515UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

Region III841 Chestnut Street

Philadelphia, Pennsylvania 19107

November 8, 1994

SUBJECT: Risk-Based Concentration Table, Fourth Quarter 1994

FROM: Roy L. Smith, Ph.D., Senior ToxicologistTechnical Support Section (3HW13)

TO: RBC Table mailing list

Attached is the EPA Region m risk-based concentration (RBC) table, which we havedistributed quarterly to all interested parties since 1991. If you are not currently on the mailinglist, but would like to be, please contact Anna Poulton (phone: 215-597-3179, fax: 215-597-9890) and give her your name, address, and phone and fax numbers. (This is the onlyinformation she needs; faxing parts of the table or cover memo is not necessary.)

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The table contains reference doses and carcinogenic potency slopes (obtained from IRISthrough October 1, 1994, HEAST through March 1994, the Superfund Health Risk TechnicalSupport Center, and other EPA sources) for nearly 600 chemicals. These toxicity constants havebeen combined with "standard" exposure scenarios to calculate RBCs - chemical concentrationscorresponding to fixed levels of risk (i.e., a hazard quotient of 1, or lifetime cancer risk of 10"*,whichever occurs at a lower concentration) in water, air, fish tissue, and soil.

The Region m lexicologists use the table to screen sites not yet on the NPL, respondrapidly to citizen inquiries, and spot-check formal baseline risk assessments. The backgroundmaterials provide the complete basis for all the calculations, with the intent of showing usersexactly how the RBCs were developed. Simply put, RBCs are risk assessments run in reverse.For a single contaminant in a single medium, under standard default exposure assumptions, theRBC corresponds to the target risk or hazard quotient

The calculations also have several important limitations. Specifically excluded fromconsideration are (1) transfers from soil to air and groundwater, and (2) cumulative risk frommultiple contaminants or media. Also, the toxicity information in the table has been assembledby hand, and (despite extensive checking and years of use) may contain errors. It's advisableto cross-check before relying on any RfDs or CPSs in the table. If you find any errors, please

flR30i266

EPA Region III Risk-Based Concentrations: R.L. Smith (11/8/94) 2

send me a note.

Lately, many callers have asked whether the risk-based concentrations can be used asvalid no-action levels or cleanup levels, especially for soils.. The answer is a bit complex.First, it is important to realize that the RBC table does not constitute regulation or guidance, andshould not be viewed as a substitute for a site-specific risk assessment. For sites where:

1. A single medium is contaminated; -

2. A single contaminant contributes nearly all of the health risk;

3. Volatilization or leaching of that contaminant from soil is expected not to besignificant;

4. The exposure scenarios used in the RBC table are appropriate for the site;

5. The fixed risk levels used in the RBC table are appropriate for the site; and

6. Risk to ecological receptors is expected not to be significant;

the risk-based concentrations would probably be protective as no-action levels or cleanup goals.However, to the extent that a site deviates from this description, as most do, the RBCs wouldnot necessarily be appropriate.

To summarize, the table should generally not be used to (1) set cleanup or no-actionlevels at CERCLA orRCRA Corrective Action sites, (2) substitute for EPA guidance for preparingbaseline risk assessments, or (3) determine if a waste is hazardous under RCRA.

This issue of the RBC table includes new toxicity constants and media concentrations,which are marked on the table in underlined boldface print.

I get many calls about the RBC table, but I'm often unavailable to answer the phone.Many of you have the same problem, so we play a lot of "phone tag". It's usually easier andmore effective to fax me (at 215-597-9890) with your technical questions and concerns, and forme to respond by return fax. Of course, If you don't have access to a fax machine, I will alsocontinue to respond to voice mail messages.

Attachment

AR3Q1267

EPA Region III Risk-Based Concentrations: R.L. Smith (11/8/94) • 3

Risk-Based Concentration TableBackground Information

General; Separate carcinogenic and non-carcinogenic risk-based concentrations were calculatedfor each compound for each pathway. The concentration in the table is the lower of the two,rounded to two significant figures. The following terms and values were used in the calcu-lations:

1 -General:

Carcinogenic potency slope oral (risk per mg/kg/d):

Carcinogenic potency slope inhaled (risk per mg/kg/d):

Reference dose oral (mg/kg/d):

Reference dose inhaled (mg/kg/d):Target cancer risk:

Target hazard quotient:

• Body weight; adult (kg):

Body weight, age 1-6 (kg):

Averaging time carcinogens (d):

Averaging time non-carcinogens (d):

Inhalation, adult (m3/d):

Inhalation, child (m3/d):

Inhalation factor, age-adjusted (m3-y/kg-d):

Tap water ingestion, adult (L/d):

Tap water ingestion, age 1-6 (L/d):

Tap water ingestion factor, age-adjusted (L-y/kg-d):

' Fish ingestion (g/d):Soil ingestion, adult (mg/d):

Soil ingestion, age 1-6 (mg/d):

Soil ingestion factor, age adjusted (mg-y/kg-d):

2-Residential: ,

Exposure frequency (d/y):

