1 

### Note to the Record: 2011 Revisions to the Integrated Risk Information System (IRIS) Assessment for Methylene Chloride ( Dichloromethane , CASRN 75

- 09

- 2)



### • In 2009, EPA publi shed a revised risk analysis for the Solvent Contaminated Wipes Rule in a Notice of Data Availability (NODA) using IRIS toxicity values available at the time for assessing cancer and non

- cancer risks from methylene chloride. In March of 2010 , EPA published draft revis ions to the IRIS assessment for methylene chloride ; in November 2011 the updated assessment was finalized 1 

### , including new toxicity values

. The table below illustrates how the IRIS toxicity values changed for methylene chloride from 2009 to the updated values in 2011 and qualitatively characterizes the effect of the change for both adults and children: Methylene Chloride
2009 Risk Analysis 2011 IRIS Value M 2 Adult Characterization Child Characterization CSF 3 7.5 x 10 - 3 ( mg/kg

- d) - 1 2 x 10 - 3 ( mg/kg

- d) - 1 √ Less Conservative Potentially More Conservative 4 URF 5 4.7 x 10 - 7 ( ug/m3) - 1 1 x 10 - 8 (ug/m3 ) - 1 √ Less Conservative Less Conservative RfD 6 6.0 x 10 - 2 mg/kg

- d 6.0 x 10 - 3 mg/kg

- d More Conservative More Conservative RfC 7 4.0 x 10 - 1 mg/m 3 6.0 x 10 - 1 mg/m 3 Less Conservative Less Conservative



### • Three of the four health benchmarks in the updated IRIS assessment are less conservative than those used in the 2009 Risk Analysis , which would result in less conservative risk values from adult exposure to methylene chloride than estimated in the 2009 Risk Analysis

.

• One health benchmark, RfD, is more conservative by a factor of 10 (or one order of magnitude) , which could result in more conservative risk values for both adult and childhood exposures to methyl ene chloride than estimate d in the 2009 Risk An alysis

.

• Additionally, the updated IRIS assessment included a mutagenic mode of action for carcinogenicity, which accounts for possible increased sensitivity of early

- life exposure. R isk analyses account for mutagenic mode of action by applying Age Depe ndent Adjustment Factors (ADAF) to the canc er values (CSF and URF) for exposures beginning prior to age 16, which can range from a factor of 10 to a factor o f 3, depending on age at exposure.

• Because the 2011 URF (inhalation) IRIS value became less conservative by a factor of 47 from the 2009 va lue, using the highest ADAF (applying a factor of 10) would still result in less conservative risk values than estimated in the 2009 Risk Analysis

.

1 EPA Integrated Risk Information System, Dichloromethane (CASRN 75

- 09

- 2), Last Revised November 18, 2011. ( http://www.epa.gov/iris/subst/0070.htm#carc )

. 2 M = Mutagenic Mode of Action , added i n 2011. 3 CSF = Oral Cancer Slope Factor 4 Whether the 2011 IRIS value for the CSF would be considered more conservative for exposure beginning during childhood than that used for the 2009 Risk Analysis would depend on which Age Dependent Adjustment Factor is applied. 5 URF = Inhalation Unit Risk Factor 6 RfD = Reference Dose for Chronic Oral Exposure 7 RfC = Reference Concentration for Chronic Inhalation Exposure2 

### • Because t he 2011 CSF (ingestion) IRIS value became less conservative by a factor of 3.7, applying ADAFs (10

- fold to 3

- fold adjustments ) could increase the CSF conservativeness as compared to the 2009 value , depending on which AD AF was applied . Any increase in conservativeness would be less than one order of magnitude.

Conclusion

• EPA estimates that the 20 11 change in IRIS values will have no impact on the final disposition of methylene chloride contaminated

- wipes in the final rule. We found that the majority of revised 2011 toxicity values for methylene chloride for both cancer and noncancer endpoints actually became less conservative than the values used in the 2009 risk analysis. For th ose values that became more conservative , we found that th ey i ncreased only one order of magnitude or less in conservativeness. G iven that the 2009 risk results for methylene chloride f el l well below the target risk thresholds 8 

### by at least five or six orders of magnitude, EPA estimates that the use of these more conservative values would still be protective of human health

.

