.605x10'
8.397xl03
8.649X103
2.057xi01;-.
1.243'xi02
1.46ixl02
1.077x10''
6.206X104
6.785X104
9.810x10"
2.938xl05
2.940xl05
6.694x10"
4.154X104
4.157xl04
DIE-OFF HIGH '
1.093x10'
5.920xl04
6.247X104
1.416x10'
1.407xl03
1.500xl03
1.383x10'
7.902xl03
8.212xl03
2.413xl02
1.425x10"
1.438x10"
1.743xl05
2.896xl05
2.898xl05
1.497xl03
9.276xl03
9.284xl05
                     67

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FCROP  [P(46)]=5xlO-6,TCROP  [P(68)]=240 and THARV [P(69)]=300.  More detailed
comparisons  of the results are made below.
       As a comparison of the effects of application practice on potential  human  exposures
to parasites in land-applied sludge, the results of model runs using site-specific data for Site
1 and  practice-specific  data  for all  five practices  are presented  in Table 6-5.  This table
shows  that ONSITE -exposures related to the grazing and feed crop applications  are lower
than those for field crops, but exposures for residential applications are even lower. Runoff
and  sediment transport are  significantly lower in the grazing  and feed crop applications,
resulting in a much lower exposure for the SWIMMER.  The probability of infection  of the
                                                                                ป
food consumer (EATER)  is higher  for aboveground crops in the residential application
than in the application  for commercial production of food crops for  human consumption.
       The effects of site-specific variables on exposure  are  demonstrated  in Table 6-6,
which  shows the maximum probability of infection at all sites, using practice-specific values
for Practice  I. The largest effect was on  the  SWIMMER  exposure because  the variation
in timing of rainfalls  had a major  effect  on the  amount  of surface  runoff arid  sediment
transport moving parasites  into the onsite pond.  Rainfall  times also  had  an  effect  on
contamination  of the  crop  surface, resulting  in slight variations  in both  ONSITE and
EATER exposures.                    .                                           	
       The effect of timing and amount of rainfall on surface runoff was studied  further by
using  the  times  and  amounts  of rainfall  events at  Site  6 (with  infrequent  but,intense
rainfall) along with other  site-specific values  for Site 1 (with  more frequent  and  more
moderate  rainfall),  and vice versa.  When  this was done  using Practice I, there  were no
significant changes in maximum  probability  of infection in the  ONSITE  or  EATER
compartments. For SWIMMER, site-specific variables were shown to be significant, but  the
rainfall  pattern  was shown to be  more  significant than  soil properties:   the  maximum
probability of infection to the SWIMMER  at Site 1 changed  from 0.14 to 0.008 when  the
rainfall  pattern of Site 6 was substituted,  and the maximum  probability  at Site  6 changed
from 0.0005 to 0.22 when the rainfall pattern of Site 1 'was substituted.
 6.2.1.  ONSITE.  The  maximum probability of infection  ONSITE was essentially the same
 at all  sites, because site-specific variables  had little time to act on the number  of organisms
 in the first three  days of the model run. The maximum probability of infection at each site,
                                           68

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                                  TABLE 6-5

              MAXIMUM  PROBABILITY OF INFECTION, SITE 1"
PRACTICE
1
2
3
4
5
ONSITE
1.907xl02
2.665xl03
2.665xl03
1.424xl03
8.667xl04
EATER
5.944xlOs
, —
—
3.057xl03
—
SWIMMER
1.388x10'
9.013xl04
9.691xl04
— .
— .
'Site-specific values for Subroutine RAINS are described in Section 5; main program values
were default  values,  except  FCROP  [P(46)] = lxlO'6,  TCROP  [P(68)]=240,  THARV
[P(69)]=300   '-
                                    69

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                             •'•:   TABLE 6-6
                                    •       •      !       •         [
           MAXIMUM PROBABILITY OF INFECTION, PRACTICE  I
SITE ONSITE
1 . 1.907x10*
2 1.907x10*.
3 1.907xlO'2
4 1.888x10*
5 1.889xlO'2
6 1.907xlO'2
EATER
, 5.944xlO-5
,6.341xlQ-5
6.015x10-*
6.279xlO'5
6.282xlO-5
6.341X10'5
SWIMMER
1. 388x10'! -
2.669x10"'
1.6l7xlO-' .
7.357xia2
3.358X10-4
4.540xlO'4
"Site-specific variables  are described in Section 5; main program  variables were default
values, except FCROP [P(46)]=5xlO'6, TCROP [P(68)]=240, THARV  [P(69)]=300.
                                       70

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using default values for SUSPND and die-off rates and a parasite density of ASCRS=5000,
was:  Practice  I, 0.191; Practices II  and III, 0.0027; Practice IV, 0.0014; and Practice  V,
0.00087.
6.2.2. Food Consumer  (EATER).   The calculated probability of infection of the food
consumer (EATER)  as  a result of consuming the crop  was < 10"16 in every model run in
which the default values for CROP [P(66)] (aboveground crop) and FCROP1  [(P46)] were
used.  However, when the on-ground crop was modeled  [P(66) =  0] and the crop was
harvested  at  the  unrealistically  early  time of  300 hours, the probability  of infection
immediately  after harvesting  was 0.068. When  a,below-ground  crop was modeled  [P(66)
         •
= -l],the probability of infection immediately after  harvesting at 300 hours was 0.146. The
reduced  probability of infection via aboveground crops reflects the assumption  that  the
exposure of aboveground crops to contaminated   soil (by blown  dust or splashing during a
rain)  is much less than the exposure of on-ground or below-ground  crops (by direct  contact
with soil).
       The  amount  of soil associated with the  crop  was  significant • in  determining  the
probability of infection.  The default  conditions include a value  of IxlO'8 for FCROP1
[P(46)], the fraction of sludge remaining  on the  aboveground crop and consumed  by  the
food eater.  Because of dilution of applied sludge by surface soil, that fraction  represents
20 g of soil on the  entire crop surface, or about  2x10^ g/crop unit (tomato).  If FCROP1
is increased  to represent  0.1 g soil remaining  on  each  crop  unit  at  harvesting,  the
probability of infection per serving of the aboveground crop became 6.47xlO'5 if the crop
was  harvested  at  300 hours  and 8.91xlO"6 if the crop  was harvested  at  150  days after
                  }    .              -          .,.. flJIr ,..,. ,t ,,,.,..„...... ...^ .. .- .„   .,.-,">-	
application of sludge.  For subsequent model runs, P(46) was, increased  to. 5x10'6,to ensure
that  there would be a significant exposure in the EATER compartment. -
       Harvesting  of on-ground and  below-ground  crops after 3600 hours (150 days) was
also  modeled.   This time was chosen to represent  a crop  planted 30 days after  sludge
application and  harvested  120 days later.  In this case, the below-ground  crop gave a risk
of infection  of 0.018/serving,  compared  to 0.0083/serving for the on-ground crop.   These
results are summarized in Table 6-7.
       Table 6-8 gives a  comparison  of infection probabilities  for food consumers  under
site-specific  conditions for all  six sites. The time specified for harvesting  in this comparison
                                          71

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                                  TABLE 6-7      '

                  MAXIMUM  PROBABILITY OF INFECTION
               BY CONSUMPTION OF CONTAMINATED  CROPS
Conditions
 g soil/
crop unit
Harvest at
300 hours
Harvest at
 150 days
Aboveground

Aboveground

On-ground

Below-ground
 0.0002

 0.1

 0.2

 0.2

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                                 TABLE 6-8

                  MAXIMUM PROBABILITY  OF INFECTION
                      OF FOOD CONSUMER  (EATER)*
Practice
Site
Aboveground
Type of Crop