Exposure duration, total (y):

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• *

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15

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ED*365

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12

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2-

1

1.09

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100

200

114.29

350

30

CPSo

CPSi

RfDo

RfDi

TR

THQ

BWa

BWc

ATc

ATn

IRA*

IRAc

IFAadj

IRWa

IRWc

IFWadj

IRF

IRSa

IRSc

IFSadj

•

EFrEDtot

flR3012'68

EPA Region III Risk-Based Concentrations: R.L. Smith (11/8/94)

<i i£ ^

Exposure duration, age 1-6 (y):

Volatilization factor (L/m3):

3-Occupational:

Exposure frequency (d/y):

Exposure duration (y):

* — Contaminant-specific tniicity parameter*

•(•j>:$&6

0.5

250

25

S- .;EDc

VF

EFo

EDo

The priority among sources of lexicological constants was as follows: (1) IRIS, (2) HEAST, (3)HEAST alternative method, (4) EPA Superfund Health Risk Technical Support Center, (5)withdrawn from IRIS or HEAST, and (6) other EPA documents. Each source was used onlyif numbers from higher-priority sources were unavailable. The EPA Superfund Health RiskTechnical Support Center, part of the Chemical Mixtures Branch of EC AO-Cincinnati, developsprovisional RfDs and CPSs on request for contaminants not in IRIS or HEAST. Theseprovisional values are labeled "e = EPA-ECAO provisional" in the table. It is possible theymay be. obsolete. If one of the "e" constants is important to a Superfund risk assessment,consider requesting, through a Regional risk assessor, a new provisional value.

Algorithms:

1. Age-adjusted factors: Because contact rates with tap water, ambient air, and residential soilare different for children and adults, carcinogenic risks during the first 30 years of life werecalculated using ageradjusted factors. These factors approximated the integrated exposure frombirth until age 30 by combining contact rates, body weights, and exposure durations for two agegroups - small children and adults. The age-adjusted factor for soil was obtained from RAGSIB; the others were developed by analogy. •

a. Air inhalation ([m3- y]/{kg- d]):

U?AHM EDc 'IRAc * (EDtot -EDc)-IRAaIFAadl = — — — — ————BWa————

b. Tap water ingestion ([L- y]/[kg- d]):

- EDc •IRWc + (EDtot -EDc)'IRWa- ——^^—— —————r————

AR3QI2&9

EPA Region m Risk-Based Concentrations: R.L. Smith (11/8/94) 5

c. Soil ingestion ([mg- y]/[kg- d]):

/jre*/tf = EDc 'IRSc + (EDtot -EDc) • IRSa-^ irtaaj Bm —————___————

2. Residential water use (/tg/L). Volatilization terms were calculated only for compounds with"***" in the "VOC" column. Compounds having a Henry's Law constant greater than 10"s wereconsidered volatile. The list may be incomplete, but is unlikely to include false positives. Theequations and the volatilization factor (VF, above) were obtained from RAGS IB. Oral potencyslopes and reference doses were used for both oral and inhaled exposures for volatile compoundsJacking inhalation values. Inhaled potency slopes were substituted for unavailable oral potencyslopes only for volatile compounds; inhaled RfDs were substituted for unavailable oral RfDs forboth volatile and non-volatile compounds.

a. Carcinogens: Calculations were based on combined childhood and adult exposure.

TR -ATc - 1000 *-EFr -([VF • IFAadj - CPSi ] + [IFWadj • CPSo])

b. Non-carcinogens: Calculations were based on adult exposure.

THQ-BWa-ATn - 1000 *- •

*3. Air (/ig/m3). Oral potency slopes and references were used where inhalation values were notavailable.

a. Carcinogens: Calculations were based on combined childhood and adult exposure.

TR -ATc • 1000 s-EFr -IFAadj • CPSi

b. Non-carcinogens: Calculations were based on adult exposure.

THQ • RfDi - BWa - ATn - 1000 %EFr • EDtot - IRAa

aR30i270

EPA Region III Risk-Based Concentrations: R.L. Smith (11/8/94)

4. Fish (mg/kg):

a. Carcinogens: Calculations were based on adult exposure.

TR-BWa-ATc_______EFr • EDtot - IRF - CPSo

1000 -

b. Non-carcinogens: Calculations were based on adult exposure.

THQ-RfDo -BWa-ATnIRFEFr -EDtot

1000

5. Soil commercial/industrial (mg/kg): The default exposure assumption that only 50% ofincidental soil ingestion occurs at work has been omitted. Calculations were based on adultoccupational exposure.

a. Carcinogens:TR-BWaATc

EFo- EDo - IR?a - CPSo106 ?s

b. Non-carcinogens:THQ'RfDo - BWa -ATn

IRSaEFo -EDo106 a*

6. Soil residential (mg/kg):

a. Carcinogens: Calculations were based on combined childhood and adult exposure.

TR -ATc ______, cpSo

10

b. Non-carcinogens: Calculations were based on childhood exposure only. .THQ'RfDo • BWc • ATn

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