# Impact of Revised Human Health Benchmarks

on S olvent Wipes Risk

- Based Mass Loading Limits (RB

- MLLs)

April 2012

Office of Resource Conservation and Recovery U.S. Environmental Protection Agency

Prepared with the support of RTI International EPA Contract Number EP

- W

- 09

- 004

### 1 

## Introduction

To support a proposed change in the regulatory status of disposed solvent

- contaminated wipes and laundry sludges, EPA developed and performed a risk analysis in 2009 to characterize the potential risks associa ted with the disposal of wipes and laundry sludge in nonhazardous waste landfills. See the original risk document in the docket for this rule ( Risk

- Based Mass Loading Limits for Solvents in Disposed Wipes and Laundry Sludges Managed in Municipal Landfills

, October 2009). Under this analysis , we estimated the risk

- based mass loading limit (RB

- MLL) for the allowable amount of solvent that can be managed in an unlined or composite

- lined landfill in any year that, if contained on disposed wipes or in laundry sl udge, would not exceed EPA’s risk criteria if these materials were disposed of in nonhazardous waste landfills.

EPA recently finaliz ed new health benchmarks for two solvents, t etrachloroethylene ( also called

p erchloroethylene, or PCE ) and t richloroethylen e (TCE). The p urpose of this document is to present the recalculated risk estimates and RB

- MLLs for these two solvents derived using the revised health benchmarks

.



## Revised Health Benchmarks

T able 1 provides a comparison between the revised IRIS benchmarks and those used in the 2009 assessment

.

Table 1

. Comparison of Benchmarks applied in 2009 Analysis to Revised Benchmarks a

Constituent CASRN Source RfD (mg/kg

- d) RfC (mg/m 3 ) CSFo (per mg/kg

- d) URF (per μg/m 3 )

Value Ref Value Ref Value Ref Value Ref

Te trachloro

ethylene 127

- 18

- 4 2009 Value 1.0E

- 02 IRIS 3.0E

- 01 ATSDR 5.4E

- 01 CalEPA b 5.9E

- 06 7.1E

- 7 b CalEPA b

Current IRIS Value 6.0E

- 03 IRIS(r) 4.0E

- 02 IRIS(r) 2.1E

- 03 IRIS(r) 2.6E

- 07 IRIS(r)

Trichloro

ethylene 79

- 01

- 6 2009 Value none NA 6.0E

- 01 CalEPA 1.3E

- 02 CalEPA 2.0E

- 06 CalEPA

Current IRIS Value 5.0E

- 04 IRIS(r) 2.0E

- 03 IRIS(r) 4.6 E

- 02 IRIS(r) 4 .1 E

- 06 IRIS(r)

a IRIS(r): Final revised IRIS values. ( September 2011, February 201 2 ) U.S. EPA (Environmental Protection Agency). 2011. Integrated Risk I nformation System (IRIS) for Trichloroethylene (CASRN 79

- 01

- 6). Washington, DC: National Center for Environmental Assessment, Office of Research and Development. http://www.epa.gov/iris/subst/0199.htm. U.S. EPA (Environmental Protection Agency). 2012. Inte grated Risk Information System (IRIS) for Tetrachloroethylene (Perchloroethylene) (CASRN 127

- 18

- 4). Washington, DC: National Center for Environmental Assessment, Office of Research and Development. http://www.epa.gov/iris/subst/0106.htm

b In 2009, two est imates were provided for tetrachloroethylene cancer risks to reflect the high and low ends of the range of

benchmarks.



### As shown in Table 1 , the revised benchmarks include both noncancer and cancer endpoints. The benchmarks for noncancer endpoints include the reference dose (RfD)

, which is applied in evaluating ingestion and dermal

exposures , and the reference concentration (RfC)

, for inhalation exposures. The benchmarks for cancer endpoints include the oral cancer slope factor (CSF) , which is used to evalu ate ingestion and dermal exposures

, and the unit risk factor (URF)

, for inhalation exposures. No RfD was available in 2009 for trichloroethylene

, but one is now available to support this current effort.

### 2 

## Revised Risk Estimates
Using the revised human health benchmarks shown in Table 1

, we performed modeling to estimate risk or HQ and RB

- MLLs for tetrachloroethylene and trichloroethylene

. C ancer risk is directly proportional to the oral CSF

or URF. N oncancer HQ is indirectly proportional to the RfC or RfD.