On-ground
                                                           Below-ground
I 1
2
3
4 .."
5
6
IV '-.. 1
2
3
4
. 5
6
5.94X10'5
6.34xlO'5
6.02xlO'5
6.28xlO'5
6.28xlO-5
6.34xlO'5
3.10xlO'3
3.20xlO'3
3.10X10'3
3.16xlO'3
1'l'OxlO*
-3:10x10*
6.80xlO'2
_:; , 7.24xlO'2
6.88xlO'2
/' ; '"''T.iTxia^;. ;";."
7.18xlO'2
- •- -7.24x10* •
3.06xlO'3
3.16xlO-3
3.06xlO'3
3.13xlO'3
3.06x10*
3.06xlQ-3
1.46x10-'
1.55x10''
1.48x10-'
1.54x10-'
1.54x10-'
1.55x10-'
1:64x10*
1.70xlO-3
1.64xlO-3
1.68xlO'3
1.64x10*
1.64x10* -:
 * Site-specific values for Subroutine RAINS are given in Section 5; main program values
   were default values, except FCROP1 [P(46)] =5x10 *, TCROP  [P(68)]=240  THARV
   [P(69)]=300.
                                    73

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was  300 hours.   Results  are shown only for Practices I and  IV because  the  calculated
probabilities  of infection  in Practices  II, III and V were < 10"'6 at all sites.  These results
show that  site-specific  variables had  little effect on  the calculated  risk; the variation in
infection probability within each type of crop and each practice  was less than  10%.  The
probability of infection from  consumption  of aboveground  crops  was calculated  to be
approximately 50-fold  higher  for home crops than  for the  agricultural  application.   In
contrast, despite  the fact that  the modeled application  rate for Practice IV was 2.5 times
the rate for Practice I,  the calculated probabilities  of infection  from consuming  on-ground
crops were lower for home gardens  by 2 to 2.5-fold and lower for consuming; below-ground
crops by  approximately  100-fold.  These results must reflect  differences between  the
practices in distribution of sludge pathogens  above, on and below the surface.
       Land  access  and crop  use restrictions are applied on  the  basis  of the extent of
pathogen reduction effected by the treatment  process .(U.S. EPA, 1989). Class A treatment
is assumed to render sludge microbiologically harmless,, requiring no waiting period before
exposure is allowed. Class B and C treatments require a waiting period of 1.8 months after
application before aboveground  and on-ground food crops can be grown, and a 60-month
waiting period before  beloW'ground  crops  can  be  grown (18 months  if there  are no
parasites in the sludge).  The  waiting period  for grazing on  sludge-amended pasture  is  1
month for Class B treatment  and 2  months for Class  C treatment.  In the computer model,
the class of treatment  is entered in response to a prompt.  A waiting period based on the
land use practice is then assigned  to the model  run.  Exposure (time of harvest)  is not
allowed before the waiting period  has elapsed.  Thus the operator  is forced to choose  a
time of harvest  [P(69)] that  exceeds the waiting period. The effect of time of harvesting
on the probability of infection by ingestion of aboveground crops was assessed  by varying
P(69) in a series of model  runs, using  the  default  application  rate and  5000/kg  as the
parasite density.  The  results are presented  in Table 6-9. The  values given  for months 15
and  18 for the aboveground  crop are  extrapolations;  the model  gives a result of 0 because
at these times the concentration  of parasites on the  crop is calculated  to  be  < IxlO'Vg,
which is  assigned  the value  of 0.   These  results  show  that  a waiting  period may be
unnecessary  for  consumption  of aboveground  crops, and  a waiting period  of  18 months
should provide adequate protection  (probability of infection <  IxlOVserving) for ingestion
                                           74

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        TABLE 6-9  "

VARIATION OF EATER  RISK
WITH TIME OF HARVESTING
10NTH
0
1
2
3
.6
9
12
15
18
ABOVEGROUND
7.439xlO'5
' . . 4.628X10'3
2.699xlO-5
1.632xlO-5
4.502xlOr6
L242xlO-6
3.195xlO'7
, <8xlO'8 , .
<2xlO;s ,
BELOW-GROUND
1.729x10'' ,
. . , ,1. 156x10.-', ,
. .. . 6.914X10"2 .....
: , 4.240X10'2 . ' '• •'. .
1 188x10'
3.290xlO-3
8.477X10-
2.351xlO;4
; 6,247xlO'5
            75

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of root crops.
6.2.3. SWIMMER.  As indicated by trial  runs with bacteria (U.S. EPA, 1990b), the most
significant source of exposure  was the surface  runoff pond.  A peak  in  probability  of
infection  for the SWIMMER  occurred after each  rainfall, which transported   significant
amounts   of contaminated  sediment  into  the  onsite pond (Figure 6-2).  The  maximum
probability of infection for the SWIMMER in Practice I, 0.139, was observed to occur  on
day  70,  after the  heavy rainfall beginning .at hour  1650.  In Practices  II and  III the
maximum probability  of infection  for  the SWIMMER  occurred  on day 66, at a level of
0.00090 in Practice II  and 0.00097 in Practice HI.  Practices II and III limit the  amount of
surface runoff and  sediment  transport  because  of the extent of ground cover characterizing
these practices.   Extensive mulching of soil not covered by crop plants in Practice I would
also be expected to reduce the' amount of transport to the onsite  pond by a small amount.
       The maximum  probability, of infection  for the SWIMMER in the onsite  pond was
dependent on site-specific variables.  The number  of organisms transferred  to the pond by
surface runoff and sediment transport  depended  on both the extent of rainfall and  the
elapsed  time during which  the organisms died off in the surface soil before they  were
transported.   The  maximum probability at'each  site and  for each practice, using default
values for SUSPND arid die-off rates, is given in Table  6-10.
       The time course of  infection  probability for Practice  I  at each site is displayed
graphically in Figure  6-3. It is clear from these results and the rainfall data presented  in
Section  5 that the maximum probability of infection  as a result  of exposure in the onsite
pond  is  closely related  to  the  timing and total  amount  of rainfall  and  to the  farming
practice.
                                           76

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                                                77

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                TABLE 6-1.0

   MAXIMUM PROBABILITY OF INFECTION
BY EXPOSURE TO RUNOFF WATER (SWIMMER)
Site
1.
2..
3.
4.
5.
6.
Anderson Co.,TN
Chaves Co.,NM :
Clinton Co.,IA
Highlands Co.,FL
Kern Co., CA
Yakima Co., WA
I
'K39xlO-'-
2.67x10-'
, 1.62x10-';,,,
7.36xlO-2 •,; -,-,.
3.36x10^
4.54xiO'4
• Practice
II
9.01xlO'4
•... 2.43X10'2
1.09X10'2
. 3.83X10'2
2.93xlO-5
2.80xlO'4
III .
9.69X10"1
6.24xlO'3 "'
LlSxlO'2
3.77xlO-2
2.93xiO'5
2.80xlO'4
                     78

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                               79

