Under the CERCLA  and RCRA programs, a baseline risk
assessment is required to detemme whether a Super fur.d sits  or
RCRA facility poses  a  current or potential risk to human healt.i
and the environment  in the absence of any remedial or corrective
action.  In tne CERCLA program, potentially responsible parties
(PRPs) may perform the baseline risk assessment, and, in the  RCRA
corrective action  program, owner/operators may perform the
baseline risk assessment.  Or, in either program, the lead agency
may instead choose to  perform the baseline risk assessment.   As  a
result, risJc assessments may be performed by either the regions,
states, PRPs , owner/operators, or their corresponding
contractors.  This practice may lead to inconsistencies in
assessing risk.  In  particular, assumptions for soil ingestion
often vary.

     The problem of  inconsistency is further exacerbated by the
various Agency guidances that may be used in developing risk
assessments.  Current  Agency guidance available for risk
assessments at CERCLA  and RCRA sites are:   (1) the Superfund
Public Health Evaluation Manual (SPHEM)  (October  19861 ; (2) the
Draft Endangerment Assessment Handbook  (August 1985);  (3) the
Draft Exposure Factors Handbook (May 1988); (4) the Final Draft
Superfund Exposure Assessment Manual (SEAM) (September  22, 1987);
(5) the Draft RCRA Proposed Corrective  Action Rule  (June  1938);
(6) the RCRA Facility  Investigation  (RFI) Guidance  (December
1987); and (7) the Surface Impoundment  Clean Closure Guidance
(October 12, 1987).  within each of these guidances a  range of
soil ingestion rates is provided for projecting actual  or
potential exposure levels.  These ranges are as follows:

                                        Daily Soil  Ingestion
     SPHEM (OSWER)  (children)               0.1  to  5  grams*
     Endangmt. Assmt.  Handbook  (OSWER)     No  rates provided
     Exposure Factors  Handbook  (OHEA)    Children:
                                           0.1-0.2  g  (average)
                                           to  0.8 g (maximum)
                                         Adults: 0.001-0. 1 g
          (OSWER)  (children)               0.05  to  0.2 g
     RCRA Proposed Corrective  Action Rule and guidances (OSW):
          A 0.1 g/day rate  is  assumed for adults (body weight  =
          70 kg and exposure duration » 70 years)  and a 0.2 g/day
          rate is  assumed for  children (body weight * 16 kg and
          exposure duration -  6  years).

     *Higher values representative of pica behavior.             o


      Tnese guidances provide different ranges  of soil ingest ion
 rates, but do not always provide guidance on selecting a specif -
 ingestion rate that is reasonabl =.   There is also no guidance
 regarding when it is reasonable to  include children vith
 mouthing behavior (pica) in exposure scenarios.

      In addition, guidance has been published  in the Federal
 Register Guidelines for Exposure Assessment regarding the use of
 limited data, uncertainty, and data ranges (FR 51 No. 185,
 September 24, 1986)  as follows:

      "When there is uncertainty in  the scientific data, it is
      Agency policy to err on the side of public safety.  The
      Agency intends to be realistic, but will  not arbitrarily
      select midranges of environmental distributions that may
      compromise human health."

      "The Guidelines 'do not encourage the use  of worst-case
      assessments based on the best  data available.... However,
      the Agency will err on the side of public health when
      evaluating uncertainties when  data are limited or
      nonexistent. "

      Consistency is  important both  within and  between the CERCLA
and RCRA programs.   It is also important to assure that
realistic,  but conservative exposure scenarios are developed
during  the  risk assessment.  Both inconsistent use of  ingestion
rates  and inapproriate inclusion of children with abnormal
mouthing behavior (pica) in exposure scenarios may lead to
inappropriate risk conclusions.

      In order to promote consistency within Agency guidance and
the use of  realistic, conservative  exposure scenarios  throughout
the CERCLA  and RCRA programs, an interim guidance will be
provided to the regions or. soil ingestion rates for  both children
and adults.   This interim guidance  will be used by regional staff
who are responsible  for conducting  and evaluating  risk
assessments in OSWER related programs.  It should be kept  in  mind
that tnis guidance may be revised to reflect new, Agency  reviewed
data vftich  could significantly affect risk assessment results.

             Interim G
     The objective  of this paper is to develop a policy for  soil
ingestion rates  for children and adults.  However, it is
important to note tnat under the RCRA Proposed Corrective Action
Rule, soil  ingestion rates are primarily targeted for childhood
exposure for noncarcinogenic effects and adulthood exposure  for
carcinogenic effects.  This issue will not be addressed in this
document .

     This  guidance does not include children who exhibir acro--ia
mouthing behavior (pica)  in the exposure  scenario because -;-.<="
data regarding  such children are inadequate and uncertain.
Further, pica behavior itself,  the  occurence of pica oehavior,
and the rate of ingestion have  not  been well defined.  While"'
certain conditions,  such  as mental  retardation [American
Psychiatric Association (1980),  Danford  (1982), Illingsvor-h
(1983), Sayetta (1986),  as cited in the OHEA Draft Exposure
Factors Handbook],  may result in higher  ingestion rates, t.K.e data
is still not clear enough to quantify  the rate.

