Drifted States
            Environmental Protection Agency
Region ill
Philadelphia, PA 19107
EPA/903/R-93-001
January 1993
            Region III
            Technical Guidance Manual
            Risk Assessment
                                                                                   U.S. r:/!
                                              Selecting  Exposure Routes ahc
                                              Contaminants  of Concern by Risk-Based
                                              Screening
                                                                          EPA Contact: Dr. Roy L Smith
                            EPA
                            Region III
  Hazardous Waste Management Division
  Office of Super-fund Programs
  January 1993
           Human health risk assessment includes effort-intensive steps which require many detailed calculations by experts. Most
           baseline risk assessments are dominated by a few chemicals and a few routes of exposure. Effort expended on minor
           contaminants and exposure routes, i.e.jhose which do not influence overall risk, is sssentiaJty wasted.  This guidance
           is intended to identify and focus on dominant contaminants of concern and exposure routes at the earliest feasible point
           in the baseline risk assessment.  Use of these methods will decrease effort and time spent assessing risk, without loss
           of protectiveness.  This guidance is not intended for other risk assessment activities, such as determining preliminary
           remediation goals.
           SELECTING CONTAMINANTS AND EXPOSURE ROUTES
           OF CONCERN

           Most samples from hazardous waste sites are analyzed
           for 103 target compounds and analytes recommended
           by tf?e EPA Superfund program.  Semi-volatile analysis
           can detect additional tentatively identified compounds
           not on the target lists.  Special analytical services
           procedures, if used, may find still more contaminants.
           The combined number of contaminants detected at a
           site sometimes exceeds one hundred.

           While EPA considers it necessary to gather information
           on many  contaminants,  very little of this data actually
           influences the overall quantitative assessment of health
           risk.  For most sites, baseline risk assessments are
           dominated by a few contaminants and a few routes of
           exposure.    The  remaining  tens,  or hundreds, of
           detected contaminants have a minimal influence on total
           risk.  This small  impact is lost by rounding.   Entire
           environmental media  may  contain  not  a   single
           contaminant at a concentration which could adversely
           affect public health. Quantitative risk calculations using
           data from such 'risk-free* media have no effect on the
           overall risk estimate for the site.

           The EPA baseline risk assessment process  at several
           points requires careful  data  evaluation by scientific
            experts.  These evaluations, which are contaminant-
            specific,  include: (1) statistical comparisons between
            site-related  and background  samples,  (2)  special
            handling of undetected contaminants, (3) calculation of
            toxicity equivalence, (4) evaluation  of frequency of
            detection, and (5) comparison  with ARARs. Because
            overall risk is usually driven by a few contaminants and
            exposure routes, effort spent in detailed evaluation of
            minor  contaminants  and routes of  exposure is
            essentially wasted.  For some sites, this wasted effort
            exceeds  90% of the total.

            The baseline risk assessment process can be made
            more efficient by focusing on dominant contaminants
            and routes of exposure at the  earliest feasible stage.
            The mechanisms recommended for this are (1) a re-
            ordering  of the process of eliminating contaminants and
            routes  of exposure,  and (2)  use of a  risk-based
            concentration screen. Appropriately used, this process
            can dramatically reduce the effort of risk assessment,
            while not changing the result significantly.

            EXISTING GUIDANCE

            Chapter 5 of 'RAGS IA' (Risk Assessment Guidance for
            Suoerfund. Volume I. Human Health Evaluation Manual
            (Pan A): EPA, 1989) provides a  detailed procedure for
            evaluating data for a baseline risk assessment.  This
903/R-
93-001

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 procedure includes steps by which the risk assessor
 selects contaminants of concern in each  exposure
 medium.  These steps are summarized in Table 1.

 There are two major limitations to the RAGS procedure.
 First, the eliminating step  (a concentration  toxicity
 screen)  comes late in the process.   Many of the
 preceding steps (e.g.. evaluation of quantitation limits,
 comparison with background, calculation  of toxicity
 equivalence, and evaluation of frequency of detection)
 are contaminant- and medium-specific. They require
 the sustained attention  of an  expert, and cannot be
 automated. If the contaminant is eliminated, this work
 is wasted.