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                                  7.  CONCLUSIONS
       Although detailed  data on survival and transport of parasites  in soil are lacking, the
model appears  to  confirm the  general  observations in  the  literature  that  parasites  are
persistent,  justifying land-use restrictions.   Model  runs  implied  that  restrictions  on the
consumption of below-ground crops may be overly conservative.  Reports  of offsite infection
by parasites  in sludge-amended  soil are rare;  model runs  confirm  the  low probability of
offsite infection except by uncontrolled  surface runoff.
         •
7.1.   SENSITIVITY ANALYSIS
       Model runs  showed that within narrow limits, the probability of infection -by parasites
as a  result of exposure  to soil  contaminated  with sewage sludge  is proportional  to  the
concentration of organisms in the sludge, the amount of sludge applied  and the amount  of
contaminated soil  to which the individual is exposed, either by casual contact or ingestion
of food  grown in  the contaminated  soil.  Direct proportionality  of response to exposure
level  is not maintained  over  a wide  range  of concentrations,  however,  because  the
probability of infection  is calculated  by a Poisson distribution,  which is an  exponential
function of exposure rather   than  a proportional  one.  Variations in the  probability  of
infection can be extrapolated  from variations in parasite  concentrations  up to a probability
of about 0.1; the  departure  from linearity  is  5%  at a probability  of 0.093  and 10% at a
probability of 0.176. Many of the parameters of the  model  seemed to have little bearing
on the probability  of infection,   apparently   because they ultimately had no. effect on the
number of organisms  to which  the  human  receptor  was exposed  in each  exposure
compartment, or  because they exerted their effect  on  survival  or transport after  the
 maximum probability of infection  had  occurred.
       The probability of infection was sensitive to the rate of inactivation or die-off of the
 parasite ova, cysts and  oocysts  and to  the  method  of application.  Subsurface  application
 resulted in no exposure to any  individual, because  the ova, cysts and oocysts are modeled
 as being unable to move significant distances in soil.  Future revisions of the model should
 probably  allow for redistribution of pathogens from  subsurface  soil into surface  soil  (see
 Section 8.2).
                                            80

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 7.2.    ONSITE EXPOSURES
  ,  .   Significant onsite .exposures were calculated  in all practices when 5000/kg dry weight
:was used as the parasite concentration in the sludge. The greatest risk, approximately: 0.02
•per day,,was associated  with Practice I, application  of sludge for production of commercial
 crops.  These calculations  imply that the field worker, who inadvertently ingests soil during
 daily activity on the sludge application  site is at significant risk of infection  by parasites.
 The results imply that there should be a waiting period before routine daily activity en.the
 site.  The length  of the waiting period should depend on  the initial  application rate and
 pathogen  concentration  as well as the die-off rate  of  the parasite;  in the  model runs
 reported  here,  the probability of infection  ONSITE in Practice  I was  >0.01 for more than
 30 days and > 10'7 for about 27, months.   ,  	 •;:.:,.   ;   •
       •The maximum risks of infection calculated- in domestic  applications  were lower
 (0.0014 for Practice  IV and 0.0009 for .Practice V), but -not low enough to be protective.
 However,  it must  be noted again  that a concentration  of 5000 parasites/kg  was used in the
 model runs, whereas U.S. EPA regulations for D&M sludge call for a limit of 1 parasite/g
 volatile sludge solids (U.S. EPA, 1989), or approximately 1000/kg dry weight. It is assumed J
 that- incorporation  in these  practices  is done by hand or with power  tools rather than -by
 farm  machinery;  therefore,  the  calculated  exposures/ include  direct  exposure -to .'non-
 incorporated sludge.  During incorporation, the parasite  concentration  is rapidly reduced
 by dilution in  soil, and by the end  of the  second day, the extrapolated   probabilityvof
 infection  is below  IxlO'7 in both practices. In summary,  it appears that * a probability of
infection  greater; than the  arbitrary  benchmark value of 1x10'4 is likely during  application
and incorporation  of D&M sludge.  A person  engaged in  these  activities  could  .probably
reduce the risk by wearing a protective mask and washing  thoroughly before handling food.

7.3.   SEDIMENT  TRANSPORT  AND SURFACE RUNOFF
       The most significant potential source of infection was exposure to runoff water and
transported   sediment after rainfall.   Rainfall  events were  modeled  as  being able-to
transport  contaminated.-. soil from the  field to  the  onsite pond,  where the suspended  or
particle-bound  parasites  accumulated.  A swimmer in the pond  was therefore  exposed  to
the parasites, either  by ingestion of ova, cysts or oocysts or  by infective larvae penetrating
                                          81

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the skin. Model runs indicated that it would be prudent to limit access to runoff water and
sediment from a sludge-amended  field, either by mulching to reduce runoff, ditching and/or
diking to contain the runoff or restricting  access to any onsite ponds receiving runoff.

7.4.   OFFSITE EXPOSURES
       No health hazard was indicated as a result of offsite transport of parasites by droplet
aerosols  or  by wind-blown dust.    This  may be  a model  limitation  caused  by over-
simplification of the Gaussian-plume  aerosol transport subroutine  in the model, or it may
reflect a very low concentration   or probability of transport of viable parasites in aerosols.
Because  it was assumed that transport of ova, cysts and oocysts to groundwater  does not
occur, no  risk from  consumption  ! of groundwater  from  a drinking water well  was
demonstrated.

7.5.   WAITING PERIOD
       Practice-specific waiting periods are required  by the U.S. EPA Pathogen Reduction
Requirements  (U.S. EPA, 1989)-before access to sludge-amended  land or  consumption of
crops grown thereon.   For exposure  comparisons, a probability  of infection  of IxlO'4 was
tentatively  chosen as a benchmark  for sufficient protection of human health  (Section 6.1).
Using this benchmark value, the default values for application rate and die-off rate, and a
parasite  density of5000/kg, the  initial maximum probability  of infection for aboveground
crops  was 
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currently  true,  but also  on sludge  application  rate  and   pathogen  concentration.    In
calculating a safe waiting period, conservative  assumptions should be made about  amounts
of soil ingested  with crops.
                                         83

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                               8. RESEARCH  NEEDS
8.1.    INFORMATION  NEEDS  FOR  PARASITES
       As indicated in Tables 3-3 and 4-1, data on the concentration  of parasite  ova, cysts
and oocysts in sewage sludge after treatment  and on survival of the organisms in sludge-
amended  soil are sparse.  A review of published  literature reveals that data are available
for only a few indicator  organisms.
       Distribution of pathogens in soil or groundwater is poorly understood.  This model
assumes random  distribution  of  pathogens  in environmental  media,  a commonly-made
assumption  that is probably  frequently violated.  Another obvious data gap, illustrated  by
this  methodology and model development,  is-the  degree  of survival and transport  of
pathogens  in the  environment.  Information  on  the fate  of parasites  in groundwater and
subsurface  soil is extremely limited.  The concentration  and  survival rates of pathogens
leaching through  soil into groundwater  are  unavailable for protozoa and  helminths (U.S.
EPA,  1986).  In addition,  the survival of these  organisms  in  soil depends  strongly on prior
conditions of treatment.  For example, mild heating or digestion alone may have little effect
on viability of Ascaris ova, whereas mild heating of digested  sludge rapidly destroys the ova
(Pike  et al., 1988).
       Characterizing the  average or typical concentration of viable ova in  treated sludge
may not be of great  significance  because  the  probability  of infection is directly related to
the concentration of parasites in the particular sample or batch  of treated  sludge.  Each
community's  treatment  system and source material  will be different in some  details  from
the ideal or  average system characterized in research studies.  The treated  sludge  from
individual treatment  systems can  be characterized  more accurately by din;ct  counts than by
assumptions  that they  conform  to  a  typical concentration  distribution.   However, it is
difficult to  characterize  the  survival  of parasites in soil in each individual  case, and a well-
characterized range  of survival under defined  conditions  would be useful.
        Reimers  et al. (1986) concluded  that,  since  Ascaris  and Toxocara are  typically
present in  most municipal sludges applied to land, the following  information  is needed  to
clarify associated health risks: (1) survival of resistant stages of parasites (ova and cysts)
in soil following land  application;  (2)  effects of sewage-treatment  method,  application
                                           84