8 The target risk thresholds used for the final rule are based on the 90 percentile for a land fill with a composite liner, cancer risk of 10 - 5 and HQ=1 . See “ Risk

- Based Mass Loading Limits for Solvents in Disposed Wipes and Laundry Sludges Managed in Municipal Landfills, ” October 2009, Tables A

- 16a and A

- 16b (also attached).

## Table A-16a. Risk Results for Select Percentiles at the Unitized Mass Loading Rate (1 kg / year) Inhalation of Ambient Air of Methylene chloride

CAS 75-09-2

Effect Receptor Percentile Pathway Risk or HQ Appendix A Theoretical Risk Distributions Draft



### Composite Liner
Adult Cancer Inhalation 4.6E-12 50 Inhalation 1.5E-11 75 Inhalation 4.1E-11 90 Inhalation 7.0E-11 95 Inhalation 1.8E-10 99 Child Cancer Inhalation 1.9E-12 50 Inhalation 6.8E-12 75 Inhalation 1.8E-11 90 Inhalation 3.1E-11 95 Inhalation 8.5E-11 99 Adult Noncancer Inhalation 1.5E-07 50 Inhalation 4.4E-07 75 Inhalation 9.9E-07 90 Inhalation 1.6E-06 95 Inhalation 3.6E-06 99 Child Noncancer Inhalation 1.6E-07 50 Inhalation 4.6E-07 75 Inhalation 1.0E-06 90 Inhalation 1.7E-06 95 Inhalation 3.7E-06 99

A-55

## Table A-16b. Risk Results for Select Percentiles at the Unitized Mass Loading Rate (1 kg / year) Groundwater Pathways of Methylene chloride

CAS 75-09-2

Effect Receptor Percentile Pathway Risk or HQ Appendix A Theoretical Risk Distributions Draft



### Composite Liner
Adult Cancer Shower 2.9E-24 50 Drinking water 1.9E-24

Dermal bathing 9.0E-26 Combined DW/SH/DM 5.8E-24 Shower 2.4E-14 75 Drinking water 2.2E-14

Dermal bathing 9.5E-16 Combined DW/SH/DM 5.5E-14 Shower 3.4E-12 90 Drinking water 2.8E-12

Dermal bathing 1.2E-13 Combined DW/SH/DM 7.2E-12 Shower 2.4E-11 95 Drinking water 2.2E-11

Dermal bathing 8.6E-13 Combined DW/SH/DM 4.9E-11 Shower 5.3E-10 99 Drinking water 3.9E-10

Dermal bathing 1.7E-11 Combined DW/SH/DM 9.7E-10 Child Cancer Drinking water 2.4E-24 50 Dermal bathing 1.6E-25

Combined DW/DM 2.5E-24 Drinking water 2.2E-14 75 Dermal bathing 1.1E-15

Combined DW/DM 2.3E-14 Drinking water 2.5E-12 90 Dermal bathing 1.3E-13

Combined DW/DM 2.7E-12 Drinking water 1.8E-11 95 Dermal bathing 9.6E-13

Combined DW/DM 1.9E-11 Drinking water 2.9E-10 99 Dermal bathing 1.6E-11

Combined DW/DM 3.0E-10 Adult Noncancer Shower 7.9E-20 50 Drinking water 3.1E-20

Dermal bathing 1.6E-21 Shower 8.6E-10 75 Drinking water 3.5E-10

Dermal bathing 1.4E-11

A-58

## Table A-16b. Risk Results for Select Percentiles at the Unitized Mass Loading Rate (1 kg / year) Groundwater Pathways of Methylene chloride

CAS 75-09-2

Effect Receptor Percentile Pathway Risk or HQ Appendix A Theoretical Risk Distributions Draft

Shower 1.0E-07 90 Drinking water 3.9E-08

Dermal bathing 1.6E-09 Shower 7.5E-07 95 Drinking water 2.6E-07

Dermal bathing 1.1E-08 Shower 1.4E-05 99 Drinking water 4.0E-06

Dermal bathing 1.8E-07 Child Noncancer Drinking water 7.2E-20 50 Dermal bathing 4.2E-21

Drinking water 7.0E-10 75 Dermal bathing 3.5E-11

Drinking water 8.3E-08 90 Dermal bathing 4.3E-09

Drinking water 5.4E-07 95 Dermal bathing 2.8E-08

Drinking water 9.3E-06 99 Dermal bathing 4.2E-07

A-59