Responses to Comments for DCM Work Plan Risk Assessment

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Summary of External Peer Review and

Public Comments and Disposition

This document summarizes the public and external peer review comments that the EPA’s Office of

Pollution Prevention and Toxics (OPPT) received for the draft work plan risk assessment for 

dichloromethane (DCM). It also provides EPA/OPPT’s response to the comments received from the 

public and the peer review panel.

EPA/OPPT appreciates the valuable input provided by the public and peer review panel. The input 

resulted in numerous revisions to the risk assessment.

Peer review charge questions1 are used to categorize the peer review and public comments into specific 

issues related to the five main themes. 

 General Issues on the Risk Assessment Document

 Occupational Exposure

 Consumer Exposure

 Hazard and Dose-Response Assessments

 Risk Characterization

A separate section called Other Public Comments organizes the response to those public comments that 

are unrelated to the main themes listed above.

 

1 These are the questions that EPA/OPPT submitted to the panel to guide the peer review process.
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General Issues on the Risk Assessment Document

Charge 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.

Charge 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.

#

Summary of Peer Review and Public Comments for 

Specific Issues Related to Charge Questions 1-1 and 1-2

EPA/OPPT Response

1 Document is not clear about the purpose of the risk 

assessment. The document would be substantially 

improved if a clear statement was made regarding the 

audience and utility of the report. 

EPA/OPPT has made significant revisions to the DCM risk assessment to 

improve the clarity of the assessment. In addition, the purpose and audience 

have been described in section 1.1 of the final DCM risk assessment.

2 EPA/OPPT did not assess dermal exposure to DCM for 

occupational and residential scenarios. Why is dermal 

exposure considered less significant than inhalation 

exposure?

By not including dermal exposure in the exposure 

assessment, exposure is likely to be underestimated.

EPA/OPPT recognizes that dermal exposure to highly volatile materials such 

as DCM can occur. However, based on the physical-chemical properties of 

DCM and the scenarios described in this assessment, EPA/OPPT believes 

that inhalation is the main exposure pathway when respiratory protection is 

not used. This assessment may underestimate total exposures resulting 

from the uses of DCM due to this assumption. Currently, there is no DCM 

PBPK model with a dermal component that would allow for route to route 

extrao0plation and aggregate exposure estimation for all routes. There is 

also a paucity of exposure information that would be needed for inputs into 

this extended modeling effort. Thus, we agree this assessment likely 

underestimates risks resulting from the uses of DCM being assessed. This has 

been acknowledged in the Executive Summary, section 1.3.2 and the 

uncertainty and data limitations section of the assessment 3.5.1.

3 EPA/OPPT’s small shop focus may not be warranted. For 

example, larger shops may have risks. The assumption 

that the small shops have exposures that are less 

controlled and monitored than those seen in large-scale 

industrial operations is not supported.

EPA/OPPT improved the focus descriptions in the Executive Summary, 

sections 1.3.3 and 3.1.1 and Appendices F and G. EPA/OPPT found that there 

were limited readily available data to support the original assumption and 

removed the assumption that small shops have < 10 workers. Therefore, 

even though the interest is for small shops, the occupational exposure 

analysis retains data and analyses for all industries and shop sizes. EPA/OPPT 

cannot rule out that any of these industries may have small shops engaging 

in paint stripping jobs. 
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In addition, EPA/OPPT revised the occupational exposure assessment to 

include a scenario approach that considers the use of respirators to control 

exposures. Section 3.1.1 contains information about the occupational 

scenarios examined in the final DCM risk assessment.

4 The draft DCM risk assessment did not identify all high 

risk uses of DCM, such as DCM-containing adhesives. 

Thus, the scope of the assessment should be expanded to 

include other DCM uses. Also, it should not be assumed 

that the other DCM uses have lower risks relative to paint 

stripping. In addition, the assessment did not provide a 

clear framework to prioritize specific use scenarios.

The final DCM risk assessment focuses on the likely highest exposure use 

(i.e., paint stripping). Other potential uses of DCM were not the focus of the 

current assessment.

Section 1.3.1 discusses the factors that EPA/OPPT considered when selecting 

the use scenarios for this assessment.

5 It was suggested that EPA/OPPT needed to conduct a 

systematic evaluation of the quality of the studies used to 

support the DCM risk assessment. 

EPA/OPPT revised the assessment to include the following data quality 

criteria used to evaluate the scientific information supporting the final DCM 

risk assessment. 

 Appendix G contains descriptions of the data quality criteria used in the 

occupational exposure assessment. Similar criteria were used for the 

consumer exposure assessment as acknowledged in section 3.2.1.

 The bioconcentration and persistence information were assessed 

according to the criteria set forth in the EPA’s New Chemical 

Premanufacture Notification Program (PMN) (EPA, 1999).

 The aquatic toxicity data were evaluated using the criteria set forth in 

the TSCA Work Plan Chemicals Methods Document (EPA, 2012) and the 

Classification Criteria for Environmental Toxicity and Fate of Industrial 

Chemicals (EPA, 1992). 

 EPA/OPPT used the U.S. EPA’s IRIS assessment for DCM for the chronic 

hazard and dose-response assessments (EPA, 2011). The DCM IRIS 

assessment considered the principles set forth by the various risk 

assessment guidelines issued by the National Research Council and the 

U.S. EPA (see Appendix I of the final DCM risk assessment). 

