PAH mixtures NASA comments 10_28_09

NASA comments on draft PAHs risk assessment

Wennerberg, Linda S. (HQ-LA000) 

to:

IRISInterAgency

10/28/2009 04:49 PM

Cc:

"Leatherwood, James (HQ-LD020)", "Schoppet, Mark J. (HQ-LD020)", "Fellows, 

Merrilee (HQ-LD000)"

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Peter:

NASA thanks EPA for the option to review and comment on EPAs draft PAH 

Mixture risk assessment under the IRIS process.

We reviewed the text and identified broad areas of concern and the 

appearance of potential inconsistencies with established policies and 

practices. We suggest expanding the current draft Peer Review questions to 

address the following issues:

Does EPA provide adequate justification for the decision to limit use of 

data to only a narrowly defined subset of data? If not, what further 

information and input is needed to support EPA’s draft risk assessment and 

its findings or should EPA reconsider its approach?

Issue: The current draft actively narrows data use to only those 

experiments performed at the same lab and does not consider the range of 

available data, especially for a diverse group of chemicals, such as PAH 

mixtures. Of particular concern is the EPA approach to limit the use to 

only “positive results”, a concern that NASA previously identified in its 

review of the draft TCE risk assessment under IRIS. Overall, this 

limitation of data raises the potential for skewed results, the appearance 

of “cherry picking” data for a desired results and would exclude much of 

the literature or data sources used consistently in other EPA risk 

assessments.

Does EPA provide adequate documentation and justification for its 

determination of the primary mode of carcinogenic action? If not, what 

additional information and justification is needed from EPA to support a 

defensible determination or should EPA reevaluate this determination. In 

addition, does EPA adequately support its subsequent determination on low 

dose estimation?

Issue: Review of the current draft found extensive discussion of mode of 

action but little to no substantiation for EPA’s actual determination of 

the primary mode of carcinogenic action. Without clarification of this 

critical factor, the subsequent decision on linear vs. nonlinear 

extrapolation at low doses is not defensible.

Does EPA provide adequate justification for its specific approach to 

quantify risk factors across a diverse group of chemicals, such as PAHs? 

Also, does the draft PAHs risk assessment meet requirements for estimation 

of relative potency factors (RFP) for mixtures?

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PAH mixtures NASA comments 10_28_09

Issue: EPA’s specific approach for PAHs raises areas of concern and 

potential inconsistencies in the application to PAH mixtures. As this 

approach has many differences from current risk assessment practices and 

EPA policies (e.g., EPA Guidelines for Carcinogen Risk Assessment (2005), 

EPA’s 2005 Supplemental Guidance for Assessing Susceptibility from 

Early-Life Exposure to Carcinogens, Guidelines for Carcinogenic Risk 

Assessment (1986)) for single chemical that EPA needs to substantiate its 

specific approach on PAH mixtures.

NASA requests that EPA strengthen and clarify its draft Peer Review 

questions to ensure consideration and peer review direction on these 

significant outstanding issues.

Again, NASA thanks EPA for the opportunity to review and comment on this 

draft risk assessment in the IRIS process.

Linda S. Wennerberg, Ph.D.

NASA HQ

Suite 5E39

300 E Street, SW

Washington, DC 20548-0001

Phone: 202/358-4558

Fax: 202/358-3948

Cell: 202/329-0153

Email: Linda.S.Wennerberg@nasa.gov

 

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