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 method, soil type, climate, and land use on survival; and  (3) degree  of risk to humans  and
 animals  based on  field  situations.
       Reimers et al. (1990) recommend further work in. the areas of (1) determining  the
 stabilization  conditions  needed to produce sludges meeting PFRP criteria; (2) investigating
 the feasibility of using combined  treatment  processes, such as digestion followed by lagoon
and/or  drying bed storage,  to inactivate pathogens in sludges processed at small Publicly
Owned  Treatment   Works;  (3)  determining  whether   petroleum  hydrocarbons  would
inactivate  pathogens in petroleum-contaminated   sludges;  and  (4)  selecting appropriate
controls  for studies of Ascaris egg survival in different  types of sludges.
       Further research  on pathogen  exposure pathways and infectious doses will facilitate
the predictive accuracy  of this model and  its successors. 'Especially  useful will be:
              Data  on  the  relation  of die-off rate  of  different  parasites  to moisture,
              temperature,  method of application  and previous sludge treatment.  No single
              organism  is really adequate to represent all other parasites.  Ascaris can serve
              as a "worst case" in most instances,  but, for example, some protozoa are much
              smaller and  thus  are more likely to be transported  through  soil  and in
             aerosols.   Data suggest that moisture  and temperature  would probably  have
             significant  effect  on  parasite   survival,  but  the one  conclusion   reached
             following  such a  field  study   is   that there  is  no  statistically  significant
             correlation between parasite egg concentration and environmental parameters
             (Leftwich  et al., 1988b).
             More detailed  quantitative information on any protection provided  by crop
             cover.  It has been  shown that  subsurface injection  of sludge increases  the
             survival of parasite ova and cysts,  but  quantitative data  on relative effects of
             grass, hay, truck crops or  forests on parasite survival are lacking.
             Data  allowing  a  mathematical  description of  die-off as  a  function  of
             environmental   conditions.   Some  authors indicate  that  environmental
             conditions  play  an essential role in determining  the die-off rate  of parasites,
             whereas  others  (Grenfell   et  al.,   1986;  Young,  1983)  see no  statistically
             significant  effects.  It is likely that a variety of confounding variables have
             obscured the effects  of easily-measured  environmental   parameters  on  die-
                                          85

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             off rates.  With sufficient study, the effects of environmental  conditions on
             survival may become  more obvious.

       In  summary,  the   following  research  priorities   are   recommended   to  allow
development of a definitive risk assessment for parasites inland-applied  sludge:
ESI Helminths:
             Standard quantitative  methods  for examining helminths  in sludge  and soil
             samples and  in liquid droplet and dry particulate  aerosols;
             Data on transport in water, soil and  aerosols;
             Die-off rates  in water, soil and  aerosols;
             The relationship  of those decay rates to  environmental  conditions,  previous
              sludge treatment,  method  of sludge  application  and various effects of crop
              cover.
gfir Protozoa:
              Standard  quantitative  methods  for examining  protozoa  in sludge  and soil
              samples and  in liquid droplet and dry particulate  aerosols;  and
        .   .  Quantitative  data  on occurrence  and survivability of protozoa  in treated
              sludge.
 If results indicate that protozoa  survive in sludge,  the  following additional research  needs
 become a priority:
              Data  on transport  in water, soil and aerosols;
              Die-off rates  in water, soil and aerosols;
              The .relationship  of those  decay rates to environmental  conditions,  previous
              sludge treatment,  method of sludge application  and various  effects of crop
              cover.
 8.2.   MODEL DEVELOPMENT
        The  current version of the Sewage Sludge Pathogen Risk Assessment model is not
 adequate  to address some of the properties  of parasite survival in soil. In particular, it has
 been  noted that cycles of freezing and  thawing may kill parasite ova more  rapidly than
 exposure  to a constant temperature at either  extreme ofthe cycle (Leftwich et al., 1988a).
                                            86

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 The  model calculates  a daily average  temperature  for each  day of the  model  run, but it
 does not address the diurnal temperature  cycle which can result in subfreezing temperatures
 at  night on days with an average  temperature  above freezing.   It  should  be possible  to
 program a diurnal cycle into the temperature  calculation  subroutine  and flag for a freeze-
 thaw cycle.  The flag can in turn result in decreasing the  population  of viable parasites by
 a fraction  specified by default  or by the  user as one of the operating parameters.
       Mathematical  descriptions of the  die-off of parasite ova  and  cysts as a function  of
 temperature and  moisture are  not yet adequate  to allow  construction of algorithms in the
 model  for die-off rates.    However,  it appears   that  a simple  relationship  between
 temperature and die-off rate  of ova may not occur (Ferris  et al., 1978; Grenfell et al., 1986;
 Young,  1983), and the equation  used to  calculate die-off rate will probably  have to be  of
 a different  form than that currently used for bacteria and viruses.
       In the present  version, the model does  not allow for direct contact with sludge
 during incorporation  in  Practices I, II and  HI.  Instead,  it is assumed  that  all exposures
 during incorporation occur via inhalation  of dry aerosols generated by the machinery used
 to incorporate  the sludge.  It might be more reasonable  to include inadvertent ingestion of
 unincorporated  sludge in these practices, as occurs in Practices  IV and V.
       The model  assumes that  tilling  will not disturb the soil below 15 cm, so parasites
 injected  into subsurface soil are not transferred to surface  soil.  However, plowing is deeper
 than  tilling and would be expected  to  redistribute  subsurface soil.  Some transfer  factor
 could be added to the model to  allow  for redistribution  of pathogens  from  subsurface to
 surface soil when the field is plowed.
       As  described  in  Section  3 above,  there  are significant differences  in  size  and
probably in survival between  helminths and protozoa, and it  might be prudent to include
 the option  to model transport of protozoa  in groundwater.  Future revision of the Pathogen
Risk  Assessment  Model  might  include  providing  separate  options for  helminths   and
protozoa, with separate sets  of default values, or a flag to enable or disable Subroutine
GRDWTR,  the groundwater  transport  subroutine.
       The  present version of the Pathogen  Risk Assessment  Model does  not include an
onsite pond in Practice  V, the home  lawn application.  For a better  description  of sludge
use on public parks and golf courses, which are more 'likely to have ponds, it might be
                                           87

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beneficial to add the option for existence of a pond onsite.  For even more flexibility, the
user could be asked to specify which exposure calculations to print in the output  table.
       The  limits  of  Subroutine  RAINS  should  be further characterizcjd   to  establish
operating boundaries  for  input  variables.  These boundaries  could be set by having the
program return  a warning  message and possibly  revise the input data to  a  value that would
not cause the program to  crash.
       Limitations  in  offsite  transport subroutines  may limit accuracy  of the model, but
constraints on the size of a model able to run on a personal computer make it unlikely that
more sophisticated  routines can be added.  For example, sophisticated air dispersion models
are large and complex and could probably not be added  to the current model.  Adding the
capacity to model more than  one windstorm (the  current  model limit)  would probably  be
feasible  without  making the  model too unwieldy.  It is likely that  further analysis of the
model  using other  pathogens  will reveal additional  areas  in which  the model can  be
improved.

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                                  9. REFERENCES


 Altaif, K.I. and A.Y. Yakoob.  1987. Development and survival of Haemorichus  contortus
 larvae on pasture in Iraq.  Trap. Anim. Hlth. Prod.  19:  88-92.         •

 Arther, R.G.,P.R. Fitzgerald and J.C. Fox.  1981. Parasite  ova in anaerobically digested
 sludge.  J. Water Poll. Contr. Fed.  53(8): 1334-1338.

 Beaver, P. and G. Deschamps.  1949. The viability of Entamoeba histolytica in soil  Am
 J. Trop. Med.  Hyg. 29: 189-191.  (Cited in U.S. EPA, 1988)    ,       :

 Beaver,  P.C.,R.C. Jung and  E.W. Cupp;  1984.  Clinical Parasitology,  9th ed.  Lea  and
 Febiger, Philadelphia,   p. 512-522.

