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This document is one of five documents that will comprise the Air Toxics Hot Spots Program Risk<br />

Assessment Guidelines. The other documents to be included in the Guidelines are Part I: Technical<br />

Support Document for the Determination of Acute Toxicity Exposure Levels for Airborne Toxicants;<br />

Part III: Technical Support Document for Determination of Noncancer Chronic Reference Exposure<br />

Levels; Part IV: Technical Support Document for Exposure Assessment and Stochastic Analysis; Part<br />

V: Air Toxic Hot Spots Program Risk Assessment Guidelines.<br />

Public workshop comments on the public comment draft of the <strong>TSD</strong> included the following suggestions:<br />

• Change the title of the <strong>TSD</strong> from "Technical Support Document for Determining Cancer Potency<br />

Factors" to "Technical Support Document for Using Cancer Potency Factors".<br />

• Include the procedures for submitting new scientific in<strong>format</strong>ion on specific chemicals to the<br />

programs whose cancer unit risk and potency values were adopted in this document.<br />

• List the documents that will comprise the Air Toxics Hot Spots Program Risk Assessment<br />

Guidelines.<br />

• Define the term "further research" used in the table "Comparison of Hot Spots Cancer Unit Risk<br />

Values Which Differ From Corresponding US EPA IRIS Cancer Unit Risk Values" in the <strong>TSD</strong><br />

section "How the Technical Support Document for Describing Available Cancer Potency Values<br />

(<strong>TSD</strong>) Addresses the RAAC Committee Recommendations".<br />

• Include a discussion of how harmonization with the new draft US EPA cancer risk assessment<br />

guidelines will occur, including the question of whether the cancer unit risk and potency values will<br />

be changed to reflect new US EPA values or methodologies.<br />

Most of the comments above resulted in revisions being made to the <strong>TSD</strong>. The title of the <strong>TSD</strong> has<br />

been changed from "Technical Support Document for Determining Cancer Potency Factors" to<br />

"Technical Support Document for Describing Available Cancer Potency Factors". The procedures for<br />

submitting new scientific in<strong>format</strong>ion on specific chemicals to the programs whose cancer unit risk and<br />

potency values were adopted in this document have been added to the <strong>TSD</strong> as Appendix G. The<br />

documents that will comprise the Air Toxics Hot Spots Program Risk Assessment Guidelines have been<br />

listed above in this Preface.<br />

Changes to the <strong>TSD</strong> were also made in response to requests made by the ARB Scientific Review Panel<br />

(SRP). In<strong>format</strong>ion summaries for chemicals which have been listed by the ARB as Toxic Air<br />

Contaminants (TACs) were adapted from the TAC documents for those chemicals.<br />

Harmonization with the new draft US EPA cancer risk assessment guidelines will be dependent on the<br />

extent to which the programs which generated the cancer unit risk and potency values adopt those<br />

guidelines when finalized, and the decisions those programs make about cancer potency values which<br />

predate the new guidelines. For example, US EPA has stated that cancer potency values listed in IRIS<br />

ii

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