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Charge Questions for the Peer Review of the draft Workplan Risk Assessment 

for Methylene Chloride (DCM)

August 2013

OPPT focused its risk assessment on the use of DCM in paint stripping. There are human health 

concerns for both cancer and non-cancer effects with DCM use-application. Only the inhalation 

route of exposure was evaluated and risk estimates were calculated for consumers and workers 

using DCM-based paint strippers. Risks also were estimated for individuals physically near the 

residential user and who are not using the DCM-based product (also referred as called bystanders 

or non-users).

General Question on the Risk Assessment Document

Issue 1. This risk assessment is divided into three chapters with eight appendices. The

first two chapters describe the scoping exercise EPA used and background

information on DCM that sets the stage for the information available and used in the

risk assessment. Chapter 3 includes the exposure, hazard assessment and risk

characterization and a section on uncertainties of the risk assessment. The risk

assessment is intended to provide a clear and transparent summary of the Agency’s

analysis.

Question 1-1: Please comment on whether the risk assessment provides a clear and 

logical summary of EPA’s analysis. Please provide specific suggestions for improving 

the clarity and transparency of the risk assessment document. 

Question 1-2: Please comment on whether appropriate background information is 

provided and accurately characterized. Please provide any other relevant literature, 

reports, or data that would be useful to support the risk assessment.

Questions on the Exposure Assessment

Issue 2: Workplace exposure estimates were developed for adults using DCM-based paint 

strippers. EPA found limited published data for DCM air concentrations in workplace 

settings during use of DCM-based paint strippers. These data were used for estimating 

occupational inhalation exposures.

Question 2-1 Please comment on the approach used, and provide any specific suggestions

or recommendations for alternative approaches, models or information that should be

considered by the Agency for improving its assessment of DCM workplace exposures, 

including specific citations (if available) of other data sources characterizing occupational 

inhalation exposures, 

Issue 3. Inhalation exposures from consumer uses of DCM-based paint strippers were 

estimated using the EPA’s Multi-Chamber Concentrations and Exposure Model 

(MCCEM). EPA conducted a sensitivity analysis of selected model parameters to identify 
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critical parameters essential to the modeling approach used to estimate inhalation 

exposures. This analysis guided the selection of exposure scenarios and provided the most 

sensitive input parameters for generating central tendency and upper-end DCM air 

concentrations.

Question 3-1. Please comment on the approach used and provide any specific suggestions 

or recommendations for alternative approaches, models, or information that should be

considered by the Agency in developing the exposure assumptions and estimates for the

consumer use of DCM-based paint strippers and for the bystander/non-users (e.g., 

children, women of childbearing age). As part of the review, please comment on the

strengths and weaknesses of the evaluation of different exposure scenarios and the choice 

of assumptions/input parameters for generating central tendency and upper-end DCM air 

concentrations.

Questions on the Hazard Assessment

Issue 4. The inherent hazards of DCM have been well characterized. EPA used a range of 

acute or chronic human health hazard values to evaluate potential non-cancer risks in 

workplace and consumer settings. For instance, EPA used the point of departures (PODs)

from the California EPA’s reference exposure level (Cal EPA REL) and the Spacecraft 

Maximum Allowable Concentration (SMAC) to evaluate potential acute risks for 

residential users and bystanders/non-users (e.g., children and women of childbearing age). 

Harmful concentrations of DCM, leading to death, have been reported in enclosed 

environments where DCM-based paint strippers were used during bathroom tub 

refinishing projects. Based on this concern, EPA also included the acute exposure 

guideline levels (AEGLs) in the analysis to determine if DCM air concentrations would be 

exceeding the AEGL thresholds for disability (AEGL-2) and lethality (AEGL-3). EPA’s 

Integrated Risk Information System (IRIS) program has recently developed reference 

concentration (RfC) and inhalation unit risk (IUR) values for DCM. This assessment used 

the POD from the EPA’s IRIS RfC to evaluate chronic non-cancer risks. The EPA’s IRIS 

IUR was used to evaluate cancer risks in this assessment.

Question 4-1. Please comment on EPA’s use of the acute PODs that were identified 

from the technical documents supporting the Cal EPA REL, SMAC and AEGL 

derivations. As part of the review, please provide your input on the appropriateness of 

the approach, including its underlying assumptions, strengths and weaknesses. Please 

provide any specific suggestions or recommendations for alternative approaches that

should be considered by the Agency in characterizing the acute inhalation risks. Please 

provide relevant data or documentation and rationale for including other studies and 

endpoints for consideration. 

Question 4-2: Please comment on EPA’s choice of PODs and IUR for evaluating the 

non-cancer and cancer risks, respectively for chronic exposures to DCM-based paint 

strippers. As part of the review, provide your input on the appropriateness of the 

approach, including its underlying assumptions, strengths and weaknesses. Please 
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provide any specific suggestions or recommendations for alternative approaches that

should be considered by the Agency in characterizing the chronic inhalation risks to 

workers. Please provide relevant data or documentation and rationale for including 

other studies and endpoints for consideration.

Questions on the Risk Assessment

Issue 5. The margin of exposure (MOE) is the ratio of the hazard value to the exposure. 

The MOE approach used the PODs identified in the Cal EPA REL and SMAC to evaluate 

potential acute risks in residential users and bystanders/non-users (e.g., children, women 

of childbearing age). Benchmark MOEs of 60 and 10 were used to determine acute risks 

based on the uncertainty analysis conducted in the Cal EPA REL and SMAC assessments, 

respectively. Hazard quotients (HQs) were used to evaluate potential acute risks in 

residential settings by comparing the AEGL values with the acute exposure estimates. 

HQs greater than 1 were interpreted as a potential acute risk. For chronic occupational 

risks, the POD from the EPA’s IRIS RfC was chosen as the basis for the non-cancer MOE 

calculations. A benchmark MOE of 30 was used to interpret chronic risks for workers

based on the uncertainty analysis in the EPA’s DCM IRIS assessment. The EPA’s IRIS 

IUR was used to evaluate potential chronic risks to cancer endpoints for the worker 

exposure scenarios. The risk characterization also provides a discussion of the 

uncertainties surrounding the risk calculations.

Question 5-1: Please comment on the assumptions, strengths and weaknesses of the

MOE and HQ approaches used to estimate the acute non-cancer risks to consumers of 

DCM-based products, including bystanders/non-users (e.g., children, women of 

childbearing age). Please also comment on the selection of composite uncertainty factors 

that were used as benchmark MOEs to determine the acute risks.

Question 5-2: Please comment on the assumptions, strengths and weaknesses of the

MOE approach used to estimate the chronic non-cancer risks for workplace exposures. 

Please also comment on the selection of composite uncertainty factors that were used as 

benchmark MOEs to determine the chronic risks.

Question 5-3: Please comment on the assumptions, strengths and weaknesses of the

cancer estimation risk approach used for the workplace exposures.

Question 5-4: Please comment on whether the risk assessment document has 

adequately described the uncertainties and data limitations in the methodology used to 

assess risks to allow the EPA to reduce risks to human health from DCM. Please 

comment on whether this information is presented in a transparent manner.