 DCM’s hazard and dose-response assessments for acute effects were 

based on the principles set forth by the Standing Operating Procedures 

for Developing Acute Exposure Guideline Levels (NRC, 2001) and the

Guidelines for Developing Spacecraft Maximum Allowable
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Concentrations for Space Station Contaminants (NRC, 1992) (see 

Appendix I of the final DCM risk assessment). 

References:

EPA (U.S. Environmental Protection Agency). 1999. Category for Persistent, 

Bioaccumulative, and Toxic New Chemical Substances. 64 Federal Register 

213 (November 4, 1999), pp. 60194-60204.

EPA (U.S. Environmental Protection Agency). 2012. TSCA Work Plan 

Chemicals: Methods Document. Office of Pollution Prevention and Toxics, 

Washington, DC. 

www.epa.gov/oppt/existingchemicals/pubs/wpmethods.pdf.

EPA (U.S. Environmental Protection Agency). 1992. Classification Criteria for 

Environmental Toxicity and Fate of Industrial Chemical. Office of Pollution 

Prevention and Toxics, Washington, DC.

EPA (U.S. Environmental Protection Agency). 2011. Toxicological Review of 

Dichloromethane (Methylene Chloride; CAS No. 75-09-2). EPA/635/R10/003F. Integrated Risk Information System, Office of Research and 

Development, Washington, DC. 

http://www.epa.gov/iris/toxreviews/0070tr.pdf.

NRC (National Research Council). 2001. Standing Operating Procedures for 

Developing Acute Exposure Guideline Levels for Hazardous Chemicals. 

National Academy Press, Washington DC. 

http://www.epa.gov/oppt/aegl/pubs/sop.pdf. 

NRC (National Research Council). 1992. Guidelines for Developing Spacecraft 

Maximum Allowable Concentrations for Space Station Contaminants 

National Academy Press, Washington, DC.
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6 EPA/OPPT received comments suggesting that the DCM 

risk assessment should be described as a screening-level 

risk assessment. 

The final DCM risk assessment is not considered a screening-level risk 

assessment. The occupational exposure assessment was based on DCM air 

monitoring data collected from relevant industries conducting paint 

stripping activities. The consumer exposure assessment used EPA’s MultiChamber Concentration and Exposure Model (MCCEM), which requires data 

requirements, such as input emission rates and decay rates, which are 

related to higher tier models. Also, the scenario approach for the consumer 

and occupational exposure assessment considered central-tendency and 

upper-end input parameters and assumptions to develop realistic exposure 

scenarios. In addition, physiologically-based pharmacokinetic (PBPK) 

modeling was conducted to derive most of the acute and chronic hazard 

values used in this assessment (i.e., human equivalent concentrations).

7 A peer reviewer noted missing hazard and risk 

information in the Executive summary.

EPA/OPPT made appropriate revisions or clarifications to the Executive 

Summary to address the issues that the peer reviewer identified.

8 The draft DCM risk assessment had inconsistent 

statements about DCM’s Global Warming Potential 

(GWP). Specifically, Table 2-3 listed the lack of GWP as a 

one of the benefits of DCM. However, the Environmental 

Fate section stated that DCM has been reported as a 

GWP chemical with a value of 8.7 (~ 8.7 times more heat 

absorptive than CO2). 

EPA/OPPT made changes to Table 2-3 (section 2.2.1) to fix the inconsistency

in the final DCM risk assessment.

9 Public comments made the observation that the draft 

DCM risk assessment did not discuss DCM replacement 

alternatives.

EPA/OPPT did not discuss the available replacement alternatives in the final 

DCM risk assessment. Such discussion will take place in the future as part of 

the risk management activities for DCM.
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10 EPA/OPPT did not acknowledge the adverse public health 

impacts arising from the large DCM air releases (and 

other environmental contamination) referred to in the 

assessment, or the relationship between the 

environmental contamination and consumer, industrial, 

and commercial uses of DCM-based paint strippers. 

EPA/OPPT is assessing the risks of chemical uses that fall under the authority 

of the Toxics Substances Control Act (TSCA), which in this assessment is the 

use of DCM in paint strippers. EPA/OPPT is concerned about the human 

health hazards of DCM as documented in section 3.3 and acknowledges that 

DCM is ubiquitously present in the environment with levels detected in 

drinking water, indoor environments, ambient air, groundwater and soil 

(section 1.2.1). Thus, EPA has taken regulatory actions through various 

statutory authorizes to reduce the environmental levels of DCM and its 

potential human health impacts (section 1.2.4). In addition, the Consumer 

Product Safety Commission, the Food and Drug Administration, the 

Occupational Safety and Health Administration (OSHA) and some U.S. States 

have also taken regulatory action to reduce exposures to DCM (Appendix A).

11 EPA/OPPT should move the biomonitoring discussion to 

the exposure section.

EPA/OPPT retained the discussion of the biomonitoring data in section 3.3

(Hazard/Dose-Response Assessment). No change was made in the final DCM 

risk assessment.
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Occupational Exposure Assessment

Charge 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.

# Summary of Peer Review and Public Comments for 

Specific Issues Related to Charge Question 2-1

EPA/OPPT Response

12 The literature search strategy should be described, and 

other references that may have relevant exposure data 

should be considered.

EPA/OPPT has added descriptions of the search strategy and quality criteria to 

Appendix G.