     With  consideration of current  Agency verified data, t.H.e
following  two options  are being  considered for both child and
adult soil ingestion rate assumptions.  These options are based
on a projected  residential land  use with  unrestricted access:

1.   A range of ingestion rates:

     Children;  Assume the rate  of  soil  ingestion for normal
     children to  be  within a range  of  0.1 to 0.2 g/day  (averace)
     to 0.8 g/day (maximum)  as presented  in the OHEA Draft
     Exposure Factors  Handbook  (May 1988).  Selection of an
     ingestion  rate  within t.ie  range could be left to the
     discretion of the assessor.

     This  range is based  on data sets  from Binder, si ai (1986)
     and Clausing, e_t  ai  (1987).  These studies used tracers in
     estimating soil ingestion  rates.  The Binder study used
     aluminum,   silicon, and titanium as tracers, and the Clausing
     study used aluminum,  silicon,  and acid insoluable  residues
     (AIR)  as tracers.  In the Binder  study titanium levels were
     considerably higher  (ten times) than the other tracers.
     This  higher  level may have  been produced by another source
     such  as  food or diaper content.   Because of this
     discreoancy, titanium data  wer« not  used in setting the
     range.  The estimate  of 0.2 g/day is suggested as  an average
     value, and the upper-range  ingestion estimate among children
     with  higher tendency  to ingest solid materials is  0.3 g/day.

      The following are data from these studies:

                            Maximum       Mean       low

      Binder, et al (1986 ) :
      aluminum            1.324 g/d    .181  g/d    .025 g/r-
      silicon              -799 g/d    .184  g/d    .031 g/d

      Clausing, et al  (1987):
      aluminum            .979 g/d     .230  g/d    .023 g/d
      ' :R                 -362 g/d     .129  g/d    .043 g/d

      Adults.:   For adults,  assume the  rate of soil  incest:-.on
      to  be  within a range  of  0.001 to 0. 1 g/day  fCaliorese,
      e_Ł  al.  (1987)  as cited in the OHEA  Draft Exposure
      Factors Handbook (May 1988)]. Selection of  an
      ingestion rate within the range  could  be left to the
      discretion of the assessor.


1.    Using  ranges is  more  reflective  of  the data  within the
      studies,  than using a single value.  The ranges provide
      the risk  assessor with more flexibility  for  developing
      site specific  risk assessments.

2.    Using  these ranges would be consistent with  ORL's draft
      guidance  and would assure that reviews of  risk
      assessment by ORD and OSWER would be done  using tne
      same assumptions for  soil exposure  scenarios.  This
      would  avoid confusion within the regions and other
      programs  regarding which guidance has  precedence.
      Because both these ranges are not extremely  broad,
      selection from within it may not result  in  significant


1.    When selection of an  ingestion rate from within a range
      is  left to the discretion of the risk  assessor, tnere
      may be  inconsistencies throughout program  risk
      assessments.   While this may not result  in significant:
      inconsistencies,  as suggested in Pro #2  above,  it may
      still cause more inconsistency than using  one value  for
      all cases.

2.    Assuming  extensive site  specific data  does  not  exists,
      no  additional  certainty  is gained when selecting  fro.-
      within  the range and  consistency may be  lost.

 2.   The  daily ingest ion rates  are:  0.2 g  (children) and 0.1  g

     Children:   In this  option  the  range of ingestion rates is
     not  used,  but rather it  is  assumed that the rate of soil
      ingestion for normal children  is  0.2  g/day.  This value
     represents the "average" for normal behavior, based on da^a
     from Binder and C.ausing studies.  In addition, more receni
     unpublished data (personal  communications with Calabrese and
     White)  suggest that this average, while reasonable, is
     conservative.   This option  could  be expanded to allow for
     deviation from this value  in extenuating circumstances
     relating  to site specificity.

     Adults;   For adults, the range  of ingestion rates is not
     used, but  it is assumed  that the  rate of soil  ingestion is
     o.l  g/day.   This value may  be  considered as a conservative
     value,  given that Hawley  (1985) estimated an average soil
     ingestion  rate of 0.065  g/day  for adults.  This option could
     be expanded to allow for deviation from this value in
     extenuating circumstances  relating to site specificicy.


     1.    Using a specific soil  ingestion  value may  result in a
           higher level of program risk assessment consistency
           than  if a range were  used.

     2.    The  specific soil  ingestion  rates of 0.2  g/day  for
           children and 0.1 g/day for adults represent
           conservative averages, resulting in a more realistic
           exposure scenario  than the lower or higher values  in
           the  range.


     1.    Using a single value  for  the ingestion  rate may not z&
           protective in  all  cases,  although  flexibility would be
           allowed where  appropriate.
Option 2 is  recommended for developing exposure scenarios for
soil ingestion  by children and adults at CERCLA and RCRA sites.
This option  includes:  (1)  using the assumption that the ingestion
rate for normal children is 0.2 g/day; and, (2) using the
assumption that the ingestion rate for adults is O.l g/day.