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 published 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 revisions to the IRIS assessment for methylene chloride; in November 2011

the updated assessment was finalized1, 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 M2 Adult 

Characterization

Child

Characterization

CSF3 7.5 x 10-3 (mg/kg-d)-1 2 x 10-3 (mg/kg-d)-1 √ Less Conservative Potentially More 

Conservative4

URF5 4.7 x 10-7 (ug/m3)-1 1 x 10-8 (ug/m3)

-1 √ Less Conservative Less Conservative

RfD6 6.0 x 10-2 mg/kg-d 6.0 x 10-3 mg/kg-d More Conservative More Conservative

RfC7 4.0 x 10-1 mg/m3 6.0 x 10-1 mg/m3 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 methylene chloride than estimated in the 2009 Risk Analysis.

• Additionally, the updated IRIS assessment included a mutagenic mode of action for 

carcinogenicity, which accounts for possible increased sensitivity of early-life exposure. Risk 

analyses account for mutagenic mode of action by applying Age Dependent Adjustment 

Factors (ADAF) to the cancer values (CSF and URF) for exposures beginning prior to age 16, 

which can range from a factor of 10 to a factor of 3, depending on age at exposure. 

• Because the 2011 URF (inhalation) IRIS value became less conservative by a factor of 47 from 

the 2009 value, 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 in 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 Exposure
2

• Because the 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 ADAF was applied. Any increase in 

conservativeness would be less than one order of magnitude.

Conclusion

• EPA estimates that the 2011 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 those 

values that became more conservative, we found that they increased only one order of 

magnitude or less in conservativeness. Given that the 2009 risk results for methylene 

chloride fell well below the target risk thresholds8 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 landfill 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 

Draft Appendix A Theoretical Risk Distributions

Composite Liner

Cancer Adult

50 Inhalation 4.6E-12

75 Inhalation 1.5E-11

90 Inhalation 4.1E-11

95 Inhalation 7.0E-11

99 Inhalation 1.8E-10

Cancer Child

50 Inhalation 1.9E-12

75 Inhalation 6.8E-12

90 Inhalation 1.8E-11

95 Inhalation 3.1E-11

99 Inhalation 8.5E-11

Noncancer Adult

50 Inhalation 1.5E-07

75 Inhalation 4.4E-07

90 Inhalation 9.9E-07

95 Inhalation 1.6E-06

99 Inhalation 3.6E-06

Noncancer Child

50 Inhalation 1.6E-07

75 Inhalation 4.6E-07

90 Inhalation 1.0E-06

95 Inhalation 1.7E-06

99 Inhalation 3.7E-06

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 

Draft Appendix A Theoretical Risk Distributions

Composite Liner

Cancer Adult

50 Shower 2.9E-24

Drinking water 1.9E-24

Dermal bathing 9.0E-26

Combined DW/SH/DM 5.8E-24

75 Shower 2.4E-14

Drinking water 2.2E-14

Dermal bathing 9.5E-16

Combined DW/SH/DM 5.5E-14

90 Shower 3.4E-12

Drinking water 2.8E-12

Dermal bathing 1.2E-13

Combined DW/SH/DM 7.2E-12

95 Shower 2.4E-11

Drinking water 2.2E-11

Dermal bathing 8.6E-13

Combined DW/SH/DM 4.9E-11

99 Shower 5.3E-10

Drinking water 3.9E-10

Dermal bathing 1.7E-11

Combined DW/SH/DM 9.7E-10

Cancer Child

50 Drinking water 2.4E-24

Dermal bathing 1.6E-25

Combined DW/DM 2.5E-24

75 Drinking water 2.2E-14

Dermal bathing 1.1E-15

Combined DW/DM 2.3E-14

90 Drinking water 2.5E-12

Dermal bathing 1.3E-13

Combined DW/DM 2.7E-12

95 Drinking water 1.8E-11

Dermal bathing 9.6E-13

Combined DW/DM 1.9E-11

99 Drinking water 2.9E-10

Dermal bathing 1.6E-11

Combined DW/DM 3.0E-10

Noncancer Adult

50 Shower 7.9E-20

Drinking water 3.1E-20

Dermal bathing 1.6E-21

75 Shower 8.6E-10

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 

Draft Appendix A Theoretical Risk Distributions

90 Shower 1.0E-07

Drinking water 3.9E-08

Dermal bathing 1.6E-09

95 Shower 7.5E-07

Drinking water 2.6E-07

Dermal bathing 1.1E-08

99 Shower 1.4E-05

Drinking water 4.0E-06

Dermal bathing 1.8E-07

Noncancer Child

50 Drinking water 7.2E-20

Dermal bathing 4.2E-21

75 Drinking water 7.0E-10

Dermal bathing 3.5E-11

90 Drinking water 8.3E-08

Dermal bathing 4.3E-09

95 Drinking water 5.4E-07

Dermal bathing 2.8E-08

99 Drinking water 9.3E-06

Dermal bathing 4.2E-07

A-59