EPA/OPPT reviewed all of the exposure-relevant references recommended by 

the public and peer review panel. A small amount of new data from Anundi et 

al., (1993), Anundi et al., (2000), Estill et al., (1996), and Hall et al., (1995), all 

within the ranges of our original data sets, has been added to the data sets in 

Appendix G.

References:

Anundi, H., S. Langworth, G. Johanson, M. L. Lind, B. Akesson, L. Friis, N. Itkes, 

E. Soderman, B. A. Jonsson, and C. Edling. 2000. Air and Biological Monitoring 

of Solvent Exposure During Graffiti Removal. Int Arch Occup Environ Health, 

73(8), 561-569.

Anundi, H., M. L. Lind, L. Friis, N. Itkes, S. Langworth, and C. Edling. 1993. High 

Exposures to Organic Solvents among Graffiti Removers. Int Arch Occup 

Environ Health, 65(4), 247-251.

Estill, C. F., and A. B. Spencer. 1996. Case Study: Control of Methylene 

Chloride Exposures During Furniture Stripping. Am Ind Hyg Assoc J, 57(1), 43-

49.

Hall, R. M., K. F. Martinez, and P. A. Jensen. 1995. Control of Methylene 

Chloride—Furniture Stripping Dip Tank. Applied Occupational and 

Environmental Hygiene, 10(3), 188-195.
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13 Several interrelated issues were raised by peer reviewers 

and public commenters regarding the worker inhalation 

monitoring data and its use in generating average daily 

concentrations (ADCs) and lifetime average daily 

concentrations (LADCs), 

a) More OSHA’s Integrated Management Information 

System (IMIS) data should be used for estimating risks.

b) Worker exposure trends due to OSHA’s permissible 

exposure level (PEL) update in 1997 should be 

analyzed quantitatively, and data before 1997 should 

be excluded.

c) Data presentation and transparency should be 

improved, including being more statistical, using 

central tendencies, or developing a probabilistic 

approach rather than using only composite ranges.

d) Exposure controls are neglected.

EPA/OPPT further considered IMIS data and found no solid criteria for 

determining which IMIS data were associated with use of DCM-containing 

strippers. Thus, EPA/OPPT has concluded that the original preference for 

literature data over IMIS is valid. The risk assessment was revised to indicate

that the IMIS data were generally excluded from use in risk estimation when 

literature monitoring data were available and preferred due to their known 

applicability to paint stripping (see section 3.1.1.2 and Appendix G, section G2-2-1), whereas IMIS exposure data may not be due to DCM-based strippers. 

However, the risk assessment used surrogate data from the IMIS database for 

the Art Restoration and Conservation industry in the absence of literature 

data for this industry. Further, EPA/OPPT analyzed the monitoring data and 

reported statistical values (e.g., arithmetic means and one 95th percentile), 

when possible, for several relevant industries, or midpoints of ranges when 

better statistical values could not be determined. These statistical 

improvements provided further support to using monitoring data over IMIS 

data.

Regarding the PEL update, EPA/OPPT re-examined the IMIS data for the 

industries that were identified to do paint stripping. These IMIS data show 

that in some industries, exposure levels increased after the PEL update, and 

for other industries, exposure levels decreased after the PEL update. Overall, 

our analysis suggested that the 1997 PEL update did not have significant 

impacts on reducing the DCM air concentrations for these industries. 

Therefore, EPA/OPPT retained the monitoring data collected before the 1997 

PEL update. This issue is discussed in Appendix G. 

Data presentation, transparency, statistics (including central tendencies), and 

exposure controls were particularly interrelated for assessment purposes. 

EPA/OPPT has improved upon the composite range approach by including 

statistical values (e.g., arithmetic means and one 95th percentile), where 

possible. When statistical values could not be provided, midpoints were 

provided as central tendency substitutes along with ranges. EPA/OPPT 

bolstered the data summaries in tables by including numbers of studies, 

numbers of data points, study dates, and data sources, along with adding 

more data to the summaries for completeness. Please refer to Appendix G for 

more information about these additions to the risk assessment.
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Moreover, there are no appropriate input distributions for most of the 

occupational exposure parameters. Thus, EPA/OPPT determined that a 

probabilistic approach is inappropriate for this assessment. 

The final DCM risk assessment included a scenario-based approach for the 

worker exposure assessment. EPA/OPPT developed exposure scenarios with 

and without respirators and using several exposure frequencies and worker

lifetimes exposure durations of 20 yrs versus 40 yrs. EPA/OPPT used 

midpoints of frequencies and worker lifetime durations of exposures as 

substitutes for central tendencies. However, the relative prevalence of 

respirator use and central tendencies of frequencies and working lifetimes is 

unknown. 

Readily available data were insufficient for quantifying exposure impacts due 

to other exposure control measures such as local ventilation, although 

anecdotal examples of such controls were included in Appendix G, where 

available.

14 The census data are too weak to be used to calculate 

worker population estimates.

EPA/OPPT considered other data sources such as EPA’s National Emission 

Standards for Hazardous Air Pollutants (NESHAP) for Paint Stripping. NESHAP 

data were usable for postulating estimates of the total population of workers 

involved in the paint stripping operations for all industries combined. Also, 

the NESHAP data were used to estimate a range of the total number of 

workers directly exposed in small shops (< 10 workers). Please see Appendix F 

for further discussion.