**Cancer Risk**
Cancer risks were calculated using Equations 1 to 3. For the oral pathway, the lifetime excess cancer risk estimates were based on the lifetime average daily dose ( LADD ) and the oral CSF as follows :

o oral 

## CSF LADD Risk × = (Equation 1 )



## where

Risk oral 

## = lifetime incremental cancer risk from the oral exposure route (unitless) LADD = lifetime average daily dose (mg/kg

- d)

CSF o 

## = oral cancer slope factor (mg/kg

- d) - 1



## .

For the groundwater dermal contact pathway, the lifetime excess cancer risk est imates were based on the dermal absorbed dose ( DAD ) and the oral CSF:

o dermal 

## CSF DAD Risk × = (Equation 2 )



## where

Risk oral 

## = lifetime incremental cancer risk from the oral exposure route (unitless)
D

A D = dermal absorbed dose (mg/kg

- d) CSF o 

## = oral cancer slope factor (mg/kg

- d) - 1



## .
For inhalation of ambient air and inhalation of indoor air during showering, lifetime excess cancer risk estimates were calculated as follows:



## A T E U RF C R is k a ir
a ir 

## × × ×

= 100

(Equation 3 )



## where

Risk air 

## = lifetime incremental cancer risk from the air exposur e route (unitless) C air 

## = concentration in air (mg/m 3 

## ) URF = inhalation unit risk factor ( [ μg/m 3 

## ] - 1 

## ) 1000 = conversion factor (μg/mg)

ED = exposure duration (yr) AT = averaging time (yr).

**Noncancer Hazard**
Noncancer hazards were calculated using Equa tions 4 to 6. Noncancer hazard from drinking water ingestion was characterized based on the average daily dose ( ADD ) during the period of exposure and the RfD:



## RfD ADD HQ dw oral 

## = (Equation 4 )

## where
HQ oral 

## = oral hazard quotient (unitless) ADD dw 

## = average daily dose from consumption of drinking water (mg/kg

- d) RfD = reference dose (mg/kg

- d).

Noncancer haza rd from dermal exposure via showering or bathing was calculated as follows :



## RfD DAD HQ dermal 

## = (Equation 5 )



## where
HQ ora l 

## = oral hazard quo tient (unitless)

D

A D = average daily dose from consumption of drinking water (mg/kg

- d) RfD = reference dose (mg/kg

- d).

Noncancer hazard from air inhalation was calculated using an RfC :



## R fC C H Q a ir
a ir 

## = (Equation 6 )



## where
HQ air 

## = air hazard quotie nt (unitless) C air 

## = air concentration (mg/m 3 

## ) RfC = reference concentration (mg/m 3 

## ).

Tables 2 through 7 present the recalculated 50th percentile and 90th percentile risk results for the different pathways (air and groundwater), for both child and adult, for unlined and composite

- lined landfills, and for noncancer and cancer risk. In the case of the combined risks, the driving pathways are identified in parentheses in the tables (i.e., DW indicates drinking water and SH indicates shower inhalation). 1 

### The r esults are presented in tables similar in format to the tables in Section 4 of the original risk document ( Risk

- Based Mass Loading Limits for Solvents in Disposed Wipes and Laundry Sludges Managed in Municipal Landfills , October 2009). As noted in the titl es of T ables 2 through 7 , these tables correspond to Tables 4

- 1 through 4

- 6, respectively, in the 2009 report.

Table 2

. Revised Ambient Air Risk Estimates at the Unitized Mass Loading Rate (1 kg/year) : Adult ( u pdates to Table 4

- 1)

Constituent 50th Percenti le 90th Percentile

NL Composite NL Composite

CANCER Risk Risk Risk Risk

Tetrachloroethylene 2.4E

- 12 2.5E

- 12 2.0E

- 11 2.1E

- 11

Trichloroethylene 3.7E

- 11 3.9E

- 11 3.1E

- 10 3.3E

- 10

NONCANCER HQ HQ HQ HQ
Tetrachloroethylene 1.3E

- 06 1.4E

- 06 9.1E

- 06 9.5E

- 0 6
Trichloroethylene 2.7E

- 05 2.9E

- 05 1.9E

- 04 1.9E

- 04

1 

### The analysis produced separate risk distributions for each pathway, as well as one for risk combined across

pathways. The results shown are the 50th or 90th percentile of these different distributions. As a result, the combined risk may not exactly equal the sum of the separate pathway risks.