 Binder, S.,D. Sokal and D. Maughan.  1986.  Estimating  soil ingestion:  The use of tracer
 elements  in estimating the amount  of soil ingested  by young children.  Arch  Environ
 Health 41:  341-345.

 Black, M.I.,P.V. Scarpino, C.J. O'Donnell,  K.B. Meyer, J.V.  Jones  and E.S. Kaneshiro.
 1982.  Survival rates of parasite  eggs in sludge during aerobic  and  anaerobic  digestion
 Appl.  Environ. Microbiol.   44(5):  1138-1143.

 Block, J.C.,Havelaar,  A.H. and  L'Hermite, P.  1986.  Epidemiological Studies of Risk
 Associated  with the Agricultural Use of Sewage Sludge: Knowledge and Needs.  Elsevier
 Applied  Science  Publishers, London,  p. 154-165.  (Cited  in  Pike et al.,  1988)

 Brudastov,  A.N., L.N.  Krasnonos,  V.R. Lemeler  and Sh. Kr. Kholmukhamedor.   1970.
 Invasiveness of Ascaris lumbricoides  eggs for man  and  guinea  pigs after a 10-year  stay in
 the soil. Med. Parazitol. Parazit. Bolezni 39(4): 447-451.  (Cited in Jakubowski,  1988)

 Bryan, F.L.  1977.- Diseases transmitted  by  foods  contaminated  by wastewater  J Food
 Protection 40(1): 45-56. (Cited in Kowal, 1985)

 Burden, D.J. and N.C.Hammet.  1979. The development and survival of  Trichuris suis ova
 on pasture plots in the  south of England. Res.  Vet. Sci.  26: 66-70.

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                                         89

-------
Carroll, J.J. and  D.R. Viglierchio.  1981. On the transport of nematodes  by the wind., J.
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                                                                                *
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                                           94

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                                         96

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                                      APPENDIX                                      ,
                                 MODEL OVERVIEW

       Five  sludge management  practices,  representing  land  application,  and  D&M
management options,  are included in the present  model and  are  numbered  I-V. They are
listed in Table A-l and illustrated in Figures A-1 through A-5.  Two of the practices use
heat-dried  or composted sludge  for residential  purposes and three  use liquid  sludge for
commercial farming operations.  Since each of these two types of sludge represents  a wide
range of sludge treatment possibilities,  the extent of treatment  or conditioning prior to land
application  must be approximated for each  case  (i.e., the pathogen  concentration  in the
applied sludge must be specified).  The computer  model represents the compartments and
transfers among compartments  of the five management  practices.  The  compartments  are
the various locations,  states or activities  in  which sludge  or  sludge-associated   pathogens
exist; they  vary to  some extent among practices. •- In each  compartment,  pathogens either
increase, decrease  or remain  the same  in  number  with time, as specified  by "process
functions"  (growth, dieoff or no population changes) and  "transfer functions" (movement
between compartments). The population in each compartment,  therefore,  generally varies
with time and is determined  by a combination  of initial, pathogen input, "transfer functions"
and  "process functions." The populations  of pathogens in the cornpartments  representing
human  exposure locations  (designated  with an asterisk  in Figures A-l through A-5 and in
Table A-2), together with appropriate intake and infective dose data, are used to estimate
human  health risk.
       Although each  practice listed in Table  A-l is different,  all  five practices  share
common characteristics.   All compartments  that appear  in one or more of the five sludge
management  practices  are listed in Table A-2.  Those compartments  with an asterisk
represent exposure sites for the human  receptor:                           •
            • 3* inhalation  or  ingestion of emissions from application of sludge or
             tilling of sludge/soil;
             5* inhalation  or ingestion  of windblown or mechanically generated
             particulates;                         .
             6* swimming  in a pond fed  by surface water runoff;
                                         .A-l

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                         TABLEAU




COMPARTMENTS INCLUDED IN. THE SLUDGE MANAGEMENT  PRACTICES
Compartment
Name and Number
• • -
Application
Incorporation
Application/Tilling
Emissions
Soil Surface
Participates
Surface Runoff
Direct Contact
Subsurface Soil
Groundwater
Irrigation Water
Soil Surface Water
Offsite Well .
Aerosols
Crop Surface
Harvesting
(Commercial) Crop
Animal Consumption
Meat
Manure
Milk
Hide
Udder
	 	 Liquid Sludge
Management Practices
• ;,,!., j 	 	 	
1
2
3* •' TV..;;-
4 "
5* '••
6* - -.
'• .7* ... '...I '.'"
8 \.
9 >.-.v.-"ป.
10 ,.™. ,
' .iju.^, '.:,:._.
ii*":',;"~--'
"134T" /"•'
14
15
16* < --.
*





II
1
2
3*
4 .
5*
6*
..7* . ' '
8
9
10
11
12* •
13*
14


17
18*
19
20*
21
22
III
V": ' '
2 ' :"
3*
4
5*
• 6*
7*
8
9
10
11
12*
13*
14
15

17
18*
19
20*
21
22
Dried/Composted
Sludge Management
Practices
IV V
1 1
3* 3*
4 ' 4
.-5* 5*
. 7* . -.. .7*
8 8


11 ' . 11 .


14 * 14
15
16* ,






'''Indicates exposure compartment
                          A-2

-------
                                                 Application/Tilling
                                                   Emissions
                            External
                            Sourca
                           FIGURE A-1
Input/Output Diagram for Practice I - Application of Liquid Sludge
  for Production of Commercial Crops for Human Consumption

-------
                           Application
Application/Tilling
   Emissions
                             Soil
                            Surface
                             Crop
                            Surface
                            Animal
                          Consumption
                            Manure
                            Irrigation
                             Watar
                            External
                            Source
                           FIGURE A-2
Input/Output Diagram for Practice II - Application of Liquid
                  Sludge to Grazed Pastures
                                A-4

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 Subsurface
   Soil
Groundwater
  Offslta
   Well
                                   Application
                   Partlculates
                                     Soil
                                    Surface
 Crop
Surface
                                      ir    15
                                   Harvesting
                                    Animal
                                  Consumption
                                    Manure
                                   Irrigation
                                    Water
                                    External
                                    Source
                       Application/Tilling
                          Emissions
                                   FIGURE A-3
  Input/Output Diagram for Practice III - Application of Liquid Sludge
    for Production of Crops Processed before Animal Consumption
                                      A-5

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Subsurfac*
  Soil
                                                              3*
                                                   Application/Tilling
                                                     Emissions
                           FIGURE A-4

    Input/Output Diagram for Practice IV- Application of Dried
     or Composted Sludge to Residential Vegetable Gardens
                               A-6

-------
Subsurface
  Soil
                                                   Application/Tilling
                                                      Emissions
                            FIGURE A-5
    Input/Output Diagram for Practice V - Application of Dried
            or Composted Sludge to Residential LaWris
                                A-7

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                                   TABLE A-2

         SLUDGE  MANAGEMENT PRACTICES  AND  DESCRIPTIONS  ;IN
                          LAND APPLICATION  MODEL
PRACTICE
DESCRIPTION
                   Application  of Liquid Treated  Sludge for .Production of Commercial
                   Crops for Human  Consumption
 H                 Application  of Liquid Treated  Sludge to Grazed Pastures

 III                Application   of  Liquid  Treated   Sludge  for  Production  of  Crops
                   Processed before Animal Consumption

 IV                Application  of Dried or Composted  Sludge to Residential  Vegetable
                   Gardens