EPA/OPPT also made revisions to Appendix F to clearly show the estimates of 

number of workers per shop in each of the industries. 

15 EPA/OPPT should include more information on label 

instructions, common industry practices, and high-end or 

extremes in stripper use.

Appendices F and G incorporated additional information about common 

industry practices when available. EPA/OPPT could not find data on high-end 

and extreme stripper use rate data. Information on labeling instructions was 

not incorporated in the final risk assessment because such instructions would 

be anecdotal. With the exception of respirator use, the inclusion of all of 

these types of information would not impact exposure estimates used in the 

risk analyses. The expected prevalence of respirator use was discussed 

qualitatively in Appendix G.
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Consumer Exposure Assessment

Charge 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.

#

Summary of Peer Review and Public Comments for 

Specific Issues Related to Charge Question 3-1

EPA/OPPT Response

16 A public comment stated that all the exposure scenarios 

were indoor and asked whether there was 

consideration of product use outside.

EPA/OPPT focused the risk assessment on the indoor residential use of 

DCM-based paint strippers. The assessment did not consider the outdoor 

use of these products. 

17 A panelist suggested expanding the paint stripping 

protocol description and insert same in body of 

document.

Section H-3 of Appendix H discusses how labeling instructions guided the 

selection of input parameters or assumptions about the stripping sequence, 

ventilation conditions (i.e., open windows) and user location during wait 

period. Details such as effects of container left open, methods to loosen 

paint, and cleanup procedures were not incorporated in the consumer 

modeling.

18 Several peer reviewers suggested that a larger surface 

area or multiple pieces of furniture for longer stripping 

periods be considered as exposure scenarios. They also 

suggested adding extra scenarios with closed windows, 

which would have lower air exchange rate (ACH). 

It was also recommended that stripping periods have 

more documentation.

A public commenter stated that EPA/OPPT overstated 

the risk of exposure via worst case (bathroom) scenario 

assessment.

Appendix H, section H-3, discusses the unlikely scenario of stripping multiple 

pieces of furniture. It also states that surface areas were selected so that 

the resulting product masses used in the modeling scenarios corresponded 

approximately to central (near the median) and upper-end (near the 80th

percentile) estimates for the amount of paint stripper used per event from 

a nationwide survey by CPSC (1992). CPSC (1992) reported larger percentile 

amounts, but given that the amounts used in the assessment indicate 

health concerns, more conservative modeling is not necessary. This is also a 

reason why modeling with lower ventilation is not needed, although such 

scenarios may occur they would produce even higher exposure estimates.

Language has been added in section 3-2 and Appendix H (section H-3) to 

state that all of the scenarios, but the bathroom scenario, were considered 

plausible and that application time was derived from EPA (1994). Moreover, 

the choices for the consumer scenario parameters, with the exception of 

those for the bathroom scenario, were supported by label suggestions for 
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ventilation (open windows) and/or by information on user behavior in CPSC

(1992), Pollack-Nelson (1995) and Riley (2001). The bathroom scenario was 

linked to worst-case exposure conditions based on a fatality case resulting 

from overexposure to DCM during a bathtub refinishing project. Please 

refer to Appendix H, section H-3, for more information. 

References:

EPA (U.S. Environmental Protection Agency). 1994. Consumer Exposure to 

Paint Stripper Solvents. Office of Pollution Prevention and Toxics, 

Washington, DC.

CPSC (Consumer Product Safety Commission). 1992. Methylene Chloride 

Consumer Products Use Survey Findings. Prepared by L. Boast from Abt 

Associates, Inc., for the U.S. Consumer Product Safety Commission, 

Bethesda, MD.

Pollack-Nelson, C. 1995. Analysis of Methylene Chloride Product Labelling. 

Ergonomics, 38(11), 2176-2187.

Riley, D. M., B. Fischhoff, M. J. Small, and P. Fischbeck. 2001. Evaluating the 

Effectiveness of Risk-Reduction Strategies for Consumer Chemical Products. 

Risk Analysis, 21(2), 357-369.

19 Peer reviewers suggested comparing modeling results 

to DCM monitoring data reported in other studies, and 

also investigating the low 33% release rate of the brushon product.

EPA/OPPT compared the consumer modeling results with monitoring-based 

exposure estimates in Appendix H, section H-5. The low release rate (33%) 

for the brush-on product was associated with the presence of a vapor 

retardant. This is discussed in Appendix H, sections H-1-1-2 and H-1-1-4.

20 A peer reviewer recommended the following:

 a correction to the near field (source cloud) 

assessment for the bathtub scenario;

 incorporation of a near field approach for the 

inhalation modeling; 

 expansion of the descriptions about the MultiChamber Concentration and Exposure Model 

(MCCEM).

EPA/OPPT corrected the source cloud (near field) mathematical error and 

associated exposure estimates for the bathtub stripping scenario. However, 

near field modeling was not considered appropriate for the workshop 

consumer exposure scenarios. Work areas within a workshop are less likely 

to promote localized accumulation of DCM vapors when compared to 

confined work areas such as a bathtub. Thus, the workshop scenario was 

modeled as a well-mixed zone. Appendix H, section H-3, discusses further 

support for this approach.
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21 A peer reviewer commented that a probabilistic 

approach could prove much more informative than the 

varying point estimate approach used for consumer 

inhalation assessment.

