On April 15, 2010, Senator Frank R. Lautenberg (D-NJ) released the text of the Safe Chemicals Act of 2010 (S.3209), which is intended to address the “core failings” of the Toxic Substances Control Act (TSCA). Also on April 15, 2010, Representatives Bobby Rush (D-IL), Chair of the Subcommittee on Commerce, Trade, and Consumer Protection, and Henry Waxman (D-CA), Chair of the Energy and Commerce Committee, released a discussion draft of their TSCA reform legislation, the Toxics Chemicals Safety Act of 2010. While the bills do not explicitly address nanomaterials, both bills consider “characteristics” of chemical substances. The House bill defines “substance characteristic” as “with respect to a particular chemical substance, the physical and chemical characteristics that may vary for such substance, and whose variation may bear on the toxicological properties of the chemical substance, including (A) chemical structure and composition; (B) size or size distribution; (C) shape; (D) surface structure; (E) reactivity; and (F) other characteristics and properties that may bear on toxicological properties.” The Senate bill defines “special substance characteristics” as such physical, chemical, or biological characteristics, other than molecular identity, that the Administrator determines, by order or rule, may significantly affect the risks posed by substances exhibiting those characteristics. In determining the existence of special substance characteristics, the Administrator may consider: (A) size or size distribution; (B) shape and surface structure; (C) reactivity; and (D) “any other properties that may significantly affect the risks posed.”  How these, and a wide range of other measures in the bills, play out will have a significant impact on new chemicals generally, and nanoscale chemical substances in particular.