 V                 Application  of Dried or Composted  Sludge to Residential  Lawns   ,
Two types of sludge are used in this model. - liquid and dried/composted.   The extent of
treatment or conditioning prior to application is variable and must be determined for each
case.
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             7* direct  contact  with sludge-contaminated  soil  or  crops  (including
             grass, vegetables, or forage crops);
             12* drinking water from an offsite well;
             13* inhalation  and subsequent ingestion of aerosols  from irrigation;
             16* consumption of vegetables grown in sludge-amended  soil;
             18* consumption of meat or
             20* consumption of milk from cattle  grazing on  or  consuming forage from
             sludge-amended fields.       " • ,
       The first 14 compartments, * most of which are common to all practices,; are described
below.                   •.-•'.-            .:        ;.
       APPLICATION  (1) represents  the application  of sludge to a field (default size 10
ha) or to a yard or garden of specified size. Liquid sludge may be applied by spread-flow
techniques,  by spray, or by  subsurface  injection.   The application  rate and pathogen
concentrations  are variables  to be entered  by the user of the model.  During spread-flow
and spray application, sludge will be spread thinly on the soil,  where it will be subject to
drying, heating and  solar radiation,  thus losing the protective  benefits provided  by bulk
sludge. It is assumed, therefore,  that inactivation  will occur at  a rate  characteristic of the
organism in soil at 5ฐC above the ambient  temperature  (Brady, 1974; USD A, 1975). It is
also assumed that  liquid sludge is absorbed by the  upper 5 cm of soil surface  during  this
time.     The  default   time  period   for   transfer   from   APPLICATION   (1)   to
INCORPORATION   (2) is 24 hours, which allows a field treated with liquid sludge to  dry
sufficiently to plow or cultivate.  If the injection option is chosen, the liquid  sludge goes
directly to SUBSURFACE SOIL (8) at hour 10.  During spray application of liquid sludge
or application  of dry  composted   sludge, droplets  or loose  particulates  may  become
airborne.  Liquid  aerosols are modeled  by a  Gaussian-plume  air dispersion  model that
calculates  the downwind concentration of airborne  particulates.. Dry particulate  emissions
are calculated using  models for generation  of dust by tilling or mechanical disturbance of
soil.      Both    are   represented    as    transfers   from    APPLICATION     (1)   to
APPLICATION/TILLING  EMISSIONS  (3).
       INCORPORATION  (2) involves the mixing, by plowing or cultivation,  of the sludge
and sludge-associated  pathogens  evenly  throughout the upper 15 cm of soil.   Process
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functions associated with this compartment are the same as for the relevant pathogen  type
in soil.  Particulate  emissions generated  by cultivation  are represented  by a. transfer from
INCORPORATION  (2) to APPLICATION/TILLING  EMISSIONS (3) beginning at hour
24, extending for enough  time to cultivate the field (at' a rate of 5 ha/hr) or till the garden
or lawn (at a rate  of 0.002 ha/hr).  At the end of this time,  all remaining  pathogens  are
transferred  to  SOIL SURFACE  (4).
      APPLICATION/TILLING  EMISSIONS  (3*) is an exposure compartment  that
receives the dust, or suspended  particulates,  generated  by application  or by the tilling of
dried sludge or sludge-soil mixture. It also receives aerosols generated  by spray application
        ป                            -
of liquid sludge.  All process  functions associated with this compartment are incorporated
in the aerosol  subroutines.   Exposure  in this compartment is by inhalation  but, as in all
inhalation  exposures, model simplification limits the exposure  to the pathogens  assumed to
be ingested after the inhaled dust or aerosol spray is trapped in the upper respiratory  tract,
swept back to  the mouth  by ciliary action and swallowed.
      SOIL SURFACE (4) describes the processes occurring in the upper 15 cm (Practices
I,  IV and V)   or  upper  5 cm  (Practices II and III) of the soil layer.   Microbes  are
inactivated  at rates characteristic  for  moist ' soil at  5ฐC  above the chosen  ambient
temperature  (Crane and  Moore,  1986; Kibbey  et  al., 1978).   Transfers  from SOIL
SURFACE (4) occur by wind to WIND-GENERATED   PARTICULATES  (5), at a time
chosen  by  the user, by surface  runoff  and  sediment  transport  after  rainfall events  to
SURFACE RUNOFF  (6), by a person  walking  through the field or contacting  soiled
implements or clothing or by other casual contact to DIRECT   CONTACT  (7), by leaching
after irrigation or rainfall  to SUBSURFACE   SOIL (8), by resuspensipn during irrigation
or rainfall to SOIL  SURFACE WATER  (11), or at  harvest to CROP SURFACE (14).
      WIND-GENERATED  PARTICULATES  (5*)  describes  the airborne  particulates
generated  by wind.  Process functions are the same as for the organism in air-dried  soil at
the ambient temperature   (Crane  and  Moore,  1986; Kibbey  et  al., 1978).  The exposed
individual  is standing in the field or at a user-specified  distance  downwind from the field
during a windstorm. The  wind-generated  exposure is calculated from user-specified values
for duration  and severity  of the windstorm (default values, 6  hr at 18 m/sec (40 mph)).
      SURFACE RUNOFF  (6*) is an exposure compartment  describing  an onsite pond
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containing pathogens transferred from SOIL SURFACE (4)'by surface runoff arid sediment
transport  after  rainfall.   These  processes  are  described  by a  separate  subroutine.
Inactivation  rates in this compartment are characteristic  of microbes in water and are much
lower than rates for soil.  Water is removed from the pond by infiltration and, recharge of
the groundwater aquifer, but it is assumed that no microbes are transferred  by this process.
The human  receptor is an individual who incidentally ingests 0.1 L of contaminated  water
while swimming in the  pond.  This  compartment is also an exposure compartment for cattle
drinking  20 L of water daily from  the pond (Practice II).
       DIRECT CONTACT (7*) is the  exposure compartment  for a worker or a child less
than 5 years old who plays  in  or walks through  the field,  yard  or garden,  incidentally
           !   -    ' :               •               .                            *
ingesting O.lgof soil or vegetation  at the daily geometric  mean concentration of pathogens.
This human receptor  represents  the  worst-case  example  of an  individual  contacting
contaminated  soil  or soiled clothing  or  implements.   No process functions are associated
with this compartment  because it  is  strictly an exposure  compartment.
       SUBSURFACE  SOIL (8) describes  the processes  and transfers for pathogens  in the
subsurface  soil between  5 or 15.cm depth  and  the water table.   It also serves  as the
incorporation   site  for subsurface  injection  of  liquid sludge.   Process  functions  in
SUBSURFACE  SOIL  (8) are  the  same  as  for moist soil  at  the ambient temperature.  The
transfer from SOIL SURFACE (4) occurs  after each rain or irrigation  event as a result of
leaching  from the soil  surface.  The time of transfer  is calculated by dividing the  depth of
rainfall  or  irrigation'  by  the  infiltration  rate.  Transfer  to GROUNDWATER    (9) is
arbitrarily set at one hour later.  At  present, the relation between  unsaturated  water flow
and  subsurface  transport  has not-  been  Well-established.    Thus, this model  lacks a
satisfactory  subroutine to describe  pathogen  transport  from • the  subsurface  soil  to
groundwater.   Instead,  user-specified  variables  are  used to  describe  the  fraction  of
pathogens transferred  from SOIL  SURFACE (4)  to SUBSURFACE  SOIL (8) and from
SUBSURFACE  SOIL  to  GROUNDWATER.
       GROUNDWATER   (9) describes  the ' flow of pathogens  in the saturated   zone.
Process functions  are  the sarhe as  for  other water  compartments.    Transfers occur to
IRRIGATION  WATER  (10) if the water is needed  for  irrigation  or to OFFSITE WELL
(12*) if the water  is used  for  drinking.   The  number  of pathogens  transferred  to
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IRRIGATION  WATER  (10)  is based  on  the  concentration   of pathogens  in  the
groundwater  compartment  and  the total  depth  of irrigation.   The transfer to OFFSITE
WELL (12) is described by a modification  of the subsurface solute transport model of van
Genuchten- and Alves (van  Genuchten and Alves, 1982).  Because microbes in suspension
are passively  transported  by bulk  water flow and interact  with soil particles by adsorption
and desorption, they behave  similarly enough  to  dissolved chemicals  that existing solute
transport models can be  used to describe  their fate in the saturated zone (Gerba, 1988).
      IRRIGATION  WATER  (10) describes  the transfers  for pathogen-contaminated
water used for irrigation.  No processes are associated  with this compartment because  it is
intended  as a transition  compartment.  Irrigation  of the field, lawn or garden  takes place
a user-specified number of times  each week.  This irrigation water  may come  from either
an onsite well fed by GROUNDWATER   (9) or from  an  outside source  of treated,  liquid
sludge.  The  default conditions vary by practice.  In either case,  AEROSOLS   (13) are
                                                        '
generated  unless a non-spray option is chosen. Spray irrigation is the default since it would
be most likely to cause a significant exposure to workers or offsite persons,,  In addition to
aerosol emissions, irrigation transfers pathogens  to CROP  SURFACE  (14) and to SOIL
SURFACE WATER (11).
      SOIL SURFACE WATER  (11) represents any irrigation water or rainfall  in contact
with the ground prior to infiltration.  This compartment  describes the temporary suspension
of pathogens  in such a water layer and their subsequent  transfer to CROP  SURFACE (14)
or  to  SOIL   SURFACE   (4).    Process  functions are  the  same  as  for other  water
compartments.                       -                       :
      OFFSITE WELL  (12*) is the  exposure site  for a human receptor  drinking 2 L/day
of contaminated  water  whose  pathogens  have been  transported  through groundwater.
Process functions  are the same as  for groundwater.  The groundwater  transport subroutine
supplies the concentration  of pathogens  in the well at a  user-specified  distance  from the
source.   No  transfers out  of the  compartment 'are specified  because  it  is an  exposure
compartment  only.
      AEROSOLS  (13*) describes fugitive emissions  from spray irrigation, which occurs
at a default  rate  of 0.5 cm/hr  for 5  hr.   The  source of irrigation  water producing
AEROSOLS  can be an onsite well-(i.e., GROUND WATER)  or liquid sludge. A  Gaussian-
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plume  model  is used to,calculate  concentrations  of airborne  microbes downwind.  The
human reqeptor  is an onsite worker or a person offsite who is  exposed  during the time of
irrigation. .-      	         ,
      ..CROP  SURFACE  (14) describes. contamination  of vegetable  or forage  crops  by
transfer of user-specified amounts  to or  from SOIL SURFACE  (4), from IRRIGATION
WATER (10), or to or from SOIL SURFACE .WATER (11).  Process functions are not
well characterized  but are  assumed to be influenced by drying, thermal  inactivation and
solar radiation; they are thus most characteristic  of pathogens  in surface soil.
                                                                         *
       These preceding  14 compartments  are common  to  most  of  the, five  practices
modeled.   The following descriptions  of the five management  practices help clarify the
differences  among the practices.                                ,