### 1 Table 3

. Revised Ambient Air Risk Estimates at the Unitized Mass Loading Rate (1 kg/year) : Child ( updates to Table 4

- 2 )

Constituent 50th Percentile 90th Percentile

NL Composite NL Composite

CANCER R isk Risk Risk Risk

Tetrachloroethylene 1.0E

- 12 1.1E

- 12 9.5E

- 12 9.8E

- 12
Trichloroethylene 1.6E

- 11 1.7E

- 11 1.5E

- 10 1.5E

- 10

NONCANCER HQ HQ HQ HQ

Tetrachloroethylene 1.5E

- 06 1.6E

- 06 9.9E

- 06 1.0E

- 05
Trichloroethylene 3.0E

- 05 3.2E

- 05 2.0E

- 04 2.1E

- 04



### Ta ble 4 . Summary of Revised 50th Percentile Solvent Wipes at the Unitized Mass Loading Rate (1kg/year) Adult Groundwater (updates to Table 4

- 3)

Constituent Drinking Water Shower Inhalation Dermal Combined DW/SH/DM

NL Composite NL Composite NL Composite NL Composite

CANCER Risk Risk Risk Risk Risk Risk Risk Risk
Tetrachloroethylene 2.5E

- 10 6.4E

- 20 5.9E

- 10 1.2E

- 19 6.1E

- 11 1.3E

- 20 1.0E

- 09(DW) 2.1E

- 19 (SH)
Trichloroethylene 6.3E

- 09 1.6E

- 18 9.8E

- 09 2.2E

- 18 2.0E

- 09 4.6E

- 19 2.1E

- 08 (SH) 5.4E

- 18 (SH)

NONCANC ER HQ HQ HQ HQ HQ HQ HQ HQ

Tetrachloroethylene 1.4E

- 04 3.3E

- 14 3.5E

- 04 7.1E

- 14 3.2E

- 05 6.4E

- 15 NA NA

Trichloroethylene 1.7E

- 03 3.6E

- 13 7.6E

- 03 1.6E

- 12 5.3E

- 04 1.1E

- 13 NA NA
SH = Driving pathway is shower inhalation.

### 2 Table 5. Summary of Revised 9 0th P ercentile Solvent Wipes at the Unitized Mass Loading Rate (1kg/year) Adult Groundwater (updates to Table 4

- 4)

Constituent Drinking Water Shower Inhalation Dermal Combined DW/SH/DM

NL Composite NL Composite NL Composite NL Composite

CANCER Risk Risk Ris k Risk Risk Risk Risk Risk

Tetrachloroethylene 1.5E

- 08 3.1E

- 11 3.9E

- 08 7.2E

- 11 3.3E

- 09 7.1E

- 12 5.8E

- 08 (SH) 1.3E

- 10 (SH)

Trichloroethylene 3.6E

- 07 6.0E

- 10 6.5E

- 07 9.4E

- 10 1.0E

- 07 1.8E

- 10 1.2E

- 06 ( DW) 1.9E

- 09 (DW)

NONCANCER HQ HQ HQ HQ HQ HQ HQ HQ

Tet rachloroethylene 6.2E

- 03 1.5E

- 05 1.9E

- 02 4.4E

- 05 1.3E

- 03 3.5E

- 06 NA NA
Trichloroethylene 7.6E

- 02 1.3E

- 04 4.1E

- 01 6.9E

- 04 2.2E

- 02 4.2E

- 05 NA NA DW = Driving pathway is drinking water

. SH = Driving pathway is shower inhalation.