Appendix H, section H-3, presents details about the modeling approach and 

the rationale for selecting the input parameters and assumptions 

supporting the consumer inhalation scenarios. EPA/OPPT believes that the 

consumer modeling approach is appropriate to evaluate DCM exposures to 

paint strippers in residential settings and thus a probabilistic approach was 

not necessary. MCCEM is a Tier 2 exposure model.

22 A peer reviewer commented that the draft DCM risk 

assessment did not address aversive worker/consumer 

behaviors.

EPA/OPPT believes that aversive behavior due to odor is not considered 

health protective. The ability to detect odors varies by individual, and 

tolerance to odors can be developed over time. Human variability in odor 

detection and tolerance may have contributed to the reported fatalities 

related to overexposure to DCM during bathtub refinishing projects. 

23 Public commenters suggested more justification for use 

of the MCCEM model.

Section 3.2.2 provides additional information about the MCCEM model, 

including a description of the model features that led us to select it for the 

consumer modeling approach.

24 Public commenters recommended that Figure 3-4 

should be moved to follow descriptions of the scenarios, 

instead of before the scenario descriptions.

EPA/OPPT performed the sensitivity analysis before running the model for 

the different consumer exposure scenarios. This allowed us to develop the 

exposure scenarios by determining which parameters had the most 

influence over the exposure estimates. Thus, the discussion of the 

sensitivity analysis (section 3.2.4.1, Figures 3-3 and 3-4) was placed before 

the presentation of the modeling scenarios (section 3.2.4.2).

25 Public commenters stated that the label “user personal 

concentration” in Fig 3-1 is confusing, as it implies a 

personal air monitor.

EPA/OPPT has removed the confusing language from Figure 3-1.

The term “personal” was used in the draft DCM risk assessment to indicate 

the modeled DCM air concentration(s) that the user would be exposed to in 

either the product use area or the rest of the house, depending on the user 

activity patterns. The user exposure may be to a combination of 

concentrations, as indicated in Appendix H, section H-4. 

26 A public commenter suggested that EPA/OPPT should 

discuss the impact of variability of measured emission 

results on model estimates. Evaluation of the emission 

chamber test data showed that the variability in the 

emission values was greater for the brush-on DCM 

product than that reported for the spray-on DCM 

product. 

As discussed in Appendix H, section H-1-1-1, the intermediate emission 

results for the monitored brush-on product were used for modeling, thus 

minimizing the effect of the larger variability of emission values for the 

brush-on product when compared to that reported for the spray-on 

product.
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27 A public commenter suggested that text in the 

consumer exposure sections should be rewritten to 

clearly distinguish which variables were influenced by 

the sensitivity analysis and which were not.

EPA/OPPT clarified text in sections 3.2.3 and 3.2.4.1 about the sensitivity 

analysis.

28 A public commenter suggested more transparency for 

the MCCEM modeling—EPA/OPPT should provide 

complete documentation for the MCCEM inputs used to 

evaluate each scenario.

Appendix H provides detailed documentation on the modeling approach, 

input parameters/assumptions and exposure calculations for the model 

outputs. Information about the MCCEM input parameters is specifically 

found in Appendix H, section H-3.

29 A public commenter asked why the interzonal air flows 

were higher than the air flow between workshop and 

outdoors. The commenter assumed that the door(s) 

between zones were closed, so the interzonal flow 

should be lower.

The interflow airflow rate was estimated using an algorithm derived from 

empirical ventilation data collected in over 4,000 U.S. residences by the 

perfluorocarbon tracer (PFT) technique (EPA, 1995). In the analysis, the 

doors between residential zones were generally considered to be open. This 

is discussed in Appendix H, section H-3 (Airflow Rates and Volumes).

Reference:

EPA (U.S. Environmental Protection Agency). 1995. Estimation of 

Distributions for Residential Air Exchange Rates. Office of Pollution 

Prevention and Toxics, Washington, DC. 

http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=910063GS.txt.

30 A public commenter stated: “EPA acknowledges that it 

is unclear whether central-tendency, as well as high-end 

exposures, fall within the range of exposures estimated 

in the assessment”

Central-tendency and upper-end values are by definition within the range of 

exposures, as described in footnotes 10 and 11 in section 3.2.4.2 and

section 3.5.2 (Uncertainties in the Consumer Exposure Estimates).

31 Peer reviewers suggested that there should be more 

explicit consideration of child bystanders, who are likely 

to have different activity patterns and be closer to the 

ground, which may affect their inhalation exposure 

levels.

EPA/OPPT estimated exposures to product users and bystanders based on 

the predicted DCM air concentrations in the different residential zones (i.e., 

room of use, rest of the house). The zones were assumed to have wellmixed DCM air concentrations. 

Bystanders, who are individuals of any age (e.g., children, adults, the 

elderly), were assumed to be in the rest of the house during product use. 

The rest-of-the-house zone, where bystanders would be located, was 

assumed to have a well-mixed DCM air concentration. In this case, the 
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exposed individual height is not relevant. The Executive Summary, Sections 

1.3.3, 3.4.1 and 3.5.3.2 identify child bystanders as a potential human 

population exposure to DCM from the use of paint strippers.

32 A peer reviewer stated that there was a lack of 

justification for exposure time during application.

Appendix H, section H-3 indicates that the application and scrape times

were deduced from the MRI chamber study (EPA 1994).