Practice I:  Application of Liquid Treated Sludge for Production  of Commercial  Crops for
Human Consumption.                      .
       Liquid  sludge  may be applied  as fertilizer/soil  conditioner  for the production  of
agricultural  crops for human consumption  or for animal forage or  prepared  feed.  Both
existing (40 CFR  257.3-6)  and proposed  (U.S. EPA,  1989)  regulations  prohibit direct
application  of sewage sludge to crop surfaces.  Therefore,  this  .model practice is designed
for a single application of liquid sludge, which is incorporated into the soil before the crop
is planted.   Regulations also require various waiting periods before the planting of crops
that will be consumed  uncooked by humans.  These restrictions, however, are optional in
the model  and can  be tested.   .....-.,.        ,                .
       Vegetables  can be grown aboveground,  on-ground  or  below-ground.   These  are
represented  by tomatoes, zucchini and carrots, respectively.  At HARVESTING (15) time,
all pathogens remaining on  CROP SURFACE (14) are transferred  to HARVESTING (15),
which represents a .single harvest of all of the crop. The same  process  functions apply as
in  CROP SURFACE (14).  The crop  is held for 24 hours before being processed.  The
number  of pathogens  is  then  transferred   to  COMMERCIAL   CROPS  (16*),  the
compartment in  which further processing  takes place. The number of pathogens/crop  unit
following processing  is calculated   in  this  compartment and  is the figure used  in  the
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vegetable-exposure   risk calculations.   A 24-hour  pathogen  exposure  is computed  by
Subroutine VEG.  Pathogen  concentrations  are determined  as number/crop  unit for each
sludge management  practice.  Before being consumed,  vegetables normally are processed
in some way. Included  in the program is a series of user-selectable processing steps. The
user has  the option of choosing  any or all processing  steps  and  of  specifying some
conditions  within  processing  steps.   The human  receptor  is a person  who consumes
minimally  prepared  vegetables  (washed, but  not peeled  or cooked)  at  a rate of 81 g
tomatoes,  80 g zucchini or 43 g carrots per eating occasion (Pao et al., 1982).
          #                  .          , "-    •      ,     '-
Practice II: Application of Liquid  Sludge to Grazed  Pastures.
       *                                 . . •.  .                    ,
       In this practice, liquid sludge is applied  as fertilizer, soil conditioner and irrigation
water for the  production of forage  crops for pasture.  This model practice is designed for
repeated  applications of liquid sludge, initially on a field with a standing forage crop used
for pasture.  It is assumed  that spray irrigation  will be used because this method is effective
for delivering  large amounts of sludge to a large area.  In this way, the pasture is also used
as a final treatment  and disposal system  for the treated sludge.  The  irrigation rate, the
total weekly  depth  and the number of times  per  week can  be specified  by the user.  A
sludge solids concentration of 5% is assumed.
       The model assumes that each hectare of pasture supports  12 head of cattle, although
both area and herd size may be varied. This may be a  higher density than is the common
practice for fields that receive no irrigation, but with adequate  irrigation,  sufficient forage
is expected  to be  produced.   Current and proposed regulations  require  various waiting
periods before animals can  be grazed.   These requirements  can also be tested  by the
model.
       ANIMAL CONSUMPTION'  (17) describes the ingestion of CROP  SURFACE (14)
by cattle  grazing in the pasture.  Transfers from ANIMAL CONSUMPTION   (17) are to
MEAT (18*), MANURE  (19) and  MILK (20*).
       MEAT (18*) is the compartment  describing transfer  of pathogens   from ANIMAL
CONSUMPTION  (17) to meat. The human  receptor  is assumed  to consume 0.256kg of
meat daily (U.S. FDA, 1978). Contamination  of meat by gut contents  during  slaughter  or
by systemic infection  by sludge-borne pathogens can be modeled.  The model  allows for
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inactivation  of pathogens in meat by cooking,  assuming reasonable  cooking times and
temperatures.
       The production  and consumption  of milk  from cattle  pastured  on  the sludge-
amended  field are modeled  when  the dairy cattle option  is chosen.  The default condition
is for consumption of raw milk because commercial production' of milk poses an extremely
small hazard  of exposure to pathogens.  In the  model,  contamination  from dirty utensils
and careless handling are combined  as  a  transfer from  the  manure-contaminated  udder
[MANURE (19)], which occurs at each milking. All three pathogens can enter  milk by this
route.   MILK (20*)  is the compartment  describing production  and  consumption  of milk
from cattle pastured  on the sludge-amended  field when the  dairy cattle option .is" chosen.
The default  condition models the consumption . of raw  milk that has  been  stored  for  24
hours.  In exposure  calculations, it is assumed that  the human receptor consumes  2  kg
milk/day, roughly three  times  the  national  average milk consumption  (U.S. FDA, 1978).

