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OPPT Proposed Draft Charge to External Peer Reviewers for the review of

the TSCA Workplan Chemical Risk Assessment of TCE

December 2012

OPPT focused its risk assessment on three specific uses of TCE: as a degreaser by workers in 

small commercial facilities, as a degreaser by consumers (hobbyists), and as a clear protective 

coating spray (an art/crafts use) by consumers (hobbyists). For all uses, only the inhalation route 

of exposure was evaluated, and risk estimates for individuals physically nearby by the user of the 

TCE product (but not using it; called either bystanders or non-users) were also calculated.

General Question on the Risk Assessment Document

Issue 1. The risk assessment is divided into three chapters and there are six appendices

and three supplemental documents. The first two chapters describe the scoping exercise 

EPA used and background information on TCE that sets the stage for the information 

available and used in the risk assessment. Chapter 3 includes the exposure, hazard and 

risk characterization and a section on uncertainties for each of the three uses of TCE which 

are the focus of this 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 characterization provides a clear and logical

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

document. 

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

and accurately characterized. Please provide any other significant literature, reports, or data 

that would be useful to complete this characterization.

Questions on the Exposure Assessment

Issue 2. Workplace exposure estimates were developed for adults working as degreasers in 

small commercial settings. These scenarios represent small businesses that use degreaser 

products/equipment regularly, but not all day during the course of their job. An example 

would be a garage/car mechanic business. Readily available data from sources such as the 

National Emissions Inventory (NEI), Toxics Release Inventory (TRI), and National 

Occupational Exposure Survey (NOES), other literature sources and assumptions were 

used to develop the workplace exposure assessment. 

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 the workplace exposure assessment; 

including the bystander/non-user estimations.

Issue 3. Exposure estimates were developed for two different consumer uses: a degreasing 

product and a clear protective coating spray product. Both products are aerosol sprays
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and appear to be available for sale and use by consumers/hobbyists in the US. There were 

no reliable data regarding the hobbyist scenarios, so OPPT estimated hobbyist exposures 

using a standard exposure assessment modeling approach (the Consumer Exposure 

Module [CEM] of the Exposure and Fate Assessment Screening Tool, or E-FAST). 

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

suggestions or recommendations for alternative approaches, models, or information (e.g., 

information on duration and number of user events) that could be considered by the 

agency in developing the exposure assumptions and estimates for the hobbyist degreaser 

and clear protective coating spray uses, and for the bystander/non-user.

Questions on the Hazard Assessment

Issue 4. Information on the inherent hazards of TCE has been well-characterized. There 

are six major domains of adverse effects (primarily in animal models) following exposure 

to TCE: non-cancer effects on the liver, kidney, nervous system, immune system, 

reproductive (predominantly male) toxicity, and developmental toxicity; as well as cancer 

effects on the liver, kidney and the immune system (Non-Hodgkins Lymphoma, or NHL). 

TCE metabolism is extensive in mammalian systems and different metabolites are likely to 

be responsible for different toxicity. The 2011 US EPA Integrated Risk Information System 

(IRIS) assessment for TCE reviewed many human and animal studies. There were 32 

endpoints/27studies identified as “candidates” for developing the reference concentration 

(called the RfC). Physiologically-based pharmacokinetic (PBPK) modeling was used by the 

IRIS program to derive different HEC (i.e., human equivalent concentration) values. 

OPPT reports all of these values, but focused on using only the 12 inhalation studies. 

Rather than use a single value to represent hazard, OPPT used the lowest lower bound 

HEC99 – the 99th percentile predicted HEC concentration -- for the effect of concern for 

each target organ. Furthermore, OPPT distinguished between effects that may occur 

following acute exposure (i.e., neurotoxicity and developmental toxicity) versus those that 

may occur following chronic exposures (i.e., liver, kidney, immunotoxicity, and male 

reproductive toxicity and cancer). 

Question 4-1: Please comment on the strengths and weaknesses of evaluating different 

endpoints based on exposure durations (i.e., acute versus chronic). 

Question 4-2: Please comment on the strengths and weaknesses of using multiple values 

for each type of adverse effect.
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Questions on the Risk Assessment

Issue 5. A margin of exposure (MOE) approach was used to evaluate potential non-cancer 

risk and the IRIS inhalation unit risk (IUR) was used to evaluate potential cancer risk. 

The small commercial degreaser workplace risk estimate assumed chronic (daily) 

exposures to TCE. The consumer use of both the degreaser and the clear protective coating 

spray used in the arts/crafts field risk estimates assumed only intermittent (acute)

exposures to TCE. As part of the risk characterization, there is a discussion of the 

uncertainties surrounding the risk calculations. 

Question 5-1: Please comment on the strengths and weaknesses of the MOE approach 

used to estimate the chronic, non-cancer risk for the workplace exposures; including nonusers. 

Question 5-2: Please comment on the strengths and weaknesses of the MOE approach 

used to estimate the acute risk to consumers; including the non-users. Specifically, 

please comment on the decision to limit the analysis to acute exposures without residual 

concern between events (i.e., once/week for users of the clear protective coating spray,

and twice/month for degreaser users).