Reference:

EPA (U.S. Environmental Protection Agency). 1994. Consumer Exposure to 

Paint Stripper Solvents. Office of Pollution Prevention and Toxics, 

Washington, DC.

33 A peer reviewer recommended that the current 

modeling results should be compared to the EPA 1994b 

report’s monitored values and also data from other 

studies (EC, 2004 and van Veen et al 2002).

Appendix H, section H-1 provides a discussion about the monitoring studies 

and section H-5 provides a comparison of monitoring and modeling results.

34 A public commenter asked why concentrations 

associated with upper-end user scenarios in Table 3-7 

were lower than those associated with upper-end nonuser (bystander) scenarios.

Table 3-7 labels the scenarios as upper-end for the user or non-user based 

on changes in parameters shown to be more sensitive for the user or nonuser. 

Table 3-7 showed that the user exposure for Scenario 3 (brush-on), where 

the most sensitive parameters were made upper-end for both the user and 

the bystander, was higher than the user exposure for Scenario 2, where the 

most sensitive parameters were made upper-end only for the user. This is 

also seen when comparing the spray-on scenarios 5 and 6. The reason for 

this observation has to do with the effect of using a higher chemical mass 

and a lower air exchange rate (ACH) in the rest of the house for Scenarios 3 

and 6. 

Changes in both chemical mass and ACH parameters are more influential 

than changes in only user location from workshop to the rest of the house, 

as occurred in Scenarios 2 and 5 (upper-end for user). Consequently, the 

user concentrations for Scenarios 3 and 6 are higher than those for 

Scenarios 2 and 5, respectively. Note that the user location was the most 
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15 | P a g e

sensitive parameter for short exposures, but much less sensitive at longer 

exposure times. Tables 3-5 and 3-6 have been revised to clarify this issue.

35 EPA/OPPT received comments about the source cloud 

approach used in the bathroom scenario. It was 

suggested to model the bathroom scenario as a single 

zone and compare the results with those obtained with 

the source cloud approach. As maximum exposure 

concentrations were predicted for the bathroom 

scenario, additional sensitivity analysis, especially with 

regard to the localized source cloud, would be 

appropriate. In addition, the near-field/far-field (NF/FF)

model was suggested for the bathroom scenario, 

instead of the current source cloud approach. The NF/FF

model is commonly used to estimate exposures in the 

breathing zone for a worker in close proximity to a

volatilizing source.

EPA/OPPT believes that the source cloud modeling is more appropriate than 

the single-zone modeling for the bathroom scenario. The user must work 

not only adjacent to, but partially within the concave bath tub. Also, 

ventilation characteristics are different for a semi-enclosed space such as a 

bathtub when compared to the surrounding room. Unlike some of the 

workshop scenarios, the user is expected to be outside the bathroom 

during the wait period. 

Figure H-15 in Appendix H, section H-4-3 compared the DCM source cloud 

concentration to those in the bathroom zone and the rest of the house.

The source cloud concentration (line Z1) was higher than the bathroom 

zone concentrations (line Z2). These results show that the source cloud 

approach captured the differences in air concentrations within the 

bathroom (near the bathtub versus the rest of the bathroom) and the rest 

of the house. EPA/OPPT expanded the discussion of the source cloud 

approach in Appendix H, section H-3.

EPA/OPPT did not conduct a sensitivity analysis for the bathtub stripping 

scenario because the model scenario recreated exposure conditions related 

to a fatality case associated with the use of a DCM-based stripper in a 

bathtub refinishing project (CDC, 2004). EPA/OPPT estimated the DCM air 

concentrations in the rest of the house while such worst-case exposure 

conditions occurred in the bathroom.

Reference:

CDC (Centers for Disease Control and Prevention). 2012. Tub Refinisher Died 

Due to Methylene Chloride Overexposure While Stripping a Bathtub. 

Michigan case report: 10M1013. Atlanta, GA. 

http://www.cdc.gov/niosh/face/stateface/mi/10MI013.html.

36 A public commenter suggested changing “peak or 

maximum TWA” to “maximum time period TWA.”

Peak and maximum TWA were used interchangeably; the assessment has 

been edited to use maximum TWA. This change is exemplified in Table 3-7.
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Hazard and Dose-Response Assessments

Charge 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.

Charge 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 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.

#

Summary of Peer Review and Public Comments 

for Specific Issues Related to

Charge Questions 4-1, and 4-2

EPA/OPPT Response

37 Peer review and public comments indicated that 

the application of the California’s acute 

reference exposure level (REL) and acute 

exposure guideline levels (AEGLs) was confusing 

in the draft DCM risk assessment and should be 

clarified.

AEGL-1, but not AEGL-2 values, should be used 

in the acute inhalation risk assessment. Other 

comments recommended using AEGL-1 values 

over the California’s acute REL.

There was confusion of why the SMACs were 

used in the assessment if they are not safe 

values and intended for spacecraft operations.

Also, commenters suggested selecting an acute 

POD for the acute risk assessment instead of 

having multiple approaches.

The acute inhalation risk assessment used the hazard and dose-response information 

supporting the derivation of DCM’s Spacecraft Maximum Allowable Concentrations 

(SMAC) (NRC, 1996), the California’s Acute Reference Exposure Level (REL) (OEHHA, 

2008), and the Acute Exposure Guideline Levels (AEGL) (NAC, 2008). These 

assessments were developed by reputable organizations and subjected to a peer 

review process. Appendix I of the final DCM risk assessment briefly summarizes the 

guidelines supporting the development of these assessments.