Practice III:   Application  of Liquid  Treated  Sludge for Production of Crops Processed
before Animal Consumption.  ,
       In this practice, liquid sludge is applied  as „fertilizer, soil conditioner  and irrigation
water for the production  of forage  crops  to be processed  and  stored  for animal  feed.  This
model practice  is designed for repeated  applications of liquid  sludge, initially on a  field
with a  standing  forage  crop.   It  is assumed  that spray irrigation  will be used  for the
application of liquid  sludge, because  this method is effective  for delivering large amounts
of sludge to a large area.   In  this way, the field is also used as a final treatment  and
disposal  system for the treated  sludge. The rate, the total weekly depth and the number
of irrigations per  week  can  be changed by the user.  A sludge solids concentration  of 5%
is assumed.   The risks  to the human receptor  are similar to those  for the preceding
practice, i.e.,exposure through meat  or milk, in addition  to direct contact with the forage
grown in the field.

Practice IV:  Application of Dried or Composted Sludge to Residential Vegetable Gardens.
       Dried or composted treated  sludge  may be sold  or given away to the  public  as a
bulk or bagged product  for use as  fertilizer  or soil, conditioner  for  the production  of
                                         A-15

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domestic  garden  crops  for human consumption.  Although  some studies  have shown that
composting  is highly effective in removing pathogens  from sludge (Wiley  and Westerberg,
1969), other  studies have shown that  bacterial pathogens may grow in dried or composted
sludge to  concentrations  of Ixltf organisms/kg  dry weight (U.S. EPA, 1988).  Exposure of
individuals to materials  used  in home gardening would be  expected  to be more frequent
than  exposure  in a commercial  agricultural setting,  Therefore,  this practice would be
expected  to pose a greater  risk of infection. This  model practice is designed  tp describe
the application  of dried or composted treated  sludge, which is incorporated   into the  soil
before the crops  are planted.
       Vegetables can  be grown  aboveground,  on-ground  or below-ground.  These  are
represented   by tomatoes,  zucchini and  carrots, respectively.   The  user  may specify  the
proportions   of above-ground,  on-ground  and  below-ground   crops  in the  garden.   At
HARVESTMG  (15)  time, all  pathogens remaining  on  CROP   SURFACE  (14)  are
transferred  to  HARVESTING  (15).   The same  process  functions apply  as  in  CROP
SURFACE  (14).  The crop is held for 24 hours before being processed.  The number of
pathogens is then transferred to CROP (16*), the compartment  in which further processing
takes place.  The number of pathogens/crop unit following  processing is calculated  in  this
compartment and is the figure used in the vegetable-exposure  risk calculations. A 24-hour
pathogen  exposure  is  computed  by Subroutine   VEG.    Pathogen  concentrations   are
determined   as number/crop   unit  for  each   sludge  management  practice.  Pathogen
concentrations  are determined  as  number/crop   unit.
       Before being consumed, vegetables  normally are processed  in some way.  Included
in the program  is a series of user-selectable processing  steps.  The  user has the option of
choosing any or all processing steps and  of specifying some conditions within processing
steps.  In  the default condition, the human  receptor is a person who consumes  minimally
prepared vegetables  (washed,  but  not  peeled or cooked) at a rate of 81 g tomatoes, 80 g
zucchini or 43  g carrots per eating occasion (Pao et al., 1982).
                                                 •            ^
Practice V:   Application  of Dried  or  Composted Sludge to  Residential  Lawns.
       Dried  or composted  treated sludge may be made available to the  public as  a bulk
or bagged product to be sold or given away for use as fertilizer or soil conditioner for  the
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preparation  'of a seed bed for domestic lawns. Individuals engaged in preparing a seed bed
for a lawn are likely to come into contact  with the soil and any additives  used to improve
the  seed  bed.   If the soil  or  the  additives contain pathogens,  this practice  would  be
expected  to  pose  a risk  of infection.  This model  practice  is-designed  to describe  the
application of dried or composted  treated  sludge, which is incorporated  into  the soil before
the lawn is seeded.
       The  main exposure in this practice  is for  the lawn  worker or for a child younger
than 5 years old who plays in or walks through the lawn  site, incidentally  ingesting  soil or
crop surface at the daily geometric mean concentration of pathogens.  This human receptor
represents  the worst-case example of an individual contacting  contaminated   soil or soiled
clothing or implements.  Before all  pathogens  have been transferred to SOIL SURFACE
(4), exposure is at  the pathogen  concentration found in undiluted  sludge whereas, after the
transfer, the  concentration  is that  calculated for the  soil-sludge mixture.
       After  840 hours, the time assumed  necessary  for  the. lawn to require mowing, the
lawn is mowed weekly, and  a fraction of the pathogens  associated with CROP SURFACE
(14) are transferred to DIRECT  CONTACT (7).  It is assumed  that the person mowing the
lawn is exposed  by inhalation and/or, ingestion at each mowing.
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                                   REFERENCES

Brady, N.C.  1974. The Nature and Properties  of Soil.  Macmillan  Publishing Co., Inc.,
New York.  p. 266-276.               '         ';

CFR  (Code of Federal Regulations).  1988.  Disease,  40 CFR 257.3-6. In:  U.S. EPA,
Criteria for classification of solid waste disposal  facilities and practices,  4(3 CFR 257.3.

Crane, S.R. and J.A. Moore.  1986. Modeling enteric bacterial  die-off:  A review.  Water
Air Soil Pollut.  27: 411-439.

Gerba, C.P. 1988. Alternative  Procedures  for  Predicting  Viral and Bacterial  Transport
from  the Subsurface into  Groundwater.  Draft.  U.S. Environmental  Protection Agency,
Cincinnati, OH.

Kibbey, HJ.,C. Hagedorn and  E.L. McCoy.  1978. Use of fecal streptococci as indicators
of pollution in soil. Appl. Environ. Microbiol.   35:711-717.

Pao, E.M.,Fleming, K.H.,Guenther,  P.M. and Mickle,  SJ. 1982. Foods commonly eaten
by individuals:  Amount per day and per eating occasion.  U.S. Department  of Agriculture,
Economics Report  No. 44.

U.S. EPA.  1983. Section  11.2, Fugitive Dust Sources.  An AP-42 Update of Open  Source
Fugitive  Dust  Emissions.   EPA  450/4-83-010.  Office of Air  Quality  Planning and
Standards,  Research Triangle Park, NC.

U.S. EPA.  1988.  Occurrence  of Pathogens in Distribution  and  Marketing  Municipal
Sludges.  Prepared  by County Sanitation  Districts  of Los Angeles  County for the  Health
Effects Research Laboratory,  Office of  Research  and Development, Research  Triangle
Park, NC.  EPA/600/1-87/014.   NTIS  PB88  154273.

U.S. EPA.   1989.  Standards for the  Disposal of Sewage  Sludge; Proposed  Rule. Federal
Register  54(23): 5886-5887.                           ,

U.S. FDA  (U.S. Food  and Drug Administration).  1978.  FY78 Total Diet  Studies.

van Genuchten,  M.T. and  W.J. Alves.  1982.  Analytical solutions on the one-dimensional
convective-dispersive solute transport equation.   USDA Technical Bulletin  No.l66i.

Wiley, B.B. and  S.C.  Westerberg.   1969.   Survival of human pathogens,  in composted
sewage.  Appl. Microbiol.   18: 994-1001. .
ซU.S. GOVERNMENT PRINTING OFFICE: 19 91 . S18 . 1.8 7,2 0 5 8 1
                                        A-18

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