 The second limitation is that the concentration toxicity
 screen compares only relative risk among contaminants
 in the same medium.  While very efficient at selecting
 dominant contaminants in each medium, this method
 does not evaluate significance of total risk for the
 medium.  Thus, the concentration toxicity screen can
 eliminate contaminants, but not routes of exposure.

 RECOMMENDED METHODOLOGY

 This guidance makes two changes intended to remove
 the   limitations  in   existing   guidance.     These
 recommendations  are  intended  for  baseline risk
 assessments.

 1.  Re-ordering of steps.  The eliminating screen is
 moved forward in trie data evaluation process to a point
 immediately following dam quality evaluation.  The new
 process is shown in Table 2. Effort-intensive steps such
 as evaluation tf quantitation limits and comparison with
 background now follow the  eliminating screen.  The
 steps are divided into  four categories: data quality
 evaluation, initial data  set reduction, re-inclusion  of
 special cases, and optional final data  set reduction.

 The  data  quality  evaluation  steps   (evaluating
 appropriateness of methods and qualifiers, significance
 of blank contamination, and need for special analyses)
 should be done e» described in RAGS IA, Chapter 5.
 Next, the risk assessor should consult wtto tf» RPM to
 discuss the use of the risk-besed concentration table
 (described in  item  [2]  below}  as • screening
 mechanism. With tr» RPM's approval,  the risk sssessor
 should reduce the data set and document the rationale
 for eliminating  contaminants and routes of exposure
 from further analysis.

After the initial data set reduction, the risk assessor and
 RPM  should   consider  re-including   specific
 contaminants on the basis of historical data, toxicity,
 mobility,persistence, bioaccumuiation, special exposure
routes, special treatability problems, or exceedance of
ARARs. These activities should proceed as described
in Section 5.9 of RAGS IA.

Finally, optional further reductions in the data set may
be justified, based on the status of a contaminant as an
essential nutrient, low frequency of detection, or no
statistical  difference between site  and background
levels.  These evaluations, the most complicated and
contaminant-specific, are saved for last.

2.   Screening by  risk-based concentrations.   The
screening  method  is  changed  from  the  relative
concentration toxicity screen of RAGS lAtoan absolute
comparison of risk.  This is done by means of a table of
risk-based  concentrations (Appendix I).   This table
contains levels  of  nearly 600 contaminants in air,
drinking water, fish tissue, and soil, which correspond
to a systemic hazard quotient of 0.1 or a lifetime cancer
risk  of 10*.   The  risk-based concentrations were
developed using protective default exposure scenarios
suggested  by EPA (1991)  and  the best available
reference doses and carcinogenic potency slopes (see
the table for sources), and represent relatively protective
environmental concentrations  at  which EPA would
typically not take action.

The risk-based concentration screen is used as follows:

(a)  The  risk  assessor  extracts   the   maximum
    concentration of each substance detected in each
    medium.

(b)  If the maximum concentration exceeds the risk?
   based  concentration  for  that medium,   the
   contaminant is retained for risk assessment, for all
   routes  of  exposure  involving  that   medium.
    Otherwise the  contaminant is  dropped for that
   medium.

(c) If a specific contaminant does not exceed its risk-
   based  concentration  for  any medium,   the
   contaminant is dropped from the risk assessment

(d) If no contaminant in a specific medium exceeds its
   risk-based concentration, the medium is dropped
   from the risk assessment

(e) All contaminants and exposure routes  which are
   dropped are kept on a sub-list and considered for
    re-inclusion, based on special properties.