EPA/OPPT preferred the SMAC hazard value [or point of departure (POD)] over the 

California’s acute REL POD as the health protective hazard value used in this 

assessment. The SMAC POD was based on multiple human observations reporting 

increased carboxyhemoglobin (COHb) levels after DCM exposure, coupled with the 

knowledge of what would be considered a no-observable-adverse effect level 

(NOAEL) based on the extensive carbon monoxide (CO) database (NRC, 1996). 

However, the California’s acute REL POD was used to estimate risks for occupational 

scenarios since an 8-hr SMAC POD was not available for the risk calculations.

Although AEGLs are intended for emergency response activities and are not safe 

levels, the AEGL PODs were used in this assessment to evaluate acute risks for nondisabling (AEGL-1) and incapacitating (AEGL-2) effects following DCM inhalation 

exposure. EPA/OPPT believes that inclusion of AEGL PODs in the assessment is 
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A peer reviewer commented on EPA/OPPT’s 

reliance on previous hazard/dose response 

assessments instead of conducting its 

independent review of the data.

reasonable based human fatalities recently reported in bathtub refinishing projects 

using DCM-based paint strippers. The selected PODs (AEGL-1 and -2) are below the 

threshold for lethality and intend to evaluate whether the occupational and 

consumer DCM air concentrations are high enough to induce non-disabling and 

incapacitating effects prior to the occurrence of death.

These clarifications about the acute PODs and why EPA/OPPT preferred certain 

values over others are discussed in section 3.3.1.

References:

NRC (National Research Council). 1996. Spacecraft Maximum Allowable 

Concentration for Selected Airborne Contaminants: Methylene Chloride (Volume 2). 

National Academy Press, Washington, DC. 

http://www.nap.edu/catalog.php?record_id=5170.

OEHHA (Office of Environmental Health Hazard Assessment). 2008. Acute reference 

exposure level (REL) and toxicity summary for methylene chloride, Sacramento, CA. 

http://oehha.ca.gov/air/hot_spots/2008/AppendixD2_final.pdf#page=187.

NAC (National Advisory Committee). 2008. Interim Acute Exposure Guideline Levels 

(AEGL) for Methylene Chloride. Washington, DC. 

http://www.epa.gov/oppt/aegl/pubs/methylene_chloride_interim_dec_2008_v1.pdf.

38 Acute and chronic case reports and 

epidemiological studies are missing from the 

hazard/dose-response assessment. Also, cancers 

following DCM exposure have not been reported 

in humans.

Section 3.3.2.2 of the final DCM risk assessment briefly summarizes the human 

toxicity data following acute exposure to DCM. Section 3.3.2.3.2 lists several 

occupational studies providing evidence for an association between cancer and DCM 

exposure.

39 Peer review and public commenters asked 

EPA/OPPT to consider adding a number of 

references to the hazard/dose-response 

assessment.

EPA/OPPT reviewed all of the suggested and incorporated MacIsaac et al. (2013).

Reference:

Maclsaac, J., R. Harrison, J. Krishnaswami, J. McNary, J. Suchard, M. Boysen-Osborn, 

H. Cierpich, L. Styles, and D. Shusterman. 2013. Fatalities Due to Dichloromethane in 

Paint Strippers: A Continuing Problem. American Journal of Industrial Medicine, 56, 

907-910.
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18 | P a g e

40 CNS toxicity studies are not described in the 

assessment.

Sections 3.3.2.2 and 3.3.2.3.1 summarize the neurological effects observed following 

acute or chronic exposure to DCM. In addition, the acute PODs were based on 

neurological effects in humans (section 3.3.1.3 and Appendix I).

41 Unclear description of acute study reporting 

immunological effects

Section 3.3.2.2 briefly discusses the potential immunotoxic effects of DCM as 

reported by Aranyi et al. (1986). This study exposed CD-1 mice to 100 ppm DCM for 

3 hrs and reported localized immunosuppressive effects in the lung. Aranyi et al. 

(1986) is discussed in the DCM IRIS assessment, Chapter 4.

42 Public comments noted a series of 

inaccuracies/deficiencies in the acute (section 

3.3.3) and chronic (section 3.2.3) sections of the 

draft DCM risk assessment. Most of the 

comments were about missing references and 

incorrect statements that needed to be 

relocated to other sections.

When appropriate, EPA/OPPT made appropriate revisions to the acute and chronic 

hazard sections, including the insertion of missing references and relocating 

statements to other sections. See section 3.3.2.2 and 3.3.2.3 of the final DCM risk 

assessment.
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Risk Characterization

Charge 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.

Charge question 5-2: Please comment on the assumptions, strengths and weaknesses of the MOE approach used to estimate the chronic noncancer 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.

Charge question 5-3: Please comment on the assumptions, strengths and weaknesses of the cancer estimation risk approach used for the 

workplace exposures.

Charge 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.

#

Summary of Peer Review and Public Comments for 

Specific Issues Related to

Charge Questions 5-1, 5-2, 5-3 and 5-4

EPA/OPPT Response

43 A peer reviewer noted that a total UF of 30 was applied 

to the non-cancer chronic POD in the DCM IRIS 

assessment, but a total UF of 10 was used in the 

EPA/OPPT risk assessment.