### Table 6 . Summary of Revis ed 50th Percentile Solvent Wipes at the Unitized Mass Loading Rate (1kg/year) Child Groundwater (updates to Table 4

- 5 )

Constituent Drinking Water Dermal Bathing Combined DW/ DM

NL Composite NL Composite NL Composite

CANCER Risk Risk Risk Risk Risk Risk
Tetrachloroethylene 2.3E

- 10 5.5E

- 20 6.4E

- 11 1.6E

- 20 3.1E

- 10 (DW) 7.5E

- 20 (DW)
Trichloroethylene 5.9E

- 09 1.1E

- 18 2.2E

- 09 4.6E

- 19 8.6E

- 09 (DW) 1.7E

- 18 (DW)

NONCANCER HQ HQ HQ HQ HQ HQ
Tetrachloroethylene 3.0E

- 04 6.1E

- 14 8.5E

- 05 1.8E

- 14 NA NA

Trichloroe thylene 3.8E

- 03 7.8E

- 13 1.4E

- 03 3.3E

- 13 NA NA DW = Driving pathway is drinking water

.

### 3 Table 7 . Summary of Revised 9 0th Percentile Solvent Wipes at the Unitized Mass Loading Rate (1kg/year) Child Groundwater (updates to Table 4

- 6)

Constituent Drinking Wat er Dermal Bathing Combined DW/ DM

NL Composite NL Composite NL Composite

CANCER Risk Risk Risk Risk Risk Risk
Tetrachloroethylene 1.2E

- 08 2.7E

- 11 3.3E

- 09 7.4E

- 12 1.6E

- 08 (DW) 3.6E

- 11 (DW)
Trichloroethylene 3.1E

- 07 5.4E

- 10 1.1E

- 07 1.8E

- 10 4.4E

- 07 (DW) 7.3E

- 10 (DW)

NONCANCER HQ HQ HQ HQ HQ HQ
Tetrachloroethylene 1.3E

- 02 3.0E

- 05 3.4E

- 03 8.6E

- 06 NA NA
Trichloroethylene 1.7E

- 01 2.9E

- 04 5.8E

- 02 1.0E

- 04 NA NA DW = Driving pathway is drinking water

.



## Revised Risk Estimates and RB

- MLLs

As described in Sect ion 5 of Risk

- Based Mass Loading Limits for Solvents in Disposed Wipes and Laundry Sludges Managed in Municipal Landfills , the RB

- MLL s are derived from the 50th and 90 th percentile risk values as follows:



##  We calculate a scaling factor to derive the mass lo ading rate that corresponds to the cancer risk values of interest (1E

- 4, 1E

- 5, or 1E

- 6) and/or an HQ of 1. The scaling factor is simply the ratio of the risk/hazard criteria to the risk/hazard estimate at the 50th or 90th percentile.



##  We then multiply the constant mass loading rate (MLR) of 1 kg/yr by the scaling factor at the selected percentile. Because the rate is a constant value of 1 kg/yr, the scaling factor is equivalent to the MLR at the percentile of interest (i.e., 1 x SF = SF = MLR). The MLR can be derived for any percentile of interest; however, the risk

- based MLRs were derived at the 90th and 50th percentiles of the distribution per EPA policy for this analysis.



##  The lowest rate represents that value that will protect at least 90 (or 50) percent of the hypothetical individuals (all receptor types) living within 2 km of a municipal solid waste landfill for all exposure pathways. This MLR is referred to as the Risk

- Based Mass Loading Limit (RB

MLL)



##  Lastly, we perform a check on the MLR to ensure tha t solubility limits are not exceeded (e.g., the MLR should not result in pure product in the landfill).

Tables 8 and 9 present the noncancer

- and cancer

- based RB

- MLLs, respectively. For comparison, these tables also present the values shown in the 2009 ris k assessment document.

### 4 Table 8 . RB

- MLLs for Noncarcinogens

Analysis

Year CAS Chemical No Liner Composite Liner

MLL (kg/yr) a Limiting P athway b MLL (kg/yr) a Limiting P athway b

90th Percentile (Table 5

- 1)

2009 127

- 18

- 4 Tetrachloroethylene 1.3E+02 DW

- Ch 5.6E+04 DW

- Ch

79

- 01

- 6 Trichloroethylene 7.3E+02 SH

- A 4.4E+05 SH

- A

201 2 127

- 18

- 4 Tetrachloroethylene 7.7E+01 DW

- Ch 3.3E+04 DW

- Ch

79

- 01

- 6 Trichloroethylene 2.4E+00 SH

- A 1.4E+03 SH

- A

50th Percentile (Table 5

- 2)