(f)  If the risk assessor wants to  include  a route of
    exposure  not   covered  in   the   risk-based
   concentration table, the  equations provided in
   Appendix I can  serve as  the basis  for new risk-

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    based concentrations.  Similarly, the risk assessor
    can use the same equations to calculate alternate
    risk  levels  (i.e.,  other than  a systemic  hazard
    quotient of 0.1 and lifetime cancer risk of 10*) to be
    the basis for screening.

 SUMMARY

 The process by  which contaminants  and exposure
 routes are selected in quantitative risk assessment can
 be made less effort-intensive by two simple changes.
 First, high-effort steps should be postponed until later in
 the selection process,  because  performing these
 operations on trivial contaminants and exposure routes
 is  pointtess.   Second,  changing from  a  relative
 concentration toxicity screen to an absolute risk-based
 concentration screen  improves the  risk  assessor's
 ability to focus on dominant contaminants and exposure
 routes at an earlier stage.

 REFERENCES

 EPA,   1991.    Human  Health  Evaluation  Manual,
    Supplemental Guidance: 'Standard Default Exposure
    Factors'.  OSWER Directive 9285.6-03, Office of
    Emergency and Remedial  Response, March 25,
    1991.

EPA, 1989. Risk Assessment Guidance for Superiund,
    Volume I, Human Health Evaluation Manual (Pan A).
    Office of Emergency  and  Remedial Response,
    December, 1989.  EPAJ540I1-891002.
For additional information, call (215) 597-6682.
Approved by:
              Thomas C. Vo
              Hazardous Waste Mbnagffnent Division

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   Tabte 1. Summary of existing EPA guidance on selecting contaminants of concern (EPA, 1989, chapter 5)
Section 5.1: Combining data from site investigations
    1.  Determine if methods are appropriate
    2.  Evaluate quantitation limits
    3.  Determine if qualifiers are appropriate
    4.  Determine if significant blank contamination exists
    5.  Determine if special analyses for tentatively identified compounds are needed
    6.  Compare site samples to background
Section 5.9: Further reduction in the number of chemicals (optional)
    7.  Consult with RPM
    8.  Document rationale for eliminating chemicals
    9.  Examine historical information
    10. Consider exceptional toxidty, mobility, persistence, or bfoaccumuiatfon
    11. Consider special exposure routes
    12. Consider special treatabfflty problems
    13. Determine if contaminants exceed ARARs
    14. Group chemicals by class, evaluate toxidty equivalence
    15. Evaluate frequency of detection
    16. Evaluate essentiality
    17. Use a concentration toxidty screen

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         Table Z EPA Region III guidance on selecting contaminants and exposure routes of concern
A.  Data quality evaluation
    1.  Determine if methods are appropriate
    2.  Determine if qualifiers are appropriate
    3.  Determine if significant blank contamination exists
    4.  Determine if special analyses for tentatively identified compounds are needed
B.  Reduce data set using risk-based concentration screen
    5.  Consult with RPM
    6.  Use risk-based concentration table to screen contaminants and exposure routes of concern
    7.  Document rationale for eliminating chemicals and exposure routes	
C.  Consider re-including eliminated chemicals and routes, based on:
    8.  Historical information
    9.  Exceptional toxtcity, mobility, persistence, or bioaccumulation
    10. Special exposure routes
    11. Special treatabiltty problems
    12. ARARs exceedance
    13. Toxicity equivalence of chemical class (e.g., CDD/CDFs, PAHs)
D.  Make further specific reductions in data set (optional)
    14. Evaluate essentiality
    15. Evaluate frequency of detection
    16. Compare site samples to background

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                                   Appendix I:
                   EPA Region in Risk-Based Concentration Table
                              Background Information

The risk-based concentrations were calculated as follows:

GENERAL; Separate risk-based concentrations were calculated for carcinogenic and non-
carcinogenic effects of each compound for each pathway. The concentration in the table is
the lower of the two, rounded to two significant figures. For non-carcinogenic effects, the
averaging time equals the exposure duration, so the exposure duration term has been used
for both. The following terms were used in the calculations:

       General:
       Oral carcinogenic slope factor (mg/kg/d)"1:       SFe
       Inhaled carcinogenic slope factor (mg/kg/d)'1:    SF,
       Oral reference dose (mg/kg/d):                R£D0
       Inhaled reference dose (mg/kg/d):             RfD,
       Target cancer risk:                           TR
       Target hazard quotient:                       THQ
       Body weight, adult (kg):                      BW.
       Body weight, child age 1-6 (kg):                BW.
       Averaging time (years of life):                 AT
       Air breathed (mVd):                         IR,
       Drinking water ingestion (L/d):                IR,
       Fish ingestion (g/d):                          ERf
       Soil ingestion - age adjusted (mg/d)            IRS*
       Soil ingestion - age 1-6 (mg/d):                IRS,
       Soil ingestion - adult (mg/d):                  IRS.

       Residential:
       Exposure frequency (d/y):                    EF,
       Exposure duration (y):                        EDr
       Volatilization factor (L/mJ):                   VF

       Commercial/Industrial:
       Exposure frequency (d/y):                    EF0
       Exposure duration (y):                        ED0

The priority among sources of lexicological constants was as follows: (1) IRIS, (2) HEAST,
(3) HEAST alternative method, (4) ECAO-Cincinnati, (5) other EPA documents, (6)
withdrawn from IRIS, and (7) withdrawn from HEAST.  Each source was used only if
numbers from higher-priority sources were unavailable.

ALGORITHMS:


                                        6

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 1. Residential water use (^g/L).  Volatilization terms were calculated only for compounds
 with "y" in the "Volatile" column.  Compounds having a Henry's Law constant greater than
 10"5 were considered volatile.  The list may be incomplete, but is unlikely to include false
 positives.  The equations and the volatilization factor (VF, above) were obtained from the
 draft RAGS IB.  Oral potency slopes and reference doses were used for  both oral and
 inhaled exposures for volatile compounds lacking inhalation values. Inhaled potency slopes
 were substituted for unavailable  oral potency slopes only for volatile compounds; inhaled
 RfDs were substituted for  unavailable oral  RfDs for both volatile and  non-volatile
 compounds.

      a. Carcinogenic effects:
                            TR • BWa  • AT • 365^ • 10002

                     EF, • EDr - ([VF  - IR. • CPS} + [flT • SFJ)

      b. Non-carcinogenic effects:
                          THQ -BW  -ED  • 365f • 10002
                             *•	«     '      r       ««

                            EF  -ED
                                         RfDi     RfD

2. Air (jug/m3). Oral potency slopes and references were used where inhalation values were
not available.
      a. Carcinogenic effects:
                           TR • BW • AT • 365i • 10002
                                    •           r
                                    _
                                    • £D, • IRt • SF.

      b. Non-carcinogenic effects:
                       THQ  • RfD. • BWt - ED  • 365i • 10002
                                        ££>
3. Fish (mg/kg):

      a. Carcinogenic effects:
                               TR  -BW  -AT -365f
                              	•	y

                              EF  -ED •	'— - SF
                                       '  10001

-------
      b. Non-carcinogenic effects:

                          THQ • RfD. • BWt - EDr
                                             IK
                                EF -ED  -     '
                                        '  10001
4. Soil commercial/industrial (mg/kg): The default exposure assumption that only 50% of
incidental soil ingestion occurs at work has been omitted.
      a. Carcinogenic effects:
                               77?- BW: AT • 365f
                                         __

                              EF • ED  •	L • SF
                                     '  10*2
      b. Non-carcinogenic effects:

                          THQ - RfDf - BWt • £D • 365f
S. Soil residential (mg/kg):


      a. Carcinogenic effects:
                              TR -BW  -AT -365'-
                                      •	r
                                        IRS
                             EF -ED	±  • CPS
                                     '10*2
      b. Non-carcinogenic effects:

                          THQ • RfD. • BWt • ED, - 365f
                                            IRS
                                EF -ED  -	1
                                        '  10* 2
                                       8

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