The final DCM risk assessment uses a total UF of 10 as the benchmark 

margin of exposure (MOE) to evaluate non-cancer chronic risks for the 

occupational scenarios (section 3.3.1.2.2, Table 3-8).

44 Peer review and public comments suggested using 

occupational values (e.g., OSHA STEL) to evaluate 

occupational risks.

EPA/OPPT did not use occupational values for risk estimation as they are 

generally not the most health protective values.

45 The draft DCM risk assessment reported most of the risk 

estimates as MOEs, but risks based on the AEGL PODs 

were reported as hazard quotients (HQs). The risk 

estimation approach should be harmonized.

The final DCM risk assessment is using only MOEs to estimate acute and 

chronic risks (section 3.4).

46 Non-cancer acute risks should be estimated for 

occupational exposure scenarios.

Non-cancer acute risks were included in the final DCM risk assessment 

(sections 3.3.1.3 and 3.4.2.2, Table 3-11).

47 EPA/OPPT should address acute risks for incapacitating 

(AEGL-2 effects). 

EPA/OPPT is concerned about those consumer and occupational scenarios 

reporting risks for incapacitating (AEGL-2 effects) and will consider the risk 

findings during risk management.
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48 EPA/OPPT is using graphs that improperly compare the 

predicted time-varying DCM exposure concentrations for 

consumer scenarios with various acute toxicity values 

(e.g., AEGL-1, AEGL-2 and AEGL-3, California’s acute REL 

and SMAC). These comparisons were shown in Figures 3-

5 through 3-8 in the draft DCM risk assessment.

EPA/OPPT deleted the graphs from the final risk assessment.

49 The draft DCM risk assessment stated that the acute risks 

for neurotoxicity may be underestimated for younger 

individuals based on a hazard value derived from 

neurotoxicity in adults. This statement was included 

section 3.5.3 of the draft DCM risk assessment.

EPA/OPPT made revisions to the statement in section 3.5.3.2.1 to 

acknowledge that the acute risks may be under- or overestimated for 

younger individuals when using a hazard values based on neurotoxicity in 

adults.

50 The chronic non-cancer and cancer risks are 

underestimated because inhalation intake rates were not 

incorporated into the calculations of average daily 

concentrations (ADCs) and lifetime average daily 

concentrations (LADC). EPA/OPPT should revise the 

ADC/LADC calculations to account for inhalation intake 

rates.

EPA/OPPT used the air concentration in air in the ADC/LADC calculations 

since the amount of chemical being inhaled is not a simple function of 

inhalation intake rates and body weight. Instead, the interaction of the

inhaled contaminant with the respiratory tract is affected by factors such as 

species-specific relationships of exposure concentrations to 

deposited/delivered doses and physiochemical characteristics of the inhaled 

contaminant (EPA, 2009). EPA guidance recommends using the 

concentration of the chemical in air as the exposure metric when estimating 

inhalation risks (EPA, 2009).

Reference:

EPA (U.S. Environmental Protection Agency). 2009. Risk Assessment

Guidance for Superfund. Volume I: Human Health Evaluation Manual (Part F, 

Supplemental Guidance for Inhalation Risk Assessment). EPA-540-R-070-002. 

Office of Superfund Remediation and Technology Innovation, Washington, 

DC. www.epa.gov/oswer/riskassessment/ragsf/pdf/partf_200901_final.pdf.

51 EPA/OPPT should avoid using the term “level of concern”

when referring to the total UF used to interpret MOE 

values.

The final DCM risk assessment refers to “benchmark MOE” to the total UF 

used to evaluate MOE values.

52 Discussion of uncertainties and limitations should be 

improved for the exposure, hazard/dose-response and 

risk characterization assessments. Directional impact on 

risk should be included, and the discussion should be 

more complete and robust.

EPA/OPPT determined gaps in the discussion and completed substantial 

improvements to section 3.5 (Discussion of Key Sources of Uncertainty and 

Data Limitations). In some cases, the impact on risk estimates was discussed 

(e.g., Table 3-34).
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53 The draft DCM risk assessment did not evaluate the 

cumulative exposure from other uses of DCM around the 

home. This is another potential source of risk underprediction that was not characterized in the draft DCM 

risk assessment.

The final DCM risk assessment acknowledged this source of uncertainty in 

section 3.5.4.

54 Several comments addressed the inclusion and exclusion 

of the 3x database uncertainty factor. 

While the IRIS DCM assessment includes a 3x database uncertainty factor for 

the chronic noncancer RfC it was not included in the benchmark margin of 

exposures evaluated for chronic duration scenarios for workers. It is 

noteworthy that the MOE approach is endpoint specific, applied for a 

specific duration and not intended to be protective for other endpoints 

which have limited data. Data gaps in the overall hazard database are 

discussed in the uncertainty section (section 3.5.3). There are a lack of data 

about developmental neurotoxicity, longer term exposures and resulting 

neurotoxicity and immunotoxicity. These endpoints do not have sufficient 

data for quantification and remain uncertain. 

Other Public Comments

# Summary of Other Public Comments EPA/OPPT Response

55 EPA/OPPT should address OSHA authorities to regulate 

occupational exposures.

EPA/OPPT will consult with other federal agencies, including the 

Occupational Safety and Health Administration (OSHA), when discussing risk 

management options for DCM exposures associated with paint stripping.