2009 127

- 18

- 4 Tetrachloroethyle ne 5.6E+03 DW

- Ch 4.0E+06 S AA

- Ch

79

- 01

- 6 Trichloroethylene 3.9E+04 SH

- A 9.3E+06 AA

- Ch

201 2 127

- 18

- 4 Tetrachloroethylene 3.3E+03 DW

- Ch 6.3E+05 S AA

- Ch

79

- 01

- 6 Trichloroethylene 1.3E+02 SH

- A 3.1E+04 AA

- Ch



### Table 9 . RB

- MLLs for Carcinogens

A nalysis

Year Risk T hreshold No Liner Composite Liner

MLL (kg/yr) a Sol Flag a Limiting Pathway b MLL (kg/yr) Sol Flag a Limiting Pathway b

90th Percentile (Table 5

- 3)

2009 127

- 18

- 4: Tetrachloroethylene (high) c

10 - 4 1.7E+01 Comb(DW)

- A 8.2E+03 Comb(D W)

- A

10 - 5 1.7E+00 Comb(DW)

- A 8.2E+02 Comb(DW)

- A

10 - 6 1.7E

- 01 Comb(DW)

- A 8.2E+01 Comb(DW)

- A

HQ=1 1.3E+02 DW

- Ch 5.6E+04 DW

- Ch

127

- 18

- 4: Tetrachloroethylene (low) c

10 - 4 2.0 E+01 Comb(DW)

- A 9.8 E+03 Comb(DW)

- A

10 - 5 2.0 E+00 Comb(DW)

- A 9.8 E+02 Comb(DW)

- A

10 - 6 2.0 E

- 01 Comb(DW)

- A 9.8 E+01 Comb(DW)

- A

HQ=1 1.3E+02 DW

- Ch 5.6E+04 DW

- Ch

79

- 01

- 6: Trichloroethylene

10 - 4 2.2E+02 Comb(SH)

- A 1.3E+05 Comb(DW)

- A

10 - 5 2.2E+01 Comb(SH)

- A 1.3E+04 Comb(DW)

- A

10 - 6 2.2E+00 C omb(SH)

- A 1.3E+03 Comb(DW)

- A

HQ=1 7.3E+02 SH

- A 4.4E+05 SH

- A

201 2 127

- 18

- 4: Tetrachloroethylene

10 - 4 1.7E+03 Comb(SH)

- A 7.7E+05 Comb( SH )

- A

10 - 5 1.7E+02 Comb(SH)

- A 7.7E+04 Comb( SH )

- A

10 - 6 1.7E+01 Comb(SH)

- A 7.7E+03 Comb( SH )

- A

HQ =1 7.7E+01 DW

- Ch 3.3E+04 DW

- Ch

### 5 79

- 01

- 6: Trichloroethylene

10 - 4 8.3E+01 Comb( DW )

- A 5.3E+04 Comb(DW)

- A

10 - 5 8.3E+00 Comb( DW )

- A 5.3E+03 Comb(DW)

- A

10 - 6 8.3E

- 01 Comb( DW )

- A 5.3E+02 Comb(DW)

- A

HQ=1 2.4E+00 SH

- A 1.4E+03 SH

- A

5 0th Percentile (Table 5

- 4 )

2009 127

- 18

- 4: Tetrachloroethylene (high) c

10 - 4 9.5E+02 Comb(DW)

- A 1.7E+06 AA

- A

10 - 5 9.5E+01 Comb(DW)

- A 1.7E+05 AA

- A

10 - 6 9.5E+00 Comb(DW)

- A 1.7E+04 AA

- A

HQ=1 5.6E+03 DW

- Ch 4.0E+06 S AA

- Ch

127

- 18

- 4: Tetrachlo roethylene (low) c

10 - 4 1.1 E+0 3 Comb(DW)

- A 1. 5 E+0 7 AA

- A

10 - 5 1.1 E+0 2 Comb(DW)

- A 1.5 E+0 6 AA

- A

10 - 6 1.1E+01 Comb(DW)

- A 1.5E+05 AA

- A

HQ=1 5.6E+03 DW

- Ch 4.0E+06 S AA

- Ch

79

- 01

- 6: Trichloroethylene

10 - 4 1.3E+04 Comb(SH)

- A 5.1E+06 AA

- A

10 - 5 1.3E+03 Comb(SH)

- A 5.1E+05 AA

- A

10 - 6 1.3E+02 Comb(SH)

- A 5.1E+04 AA

- A

HQ=1 3.9E+04 SH

- A 9.3E+06 AA

- Ch

201 2 127

- 18

- 4: Tetrachloroethylene

10 - 4 1.0E+05 Comb(DW )

- A 4.0E+07 AA

- A

10 - 5 1.0E+04 Comb(DW )

- A 4.0E+06 AA

- A

10 - 6 1.0E+03 Comb(DW )

- A 4.0E+05 AA

- A

HQ=1 3.3E+03 DW

- Ch 6.3E+05 S AA

- Ch

79

- 01

- 6: Trichloroethylene

10 - 4 4.8E+03 Comb(SH)

- A 2.6E+06 AA

- A

10 - 5 4.8E+02 Comb(SH)

- A 2.6E+05 AA

- A

10 - 6 4.8E+01 Comb(SH)

- A 2.6E+04 AA

- A

HQ=1 1.3E+02 SH

- A 3 .1E+04 AA

- Ch

a S = Based on solubility limit.

b Limiting Pathway is denoted as Pathway

- Receptor, where:

AA = ambient air; Comb = combined drinking water, shower inhalation, shower/bath dermal; DM = shower/bath dermal; DW = drinking water; SH = shower inhalation

. For combined (Comb) risks, the associated limiting pathway is provided in parentheses. A = Adult, Ch = Child

. C In 2009, two estimates were provided for tetrachloroethylene cancer risks to reflect the high and low end s of the

range of bench marks.

### 6 Tables 10

, 11 , and 12 present the recalculated 50th percentile and 90th percentile RB

- MLLs that represent the changes to the Executive Summary tables contained in the original risk document. As noted in the titles of Tables 10 through 12 , these tab les correspond to Tables ES

- 2, ES

- 3 , and ES

- 4, respectively, in the 2009 report



## .

Table 10. RB

- MLLs Based on a Cancer Risk Level of 10 - 4 

### or an HQ of 1 for 5 Solvents Analyzed Both as Carcinogens and Noncarcinogens (kg/year) [updates to Table ES

- 2]

Solvent No Liner Composite

50%ile a 90%ile a 50%ile a 90%ile a
Tetrachloroethylene b 3.3E+03 N 7.7E+01 N 6.3+E05 N 3.3E+04 N
Trichloroethylene b 1.3+02 N 2.4E+00 N 3.1E+04 N 1.4E+03 N

a N = based on noncancer risk..



### Table 11. RB

- MLLs Based on a Cancer Risk Lev el of 10 - 5 

### or an HQ of 1 for 5 Solvents Analyzed Both as Carcinogens and Noncarcinogens (kg/year) [updates to able ES

- 3]

Solvent No Liner Composite

50%ile a 90%ile a 50%ile a 90%ile a
Tetrachloroethylene c 3.3E+03 N 7.7E+01 N 6.3E+05 N 3.3E+04 N

Trichloroet hylene c 1.3E+02 N 2.4E+00 N 3.1E+04 N 1.4E+03 N

a N = based on noncancer risk.



### Table 12. RB

- MLLs Based on a Cancer Risk Level of 10 - 6 

### or an HQ of 1 for 5 Solvents Analyzed Both as Carcinogens and Noncarcinogens (kg/year) [updates toTable ES

- 4]

Solvent No Liner Composite

50%ile a 90%ile a 50%ile a 90%ile a
Tetrachloroethylene c 1.0E+03 C 1.7E+01 C 4.0E+05 C 7.7E+03 C
Trichloroethylene c 4.8E+01 C 8.3E

- 01 C 2.6E+04 C 5.3E+02 C

a C = based on cancer risk.



### Finally, the tables attached to the end of this document present the updated results for tetrachloroethylene and trichloroethylene contained in Appendix A of the original risk document. This appendix presents chemical

- specific results for a series of percentiles (50th, 75th, 90th, 95th, and 99th) and s cenarios that represent the theoretical risk distributions based on the unitized mass loading rate of 1 kg /year. Separate tables present the data for each solvent ( Tables 17a and 17b for tetrachloroethylene and Tables A

- 19a and A

- 19b for trichloroethylene )

. Tables labeled with an a present results for the ambient air pathway and those labeled b present the results for the groundwater pathway.